7.6: Key Words and Terms - Biology

7.6: Key Words and Terms - Biology

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active transport of protons

energy efficiency of glucose metabolism

PEP carboxylase

ATP synthase

energy flow in glycolysis

pH gradient

bacterial flagellum

energy flow in the Krebs Cycle


C4 photosynthesis

F1 ATPase


Calvin Cycle



CAM photosynthesis


proton gate


Light-dependent reactions

proton gradient

chemiosmotic mechanism

Light-independent reactions

proton pump

Chlorophyll a

Malic acid

PSI electron acceptor

Chlorophyll b


PSII electron acceptor

molecular motor

redox reactions

complex I, II, III, IV


reduced electron carriers




cristal membrane



Cyclic photophosphorylation


Splitting water


outer membrane

stoichiometry of glycolysis

Dark Reactions

oxidative phosphorylation

stoichiometry of the Krebs Cycle

electrochemical gradient

oxidative phosphorylation

substrate-level phosphorylation

electron transport

system (chain)



endosymbiotic theory


7.6: Key Words and Terms - Biology

Extinction: When a species no longer lives on Earth.

Fats- Lipid Molecules containing glycerol and fatty acids.

Invertebrates- Animals that do not have a backbone.

Joints- The sections of the skeleton where two bones meet.

Kingdoms- Groups which organise and sort living organisms.

Lactic Acid: A product of anaerobic respiration.

Menstruation: The breaking down of the uterus allowing blood and cells to enter the vagina.

Metabolism: All the chemical reactions that occur in an organism.

Nutrition: Consuming food and in order to provide energy for processes such as growth and repair.

Obesity- The condition when someone is extremely overweight.

Stimulus: A minor or major change in the environment.

Tendon- A group of fibres that attach muscles to bones.

Virus- A micro-organism that can only reproduce inside living cells.

Vertebrates- Animals that have a backbone.

White Blood Cells- Cells that protect the body from invading pathogens via a series of different processes and responses.

Key Word Lists for AS and A2 AQA Biology

I am a teacher of Biology and Chemistry based in Devon. Currently teaching in Exeter. Currently teaching AQA iGCSE to Year 11 pupils, just switched to Edexcel iGCSE for Year 9 & 10 pupils and teaching AQA Biology (new specification) to AS/A2 pupils. I try to make engaging resources that involve a mix of collaborative activities as well as resources to encourage pupils to work independently. Also interested in promoting more of an awareness of mental health. Twitter: @missjmbooth

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Key word lists in full for all topics and then a document for each topic so that pupils can fill in the key terms.

Would be good for revision or at the end of a topic or give out at the beginning of a topic and get pupils to fill through as you go through the topic.

Please let me know any feedback by tweeting @missjmbooth including if you would improve any definitions!

Topic 6 & 8 have been updated to correct the numbers down the side!

If you want discount from a quizlet teacher account so you can track students progress of learning these key terms use this link: to get 20% off.


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Taxonomic Keys: Meaning, Suggestions and Types

A key is a device, which when properly constructed and used, enables a user to identify an organism. Keys are devices consisting of a series of contrasting or contradictory statements or propositions requiring the identifier to make comparisons and decisions based on statements in the key as related to the material to be identified.

Thus, a taxonomic key is a device for quickly and easily identifying to which species an unknown plant belongs.

The key consists of a series of choices, based on observed features of the plant specimen. It provides a choice between two contradictory statements resulting in the acceptance of one and the rejection of the other.

A single pair of contradictory statements is called a couplet and each statement of a couplet is termed a lead. By making the correct choice at each level of the key, one can eventually arrive at the name of the unknown plant.

Suggestions for the Use of Taxonomic Keys:

(a) Appropriate keys should be selected for the materials to be identified. The keys may be in a flora, manual, guide handbook, monograph, or revision. If the locality of an unknown plant is known, a flora, guide, or manual treating the plants of that geographic area may be selected.

If the family or genus is recognized, one may choose to use a monograph or revision. However, if the locality is unknown a general work may be selected. If materials to be identified are cultivated, one of the manuals treating such plants should be selected, since most floras do not include cultivated plants unless naturalized.

