Do ectotherms think slower when they are cold?

Do ectotherms think slower when they are cold?

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Animals near the ectotherm side of the endotherm-ectotherm spectrum rely on external heat sources to regulate their body temperature. When they are cold, overal enzyme activity and metabolic rate is lower.

My question is if these animal tend to 'think' slower when cold?

To be honest, my knowledge of brain physiology is very sketchy, I'm not sure biochemical activity plays a large role vs. electrical and diffusion processes and the latter would be less temperature dependant. So I'm not sure we would expect ectotherms to 'think' slower.

OTOH, wikipedia on endotherms states…

Some ectotherms, including several species of fish and reptiles, have been shown to make use of regional endothermy, where muscle activity causes certain parts of the body to remain at higher temperatures than the rest of the body. This allows for better locomotion and use of the senses in cold environments.

The source for this claim is on google books, just not the relevant pages (Willmer, Pat; Stone, Graham; Johnston, Ian (2009). Environmental Physiology of Animals)

I'm also not sure how to define 'thinking' within this wide range of animals, I'll take any metric for speed at cognitive tasks or reacting to external stimuli.

I would assume as the temperature decreases, even as an ectotherm organism that the neuro processes would decrease. From my experience in chemistry, the colder the temperature the slower the molecules vibrate. As a result, it would take a longer time for the sodium and calcium molecules to move from the end of the neurons to the synapses resulting in delayed thinking. If they are absorbing the energy necessary, then their neuro processes should be functioning normally.

I can't see why it would be different for ectothermal animals than endothermal animals. By lower temperatures, I'm not considering a few degrees one way or the other; there is probably a maximal temperature range for the nervous system to operate, followed by decreases in lower ranges.

You write

Some ectotherms, including several species of fish and reptiles, have been shown to make use of regional endothermy, where muscle activity causes certain parts of the body to remain at higher temperatures than the rest of the body. This allows for better locomotion and use of the senses in cold environments.

Protective mechanisms are also in place in humans, where shivering generates heat, and blood is shunted away from cold areas to core (warmer) areas to protect executive functioning (thinking) and heartbeat regularity. It doesn't mean that once thes compensatory mechanism (and others) are overcome by falling temperatures, that cognition remains unaffected.

Given extremes, there are iguanas falling frozen (not necessarily dead, though) from the trees in Florida. I doubt they even know they're falling. Maybe a muddled "Huh?" when they hit the ground, a car, etc. But I would wager that, could we read their thoughts, they are not racing with anxiety:

My ---, I'm stiff as a board! Someone help me, I can't move a muscle! What's happening? Is this a bad dream where I can't move? Am I dead? Is this HELL? Oh, ---, I wish I had spent more time with my wives and kids! Is a deathbed confession acceptable now? Can anyone hear me? Am I even talking? How could I be talking if I can't move my mouth?!

Hypothermia definitely slows down thinking in humans, e.g. in studies to try to understand the effect of cold on astronauts (not done on astronauts, though):

Chronic multifactorial stress impaired cognitive function and mood; the addition of moderate, acute cold stress further degraded vigilance and mood. When such circumstances occur, such as during disasters or military operations, measures to prevent adverse cognitive and physiological outcomes are recommended.


Cold stress is experienced in occupational (military, fishing trawlers, emergency disaster workers) and athletic (winter sports) settings (Muller et al., 2012). It appears that both moderate and extreme reductions in ambient temperature may have a negative effect on cognitive function (Banderet et al., 1986; Palinkas, 2001). Specifically, cold exposure (−20 to 10°C) has led to decrements in memory [complex task (Thomas et al., 1989; Patil et al., 1995)], vigilance [complex task (Flouris et al., 2007)], reaction time [simple task (Teichner, 1958; Ellis, 1982)], and decision making [complex task; see Table ​Table4;4; (Watkins et al., 2014)]. Such consistent findings across such diverse ambient temperatures may be explained by traditional theories of cold induced cognitive decrement (Teichner, 1958; Enander, 1987; Muller et al., 2012)… Regression analysis from a recent study (Watkins et al., 2014) reported a significant relationship between alterations in thermal comfort and cognitive function in the cold.

So, yes, at sufficiently lower temperatures, cognition is decreased. One theory is that initially it is decreased because attention is directed at the discomfort of being cold (1958), but fMRI studies might clear up that issue nicely.

Cognitive function and mood during acute cold stress after extended military training and recovery.
The Impact of Different Environmental Conditions on Cognitive Function: A Focused Review

What Does Ectothermic Mean?

An ectothermic animal, also commonly known as a "cold-blooded" animal, is one who cannot regulate its own body temperature, so its body temperature fluctuates according to its surroundings. The term ectotherm comes from the Greek ektos, meaning outside, and thermos, which means heat.

While common colloquially, the term "cold-blooded" is misleading because ectotherms blood isn't actually cold. Rather, ectotherms rely on external or "outside" sources to regulate their body heat. Examples of ectotherms include reptiles, amphibians, crabs, and fish.

Ectotherms vs. endotherms

Do you know the difference between an ectotherm and an endotherm—or even what these terms mean? They both refer to the ways that animals stay warm. When the weather outside is frightful, a blog post about thermoregulation is so delightful! Keep reading to find out which animals need help from the environment to stay warm (ectotherms), and which animals produce their own heat (endotherms).

For these animals, heat comes from outside (ecto-) their bodies—their environment provides their warmth. That means they require less food, and are consequently able to inhabit places that would be off-limits to endotherms. However, their activity level is limited by the surrounding conditions. If it gets too cold, they simply can’t move.

Banggai cardinalfish (Pterapogon kauderni)

Like most fish, Banggai cardinalfish are ectotherms. Because of this, these fish appear less hungry during winter months.

Widehand hermit crabs (Elassochirus tenuimanus)

Hermit crabs, along with all invertebrates, are ectotherms. Since invertebrates account for more than 95 percent of animal species, that means that most animals are ectotherms

Tripod fish (Family Ipnopidae)

These fish live in the abyssal zone, where conditions are so stable that their body temperatures don’t change.

These animals produce their own heat inside (endo-) their bodies. Creating that warmth speeds up their body processes: muscles, neurons and all of their processes work faster. That also means they require a lot of food—between five and 20 times more food than an ectotherm of the same size!

Sea otters (Enhydra lutris)

These marine mammals have to eat roughly 25 percent of their body weight per day to keep their bodies warm.

Anna’s hummingbirds (Calypte anna)

These high-energy birds have needs that can’t be met at night when they’re at rest. The solution? Torpor, a state of deep sleep and lowered metabolism. Some animals extend torpor over the whole winter this is called hibernation.

Opahs (Lampris guttatus)

These fish generate heat mainly by constantly flapping their pectoral fins, which helps their bodies stay warmer than the water even when they dive over 1,500 feet below the surface. Opahs have been sighted in Washington waters twice since 1935.

Steelhead biology for anglers

One thing you will notice about anglers who have spent a lot of time on the water, and I mean a potentially unhealthy amount of time on the water, is they catch fish. This can be frustrating to new anglers who are just learning to steelhead fish and spend many fishless days casting.

There is no substitute for time on the water, but understanding the biology of steelhead can certainly make us better anglers. There are two basic biological principles underpinning all of the mumbo jumbo steelheaders spew about catching fish in various weather and river conditions.

  1. Vision: If a steelhead cannot see your fly or lure it is not likely to bite it, despite having a variety of finely tuned senses, steelhead are primarily visual predators. Visibility can be obscured by a number of things but the most common is turbidity resulting from high stream flows caused by snowmelt or rain. High flows mobilize sediment, which turns rivers various shades of gray and brown. In general, 2-3’ of visibility is considered adequate for steelheading, but many of us have caught fish with less visibility, probably because we managed to get the fly/lure right in front of it. This highlights that during periods of poor visibility it is most important to maintain the offering in “the fish zone” for as long as possible, which means slowing down the presentation and being methodical. As visibility improves fish will move much further to strike a fly or lure and it is less critical to hit them in the face.

  1. Metabolism: Steelhead are ectotherms and as such their body temperature is regulated by their watery environment. In cold water a steelhead’s metabolism is slower and therefore it will not move as far to grab and will generally strike in a less aggressive manner. The same is true when water temperatures become too warm and the fish become lethargic. Traditional wisdom tells us that low and clear conditions make steelhead fishing tough, but in reality it may not be the stream flows as much as it is the water temperatures. For instance, streams tend to get low in winter when it is cold and low in summer when it is warm. In either case the water temperatures are at their lower or upper extremes, meaning that fish are also at their metabolic extremes and consequently, are less responsive to an angler’s offerings. A fine example of this is during late summer and early fall when stream flows are low but temperatures often fall within the wheel-house of maximum activity for steelhead (50-65°F) and they are highly aggressive. Basically this means that we can’t consider stream flows without considering water temperature because it is the latter that is truly driving the metabolism of steelhead.

There are several other factors, often correlated with the visibility and water temperature, that also influence the aggressiveness of steelhead. Each of those factors may provide an angler with a bit more information about how and when to fish for steelhead.

The first is weather. Many anglers have a ritual of checking all of their weather, surf forecast and stream flow websites prior to their trip. While all that information will tell an angler how to dress for their upcoming trip, weather is a secondary factor and the effects of variable weather is underpinned by visibility and temperature. For instance, winter storms are generally warm and full of moisture, which tends to increase water temperatures. This warming trend will increase a fish’s metabolic rate and fishing can be at its best if the warming temperatures are coupled with a reduction in visibility to the point where fish feel safe but can also easily see the fly or lure. Think about the old adage, “three feet of vis and dropping and clearing”. We can assume that a storm has brought in warm rain which has raised the level of the river as well as warming the water. The storm may have brought in new fish but there are also plenty of fish mixed in that were unwilling to bite just a few days prior when the water temps were significantly lower.

The opposite is true in summer. Rain storms tend to decrease air and water temperatures. If the streams were too warm the reduction in temperature can improve the metabolic ability of steelhead. And as with winter, the challenge is finding the proper balance between water temperature, stream flow and visibility.

The second is cloud cover, a symptom of the weather, and shade. As all steelheaders know, fishing tends to be best on those gray muggy days when there is little variation in temperature from morning to evening. Similarly, steelheaders often seek out shaded runs during sunny days, presumably because prolonged periods of high sun tend to force steelhead down to the stream bottoms where they will hold until evening and morning. This means that being successful during the middle of hot summer days requires looking for and identifying shaded areas where steelhead feel more comfortable holding and being active. Regardless of the season, maximizing success depends not only on visibility, water temperature and weather, but also being very specific about reading the water to find those micro-habitats where steelhead are most likely to be aggressive.

Third, many anglers pay attention to barometric pressure and it is commonly felt that a falling barometer is a poor time to fish while rising pressure is ideal. Fish can sense pressure using their air filled swim bladders, however water is denser than air which means that a fish moving up or down three feet in the water column will be exposed to a much greater change in pressure than from an approaching storm. Hence, migratory fish coming in from the ocean and moving up through shallow riffles and pools would experience relatively large changes in pressure, greater than we would typically expect them to notice when the atmospheric pressure changes. This means that barometric pressure is a bit of a red herring for anglers. The fish are most likely responding to other cues such as rainfall and changing temperatures rather than specific changes in barometric pressure.

Lastly, and perhaps the titan of all factors influencing steelhead success is fishing pressure. Hundreds to thousands of anglers are fishing many of our best steelhead rivers in the lower-48. That means a tremendous amount of fish are hooked and landed or lost, and that fish are seeing multitudes of different flies, lures and baits over the course of a season.

Pressured fish are less likely to bite regardless of conditions. Period. Whether it is a fish that has been hooked and played or simply reacting to dozens of boats going overhead, large numbers of anglers generally spook fish. This sends them in to hiding and makes them less aggressive. Why? Well we are not exactly sure of the specific causes, but it is likely related to stress. Steelhead and humans share the same stress hormone known as cortisol. Once this is released into our bodies it must be metabolized and it does not dissipate immediately once a threat is gone. On heavily pressured rivers then, steelhead could be responding to the threats with elevated cortisol levels. While this hormone helps them, and us, survive by causing cautious behavior and even hiding, it makes fishing for them that much more challenging. Steelheaders get up early for one main reason, to get first water so they are not fishing over stressed fish, and another reason that the internet chat boards have chastised any and all anglers to keep a zipper on it when mentioning specific places that are less fished.

Ultimately, when thinking about fishing for steelhead we need to think like a steelhead and understand the reasons for their behavior. This typically boils down to considering two major factors, can a fish see your presentation and it is active enough to move and take it. As we covered here, there are many factors that play into this but they all likely depend on the basic biological needs of steelhead.

Of course, there are other factors we did not discuss that can mitigate certain conditions, such as speed and depth of the presentation, color and size of the fly or lure, and what parts of the river to focus on during different types of conditions. Regardless, don’t get too caught up in all the talk, the most important thing is to get out and spend time on the water. There is no golden rule for steelheading except that being on the water and actually wetting the line is necessary to catch a fish. We have all likely caught steelhead in less than optimal conditions, but we also know that our most glorious successes tend to come when there is a magical confluence of appropriate visibility, perfect water temperatures, fewer anglers and ideal weather conditions. However some of the most memorable fishing days occur during times we did not expect the fishing to be very good at all, so most importantly, just go fishing.

Answer of Question of Temperature & Body Fluid Regulation

Thermoregulation maintains body temperature within a range conducive to metabolism. The maintenance of body temperature within a range that enables cells to function efficiently involves heat transfer between the organism and the external environment. Heat exchange involves the physical processes of conduction, convection, evaporation and radiation. Ectotherms derive body heat mainly from their surroundings and endotherms derive it mainly from metabolism. Homeotherms generally have a relatively constant core body temperature, while heterotherms have a variable body temperature. Comparative physiology reveals diverse mechanisms of Thermoregulation among animals. Many large flying insects generate metabolic heat by muscle contractions, and many have countercurrent heat exchangers that retain it. Although the body temperature of most fishes matches the environment, some large, active species maintain a higher current heat exchanger. Reptiles and amphibians maintain internal temperatures within tolerable ranges mainly by various behavioral adaptations. Birds may thermoregulate by panting, increasing evaporation from a vascularized pouch in the mouth, and by passing blood going to legs through a rete mirabile system. Mammals and birds can adjust their rate of metabolic heat production by shivering and non-shivering thermogenesis. The marine mammals maintain their high body temperatures in cold waters by a thick layer of insulating blubber and countercurrent heat exchange between arterial and venous blood. Thermogenesis involves mainly shivering, enzymatic activity, brown fat, and high cellular metabolism. Thermoregulatory areas of the hypothalamus serve as the body’s thermostat, receiving nerve signals from warm and cold receptors and responding by initiating either cooling or warming processes. Torpor, including hibernation and aestivation, is a physiological state characterized by a decrease in metabolic, heart, and respiratory rates. This state enables the animal to temporarily withstand varying periods of unfavorable temperatures or the absence of food and water. Some Invertebrates have contractile vacuoles, flame-cell systems, antenna! (green) glands, maxillary glands, coxal glands, nephridia, or Malpighian tubules for osmoregulation. The osmoregulatory system of vertebrates governs the concentration of water and ions the excretory system eliminates metabolic wastes, water, and ions from the body. Freshwater animals tend to lose ions and take in water. To avoid hydration, freshwater fishes rarely drink much water, have impermeable body surfaces covered with mucus, excrete a dilute urine, and take up ions through their gills. Marine animals tend to take in ions from the seawater and to lose water. To avoid dehydration, they frequently drink water, have relatively permeable body surfaces, excrete a small volume of concentrated urine, and secrete ions from their gills. Amphibians can absorb water across the skin and urinary bladder wall. Desert and marine reptiles and birds have salt glands to remove and secrete excess salt. In terrestrial animals, such as reptiles, birds and mammals, the kidneys are important osmoregulatory structures. The functional unit of the kidney is the nephron, composed of the glomerular capsule, proximal convoluted loop of the nephron, distal convoluted tubule, and collecting duct. The loop of the nephron and the collecting duct are in the kidney’s medulla the other nephron parts lie in the kidney’s cortex. Urine passes from the pelvis of the kidney to the urinary bladder. To make urine, kidneys produce a filtrate of the blood and reabsorb most of the water, glucose, and needed ions, while allowing wastes to pass from the body. Three physiological mechanisms are involved: filtration of the blood through the glomerulus, reabsorption of the useful substances, and secretion of toxic substances. In those animals with a loop of nephron, salt (Nace) and urea are concentrated in the extra cellular fluid around the loop, allowing water to move by osmosis out of the loop and into the peritubular capillaries.

Answers to the Questions

Q.1. What is Thermoregulation?

Ans. Thermoregulation is the maintenance of body temperature within a range that enables cells to function efficiently. It involves the nervous, endocrine, respiratory and circulatory systems in higher animals. Metabolism is very sensitive to changes in the temperature of an animal’s internal environment. For example, the rate of cellular respiration increases when temperatures are high enough to begin denaturing enzymes. The properties of membranes also change with temperature. Although different species of animals are adapted to different temperature range, within that range many animals can maintain a constant internal temperature as the external temperature fluctuates.

Q.2. How do temperature extremes affect metabolic reactions?

Ans. Every animal’s physiological functions are inexorably linked to temperature, because metabolism is sensitive to changes in internal temperature. Biochemical reactions are also extremely sensitive to temperature. All enzymes have an optimum temperature range beyond which (above or below) enzyme function is impaired. Temperature therefore, is a severe constraint for animals, all of which must maintain biochemical stability. When body temperature drops too low, metabolic processes slow down, reducing the amount of energy the animal can muster for activity and reproduction. If body temperature rises too high, metabolic reactions become unbalanced and enzymatic activity is hampered or even destroyed. Thus animals can succeed only in restricted range of temperature, usually between 0°C to 40°C. For example, a digestive enzyme in a trout might function optimally at 10C, whereas another enzyme in the human body that catalyzes the same reaction functions best at 37°C. Higher temperatures cause the proteins in nucleic acids to denature, and lower temperatures may cause membranes to change from a fluid to a solid state, which can interfere with many cellular processes, such as active-transport pumps.

Animals can guard against these damaging effects of temperature fluctuations by: either finding a habitat where they do have to contend with temperature extremes, or they must develop means of stabilizing their metabolism independent of temperature extremes.

Q.3. How can you express the animal’s body temperature?

Ans. Animals produce heat as a by-product of metabolism and either gain heat from, or lose it to, the environment. The total body temperature is a result of an interaction of these factors and can be expressed as:

Body temperature = heat produced metabolically

+ Heat gained from the environment

– Heat lost to the environment

Q.4. Describe the processes by which animals exchange heat with the environment.

Ans. An organism like all objects, exchanges heat with its external environment by four physical processes: conduction, convection, evaporation, and radiation.

Conduction is the direct transfer of thermal motion (heat) between molecules of the environment and those of the body surface, as when an animal sits in a pool of cold water or in a hot rock. Heat will always he conducted from a body of higher temperature to one of lower temperature. For example, when we sit on the cold ground, we lose heat, and when we sit on warm sand, we gain heat.

Water is 50 to 100 times more effective than air in conducting heat. This is one reason we can rapidly cool our body on a hot day just by standing in cold water.

Convection is the transfer of heat by the movement of air or liquid past the surface of a body, as when a breeze contributes to heat loss from the surface of an animal with dry skin. Convection also contributes to the comfort a fan brings on a hot, still day, but most of this effect is due to evaporative cooling. On the other hand, a wind-chill factor compounds the harshness of cold winter temperature. On a cool day, our body loses heat by convection because our skin temperature is higher than the surrounding air temperature.


Evaporation is loss of heat from a surface as water molecules escape in the form of a gas. It is useful only to terrestrial animals. For example, humans and some other mammals (chimpanzees and horses) have sweat glands that actively move watery solutions through pores to the skin surface. When skin temperature is high, water at the surface absorbs enough thermal energy to break the hydrogen ‘bonds holding the individual water molecules together, and they depart from the surface, carrying heat with them. As long as the

environment humidity is low enough to permit complete evaporation, sweating can rid the mammalian body of excess heat however, the water must evaporate. Sweat dripping from a mammal has no cooling effect at all as we experience in humid atmosphere.

Radiation is the emission of electromagnetic waves produced by all objects warmer than absolute zero, including an animal’s body and sun. Radiation can transfer heat between objects that are not in direct contact with each other, as an animal absorbs heat radiating from the sun. Researchers have recently discovered a specific adaptation for exploiting solar radiation in polar bears. The fur of these animals is actually clear, not while. Each hair functions somewhat

like an optical fiber that transmits ultraviolet radiation to the black skin, where the energy is absorbed and converted to body heat.

If you were to sit at rest in still air at a comfortable temperature cooler than your body (for example, an air temperature of 23 .- C), conduction could account for only about 1% of your heat loss, convection for about 40%, radiation for another 50%, and evaporation for about 9%• Convection and evaporation are the most variable causes of heat loss. A breeze of just 15km/hr will increase total heat loss substantially by increasing convection fivefold. Fig. 6.1, 6.2.

Q.5. What are three basic ways animals cope with temperature fluctuations?

Ans. Animals cope with temperature fluctuations in one of three basic ways.

  1. They can occupy a place in the environment where the temperature remains constant and compatible with their physiological processes.
  2. Their physiological processes may have adapted to the range of temperatures in which the animals are capable of living or
  3. They can generate and trap heat internally to maintain a constant body temperature, despite fluctuations in the temperature of the external environment.

Q.6. How can animals be categorized on the basis of their source of body heat?

Ant Animals can be categorized as ectotherms or endotherms, based on whether their source of body heat is from internal processes or derived from the environment.

Ectotherms (Gr.etos, outside) warm their body mainly by absorbing heat from its surroundings. The amount of heat it derives from its own metabolism is usually negligible. They have low rates of metabolism and are poorly insulated. Most invertebrates, fishes, amphibians, and reptiles are ectotherms, although a few reptiles, insects, and fishes can raise their internal temperature. Ectotherms tend to move about in their environment and find places that minimize heat or cold stress to their bodies. For example, many ectothermic marine fishes and invertebrates inhabit water with such stable temperatures that their body temperature varies less than that of humans and other endotherms.

An endotherm (Gr.endos, within) derives most or all of its body heat from its own metabolism. Mammals, birds, some fishes, and numerous insects are endotherms. Many endotherms maintain a consistent internal temperature even as the temperature of their surroundings fluctuates. Most endotherms have bodies insulated by fur or feathers and a relatively large amount of fat. This insulation enables them to retain heat more efficiently and to maintain a high core temperature (“Core” refers to the body’s internal temperature as opposed to the temperature near its surface). Endothermy allows animals to stabilize their core temperature so that biochemical processes and nervous system functions can proceed at steady, high levels. Endothermy allows some animals to colonize habitats denied lo ectotherms.

Q.7. What are homeotherms and heterotherms?

Ans. The term heterotherm (variable body tempenzture) and homeotherms (constant body temperature) are frequently used by zoologists as alternatives to “cold-blooded” and “warm blooded” respectively. Most endotherms are homeotherms, and most ectotherms are heterotherms. These terms, which refer to variability of body temperature, are more precise and more informative, but still offer difficulties. Some endotherms vary their body temperature seasonally (e.g., hibernation) other vary it on a daily basis. For example, deep-sea fishes live in an environment having no perceptible temperature change. Even though their body temperature is absolutely stable, day in and day out, to call such fishes homeotherms would distort the intended application of the term. Further more, among the homeothermic birds and mammals there are many that allow their body temperature to change between day and night, or, as with hibernators, between seasons. Some ectotherms can maintain fairly constant body temperatures. Among these are a number of reptiles that can maintain fairly constant body temperatures by changing position and location during the day to equalize heat gain and loss.

Q.8. Define (a) daily torpor (b) hibernation (c) aestivation.

Ans. (a) Daily Torpor: Many small mammals and birds, such as bats and humming birds etc, maintain high body temperatures when active but allow their body temperature to drop profoundly when inactive and asleep. This is called daily torpor, an adaptive hypothermia that provides enormous saving of energy to small endotherms that are never more than a few hours away from starvation at normal body temperatures.

(b) Hibernation: Many small and medium-sized mammals in northern temperate regions solve. the problem of winter scarcity of food and low tomperature by entering a prolonged and controlled state of dormancy called hibernation. True hibernators, such as ground squirrels, jumping mice, marmots, and wood chucks prepare for hibernation by storing body fat.

Some mammals, such as bears, badgers, raccoons, and opossums, enter a state of prolonged sleep in winter (winter sleep) with little or no decrease in body temperature. Prolonged sleep is not true hibernation. Bears of the northern forest, sleep for several months.

(c) Aestivation: Aestivation, or summer torpor, is characterized by slow metabolism and inactivity. It enables an animal to survive long periods of the temperatures and scarce water supplies. Hibernation and aestivation are often triggered by seasonal changes in the length o daylight. As the day shorten, some animals will eat huge quantities of food before hibernating. Ground squirrels, for instance, will more than double their weight in a month of gorging.