(b) The introductory comments on format details, abbreviations, etc. should be read before using the key.

(c) Both the leads of a couplet should be read before making a choice. Even though the first lead may seem to describe the unknown material, the second lead may be even more appropriate.

(d) A glossary should be used to check the meaning of terms, which one does not understand.

(e) Several similar structures should be measured, when measurements are used in the key, e.g. several leaves and not a single leaf should be measured. No decision should be made on a single observation. Rather it is often desirable to examine several specimens.

(f) The results should be verified by reading a description, comparing the specimen with an illustration or an authentically named herbarium specimen.

Suggestion for Construction of Taxonomic Keys:

(a) Constant characteristics rather than variable ones should be used.

(b) Proper measurements rather than terms like “large” and “small” should be used.

(c) Characteristics that are generally available to the user of the key rather than seasonal characteristics or those seen only in the field should be used.

(d) A positive choice should be made. The term “is” instead of “is not” should be used.

(e) If possible one should start both choices of a pair with the same word.

(f) If possible, different pairs of choices should be started with different words.

(g) The descriptive terms should be preceded with the name of the part to which they apply.

Types of Taxonomic Keys:

There are two types of keys:

(b) Poly clave (also called Multiple Access or Synoptic).

i. Dichotomous Keys:

Keys in which the choices allow only two (mutually exclusive) alternative couplets are known as dichotomous keys. In constructing a key, contrasting characters are chosen that divide the full set of possible species into smaller and smaller groups i.e. the statements typically begin with broad characteristics and become narrower as more choices are required.

Each time a choice is made, a number of species are eliminated from consideration and the range of possible species to which the unknown specimen may belong is narrowed. Eventually, after sufficient choices have been made, their range reduces to a single species and the identity of the unknown plant is revealed. Dichotomous comes from the Greek root dich meaning “two” and temnein meaning “to cut“.

Couplets can be organized in several forms. The couplets can be presented using numbers (numeric) or using letters (alphabetical). The couplets can be presented together or grouped by relationships. There is no apparent uniformity in presentation of dichotomous keys.

(a) Types of Dichotomous Keys:

There are two types of dichotomous keys. They differ in the method by which the couplets are organized and how the user is directed to successive choices.

(i) Indented Keys (also called yoked):

Indents the choices (leads) of the couplet an equal distance from the left margin. The two choices of the couplet are usually labelled 1 and 1′ or la and lb. It is not necessary that the choices are numbered, but it helps. The user goes to the next indented couplet following the lead that was selected.

Provides both choices side-by-side. The choices of the couplet must be numbered (or lettered). It is very helpful if the previous couplet is given. This key has exactly the same choices as the first example. The choices are separated, but it is easy to see the relationships. While this key might be more difficult to construct, it gives more information to the user.

(b) Problems using Dichotomous Keys:

A key may be difficult to use at times because:

I. The key may not include all potential variations in the species

II. The key may rely on features not present in that season

III. The key may not include “all” species of interest

IV. One may misinterpret a feature or make a mistake.

ii. Poly Clave Keys:

Another type of key, which is relatively a new alternative to dichotomous keys and becoming increasingly popular, especially because of the ease of computerizing them, is termed multiple access or poly clave or synoptic key. The advantage of these keys is that they allow the user to enter the key at any point.

This key is based on the identification of organisms by a process of elimination. In a written poly clave key there is a series of characters and character states. Each state is followed by a number or code for the species that possess that feature.

The user needs to select any character and then copy down the list of species that possess the feature. Then the user has to select another character and eliminate any species that is not common to both lists. This process has to be continued until the specimen is identified.

It’s easy to imagine how these keys are computerized. Consider a series of standard playing cards. Imagine each card has four holes punched into it along the top margin. If the card is a spade we cut the first hole through the margin if a club, the second hole is notched to the margin a heart the third hole is notched and finally if it is a diamond the fourth hole is notched.

Further imagine that along the bottom of the card we punch 14 holes (2 – 10, J, K, Q, A) and cut a notch for the appropriate number. Thus, the Queen of Hearts will have a notch cut into the third hole on the top of the card, and the Queen notch on the bottom of the card.