Q.9. Describe the geographic distribution of ectotherms and endotherms?

Ans. In general, ectotherms are more common in the tropics because they do not have to expend as much energy to mairktain body temperature there, and they can devote more energy to food gatharing and reproduction. Indeed in the tropics, amphibians are far more abundant than mammals. Conversely, in moderate to cool environments, endbthermS have d.eelective advantage and are

more abundant. Their high metabolic rates and insulation allow them to occupy even the polar regions (e.g. polar bears). In fact, the efficient circulatory systems of birds and mammals can be thought of as adaptations to endothermy and a high metabolic rate.

Q.10. What are thermo conformers?

Ans. Many invertebrates have relatively low metabolic rates and have no thermoregulatory mechanisms thus, they passively conform to the temperature of their external environment. These invertebrates are termed thermoconformers. Some higher invertebrates can directly sense differences in environmental temperatures however, specific receptors are either absent or unidentified. Many arthropods, such as insects, crustaceans, and the horseshoe crab (Limu/us), can sense thermal variation. For example, ticks of warm-blooded vertebrates can sense the ‘warmth of a nearby meal” and drop on the vertebrate host.

Q.11. How temperature is regulated in invertebrates?

do adjust temperature by behavioral or physiological mechanisms. For example

1. Temperate-zone insects avoid freezing by reducing the water content in their tissues as winter approaches.

2. Some insects of temperate zone can produce glycerol or

other glycoproteins that act as an antifreeze

4. The desert locust, must reach a certain temperature to become active. It orients in a direction that minimizes the absorption of sunlight.

5. Some species of large flying insects, such as bees and large moths, can generate internal heat and are endothermic. They are able to “warm up” before taking off by contracting all of the flight muscles in synchrony, so that only slight movements of the wings occur but large amounts of heat are produced. This higher temperature of the flight muscles enables the insects to sustain the intense activity required for flight on cold days and nights.

6. Endotherms such as bumblebees, honeybees, and certain moths called noctuids that survive and fly during cold winter moths have a countercurrent heat exchanger that helps maintain a high temperature in the thorax.

7. Most large, flying insects have evolved a mechanism to prevent overheating during flight blood circulating through the flight muscles carries heat from the thorax to the abdomen, which gets rid of the heat.

8. Certain cicadas (Diceroprocta apache) that live in the sonorant desert have cooling by evaporation like vertebrates. When threatened with overheating, these cicadas extract water from their blood and transport it through large ducts to the surface of their body, where it passes through sweat pores and svaporates. In other words, these insects can sweat.

  1. Body posture and orientation of wings to the sun can markedly affect the body temperature of basking insects. For example, perching dragonflies and butterflies can regulate their radiation heat gain by postural adjustment. Fig.6.3.
  2. To prevent overheating, many ground-dwelling arthropods (Tenebrio beetles, locusts, scorpions) raise their bodies as high off the ground as possible to minimize heat gain from the ground.

10 Some caterpillars and locusts orient with reference to both the sun and wind to vary both radiation heat gain and convective heat loss.

11 Some desert-dwelling beetles can exude waxes from thousands of tiny pores on their cuticle. These “wax blooms” prevent dehydration and also are an extra barrier against the desert sun.

12. Color has a significant effect on thermoregulation. Many black beetles may be more active earlier in the day because they absorb more radiation and heat faster. Conversely, white beetles are more active in the hotter parts of the day because they absorb less heat.

13. Honeybees use an additional mechanism that depends on social organization to increase body temperature. In cold weather, they increase their movements and huddle together, thereby retaining heat. They maintain a relatively constant temperature by changing the density of the huddling. Individuals move from the cooler outer edges of the cluster to the warmer center and back again, thus circulating and distributing the heat.

14. Honeybees also control the temperature of their hive by transporting water to it in hot weather and fanning with their wings, which promotes evaporation and convection.

Q.12. How do fishes maintain their body temperature? Ans. Temperature Regulation in Fishes

Ans. The body temperature of most fishes is usually within 1° — 2° of the surrounding water. temperature. Fishes that live in extremely cold water have “antifreeze” materials in their blood. i.e.

  1. Polyalcohols (e.g. sorbitol, glycerol) or water soluble peptides and glycopeptides lower the freezing point of blood plasma and other body fluids.
  2. These fishes also have proteins or protein-sugar compounds that stunt the growth of ice crystals that begin to form.

These adaptations enable these fishes to stay flexible and swim freely in a super cooled state i.e. at a temperature below the normal freezing temperature of a solution. Some active fishes maintain a core temperature significantly above the temperature of the water. Endothermic fishes include several large, active species such as blue fin tuna, swordfish, and the great white shark. Their swimming muscles produce enough metabolic heat to elevate temperatures at the body core, and adaptations of the circulatory system retain the heat. Large arteries convey most of the cold blood from the gills to tissues just under the skin. Branches deliver blood to the deep muscles, where the small vessels are arranged into a countercurrent heat exchanger. This arrangement of blood vessels enhances vigorous activity by keeping the swimming muscles several degrees warmer than the tissue near the surface of the fish. Their muscular contractions can have four times as much power as those of similar muscles in fishes with cooler bodies. Thus, they can faster and range more widely through various depths other predatory fishes more limited to given water depths and temperatures. Fig. 6.4.

Q.13. What is the function of rete mirabile in fishes?

Ans. Rete Mirabile (L. wonder net) is a network of small blood vessels so arranged that the incoming blood runs countercurrent to the outgoing blood and thus makes possible efficient exchange between the two blood streams. Such a mechanism serves to maintain the high concentration of gases in the fish swim bladder. The amazing effectiveness of this device is exemplified by a fish living a depth of 2400 m (8000 feet). To keep the bladder inflated at the depth, the gas inside (mostly oxygen, but also variable amounts of nitrogen, carbon dioxide, argon, and even some carbon monoxide) must have a pressure exceeding 240 atmospheres, which is much greater than the pressure in a fully charged steel gas cylinder. Yet the oxygen pressure in the fish’s blood cannot exceed 0.2 atmosphere – equal to the oxygen pressure at the sea surface. In brief, the gas gland secretes lactic acid, which enters the blood, causing a localized high acidity in the rete mirabile that forces hemoglobin to release its load of oxygen. The capillaries in the rete are arranged so that the released oxygen accumulates in the rete, eventually reaching such a high pressure that the Oxygen diffuses into the swim bladder. The final gas pressure attained in the swim bladder depends on the length of the rete capillaries they are relatively short in fishes living near the surface, but are extremely long in deep-sea fishes.

the oxygen pressure at the sea surface. In brief, the gas gland secretes lactic acid, which enters the blood, causing a localized high acidity in the rete mirabile that forces hemoglobin to release its load of oxygen. The capillaries in the rete are arranged so that the released oxygen accumulates in the rete, eventually reaching such a high pressure that the Oxygen diffuses into the swim bladder. The final gas pressure attained in the swim bladder depends on the length of the rete capillaries they are relatively short in fishes living near the surface, but are extremely long in deep-sea fishes.

Q.14. Describe the temperature regulation in amphibians and reptiles? Ans. Temperature Regulation in Amphibians and Reptiles

Ans. Animals, such as amphibians and reptiles, that have air rather than water as a surrounding medium face marked daily and seasonal temperature changes. Most of these animals are ectotherms. They divert heat from their environment, and their body temperatures vary with external temperatures. Amphibians The optimal temperature range for amphibians varies substantially with the species. Amphibians produce very little heat, and most lose heat rapidly by evaporation from their body surfaces, making it difficult to control body temperature. However, behavioral adaptations enable them to maintain body temperature within a sa:isfactory range, most of the time, by moving to a location, where solar heat is available or into water. When the surroundings are too warm. the animals seek cooler microenvironments, such as shaded areas. Some amphibians, including bullfrogs, can vary the amount of mucus they secrete from their surface, a physiological response that regulates evaporative cooling. Reptiles Reptiles have dry rather than moist skin, which reduces the loss of body heat through evaporative cooling of the skin. They also have an expandable rib
cage, which allows for more powerful and efficient ventilation. Reptiles are generally ectotherms with

relatively low metabolic rates that contribute little to normal body temperatures. Reptiles warm themselves mainly by behavioral adaptations. They seek warm places, orienting themselves toward heat sources to increase heat uptake and expanding the body surface exposed to a heat source. Reptiles do not simply maximize heat uptake, however they may behave in such a way as to truly regulate their temperature within a range If a sunny spot is too warm, for instance, a lizard may sit alternately in the sun and in the shade, or turn in another direction, thereby reducing the surface area exposed to the sun. By seeking favorable microclimates within the environment, many reptiles maintain body temperatures that are quite stable. Some reptiles also have physiological adaptations that regulate heat loss. For example, diving reptiles (e.g., sea turtles, sea snakes) conserve body heat by routing blood through circulatory shunts into the center of the body. These animals can also increase heat production in response to the hormones thyroxin and epinephrine. In addition, tortoises and land turtles can cool themselves through salivating and frothing at the mouth, urinating on the back legs, moistening the eyes, and panting. A few reptiles are endothermic for brief periods of time. For instance when incubating eggs, female phythons increase their metabolic rate by shivering, generating enough heat to maintain their body temperature 5° to 7°C above the surrounding air.

0.15. How do birds and mammals regulate their body temperature? Ans. Temperature Regulation in Birds and Mammals?

Ans. Birds and mammals are the most active and behaviorally complex vertebrates. They can live in habitats all over the earth because they are homeothermic endotherms they can maintain body temperatures between 35 and 42°C with metabolic heat. Birds Various cooling mechanisms prevent excessive warming in birds.

  1. As they have no sweat glands, birds pant to lose heat through evaporative cooling.
  1. Some birds have a vascularized pouch in the floor of the mouth that they can flutter to increase evaporation from the respiratory system.
  1. Feathers are excellent

insulators for the body, especially down type feathers (gular flutter), that trap a layer of air next to the body to reduce heat loss from the skin.

4. Aquatic species, which lose heat from their legs and feet, have peripheral

countercurrent heat exchange vessels called a rete mirabile in their legs to reduce heat loss. The arteries carry warm blood down the legs to warm the cooler blood in the veins, so that the heat is carried back to the body rather than lost through the feet that are in contact with a cold surface. Fig. 6.6.

  1. Mammals that live in cold regions, such as the arctic fox and barren-ground caribou, have rete mirabile in their extremities (e.g., tails, ears, and nose).
  2. Animals in hot climates, such as jack rabbits, have mechanisms, (e.g., large ears) to rid the body of excess heat. Fig. 6.2.
  3. Humans rely more on a layer of fat just beneath the skin as insulation against heat loss.

4 Thick pelts and a thick layer of insulating fat called blubber just under the skin help marine animals, such as seals and whales, to maintain a body temperature of around 36 to 38°C.

  1. The flippers or tail of a whale or seal lack insulating blubber, but countercurrent heat exchangers effectively reduce heat loss in these extremities, as they do in the legs of many birds.
  2. Many terrestrial mammals have sweat glands, which are controlled by the nervous system
  3. Other mechanics that promote evaporative cooling include spreading saliva on body surfaces, an adaptation of some kangaroos and rodents for combating severe heat stress.
  4. Some bats use both saliva and urine to enhance evaporative cooling.

Birds and mammals also use behavioral mechanisms to cope with external temperature changes. Like ectotherms, they sun themselves or seek shade as the temperature fluctuates. Many animals huddle to keep warm: others share burrows for protection from temperature extremes. Migration to warm climates and hibenation enable many different birds and mammals to survive the harsh winter months. The desert camel, have a multitude of evolutionary adaptations for surviving in some of the hottest and driest climates on earth.

Q.16. What is blubber?

Ans. Blubber is a thick pelt and a thick layer of fat found between the skin and muscle of whales and other cetaceans, from which oil is made. The function of blubber is to insulate the body of animal and to maintain a body temperature of around 36° to 38°C.

Q.17 What is gular flutter?

Ans. Gular flutter is a type of breathing in some birds. Some species of birds have a highly vascularized pouch (gular pouch) in their throat that they can flutter to increase evaporation from the respiratory system, as in pelicans.

Q.18. How do birds and mammals generate heat? Ans. Heat Production in Birds and Mammals

Ans. In endotherms, heat generation can warm the body as it dissipates throughout tissues and organs. Birds and mammals can generate heat (thermogenesis) by muscle contraction, ATPase pump enzymes, oxidation of fatty acids in brown fat, and other metabolic process.

Shivering Thermogensis

In severely cold conditions all mammals can produce more heat by augmented muscular activity through exercise or shivering. Every time a muscle cell contracts, the actin myosin filaments sliding cver each other, and the hydrolysis of ATP molecules generate heat. Both voluntary muscular work (e.g., running flying, jumping) and involuntary muscular work (e.g., shivering) generate heat. Heat generation by shivering is called shivering thermogenesis.