Now, let’s use our punch card deck of cards to identify an unknown card. Shuffle another deck of cards and pick any card. Let’s assume that this “unknown” card is the Ace of Spades. To identify this unknown, we analyse the characters and two are obvious, suit and number.

Let’s start with suit – take a long needle and stick it through the “spades hole“. Since, only spades are notched, the other suits will remain on the needle and spades will drop out of the deck.

Now, collect the spades cards and put a needle through the next character, the Ace and, viola, the Ace of Spades falls out. This is the general principle of how the computerized version of poly clave keys work. The main difference is that a computer allows for countless holes (characters) and notches (states) to be included and does the needlework for us.

An example of a Poly clave key:

Poly clave Key to Pollination Type:

Pollination is the process of transferring pollen from one flower to another. Since plants can’t move, they utilize vectors such as wind, water and animals to accomplish this process for them. Flowers are specialized by shape, colour, door, nectar etc. in order to maximize the chance that a certain vector will accomplish pollination. These flower adaptations are collectively known as pollination syndromes or systems.

Plants differ in the degree of their specialization for a particular pollination system. For example, many orchids are pollinated by only a single type of bee.

Other flowers are not as specialized and may be pollinated by a variety of bees or perhaps beetles. In other cases, insects may visit flowers without actually transferring pollen. These factors make it difficult to determine with absolute certainty the pollination system by the poly clave key.

(a) Advantages of Poly clave Keys:

The advantages of a poly clave (multiple-access) key are:

II. They allow multi-entry i.e. the user can start anywhere. This is a significant advantage because the user can rely on characters that are most easy to observe, rather than having to deal with characters that may not be present in the specimen or are poorly developed.

III. They are order-free i.e. the user can work in any direction with any character.

V. They are easily computerized. In fact, these keys are most commonly used in this form. Paper versions are typically large and unwieldy because each character needs to list all possible taxa.

(b) Suggestions to use a Poly clave Key:

I. Read through the list of characters to become familiar with the possibilities.

II. Scan the list to find a character with a state that you observe in your specimen. Start with a readily identifiable character that has only a few numbers (taxa) associated with it.

III. Write a brief description of the character and state and the numbers of the taxa that can be described by this state.

IV. Choose another character and state that describes your taxa. Write a brief description of this state below the name of the first state chosen. Then, scratch off the original list of any taxon that doesn’t appear in the second.

V. Continue this process until just one taxon remains for all of the states. If there is no single taxon described by the states chosen, and two or more remain, go back and check for errors.

VI. Read the name of the taxon after its number in the list of taxa. Check your identification with a description in a manual or the herbarium.

Want to learn how to respond to NESA Key Words?

When answering HSC questions, it is important you understand how you are expected to respond. NESA has provided a glossary of keywords for students to refer to. As a student, you should read through this glossary to familiarise themselves with NESA’s definitions of these words so you know how to respond to questions and instructions.


Chronic stress and a lack of coping resources available or used by an individual can often lead to the development of psychological issues such as delusions, [7] depression and anxiety (see below for further information). [8] This is particularly true regarding chronic stressors. These are stressors that may not be as intense as an acute stressor like a natural disaster or a major accident, but they persist over longer periods of time. These types of stressors tend to have a more negative effect on health because they are sustained and thus require the body's physiological response to occur daily. [9]

This depletes the body's energy more quickly and usually occurs over long periods of time, especially when these microstressors cannot be avoided (i.e. stress of living in a dangerous neighborhood). See allostatic load for further discussion of the biological process by which chronic stress may affect the body. For example, studies have found that caregivers, particularly those of dementia patients, have higher levels of depression and slightly worse physical health than non-caregivers. [9]

When humans are under chronic stress, permanent changes in their physiological, emotional, and behavioral responses may occur. [10] Chronic stress can include events such as caring for a spouse with dementia, or may result from brief focal events that have long term effects, such as experiencing a sexual assault. Studies have also shown that psychological stress may directly contribute to the disproportionately high rates of coronary heart disease morbidity and mortality and its etiologic risk factors. Specifically, acute and chronic stress have been shown to raise serum lipids and are associated with clinical coronary events. [11]