Nonshivering Thermogenesis

The hormonal triggering of heat production is called nonshivering thermogenesis. Birds and mammals have a unique capacity to generate heat by using specific enzymes of ancient evolutionary origin—the ATPase pump enzymes in the plasma membranes of most cells. When the body cools, the thyroid gland releases the hormone thyroxin. Thyroxin increases the permeability of many cells to sodium (Na”) ions, which leak into the cells. The ATPase pump quickly pumps these ions out. In the process, ATP is hydrolyzed, releasing heat

Brown fat is a specialized type of fat found in newborn mammals, in mammals that live in cold climates, and in mammals that hibernate. Deposits of brown fat are beneath the ribs and in the shoulders. A large amount of heat is produced when brown fat cell oxidize fatty acids, because little ATP is made. Blood flowing past brown fat is heated and contributes to warming the body. Fig. 6.7.

Hypothalamic Control to Thermogenesis

In amphibians, reptiles, birds, and mammals, specialized cells in the hypothalamus of the brain control The two hypothalamic thermoregulatory areas are the heating center and the cooling center. The heating center controls vasoconstriction of

superficial blood vessels, erection of hair and fur, and shivering or nonshivering thermogenesis. The cooling center controls vasodilatation of blood vessels, sweating and panting. Overall, feedback mechanism with the hypothalamus acting as a thermostat) trigger either the heating or cooling of the body and thereby control body temperature. Specialized neuronal receptors in the skin and other parts of the body sense temperature changes. Warm neuronal receptors excite the cooling center and inhibit the heating center. Cold neuronal receptors have the opposite effects. Fig. 6.8

Torpor is an alternative physiological state in which metabolism decreases and the heart and respiratory system slow down. Many endotherms e.g. hummingbirds, bats etc. at night enter a state of daily torpor in which their, body temperature declines. In effect, their body’s thermostat is turned down, thereby conserving energy when food supplies are low and environmental temperatures are extreme. Humming birds can only maintain a high body temperature for a short period, because they usuey weigh less than 10 gm, and have almost no reserve energy providing source. They devote much of the day to locating and sipping nectar. When not feeding (during night) they run out of energy, and as such their metabolic rate decreases.


During the winter, various endotherms (e.g., bats, wood chucks, chipmunks, ground squirrels) go into hibernation. During hibernation, the metabolic rate slows, as do the heart and breathing rates. Mammals prepare for hibernation by building up fat reserves and growing long winter pelts. All hibernating animals have brown fat. Decreasing day length stimulates both increased fat deposition and fur growth.


It is characterized by slow metabolism and inactivity. It enables some animals to survive long periods of high temperatures and scarce water supplies. Aestivation is an adaptation in desert environments. Thus most of the animals including predators are nocturnal (active during night), when temperature is relatively low.

Winter Sleep

Some animals, such as badgers, bears, opossums, raccoons, and skunks, enter a state of prolonged sleep in winter. Since their body temperature remains near normal, this is not true hibernation. The basal metabolic rate of birds and mammals is high and also produces as an inadvertent but useful by product.

Q.19. What is brown fat?

  1. Placental mammals are unique in having a dark adipose tissue called brown fat,
    specialized for generation of heat. Newborn mammals, including human infants, have much more brown fat than adults. In human infants brown fat is located in the chest, upper back, and near the kidneys. In adults it is mostly found in the neck and between the shoulders. The abundant mitochondria in brown fat contain a membrane protein called thermogenin that acs to uncouple production of ATP during oxidative phosphorylation.

Q.20. How do excretion and osmoregulation differ?

Ans. Excretion (. excretion, to eliminate) can be defined broadly as “The disposal of nitrogen-containing waste products of metabolism from an animal’s body”. These products include carbon dioxide and water (which cellular respiration primarily produces), excess nitrogen (which is produced as ammonia, urea or uric acid from metabolism of proteins and nucleoproteins), and solutes (various ions). Osmoregulation is the maintenance of proper internal salt and water concentrations in a cell or in the body of a living organism. Animal cells require more critical balance of water and solutes in body as they cannot survive a net water gain or loss. Water continuously leaves and enters the cells however, the quantity of the water and the solutes is kept in balance.

Q.21. How do osmoconformers differ from osmoregulators?

Ans. The animals, which do not actively adjust their internal osmolarity are know as
osmoconformers. By control, animals whose body fluids are not isotonic with the outside environment, called osmoregulators, must either discharge excess water if they live in a hypotonic environment or continuously take in water to offset osmotic loss if they inhabit a hypertonic environment. A net movement of water occurs only in an osmotic gradient (from a region of lower osmolarity to a region of higher osmolarity), and osmoregulators must expend energy to maintain osmotic gradients, to move water lither in or out. They do so by manipulating solute concentrations in their body fluids. Most marine invertebrates are osmoconformers. Among the vertebrates, the hagfishes are isotonic with the surrounding seawater. All freshwater, terrestrial. and many marine animals are osmoregulators.

Q.22. What is the function of the contractile vacuole, and where would you find one?

Ans. Contractile Vacuoles Many unicellular and simple multicellulair animals have no special excretory structures. Nitrogenous wastes are simply excreted across the general cell membranes into the surrounding water. Many freshwater species (protozoa, sponges), do, however, have a special excretory organelle, the contractile vacuole that pump out excess water. Though there is now evidence that contractile vacuoles excrete some nitrogenous wastes, it seems clear that their primary function is elimination of excess water. In most protozoa the vacuole is surrounded by a layer of tiny vesicles and these, in turn, are surrounded by a layer of mitochondria. The vesicles initially contain a fluid isotonic with the cytosol, but later actively pump out ions, using energy from ATP manufactured in the mitochondria. Thus contractile vacuoles are energy requiring devices that expel excess water from individual cells exposed to hypoisonotic environments.

Q.23. How do protonephridia and metanephridia function?

Ans. Protonephridia A protonephriaium (Gr. porotos, first + nephridium) is a network of closed tubules lacking internal openings. The tubules branch throughout the body, and the smallest branches are capped by a cellular unit called a flame bulb. Interstitial fluid bathing the tissues of the animal passes through the flame bulb and enters the tubule system. The flame bulb has a tuft of cilia projecting into

the tubule, and the beating of these cilia propels fluid along the tubule, away from the flame bulb. In planaria, tributaries of the tubular system drain into excretory ducts that empty into the external environment through numerous openings called nephridiopores. Fig. 6.9. The flame-bulbs systems of fresh water flatworms function mainly in osmoregulation most metabolic wastes diffuse out from the body surface or are exerted into the gastrovascular cavity and eliminated through the mouth. However in some parasitic flatworms, which are isotonic to the surrounding fluids of their host organisms, protonephridia function mainly in excretion, disposing of nitrogenous wastes. Protonephridia are also found in rotifers, some annelids, the larvae of molluscs, and lancelets, which are invertebrate chordates.


A more advanced type of excretory structure among invertebrates is the metanephridium (Gr. meta, beyond + nephridium). Protonephridia and metanephridia have critical structural differences. Both open to the outside, but metanephridia:

2.are multicullular. Metanephridia are found in most annelids (including earthworms) and a variety of other invertebrates. Each segment of earthworm has a pair of metanephridia, which are tubules immersed in coelomic fluid and enveloped by a network of capillaries. The internal opening of a metanephridium is surrounded by a ciliated funnel, the nephrostome, that collect coelomic fluid. An earthworm’s metanephridia have excretory and osmoregulatory functions. As the fluid moves along the tubule, the transport epithelium bordering the lumen pumps essential salts out of the tubule, and the salts are reabsorbed into the blood circulating through the capillaries. The urine that exits through the nephridiopore contains nitrogenous wastes and is hypotonic to the body fluids. By excreting this dilute urine in amounts up to 60% of the body weight of the worm per day. the metanephridia offset the continuous osmosis taking place across the skin of the animal from the damp soil. Fig. 6.10. The excretory system of molluscs includes protonephridia in larval stages and metanephridia in adults.

Q.24. How do antenna! (green) glands and maxillary glands function? or How do excretion occurs in Crustacea? Ans. Antenna! (Green) and Maxillary Glands

Ans. In crustaceans that have gills, nitrogenous wastes are removed by simple diffusion across the gills. Most crustaceans release ammonia, although they also produce some urea and uric acid as waste products. Thus, the excretory organs of fresh water species may be more involved with the reabsorption of ions and elimination of water than with the discharge of nitrogenous wastes. The excretory organs in some crustaceans (crabs, crayfish) are antennal glands or green glands because of their location near the antenna and their green color. The glands remove the water and nitrogenous waste substances from the surrounding blood into the end sac by the process of ultra filtration. The filtrate called the primary urine, passes to the labyrinth. The useful and necessary substances are reabsorbed and then passed to the blood. The remaining fluid is now called the final urine. The urine passes into the bladder and then expelled out of the body through the renal aperture.

In other crustaceans (some malacostracans [crabs, shrimp, pillbugs]), the excretory organs are near the mixillary segments and are termed maxillary glands. In maxillary glands fluid collects within the tubules from the urrounding blood of the hemocoel, and this primary urine is modified substantiallythy selective reabsorption and secretion as it moves through the excretory system and rectum. Fig. 6.11..

Q.25. Write an account on Malpighian tubules of insects,

Ans. Malpighian tubules Insects have open circulatory systems, with tissues bathed directly in hemolymph contained in sinuses. Their excretory organs, called Malpighian tubules, remove nitrogenous wastes from the hemolymph and also function in osmoregulation. These organs open into the digestive tract at the juncture of the midgut and hindgut. The tubules, with dead-end at the tips away from the digestive tract, are immersed in the hemolymph. The transport epithelium that lines a tubule pumps certain solutes, including potassium ions and nitrogenous wastes, from the hemolymph into the lumen of the tubule. The fluid within the tubule then passes through the hindgut into the rectum. The epithelium of the rectum pumps most of the salt back into the hemolymph, and water follows the salts by osmosis. The nitrogenous wastes are eliminated as almost dry matter along with the

Figure 6.12a

Malpighian tubules of insects. Malpighian tubules are ouffoldings of the digestive tract. The tubules accumulate nitrogenous wastes and salts from the hemolymph, and water follows these solutes by osmosis. Most of the salts and water are reabsorbed across the epithelium of the rectum, and the dry nitrogenous wastes are eliminated with the faces. feces. The insect excretory system is one adaptation that has contributed to the tremendous success of these animals on land, where conserving water is essential. Fig. 6.12. 6.12a

Q.26. Describe the excretory organs in arachnids. OR What are coxal glands?

Ans. Coxal (L coxa, hip) glands are common among arachnids (spiders, scorpions, .ticks mites) These spherical sacs resemble. annelid nephridia Wastes an collected from the surrounding hemolymph of the hemocoel and discharged through pores on from one to several pairs of appendages near the proximal joint (coxa) of the leg Recen’ evidence suggests that the coxai glands may also function in the release of pheromones. Other arachnid species have Malpighian tubules instead of. or in addition to, the coxal glands. In some of these species, however Malpighian tubules seem to function in silk production rather than in excretion. Fig. 6.13.

Q.27. How does a vertebrate losewater from its body? How does it gain water?

Ans. On land the greatest threat to life is desiccation. Water is lost by (1) evaporation from the respiratory surfaces- lungs. trachea, etc.) (2) by evaporation from the general body surface, (3) by sweating or panting (4) by elimination in the feces, and (5) by excretion in the urine. The lost water must obviously be replaced if life is to continue. It is replaced (1) by drinking (2) by eating foods containing water (3) by the oxidation of nutrients (metabolic reactions yield water as end product) (4) certain insects (e.g., desert roaches, certain ticks and mites, and the mealworm) are able to absorb water vapor directly from atmospheric air.

Of particular interest is a comparison of water balance in human beings (non-desert mammals that drink water) with that of kangaroo rats (desert rodents that may drink no water at all). Kangaroo rats acquire all their water from their food: 90% is metabolic water derived from oxidation of foods, and 10% as free moisture in food. Even though we eat foods with a much higher water content than ‘ the dry seeds that make up much of a kangaroo rat’s diet, we still must drink half our total water requirement.

Q.28. How solute losses and gains are done in vertebrates?
Ans. Solute losses must be balanced by solute gains. Vertebrates take in solutes:
1. by absorption of minerals from the small and large intestines.
2. through the integument or gills,
3. from secretions of various glands or gills, and
4. by metabolism (e.g., the waste products of degradative reactions).
Vertebrate lose solutes in sweat, feces, urine, and gill secretions, and as metabolic wastes. The major metabolic wastes that must be eliminate are ammonia, urea or uric acid.

Q.29. How various vertebrates maintain water and salt balance?

Q.30. How do vertebrates achieve osmoregulation?

Ans. A variety of mechanisms have evolved in vertebrates to cope with their osmorgulatory problems. These are:

  1. Most terrestrial animals are covered by relatively impervious surfaces that help prevent dehydration.
  2. The multiple layers of dead, keratinized skin cells covering most terrestrial vertebrates prevents loss of water.
  3. Behavioral adaptations, such as nervous and hormonal mechanisms that control thirst, are important osmoregulatory mechanism in land-dwelling animals.
  4. Many terrestrial animals, especially in deserts, are nocturnal, the important behavioral adaptation that reduces dehydration.
  5. The kidneys and other excretory organs of terrestrial animals often exhibit adaptations that help conserve water.
  6. Some mammals are so well adapted to minimizing water loss that they can survive in deserts without drinking.

Q.31. What are three functions of the kidneys?

  1. Following three key functions take place in kidneys:
  2. Filtration: During filtration blood passes through a filter that retains blood cells, proteins, and other large solutes but lets small molecules, ions, and urea to pass through.
  3. Reabsorption: During reabsorption selective ions and molecules (such as vital nutrients and water) are reabsorbed from the filtrate into the blood stream.
  4. Secretion: During secretion, drugs, selected ions, and end products of metabolism (e.g., K + ,. H + , NH3) that are in the blood are selectively secreted into the filtrate for removal from the body. The overall effect of filtration, secretion, and reabsorption is analogous to cleaning out a drawer (blood) by first removing all the small articles (filtration), returning useful items to the blood (reabsorption), adding additional useless items to the refuse pile (secretion), and then is carding all the unwanted objects (excretion). These main functions of the kidneys are central to homeostasis, for they enable the kidney to clear the blood of metabolic wastes and respond to imbalances in body fluids by excreting more or less of a particular ion.

Q.32. Describe the types (or variations) of kidneys in vertebrates. Ans. Vertebrate Kidney Variations

Ans. Vertebrates have two kidneys that are in the back of the abdominal cavity, on either side of the aorta. Each kidney has a coat of connective tissue called the renal capsule (L. renes, kidney). The inner portion of the kidney is called the medulla the region between the capsule and the medulla is the cortex. There are three kinds of vertebrate kidneys.

The most primitive type of kidney functional in adult vertebrates is the Pronephros. The Pronephros is believed to represent the most anterior part of the ancestral archinephros. Distribution of Pronephros: The pronephric tubules continue to function in the adult hagfish and in some teleosts. The pronephros is also a functional structure in many immature fishes as in the larvae of some amphibians and appears transitorily in the embryos of all the higher vertebrates.

The mesonephros is the kidney tissue that develops posterior to the pronephros. These kidneys form discrete organs that readily look like kidneys. Distribution of Mesonephros: The mesonephros is the functional kidney of the adult lamprey, cartilaginous fishes, bony fishes, and amphibians. The mesonephros also functions in the embryos of reptiles, birds and mammals.

3. Metanephros

The metanephric kidney develop from the most posterior portion of the mesonephros and it’s the most compact of any of the vertebrate renal structures. The body of metanephros has a two fold origin. Part of it develops from the posterior end of the mesonephros, while part forms as a new and unique metanephric structure.Distribution of the Metanephros The metanephros becomes functional in most reptilian, avian and mammalian embryos and is the functional kidney of all adult amniotes. Fig. 6.14.

Q.33. What are the physiological differences between three types of vertebrate kidneys?

Ans. The physiological differences between three kidney types are primarily related to the number of blood-filtering units they contain. The pronephric kidney forms in the anterior portion of the body cavity and contains fewer blood-filtering units than either the mesonephric or metanephric kidneys. The large number of filtering units in the latter has allowed vertebrates to face the rigorous osmoregulatory and excretory demands of freshwater and terrestrial environments.

Q.34.How sharks have solved their osmotic problems?

Ans. Sharks and their relatives (skates and rays) have mesonephric kidneys and rectal glands that secrete a highly concentrated salt (fnlaCI) solution. Despite its relatively low salt concentration, a marine shark is slightly hypertonic to seawater. It does not drink water, and the water that enters its body by osmosis is disposed of in urine, the waste fluid formed by the excretory organs, the kidneys. To reduce water loss, sharks use two organic molecules—urea and trimethylamine oxide (TMO) in their body fluids to raise the osmotic pressure to a level equal to or higher than that of the seawater. Urea denatures proteins and inhibits enzymes, whereas TMO stabilizes proteins and activates enzymes. Together in the proper ratio, they counteract each other, raise the osmotic pressure, and do not interfere with enzymes or proteins. This reciprocity is termed the counteracting osmolyte strategy.

Q.35. How do teleost fishes osmoregulate?

Ans. Teleost FishesMost teleost fishes have mesonephric kidneys.

1. Freshwater Fishes: Because the body fluids of freshwater fishes are hyperosmotic relative to freshwater, water tends to enter the body of fishes, causing excessive hydration or bloating. At the some time, body ions tend to move outward into the water. To Solve this problem, freshwater fishes:

(i) usually do not drink much water,

(ii) their bodies are coated with mucus, which helps stem inward water movement,

(iii)water that inevitably enters by osmosis across the gills is pumped out by

the kidney, which is capable of forming very dilute urine,

(iv) special salt-absorbing cells located in the gills move salt ions, from the water to the blood. Fig. 6.15a.

2. Marine Fishes: Marine bony fishes are hypotonic relative to the surrounding water, and have the problem of excessive water loss and excessive salt intake. To compensate dehydration, marine fishes: Fig. 6.15b.

(i) drink almost continuously to replace the water they are constantly losing. This seawater is absorbed from the intestine,

(ii) they secrete Na t , C[, and K + ions through specialized salt-secreting cells in their gills,

(iii)channels in plasma membranes of their kidneys activity transport the multivalent ions that are abundant in seawater (e.g., Ca 2+ , Mg 2+ , S0 2 4 – , and PO ° 4 ) out of the extracellular fluid and into the nephron tubes. The ions are then excreted in a concentrated urine. 3 Some fishes encounter both fresh-and saltwater during their liVes. Newborn Atlantic salmon swim downstream from the freshwater stream after their birth and enter the Instead of continuing to pump ions in, as they have done in freshwater, the salmon must now rid their bodies of salt. Years later, these same salmon migrate from the sea to their freshwater home to spawn. As they do so, the pumping mechanism reverse themselves.

Osmoregulation, Osmoregulation by (a) freshwater and (b) marine fishes. Large black arrows indicate passive uptake or loss of water or ions. Small black and white arrows indicate active transport processes at gill membranes and kidney tubules. Insets of kidney nephrons depict adapta­tions within the kidney. Water, ons, and small organic molecules are filtered from the blood at the glomerulus of the nephron. Essential components of the filtrate can be reabsorbed within the tubule system of the nephron. Marine fishes conserve water by reducing the size of the glomerulus of the nephron, and thus reducing the quantity of water and ions filtered from the blood. Ions can be secreted from the blood into the kidney tubules. Marine fishes can produce urine that is isoomotic with the blood. Freshwater fishes have enlarged glomeruli and short tubule systems. They filter large quantities of water from the blood, and tubules reabsorb some ions from the filtrate. Freshwater fishes produce a hypoosmotic urine.

Q.36. How do amphibians conserve water?

Ans. The amphibian kidney is identical to that of freshwater fishes, because amphibians spend a large portion of their time in freshwater, and when on land, they tend to seek out moist place. Amphibian take up water and ions:

(i) in their food and drink,

(i) through their skin that is in contact with moist substrate, and through the urinary bladder, This uptake counteracts what is lost through evaporation and prevents osmotic imbalance, Figure 6.16.The urinary bladder of frog, toad or salamander is an important water and ion reservoir. For example, when the environment becomes dry, the bladder enlarges for storing more urine. If an amphibian becomes dehydrated, a brain hormone causes water to leave the bladder and enter the body fluid.

0.37. What are salt glands? In which type of animals these are found?

Ans. Some desert and marine birds and reptiles have evolved an effective solution for execrating large loads of salt eaten with their food. In these animals, salt glands are
present, located above each eye. These are capable of excreting a highly concentrated
solution of sodium chloride (Nacl), up to twice the concentration of seawater. In marine birds, the salt solution runs out the nares. Marine lizards and turtles, like Alice in wonderland’s Mock turtle, shed their salt gland secretion as salty tears. Salt glands are important accessory organs of salt exertion in these animals

because their kidney cannot produce concentrated urine, as can mammalian kidney. Fig. 6.17.

Q.38. What are the primary regulatory organ for osmotic balance in amniotes?

Ans. Reptiles, birds, and mammals all possess metanephric kidneys. Their kidneys are by far the most complex animal kidneys, well suited for these animal’s high rates of metabolism In most reptiles, birds, and mammals, the kidneys can remove far more water than can those in amphibians, and the kidneys are the primary regulatory organs for controlling the osmotic balance of the body fluids.

Q.38. How do nasal cavities help conserve water? •

Ans. Major sites of water loss in mammals are the lungs. To – reduce this evaporative loss, many mammals have nasal cavities that act as countercurrent exchange systems. When the animal inhales, air passes through the nasal cavities and is warmed by the surrounding tissues. In the process, the temperature, of this tissue drops. When the air gets deep into the lungs, it is further warmed and humiuiried. During exhalation, as me warm moist air passes up the respiratory tree, it gives up its heat to the nasal cavity. As the air cools, much of the water condenses on the nasal surfaces and does not leave the body. This mechanism explains why a dog’s nose is usually cold and moist. Fig. 6.18.

Q. 40. How does metanephric kidney function?

Ans. Metanephric Kidney The filtration device of the metanephric kidney consists of over one million individual filtration, secretion, and absorption structures called nephrons (Gr. nephros, kidney + on, neuter). At the beginning of the nephron is the filtration apparatus called the glomerular capsule (formerly Bowman’s capsule), which looks rather like a tennis ball that has been punched in on one side. The capsules are in the cortical (outermost) region of the kidney. In each capsule, an afferent (“going to”) arteriole enters and branches into a fine network of capillaries called the glomerulus. The walls of these glomerular capillaries contain small perforations called filtration slits that act as filters. Blood pressure forces fluid through these filters. The fluid is now known as glomerular filtrate Because the filtration slits are so small, large proteins and blood remain in the blood and leave the glomerulus via the efferent (“outgoing”) arteriole. The efferent arteriole then divides into a set of capillaries called the peritubular capillaries that wind profusely around the tubular portion of the nephron. Eventually they merge to form veins that carry blood out of the kidney. and contains small molecules, such as glucose, ions (Ca 2+ , PO4 ), and the primary nitrogenous waste products of metabolism — urea and uric acid.

Figure 6-19 Urinary system of humans, with enlargements showing detail of the kidney and a single nephron ,

Beyond the glomerular capsule are the proximal convoluted tubule, the loop of the nephron (formerly the loop of Henle), and the distal convoluted tubule. At various places along these structures, the glomerular filtrate is selectively reabsorbed, returning certain ions (e.g. Na t , K + , CI ) to the bloodstream. Both active (ATP requiring) and passive procedures are involved in the recovery of these substances. Potentially harmful compounds, such as hydrogen (he) and ammonium (NH) ions, drugs, and various other foreign materials are secreted into the nephron lumen. In the last portion of the nephron, called the collecting duct, final water reabsorption takes place so that the urine contains an ion

Q.41. Describe the human urinary system.

Ans. In humans, the kidneys are a pair of bean-shaped organs about 10 cm long. Blood enters each kidney via the renal artery and leaves each kidney via the renal vein. Although the kidneys account for less than 1% of the weight of the human body, they receive about 20% of the blood pumped with each heart-beat. Urine exits the kidney through a duct called the ureter. The ureters of botll kidneys drain into a common urinary bladder. During urination, urine leaves the body from the urinary bladder through a tube called the urethra, which empties near the vagina in females or through the penis in males. Sphincter muscles near the junction of the urethra and the bladder control urination. Fig. 6.20.

Q.42. How does the countercurrent flow mechanism in the kidney functions?