However, it is possible for individuals to exhibit hardiness—a term referring to the ability to be both chronically stressed and healthy. [12] Even though psychological stress is often connected with illness or disease, most healthy individuals can still remain disease-free after being confronted with chronic stressful events. This suggests that there are individual differences in vulnerability to the potential pathogenic effects of stress individual differences in vulnerability arise due to both genetic and psychological factors. In addition, the age at which the stress is experienced can dictate its effect on health. Research suggests chronic stress at a young age can have lifelong effects on the biological, psychological, and behavioral responses to stress later in life. [13]

The term "stress" had none of its contemporary connotations before the 1920s. It is a form of the Middle English destresse, derived via Old French from the Latin stringere, "to draw tight". [14] The word had long been in use in physics to refer to the internal distribution of a force exerted on a material body, resulting in strain. In the 1920s and '30s, biological and psychological circles occasionally used the term to refer to a mental strain or to a harmful environmental agent that could cause illness.

Walter Cannon used it in 1926 to refer to external factors that disrupted what he called homeostasis. [15] But ". stress as an explanation of lived experience is absent from both lay and expert life narratives before the 1930s". [16] Physiological stress represents a wide range of physical responses that occur as a direct effect of a stressor causing an upset in the homeostasis of the body. Upon immediate disruption of either psychological or physical equilibrium the body responds by stimulating the nervous, endocrine, and immune systems. The reaction of these systems causes a number of physical changes that have both short- and long-term effects on the body. [ citation needed ]

The Holmes and Rahe stress scale was developed as a method of assessing the risk of disease from life changes. [17] The scale lists both positive and negative changes that elicit stress. These include things such as a major holiday or marriage, or death of a spouse and firing from a job.

Homeostasis is a concept central to the idea of stress. [18] In biology, most biochemical processes strive to maintain equilibrium (homeostasis), a steady state that exists more as an ideal and less as an achievable condition. Environmental factors, internal or external stimuli, continually disrupt homeostasis an organism's present condition is a state of constant flux moving about a homeostatic point that is that organism's optimal condition for living. [19] Factors causing an organism's condition to diverge too far from homeostasis can be experienced as stress. A life-threatening situation such as a major physical trauma or prolonged starvation can greatly disrupt homeostasis. On the other hand, an organism's attempt at restoring conditions back to or near homeostasis, often consuming energy and natural resources, can also be interpreted as stress. [20]

The ambiguity in defining this phenomenon was first recognized by Hans Selye (1907–1982) in 1926. In 1951 a commentator loosely summarized Selye's view of stress as something that ". in addition to being itself, was also the cause of itself, and the result of itself". [21] [22]

First to use the term in a biological context, Selye continued to define stress as "the non-specific response of the body to any demand placed upon it". Neuroscientists such as Bruce McEwen and Jaap Koolhaas believe that stress, based on years of empirical research, "should be restricted to conditions where an environmental demand exceeds the natural regulatory capacity of an organism". [23] Indeed, in 1995 Toates already defined stress as a "chronic state that arises only when defense mechanisms are either being chronically stretched or are actually failing," [24] while according to Ursin (1988) stress results from an inconsistency between expected events ("set value") and perceived events ("actual value") that cannot be resolved satisfactorily, [25] which also puts stress into the broader context of cognitive-consistency theory. [26]

Stress can have many profound effects on the human biological systems. [27] Biology primarily attempts to explain major concepts of stress using a stimulus-response paradigm, broadly comparable to how a psychobiological sensory system operates. The central nervous system (brain and spinal cord) plays a crucial role in the body's stress-related mechanisms. Whether one should interpret these mechanisms as the body's response to a stressor or embody the act of stress itself is part of the ambiguity in defining what exactly stress is.