Ans. Countercurrent Exchange The loop of the nephron increases the efficiency of reabsorption by a countercurrent flow. Generally, the longer the loop of the nephron, the more water and ions that can be reabsorbed. It is why that desert rodents (e.g., the kangaroo rat) that form highly concentrated urine have long nephron loops. Similarly, amphibians that are closely associated with aquatic habitats have nephrons that lack a loop. Figure 6.21 shows the countercurrent flow mechanism for concentrating urine. The process of reabsorption in the proximal convoluted tubule removes some salt (NaCI) and water from the glomerular filtrate and reduces its volume by approximately 25%. However, the concentrations of salt and urea are still isoosmotic with the extracellular fluid. As the filtrate moves to the descending limb of the loop of the nephron, it becomes further reduced in volume and more concentrated. Water moves out of the tubule by osmosis due to the high salt concentration (the “brine-bath”) in the extracellular fluid. As the filtrate passes into the ascending limb, sodium (Na t ) ions are actively transported out of the filtrate into the extracellular fluid, with chloride (Cr) ions following passively. Water cannot flow out of the ascending limb because the cells of the ascending limb are impermeable to water. Thus, the salt concentration of the extracellular fluid becomes very high. The salt flows passively into the descending loop, only to move out again in the ascending loop, creating a recycling of salt through the loop and the extracellular fluid. Because the flows in the descending and ascending limbs are in opposite directions, a countercurrent gradient in salt is set up. The osmotic pressure of the extracellular brine bath is made even higher because of the abundance of urea that moves out of the collecting ducts. Finally, the distal convoluted tubule empties into the collecting duct, which is permeable to urea, and the concentrated urea in the filtrate diffuses out into the surrounding extracellular fluid. The high urea concentration in the extracellular fluid, coupled with the high concentration of salt, forms the urea-brine bath that causes water to move out of the filtrate by osmosis as it moves down the descending limb. Finally, the many peritubular capillaries surrounding each nephron collect the water and return it to the systemic circulation. The renal pelvis of the mammalian kidney is continuous with a tube, the ureter that carries

urine to a storage organ called the urinary bladder. Urine from two ui eters (one from each kidney) accumulates in the urinary bladder. The urine leaves the body through a single tube, the urethra, which opens at the body surface at the end of the penis On human males) or just in front of the vaginal entrance (in human females). As the urinary bladder fills with urine, tension increases in its smooth muscle walls. In response to this tension, a reflex response relaxes sphincter muscles at the entrance to the urethra. This response is called urination. The two kidneys, two ureters, urinary bladder, and urethra constitute the urinary system of mammals.

The Thermoregulating Ectotherm

By Jake Zadik, a former communications intern with The Ocean Foundation who is now studying in Cuba.

So, you ask, what is a thermoregulating ectotherm? The word “ectotherm” refers to animals that generally have a body temperature comparable to their surrounding environment. They cannot internally regulate their body temperature. People often refer to them as “cold-blooded”, but this term tends to misdirect people more often than not. Ectotherms include reptiles, amphibians, and fish. These animals tend to thrive in warmer environments. Sustained energy output of a warm-blooded (mammal) and a cold-blooded (reptile) animal as a function of core temperature.

“Thermoregulating,” refers to the ability of animals to maintain their internal temperature, with little regard to the temperature. When it is cold outside, these organisms have the ability to stay warm. When it is hot outside, these animals have the ability to cool themselves down and not overheat. These are the “endotherms,” such as birds and mammals. Endotherms have the ability to maintain a constant body temperature and are also referred to as homeotherms.

So, at this point you may realize that the title of this blog is actually a contradiction—an organism that cannot regulate its body temperature but actually has the ability to actively regulate its body temperature? Yes, and it is a very special creature indeed.

This is sea turtle month at The Ocean Foundation, which is why I have chosen to write about the leatherback sea turtle and its special thermoregulation. Tracking research has shown this turtle to have migration routes across oceans, and be constant visitors to a wide array of habitats. They migrate to the nutrient rich, but very cold waters as far north as Nova Scotia, Canada, and have nesting grounds in tropical waters throughout the Caribbean. No other reptile actively tolerates such a wide range of temperature conditions—I say actively because there are reptiles that tolerate below freezing temperatures, but do so in a hibernating state. This has fascinated herpetologists and marine biologists for many years, but it has been more recently discovered that these massive reptiles physically regulate their temperature.

…But they are ectotherms, how do they do this??…

Despite being comparable in size to a small compact car, they do not have the built in heating system that comes standard. Yet their size does play a significant role in their temperature regulation. Because they are so large, leatherback sea turtles have a low surface area to volume ratio, thus the core temperature of the turtle changes at a much slower rate. This phenomenon is called “gigantothermy.” Many scientists believe this was also a characteristic of many large prehistoric animals during the climax of the ice age and it eventually led to their extinction as temperatures began to rise (because they could not cool down fast enough).

The turtle is also wrapped up in a layer brown adipose tissue, a strong insulating layer of fat most commonly found in mammals. This system has the ability to retain more than 90% of heat at the core of the animal, decreasing the heat loss through the exposed extremities. When in high temperature waters, just the opposite occurs. Flipper stroke frequency decreases dramatically, and blood moves freely to the extremities and expels heat through the areas not covered in the insulating tissue.

Leatherback sea turtles are so successful at regulating their body temperature that they have the ability to maintain constant body temperature 18 degrees above or below the ambient temperature. That is so incredible that some researchers argue because this process is metabolically accomplished leatherback sea turtles are actually endothermic. However, this process is not anatomically conducted, therefore most researchers suggest this is a diminutive version of endothermy at best.

Leatherback turtles aren’t the only marine ectotherms to possess this ability. Bluefin tuna have a unique body design that keeps their blood at the core of their body and have a similar counter current heat exchanger system to the leatherback. Swordfish retain heat at their head through a similar insulating brown adipose tissue layer to increase their vision when swimming in deep or cold waters. There are also other giants of the sea that lose heat at a slower process, such as the great white shark.

I think thermoregulation is just one incredibly fascinating characteristic of these beautiful majestic creatures with so much more than meets the eye. From the tiny hatchlings making their way to the water to the ever-ranging males and the returning nesting females, much about them remains unknown. Researchers are unsure where these turtles spend the first few years of their lives. It remains something of a mystery on how these great distance-traveling animals navigate with such precision. Unfortunately we are learning about sea turtles at a rate that is much slower than the rate of their population decline.

In the end it will have to be our determination to protect what we do know, and our curiosity about the mysterious sea turtles that leads to stronger conservation efforts. There is so much unknown about these fascinating animals and their survival is threatened by the loss of nesting beaches, plastic and other pollution in the sea, and accidental bycatch in fishing nets and longlines. Help us at The Ocean Foundation support those who devote themselves to sea turtle research and conservation efforts through our Sea Turtle Fund.

Not too fast, not too slow: Researchers untangle energetics of extinct dinosaurs

Growth rates across an evolutionary tree. Dinosaurs growth rates fall in between warm blooded mammals and birds ('endotherms') in red, and cold-blooded fish and reptiles ('ectotherms') in blue. They are closest to living mesotherms. Credit: John Grady.

( —Dinosaurs dominated the landscape for more than 100 million years, but all that remains today are bones. This has made it difficult to solve a long-standing and contentious puzzle: were dinosaurs cold-blooded animals that lumbered along or swift warm-blooded creatures as depicted in Jurassic Park? The answer, according to scientists at the University of New Mexico, is neither. Instead, dinosaurs took a middle path between warm-blooded mammals ('endotherms') and cold-blooded reptiles ('ectotherms').

"Most dinosaurs were probably mesothermic," said John Grady, a graduate student at UNM who led the research. "A thermally intermediate strategy that only a few species – such as egg laying echidnas or great white sharks – use today."

The study, Evidence for mesothermy in dinosaurs, released today in the prestigious journal Science, is the first to quantitatively explore the relationship between growth rate and metabolic rates in animals and extend that to long extinct animals such as dinosaurs.

The research, supported by fellowships from the NIH funded Program in Interdisciplinary Biology and Biomedical Science (PiBBs) to Grady and two fellow graduate students, Eva Dettweiler-Robinson and Natalie Wright, was supervised by Professor and PiBBs Director Felisa Smith from the University of New Mexico, and Professor Brian Enquist from the University of Arizona.

Using an extensive database of animal growth and energy use developed by Grady, researchers first demonstrated that animals that grow faster, not only require more energy, but have higher body temperatures. Then, using growth estimates made by paleontologists for extinct dinosaurs, the researchers calculated dinosaur metabolic rates. The result was unexpected: dinosaurs were clearly intermediate between modern mammals and reptiles.

Energy use in dinosaurs and other vertebrates. Credit: John Grady

"I think we were all surprised by this," Smith said. "The idea certainly took some getting used to. But, the patterns were so robust." Grady analyzed the data with help from Dettweiler-Robinson and Wright. "John spent years compiling this information', said Dettweiler-Robinson. "Collecting more than 30,000 rows of data was quite a feat."

The researchers found that feathered dinosaurs and primitive birds grew distinctly slower than their descendants, modern birds. 'Archaeopteryx, the first bird' explains Grady, 'took two years to reach maturity. But, a red-tailed hawk, which is about the same size, only takes 6 weeks'. While dinosaurs didn't grow as fast as modern birds or mammals, they did grow significantly faster than modern reptiles.

"This higher energy use probably increased speed and performance," Grady said. "Mesothermic dinsoaurs were likely faster predators or better able to flee from danger than the large reptiles found earlier in during the Mesozoic." Dinosaurs quickly became the new ecological incumbents.

Mesothermy in dinosaurs may have helped them become ecologically dominant and probably also helped them become enormous. "A lion the size of a T-Rex," said Smith "while a frightening thought, would quickly starve to death because it would be so hard to find enough food." By adopting a medium-powered energetic strategy, mesothermy may have provided the perfect solution. "It allows a performance advantage over ectothermic reptiles," Grady said. 'but without the high overhead costs of modern birds and mammals. In any case, it was a successful formula for a long reign in the Mesozoic," Smith added.

Do ectotherms think slower when they are cold? - Biology

A Quick Course in Ichthyology

by Jason Buchheim
Director, Odyssey Expeditions

  • FISH Definition
  • FISHES- class agnatha
  • FISHES- Class Chondrichthyes
    • Shark Attack
    1. ________________
    2. ________________
    3. ________________
    4. ________________
    5. ________________
    6. ________________
    7. Fish are fun!

    FISH : Any of a large group of cold-blooded, finned aquatic vertebrates. Fish are generally scaled and respire by passing water over gills.Modern fish are divided into three classes.

    I. AGNATHA, primitive jawless fish.Lampreys and Hagfish

    II. CHONDRICHTHYES, the jawed fish with cartilaginous skeletons. Sharks, Rays, Rat-Fishes

    III. OSTEICHTHYES, fish with bony skeletons.Lungfish, Trout, Bass, Salmon, Perch, Parrot Fish

    Fish come in all shapes and sizes, some are free swimming, while others rest on the bottom of the sea, some are herbivores and others are carnivores, and some lay eggs while others give live birth and parental care to their young.
    FISH: the members of a single species
    FISHES: more than one species of fish
    FISHES- class Agnatha

    • Primitive
    • No jaws
    • Cartilaginous skeleton
    • Scaleless skin
    • Oral sucker in place of jaws
    • Predators and filter feeders
    • anticoagulating saliva
    • fresh and salt water
    • some anadromous
    • Cartilaginous skeleton
    • Skin covered with denticles, not scales
    • Five to seven gill slits per side
    • No swim bladder
    • Internal fertilization
    • Spiral valve intestines
    • Five to seven gill arches
    • Cartilaginous jaws, loosely attached lower jaws

    In fact, most sharks are entirely incapable of this feat. The largest fish of all, the Whale Shark, which can reach sizes of up to 59 feet and weigh 88,000 lb., is a very calm and approachable plankton feeder. There are many species of sharks which can inflict severe bodily injury and require the utmost of respect. The most feared of all, the Great White Shark, has been responsible for most of the fatal shark attacks off the California and Australian coastlines. While the Great White gets all the notoriety, pound for pound, the Bull Shark is probably the most ferocious. The Great White generally attacks a person because it has confused it with its favorite food, the seals and sea lions, but the Bull Shark will attack a person just because they are there. Even with these dangerous animals roaming the ocean, your chances of getting attacked by a shark are very remote.

    Worldwide, there are only about three hundred documented shark attacks a year. The chances are much higher that you will be hit by a drunk driver while driving to the beach then they are that you will even encounter a dangerous shark when you get there. There are some activities that will greatly increase your chance of a shark attack, such as carrying speared fish with you while diving or collecting abalone in turbid waters. Statistics of 1,652 shark attacks show that males are much more likely to be attacked than females (10 to 1 ratio), this is probably because males are much more active in the water, surfing and going to deeper depths where sharks are more common.

    The presence of large numbers of fish, or fish behaving in an unusual manner, has been reported preceding many attacks. In 40 percent of the reported shark attacks, people were pole-fishing or spear-fishing in the area of an attack. A comparison of the number of people swimming to those fishing and spear-fishing seems to show that these two pastimes have by far the highest risk of inducing an attack. While swimming, the chance of drowning is more than 1,000 times greater than that of dying from a shark attack.

    Most shark attacks occur in shallow water, where most bathers are, and in 94 percent of the cases the attack was by an individual shark acting alone. About 10 percent of reported shark attacks are on divers since the number of divers in the water at one time must be much smaller than 10 percent of beach bathers, the odds of being attacked must be significantly greater for divers.

    Close passes were seldom made before the attack, and in the majority of the cases there was only one strike. Few attacks involved more than one bite. This indicates that in many cases the attacking shark mistook the victim for a more usual kind of food and did not attack any further when the error was discovered. It is fortunate that sharks, in most cases, do not consider humans to be suitable food. This information also refutes the long-standing notion that fresh human blood is a powerful attractant that excites sharks into a feeding frenzy. If this were so, the presence of blood would certainly have induced that attacking shark to strike the victim repeatedly. Most wounds occur on the appendages- the hands, arms, legs, and feet. Lacerations of varying severity are the most common types of injury. About 25 percent of attacks kill the victim. The most usual cause of death is shock, combined with a severe loss of blood.


    Swimmers and divers can reduce the chance of being attacked by following a few simple rules: Never swim in areas where sharks are known to be common. Never enter the water where people are fishing, either from the beach or from inshore boats. If there are a number of people in the water, do not separate yourself from them. There is safety in numbers. Avoid swimming near deep channels, or where shallow water suddenly becomes deeper. Do not swim alone, or at dusk or after dark, when sharks are feeding actively and are likely to be closer to the shore. Do not enter the water, or if in the water leave immediately, if large numbers of fish are seen, or if fish seem to be acting strangely. Be alert for unusual movements in the water. Do not wear a watch or other jewelry that shines and reflects light. Do not enter the water with an open wound, and women should not swim during their menstrual periods.

    FISHES- Chondrichthyes, Sharks

    Sharks are animals that are superbly adapted to their environment. Almost all are carnivores or scavengers, although the species that live close to the sea floor feed mostly on invertebrates. Most possess a keen sense of smell, a large brain, good eyesight, and highly specialized mouth and teeth. Their bodies are usually heavier than water, and they do not have an air filled swim bladder for buoyancy like most bony fishes. All sharks have an asymmetric tail fin, with the upper lobe being larger than the lower one. This feature, together with flattened pectoral fins, and an oil-filled liver compensates for the lack of a swim bladder. There are 344 known species of sharks living in all parts of the oceans, from shallow to deep water and from the tropics to the polar regions. A few even venture into fresh water and have been found in rivers and lakes. Contrary to popular belief, most sharks are harmless to humans. Sharks are classified into eight orders:

    1. Sawsharks (Pristophoriformes), one family, five sp.Live on the bottom in warm temperate or tropical seas. Easily recognized because of tube, blade like snouts. Bear live young.

    2. Dogfish Sharks (Squaliformes), three families, 73 sp. Bottom dwelling deep water sharks, distributed worldwide. Bear live young and eat bony fishes, crustaceans, squid and other sharks. Harmless to humans.

    3. Angel Sharks (Squatiniformes), one family, 13 sp. Flattened, bottom dwelling sharks. Found on continental shelves and upper slopes of cold temperate and tropical seas. Have very sharp, awl-like teeth that are used to impale small fish and crustaceans.

    4. Bullhead Sharks (Heterodontiformes), one family, 8 sp. Live on rocky reefs where there are plenty of cracks and crevices. Found in Pacific and Indian Ocean. Eat invertebrates.
    5. Gilled Sharks (Hexanchiformes), two families, five sp. Deep-water, bottom-dwelling sharks. Worldwide distribution. Only shark with six or seven gill slits. Bear live young and eat bony fish, crustaceans, and other sharks.

    6. Mackerel Sharks (Lamniformes), seven families, 16 sp. Small, highly diverse order. Found in tropical to cold temperate or even Arctic waters. Oceanic and coastal. Most very large, eat bony fish, other sharks, squid, and marine mammals. Includes the Mako and Great White and the plankton eating Megamouth and Basking Sharks.

    7. Carpet Sharks (Otectolobiformes) seven families, 31 sp. Warm tropical to temperate waters. All members except whale shark live on bottom. Flattened. Most eat small fishes and invertebrates. Whale shark is plankton feeder. Some bear live young and others lay eggs.

    8. Ground Sharks (Carcharhiniformes) 8 families, 193 sp. Largest order of sharks. Worldwide distribution, temperate and tropical waters. Most live near coast, although some found in deeper waters. Eat bony fishes, other sharks, squid, and small invertebrates. Includes the dangerous Tiger shark.

    Sharks have numerous structural and physiological features that make them unique among the fishes. They have a simple cartilaginous skeleton with no ribs, and a cartilaginous jaw, backbone, and cranium.

    Thick skin supports the flimsy skeleton. The skin is elastic and aids in movement when the tail is arched, it pulls on the skin, which pulls back like a rubber band. The jaws are not connected to the skull and become unhinged, protruding forward from the skull allowing for a wider gape when feeding. The teeth are ossified with minerals known as 'apatite'. They form a conveyer belt with as many as eight teeth in a row. When a shark looses a tooth, another one just pops up. Sharks go through up to 2,400 teeth a year.

    Sharks have placoid scales which are fixed, slightly ossified and layered. They are smooth to the touch in one direction and extremely course in another. Just rubbing a shark the wrong way can inflict serious wounds.

    All sharks, rays, and skates are carnivores. They have normal sensory modalities, a small brain (most of which is dedicated to the olfactory lobes giving them an acute sense of smell) and well developed eyes with color vision and adaptation to low light levels.

    Some sharks lay eggs (all skates and ratfish do), but most are ovoviviparous (all rays are). The young develop with their yolk sacks within the mother, but without a placenta or umbilical cord. Some sharks (the Great White) are oviphagous the young eat the other developing young and embryos inside their mother and only the fiercest is born! A few sharks (hammerheads and reef sharks) are viviparous like mammals, the young are nourished with a placenta within the mother. The gestation period is around 22 months and 2-80 pups are born per litter. Because most sharks are ovoviviparous or viviparous, they do not produce mass numbers of young like other fish do. They are slow to develop and for this reason shark population numbers have been decreasing rapidly due to the recent popularity of shark fin soup. Fishermen are taking many more sharks than the maximum sustainable yield will allow. Some sharks will soon be endangered species. Rays

    Rays in general are physiologically exactly like sharks except the rays pectoral fins are fussed to their heads. Their gills are ventrally located. They swim with their ventral fins, like wings. Their eyes are dorsally [top] located and have spericules behind them. The spericules are used to breathe in with.

    Rays are modified as bottom feeders, feeding on invertebrates found in the sand. Sometimes you can watch a ray making quite a ruckus on the sand bottom in search of the invertebrates.

    Manta rays are planktivores and cruise the open water filter feeding out small animals. Mantas are the largest of the rays.

    Electric rays swim with their caudal fin and use their modified pectoral fins to electrically shock and stun their prey.

    Sawfish look like sharks but have true fused pectoral fins and gills on the ventral surface.

    Stingrays have a toxin filled spine at the base of their tail. Stingrays are not the mean creatures roaming the waters to hurt swimmers, as many people believe them to be. Stingrays are actually very approachable and can be hand fed and petted, just don't step on them!


    The bony fish comprise the largest section of the vertebrates, with over 20,000 species worldwide. They are called bony fish because their skeletons are calcified, making them much harder than the cartilage bones of the chondrichthyes. The bony fishes have great maneuverability and speed, highly specialized mouths equipped with protrusible jaws, and a swim bladder to control buoyancy.

    The bony fish have evolved to be of almost every imaginable shape and size, and exploit most marine and freshwater habitats on earth. Many of them have complex, recently evolved physiologies, organs, and behaviors for dealing with their environment in a sophisticated manner.

    Eels -Anguilliformes 597 spp

    Salmon -salmoniformes 350 spp

    Flyingfishes -Cyprinodontiformes 845 spp

    Silversides -Atheriniformes 235 spp

    Squirrelfishes -Beryciformes 164 spp

    Scorpionfishes -Scopaeniformes 1160 spp

    Flatfish -Pleuronectiformes 538 spp

    Triggerfish -Tetraodontiformes 329 spp

    Perch Like -Perciformes 7791 spp, largest order

    Deep Sea Fish -Stomiiformes 250 spp Gobies -Gobiesociformes 114 spp Trumpetfish -Syngnathiformes 257 spp

    FISH SEX- how fish reproduce

    Fish have come up with three modes of reproduction depending on the method they care for their eggs.

    • Ovopartity -- Lay undeveloped eggs, External fertilization (90% of bony fish), Internal fertilization (some sharks and rays)
    • Ovoviviparity - Internal development- without direct maternal nourishment-Advanced at birth (most sharks + rays)-Larval birth (some scorpeaniforms-rockfish)
    • Viviparity - Internal development- direct nourishment from mother-Fully advanced at birth (some sharks, surf perches)

    Parental care: In fishes, parental care is very rare as most fish are broadcast spawners, but there are a few instances of parental care. Male gobies guard the eggs in a nest until they are born. The male yellowhead jawfish actually guards the eggs by holding them in his mouth! Weird Fish Sex!

    Some fish are very kinky creatures by human standards, displaying behavior that would probably get a human incarcerated for a long time.

    • Hermaphroditism : Some fish individuals are both males and females, either simultaneously or sequentially. There is no genetic or physical reason why hermaphroditism should not be present. About 21 families of fish are hermaphrodites.
    • Simultaneous hermaphrodite : There are some instances where being a member of both sexes could have its advantages. Imagine all the dates that you could have! In the deep sea, the low light levels and limited food supply make for a very low population density meaning that potential mates are few and far between. Members of the fish family Salmoniformes (eg salmon) and Serranidae (hamlets) are simultaneous hermaphrodites they can spawn with any individual encountered.
    • Sequential hermaphrodite: Very strange life histories develop in species whose individuals may change sex at some time in their life. They may change from being males to females (protandry) or females to males (protogyny).

    A classic example of protogyny is found in the wrasses and parrotfishes. The males in these species form harems, with one large male sequestering and defending a group of smaller females. The male enjoys spectacular reproductive success, as it has many females to mate with. The females also enjoy a limited reproductive success, producing as many eggs as they can, all fertilized by the one male. The male has the advantage over the females it has many females producing eggs for him to fertilize, whereas the females only have themselves. It is great to be the king!

    The weird sex stuff comes in when we analyze what the reproductive success of a smaller male may be. As only the largest male, the 'SuperMale' gets to mate with the females, a smaller male would enjoy zero reproductive success. There is no advantage to being a small male, and this is where the hermaphrodism comes in. If all the smaller fish were females, they could all enjoy a limited reproductive success while they are growing. If the male dies, the one that has grown to be the largest female will change sexes and become the male, in turn enjoying a much greater reproductive success than if she did not switch. So there are no small males and everything is all said and done, but wait! Evolution has a keen ability in finding weaknesses in any system, and it has done so with the parrotfish. In nature, we do find smaller male parrotfish, why should this be so? It has to do with the kind of thing that if a parrotfish was a human, could get the parrotfish into a great deal of trouble. The 'supermale' has to run around all of the time keeping track of and protecting all of his females as well capturing and eating food himself, so he does not necessarily have time to pay close attention to the details. When parrotfish mate, they form a spawning aggregation where the supermale will release his sperm into the water and the many females release their eggs. The sperm and egg find each other in the water column and fertilization takes place, and this is where the weakness of the system lays. Along comes the smaller male, who has evolved to look just like a female. Most of the time the smaller male will make itself completely inconspicuous by behaving just like the females, but during the spawning aggregations, he will be releasing sperm instead of eggs. The supermale will probably not even know that he has been conned. Everything gets really mixed up as males are changing into females changing into males. FISH- Schooling Behavior

    Everyone has heard of a school of fish, an aggregation of fish hanging out together but why, they are obviously not learning reading, writing, and arithmetic. Schools of fish may be either polarized (with all the fish facing the same direction) or non polarized (all going every which way)

    There are some factors that can make it advantageous to hang out with other fish.

      A. Confusion effect. A large school of fish may be able to confuse a potential predator into thinking that the school is actually a much larger organism.

    B. Dilution affect. If a fish hangs out with a lot of other fish and a predator does come around, the predator must usually select one prey item. With so many choices, the chances are that it will not be you. This is known as the 'selfish herd'.