The central nervous system works closely with the body's endocrine system to regulate these mechanisms. The sympathetic nervous system becomes primarily active during a stress response, regulating many of the body's physiological functions in ways that ought to make an organism more adaptive to its environment. Below there follows a brief biological background of neuroanatomy and neurochemistry and how they relate to stress. [ citation needed ]

Stress, either severe, acute stress or chronic low-grade stress may induce abnormalities in three principal regulatory systems in the body: serotonin systems, catecholamine systems, and the hypothalamic-pituitary-adrenocortical axis. Aggressive behavior has also been associated with abnormalities in these systems. [28]

The brain endocrine interactions are relevant in the translation of stress into physiological and psychological changes. The autonomic nervous system (ANS), as mentioned above, plays an important role in translating stress into a response. The ANS responds reflexively to both physical stressors (for example baroreception), and to higher level inputs from the brain. [29]

The ANS is composed of the parasympathetic nervous system and sympathetic nervous system, two branches that are both tonically active with opposing activities. The ANS directly innervates tissue through the postganglionic nerves, which is controlled by preganglionic neurons originating in the intermediolateral cell column. The ANS receives inputs from the medulla, hypothalamus, limbic system, prefrontal cortex, midbrain and monoamine nuclei. [30]

The activity of the sympathetic nervous system drives what is called the "fight or flight" response. The fight or flight response to emergency or stress involves mydriasis, increased heart rate and force contraction, vasoconstriction, bronchodilation, glycogenolysis, gluconeogenesis, lipolysis, sweating, decreased motility of the digestive system, secretion of the epinephrine and cortisol from the adrenal medulla, and relaxation of the bladder wall. The parasympathetic nervous response, "rest and digest", involves return to maintaining homeostasis, and involves miosis, bronchoconstriction, increased activity of the digestive system, and contraction of the bladder walls. [29] Complex relationships between protective and vulnerability factors on the effect of childhood home stress on psychological illness, cardiovascular illness and adaption have been observed. [31] ANS related mechanisms are thought to contribute to increased risk of cardiovascular disease after major stressful events. [32]

The HPA axis is a neuroendocrine system that mediates a stress response. Neurons in the hypothalamus, particularly the paraventricular nucleus, release vasopressin and corticotropin releasing hormone, which travel through the hypophysial portal vessel where they travel to and bind to the corticotropin-releasing hormone receptor on the anterior pituitary gland. Multiple CRH peptides have been identified, and receptors have been identified on multiple areas of the brain, including the amygdala. CRH is the main regulatory molecule of the release of ACTH. [33]

The secretion of ACTH into systemic circulation allows it to bind to and activate Melanocortin receptor, where it stimulates the release of steroid hormones. Steroid hormones bind to glucocorticoid receptors in the brain, providing negative feedback by reducing ACTH release. Some evidence supports a second long term feedback that is non-sensitive to cortisol secretion. The PVN of the hypothalamus receives inputs from the nucleus of the solitary tract, and lamina terminalis. Through these inputs, it receives and can respond to changes in blood. [33]

The PVN innervation from the brain stem nuclei, particularly the noradrenergic nuclei stimulate CRH release. Other regions of the hypothalamus both directly and indirectly inhibit HPA axis activity. Hypothalamic neurons involved in regulating energy balance also influence HPA axis activity through the release of neurotransmitters such as neuropeptide Y, which stimulates HPA axis activity. Generally, the amygdala stimulates, and the prefrontal cortex and hippocampus attenuate, HPA axis activity however, complex relationships do exist between the regions. [33]

The immune system may be heavily influenced by stress. The sympathetic nervous system innervates various immunological structures, such as bone marrow and the spleen, allowing for it to regulate immune function. The adrenergic substances released by the sympathetic nervous system can also bind to and influence various immunological cells, further providing a connection between the systems. The HPA axis ultimately results in the release of cortisol, which generally has immunosuppressive effects. However, the effect of stress on the immune system is disputed, and various models have been proposed in an attempt to account for both the supposedly "immunodeficiency" linked diseases and diseases involving hyper activation of the immune system. One model proposed to account for this suggests a push towards an imbalance of cellular immunity(Th1) and humoral immunity(Th2). The proposed imbalance involved hyperactivity of the Th2 system leading to some forms of immune hypersensitivity, while also increasing risk of some illnesses associated with decreased immune system function, such as infection and cancer. [6]