    Enhanced Foraging: A school of fish may have better abilities to acquire food. With many more eyes to detect food, many more meals may be found but there would also be many more mouths to feed. By working as a team, the school may be able to take larger food items than any one individual could manage to capture.

    Migration: The migration abilities of fish in schools may possibly be enhanced due to better navigation, etc. Hydrodynamic efficiency: Due to the complex hydrodynamic properties of water (properties the fish probably discovered only by accident), a fish may gain a swimming advantage by being in a school. The slipstream from the fish ahead of it may make it easier to pass through the water. Good for all the fish except for the ones in front.

    The density of water makes it very difficult to move in, but fish can move very smoothly and quickly.

    A swimming fish is relying on its skeleton for framework, its muscles for power, and its fins for thrust and direction.

    The skeleton of a fish is the most complex in all vertebrates. The skull acts as a fulcrum, the relatively stable part of the fish. The vertebral column acts as levers that operate for the movement of the fish.

    The muscles provide the power for swimming and constitute up to 80% of the fish itself. The muscles are arranged in multiple directions (myomeres) that allow the fish to move in any direction. A sinusoidal wave passes down from the head to the tail. The fins provide a platform to exert the thrust from the muscles onto the water.

    Diagram of forces when a fish swims.

    Thrust- force in animal's direction

    Lift- force opposite in right angles to the thrust

    Drag- force opposite the direction of movement

    • Cruisers: These are the fish that swim almost continuously in search for food, such as the tuna. Red Muscle- richly vascularized (blood-carrying capacity), rich in myoglobin (oxygen holder and transferor into the muscles active sites) * able to sustain continuous aerobic movement.
    • Burst Swimmers: These fish usually stay relatively in the same place such as most reef fish.
    • Caudal fin-- provides thrust, and control the fishes direction
    • Pectorals-- act mostly as rudders and hydroplanes to control yaw and pitch. Also act as very important brakes by causing drag.
    • Pelvic fins-- mostly controls pitch
    • Dorsal/anal-- control roll
    • A tuna fish which has a fusiform similar to a torpedo can cruise through the water at very high speeds.
    • The attenuated shape of the eel allows it to wiggle into small crevices where it hunts prey.
    • The depressed shape of the angler fish is advantageous for its "sit and wait" strategy of hunting.
    • The compressed shape found on many reef fishes such as the butter fish gives the fish great agility for movement around the reef and can support sudden bursts of acceleration.
    • Ectothermic: fish derive their heat from the environment
    • Poikilothermic : fish conform to the heat in the environment

    They maintain a higher body temperature through the use of a specialized counter-current heat exchanger called a reta mirabile. These are dense capillary beds within the swimming muscle that run next to the veins leaving the muscles. Blood passes through the veins and arteries in a counter current (opposite) direction. The heat produced from the muscle contraction flows from the exiting veins into the incoming arteries and is recycled.

    Why should they bother having an elevated body temperature? To increase the speed of the fish. The higher the body temperature, the greater the muscular power. Thirty degrees Celsius is the optimum temperature for muscular speed. With increased speed, the tuna can capture the slower, cold blooded fish it prey upon. Tuna have been clocked at record speed of 50-70 mph!

    Bony fish have swim bladders to help them maintain buoyancy in the water. The swim bladder is a sac inside the abdomen that contains gas. This sac may be open or closed to the gut. If you have ever caught a fish and wondered why its eyes are bulging out of its head, it is because the air in the swim bladder has expanded and is pushing against the back of the eye. Oxygen is the largest percentage of gas in the bladder nitrogen and carbon dioxide also fill in passively.

    Physoclistous- swim bladder is closed to the gut. The gas gets in through a special gas gland in the front of the swim bladder. Gas leaves the bladder through an oval body in the back of the swim bladder. The system works in a pretty miraculous way. Oval body, filled by venous blood -gasses leave here

    Gas gland, fed by arterial blood -gasses enter here

    inside the spots= giant secretory cells- secrete lactate -in capillary clusters rete mirabile

    Increased lactate levels from the giant secretory cells lower the surrounding pH, causing the blood hemoglobin to dump off its oxygen. The oxygen diffuses back into the incoming capillary, increasing the partial pressure of oxygen in the incoming capillary. This continues until the partial pressure of the oxygen in the capillary is higher than that of the swim bladder (which has a high concentration of oxygen). This complex system is necessary because the concentration of oxygen is higher in the swim bladder than it is in the blood, so simple diffusion would tend to pull the oxygen out of the bladder instead of pushing it in. If the fish wants more buoyancy, it must tell its secretory cells to release more lactate. Since oxygen diffuses easily with oxygen-poor venous blood, the gas can be forced out.

    *Fish that migrate vertically tend to have high oxygen levels in their bladders because it fills in faster and leaves faster.

    *Fish that maintain a stable depth tend to have more nitrogen because it is inert, enters slowly, and exits slowly.

    How in the heck can a fish, which is underwater, breath if there is no air? When we go under water, we have to bring air with us to survive. Whales and dolphins have lungs that store air from the surface. Fish don't have lungs, and they rarely ever venture into the air, so how do they survive. We all know it has something to do with gills, but what exactly.

    The water surrounding a fish contains a small percentage of dissolved oxygen. In the surface waters there can be about 5 ml. of oxygen per liter of water. This is much less than the 210 ml. of oxygen per liter of air that we breath, so the fish must use a special system for concentrating the oxygen in the water to meet their physiological needs. Here it comes again, a counter current exchange system, similar to the one we found in the fish's swim bladder and in the tuna's muscles.

    The circulation of blood in fish is simple. The heart only has two chambers, in contrast to our heart which has four. This is because the fish heart only pumps blood in one direction. The blood enters the heart through a vein and exits through a vein on its way to the gills. In the gills, the blood picks up oxygen from the surrounding water and leaves the gills in arteries, which go to the body. The oxygen is used in the body and goes back to the heart. A very simple closed-circle circulatory system.

    • The blood flows thorough the gill filaments and secondary lamellae in the opposite direction from the water passing the gills. This is very important for getting all of the available oxygen out of the water and into the blood.
    • If the blood flowed in the same direction as the water passing it, then the blood would only be able to get half of the available oxygen from the water. The blood and water would reach an equilibrium in oxygen content and diffusion would no longer take place.
    • By having the blood flow in the opposite direction, the gradient is always such that the water has more available oxygen than the blood, and oxygen diffusion continues to take place after the blood has acquired more than 50% of the water's oxygen content. The countercurrent exchange system gives fish an 80-90% efficiency in acquiring oxygen.
    • When fish are taken out of the water, they suffocate. This is not because they cannot breathe the oxygen available in the air, but because their gill arches collapse and there is not enough surface area for diffusion to take place. There are actually some fish that can survive out of the water, such as the walking catfish (which have modified lamellae allowing them to breathe air.
    • It is possible for a fish to suffocate in the water. This could happen when the oxygen in the water has been used up by another biotic source such as bacteria decomposing a red tide.

    --Ram Ventilation: Swim through the water and open your mouth. Very simple, but the fish must swim continuously in order to breathe, not so simple.

    Successful survival in any environment depends upon an organism's ability to acquire information from its environment through its senses. Fish have many of the same senses that we have, they can see, smell, touch, feel, and taste, and they have developed some senses that we don't have, such as electroreception. Fish can sense light, chemicals, vibrations and electricity.

    Light: photoreception [Vision]. Fish have a very keen sense of vision, which helps them to find food, shelter, mates, and avoid predators. Fish vision is on par with our own vision many can see in color, and some can see in extremely dim light.

    Fish eyes are different from our own. Their lenses are perfectly spherical, which enables them to see underwater because it has a higher refractive index to help them focus. They focus by moving the lens in and out instead of stretching it like we do. They cannot dilate or contract their pupils because the lens bulges through the iris. As the depth at which fish are found increases, the resident fish's eye sizes increase in order to gather the dimmer light. This process continues until the end of the photic zone, where eye size drops off as their is no light to see with. Nocturnal fish tend to have larger eyes then diurnal fish. Just look at a squirrelfish, and you will see this to be so. Some fish have a special eye structure known as the Tapetum lucidum, which amplifies the incoming light. It is a layer of guanine crystals which glow at night. Photons which pass the retina get bounced back to be detected again. If the photons are still not absorbed, they are reflected back out of the eye. On a night dive, you may see these reflections as you shine your light around!

    Chemicals: chemoreception [Smell and Taste]. Chemoreception is very well developed in the fishes, especially the sharks and eels which rely upon this to detect their prey. Fish have two nostrils on each side of their head, and there is no connection between the nostrils and the throat. The olfactory rosette is the organ that detects the chemicals. The size of the rosette is proportional to the fish's ability to smell. Some fish (such as sharks, rays, eels, and salmon) can detect chemical levels as low as 1 part per billion.

    Fish also have the ability to taste. They have taste buds on their lips, tongue, and all over their mouths. Some fish, such as the goatfish or catfish, have barbels, which are whiskers that have taste structures. Goatfish can be seen digging through the sand with their barbels looking for invertebrate worms to eat and can taste them before they even reach their mouths.

    Vibrations: mechanoreception [Hearing and touch]. Have you ever seen a fish's ear. Probably not, but they do have them, located within their bodies as well as a lateral line system that actually lets them feel their surroundings.

    Fish do not have external ears, but sound vibrations readily transmit from the water through the fish's body to its internal ears. The ears are divided into two sections, an upper section (pars superior) and a lower section (utriculus) The pars superior is divided into three semicircular canals and give the fish its sense of balance. It is fluid-filled with sensory hairs. The sensory hairs detect the rotational acceleration of the fluid. The canals are arranged so that one gives yaw, another pitch, and the last- roll. The utriculus gives the fish its ability to hear. It has two large otoliths which vibrate with the sound and stimulate surrounding hair cells.

    Fish posses another sense of mechanoreception that is kind of like a cross between hearing and touch. The organ responsible for this is the neuromast, a cluster of hair cells which have their hairs linked in a glob of jelly known as 'cupala'. All fish posses free neuromasts, which come in contact directly with the water. Most fish have a series of neuromasts not in direct contact with the water. These are arranged linearly and form the fishes lateral lines. A free neuromast gives the fish directional input.

    A lateral line receives signals stimulated in a sequence, and gives the fish much more information (feeling the other fish around it for polarized schooling, and short-range prey detection 'the sense of distant touch').

    Marine Biology resources by Odyssey Expeditions Tropical Marine Biology Voyages

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    Competitive Inhibitors

    Enzyme activity can be stopped by adding a molecule that binds to and blocks the enzyme. Lowering the temperature increases the effectiveness of some of these inhibitor molecules. Each enzyme has a special part called an active site, which is like a mouth. Reversible competitive inhibitors are molecules that fit into the mouth of the enzyme and jam it so that the enzyme cannot bite anything else. The binding between a reversible competitive inhibitor and an enzyme is only temporary, meaning the inhibitor eventually falls off but can climb back in again. Lowering the temperature of the mixture of molecules can make inhibitors more effective, but they don’t fall off the active site as often.

    Journal of Introductory Biology Investigations

    Ectotherms are dependent on their environment to maintain body temperature. It is important for ectotherms to be able to maintain body temperature because in an environment that is too hot or too cold, they could possibly have a threat in survival. Although other factors influence the metabolic rate of ectotherms, temperature and group activity are the most relevant factors in metabolic rate. In this experiment, we will test whether temperature and group size affect the metabolic rate of crickets. We hypothesize that crickets will have a higher metabolic rate when the environment is a warmer temperature and they are in a larger group size because their respiration will increase due to the interchange of heat whenever more crickets are gathered together. This experiment can help scientists better understand the importance of activity in a large population, as well as how climate changes can affect the individual activity of the cricket. We used a small chamber, an O2 probe, a temperature probe, and a balance for this experiment. We measured the O2 levels of five different group sizes of crickets at room temperature, below room temperature, and above room temperature for 180 seconds. Our experiment showed that heat and larger group size increased the metabolic rate of crickets, while the cold and room temperatures and smaller group sizes decreased the metabolic rate. Our hypothesis was supported by the data collected.

    Full Text:


    French, D. 2016. Investigating Biology. Fountainhead Press, Southlake, TX.

    Gayaldo, S., H. Osburn, K. Roberson, and C. Barnes. 2016. Larger group size negatively affects respiration of madagascar hissing cockroaches. Journal of Introductory Biology Investigations.

    Hoefnagels, M., 2015. Biology Concepts and Investigations. McGraw-Hill, New York.

    Watch the video: Your reptilian brain, explained. Robert Sapolsky. Big Think (July 2022).


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