Chronic stress is a term sometimes used to differentiate it from acute stress. Definitions differ, and may be along the lines of continual activation of the stress response, [34] stress that causes an allostatic shift in bodily functions, [4] or just as "prolonged stress". [35] For example, results of one study demonstrated that individuals who reported relationship conflict lasting one month or longer have a greater risk of developing illness and show slower wound healing. Similarly, the effects that acute stressors have on the immune system may be increased when there is perceived stress and/or anxiety due to other events. For example, students who are taking exams show weaker immune responses if they also report stress due to daily hassles. [36] While responses to acute stressors typically do not impose a health burden on young, healthy individuals, chronic stress in older or unhealthy individuals may have long-term effects that are detrimental to health. [37]

Immunological Edit

Acute time-limited stressors, or stressors that lasted less than two hours, results in an up regulation of natural immunity and down regulation of specific immunity. This type of stress saw in increase in granulocytes, natural killer cells, IgA, Interleukin 6, and an increase in cell cytotoxicity. Brief naturalistic stressors elicit a shift from Th1(cellular) to Th2(humoral) immunity, while decreased T-cell proliferation, and natural killer cell cytotoxicity. Stressful event sequences did not elicit a consistent immune response however, some observations such as decreased T-Cell proliferation and cytotoxicity, increase or decrease in natural killer cell cytotoxicity, and an increase in mitogen PHA. Chronic stress elicited a shift toward Th2 immunity, as well as decreased interleukin 2, T cell proliferation, and antibody response to the influenza vaccine. Distant stressors did not consistently elicit a change in immune function. [6]

Infectious Edit

Some studies have observed increased risk of upper respiratory tract infection during chronic life stress. In patients with HIV, increased life stress and cortisol was associated with poorer progression of HIV. [34]

Chronic disease Edit

A link has been suggested between chronic stress and cardiovascular disease. [34] Stress appears to play a role in hypertension, and may further predispose people to other conditions associated with hypertension. [38] Stress may also precipitate a more serious, or relapse into abuse of alcohol. [4] Stress may also contribute to aging and chronic diseases in aging, such as depression and metabolic disorders. [39]

The immune system also plays a role in stress and the early stages of wound healing. It is responsible for preparing the tissue for repair and promoting recruitment of certain cells to the wound area. [36] Consistent with the fact that stress alters the production of cytokines, Graham et al. found that chronic stress associated with care giving for a person with Alzheimer's disease leads to delayed wound healing. Results indicated that biopsy wounds healed 25% more slowly in the chronically stressed group, or those caring for a person with Alzheimer's disease. [40]

Development Edit

Chronic stress has also been shown to impair developmental growth in children by lowering the pituitary gland's production of growth hormone, as in children associated with a home environment involving serious marital discord, alcoholism, or child abuse. [41]

More generally, prenatal life, infancy, childhood, and adolescence are critical periods in which the vulnerability to stressors is particularly high. [42] [43]

Psychopathology Edit

Chronic stress is seen to affect the parts of the brain where memories are processed through and stored. When people feel stressed, stress hormones get over-secreted, which affects the brain. This secretion is made up of glucocorticoids, including cortisol, which are steroid hormones that the adrenal gland releases, although this can increase storage of flashbulb memories it decreases long-term potentiation (LTP). [44] [45] The hippocampus is important in the brain for storing certain kinds of memories and damage to the hippocampus can cause trouble in storing new memories but old memories, memories stored before the damage, are not lost. [46] Also high cortisol levels can be tied to the deterioration of the hippocampus and decline of memory that many older adults start to experience with age. [45] These mechanisms and processes may therefore contribute to age-related disease, or originate risk for earlier-onset disorders. For instance, extreme stress (e.g. trauma) is a requisite factor to produce stress-related disorders such as post-traumatic stress disorder. [5]

Chronic stress also shifts learning, forming a preference for habit based learning, and decreased task flexibility and spatial working memory, probably through alterations of the dopaminergic systems. [30] Stress may also increase reward associated with food, leading to weight gain and further changes in eating habits. [47] Stress may contribute to various disorders, such as fibromyalgia, [48] chronic fatigue syndrome, [49] depression, [50] and functional somatic syndromes. [51]

Eustress Edit

Selye published in year 1975 a model dividing stress into eustress and distress. [52] Where stress enhances function (physical or mental, such as through strength training or challenging work), it may be considered eustress. Persistent stress that is not resolved through coping or adaptation, deemed distress, may lead to anxiety or withdrawal (depression) behavior.

The difference between experiences that result in eustress and those that result in distress is determined by the disparity between an experience (real or imagined) and personal expectations, and resources to cope with the stress. Alarming experiences, either real or imagined, can trigger a stress response. [53]

Coping Edit

Responses to stress include adaptation, psychological coping such as stress management, anxiety, and depression. Over the long term, distress can lead to diminished health and/or increased propensity to illness to avoid this, stress must be managed.

Stress management encompasses techniques intended to equip a person with effective coping mechanisms for dealing with psychological stress, with stress defined as a person's physiological response to an internal or external stimulus that triggers the fight-or-flight response. Stress management is effective when a person uses strategies to cope with or alter stressful situations.

There are several ways of coping with stress, [54] such as controlling the source of stress or learning to set limits and to say "no" to some of the demands that bosses or family members may make.

A person's capacity to tolerate the source of stress may be increased by thinking about another topic such as a hobby, listening to music, or spending time in a wilderness.

A way to control stress is first dealing with what is causing the stress if it is something the individual has control over. Other methods to control stress and reduce it can be: to not procrastinate and leave tasks for the last minute, do things you like, exercise, do breathing routines, go out with friends, and take a break. Having support from a loved one also helps a lot in reducing stress. [45]

One study showed that the power of having support from a loved one, or just having social support, lowered stress in individual subjects. Painful shocks were applied to married women's ankles. In some trials women were able to hold their husband's hand, in other trials they held a stranger's hand, and then held no one's hand. When the women were holding their husband's hand, the response was reduced in many brain areas. When holding the stranger's hand the response was reduced a little, but not as much as when they were holding their husband's hand. Social support helps reduce stress and even more so if the support is from a loved one. [45]

Cognitive appraisal Edit

Lazarus [55] argued that, in order for a psychosocial situation to be stressful, it must be appraised as such. He argued that cognitive processes of appraisal are central in determining whether a situation is potentially threatening, constitutes a harm/loss or a challenge, or is benign.

Both personal and environmental factors influence this primary appraisal, which then triggers the selection of coping processes. Problem-focused coping is directed at managing the problem, whereas emotion-focused coping processes are directed at managing the negative emotions. Secondary appraisal refers to the evaluation of the resources available to cope with the problem, and may alter the primary appraisal.

In other words, primary appraisal includes the perception of how stressful the problem is and the secondary appraisal of estimating whether one has more than or less than adequate resources to deal with the problem that affects the overall appraisal of stressfulness. Further, coping is flexible in that, in general, the individual examines the effectiveness of the coping on the situation if it is not having the desired effect, s/he will, in general, try different strategies. [56]

Health risk factors Edit

Both negative and positive stressors can lead to stress. The intensity and duration of stress changes depending on the circumstances and emotional condition of the person suffering from it (Arnold. E and Boggs. K. 2007). Some common categories and examples of stressors include:

  • Sensory input such as pain, bright light, noise, temperatures, or environmental issues such as a lack of control over environmental circumstances, such as food, air and/or water quality, housing, health, freedom, or mobility.
  • Social issues can also cause stress, such as struggles with conspecific or difficult individuals and social defeat, or relationship conflict, deception, or break ups, and major events such as birth and deaths, marriage, and divorce.
  • Life experiences such as poverty, unemployment, clinical depression, obsessive compulsive disorder, heavy drinking, [57] or insufficient sleep can also cause stress. Students and workers may face performance pressure stress from exams and project deadlines.
  • Adverse experiences during development (e.g. prenatal exposure to maternal stress, [58][59] poor attachment histories, [60]sexual abuse) [61] are thought to contribute to deficits in the maturity of an individual's stress response systems. One evaluation of the different stresses in people's lives is the Holmes and Rahe stress scale.

General adaptation syndrome Edit

Physiologists define stress as how the body reacts to a stressor - a stimulus, real or imagined, that causes stress. Acute stressors affect an organism in the short term chronic stressors over the longer term. The general adaptation syndrome (GAS), developed by Hans Selye, is a profile of how organisms respond to stress GAS is characterized by three phases: a nonspecific mobilization phase, which promotes sympathetic nervous system activity a resistance phase, during which the organism makes efforts to cope with the threat and an exhaustion phase, which occurs if the organism fails to overcome the threat and depletes its physiological resources. [62]

Stage 1 Edit

Alarm is the first stage, which is divided into two phases: the shock phase and the antishock phase. [63]

  • Shock phase: During this phase, the body can endure changes such as hypovolemia, hypoosmolarity, hyponatremia, hypochloremia, hypoglycemia—the stressor effect. This phase resembles Addison's disease. The organism's resistance to the stressor drops temporarily below the normal range and some level of shock (e.g. circulatory shock) may be experienced.
  • Antishock phase: When the threat or stressor is identified or realized, the body starts to respond and is in a state of alarm. During this stage, the locus coeruleus and sympathetic nervous system activate the production of catecholamines including adrenaline, engaging the popularly-known fight-or-flight response. Adrenaline temporarily provides increased muscular tonus, increased blood pressure due to peripheral vasoconstriction and tachycardia, and increased glucose in blood. There is also some activation of the HPA axis, producing glucocorticoids (cortisol, aka the S-hormone or stress-hormone).

Stage 2 Edit

Resistance is the second stage. During this stage, increased secretion of glucocorticoids intensifies the body's systemic response. Glucocorticoids can increase the concentration of glucose, fat, and amino acid in blood. In high doses, one glucocorticoid, cortisol, begins to act similarly to a mineralocorticoid (aldosterone) and brings the body to a state similar to hyperaldosteronism. If the stressor persists, it becomes necessary to attempt some means of coping with the stress. The body attempts to respond to stressful stimuli, but after prolonged activation, the body's chemical resources will be gradually depleted, leading to the final stage.

Stage 3 Edit

The third stage could be either exhaustion or recovery:

  • Recovery stage follows when the system's compensation mechanisms have successfully overcome the stressor effect (or have completely eliminated the factor which caused the stress). The high glucose, fat and amino acid levels in blood prove useful for anabolic reactions, restoration of homeostasis and regeneration of cells.
  • Exhaustion is the alternative third stage in the GAS model. At this point, all of the body's resources are eventually depleted and the body is unable to maintain normal function. The initial autonomic nervous system symptoms may reappear (sweating, raised heart rate, etc.). If stage three is extended, long-term damage may result (prolonged vasoconstriction results in ischemia which in turn leads to cell necrosis), as the body's immune system becomes exhausted, and bodily functions become impaired, resulting in decompensation.

The result can manifest itself in obvious illnesses, such as general trouble with the digestive system (e.g. occult bleeding, melena, constipation/obstipation), diabetes, or even cardiovascular problems (angina pectoris), along with clinical depression and other mental illnesses. [ citation needed ]

The current usage of the word stress arose out of Hans Selye's 1930s experiments. He started to use the term to refer not just to the agent but to the state of the organism as it responded and adapted to the environment. His theories of a universal non-specific stress response attracted great interest and contention in academic physiology and he undertook extensive research programs and publication efforts. [64]

While the work attracted continued support from advocates of psychosomatic medicine, many in experimental physiology concluded that his concepts were too vague and unmeasurable. During the 1950s, Selye turned away from the laboratory to promote his concept through popular books and lecture tours. He wrote for both non-academic physicians and, in an international bestseller entitled Stress of Life, for the general public.

A broad biopsychosocial concept of stress and adaptation offered the promise of helping everyone achieve health and happiness by successfully responding to changing global challenges and the problems of modern civilization. Selye coined the term "eustress" for positive stress, by contrast to distress. He argued that all people have a natural urge and need to work for their own benefit, a message that found favor with industrialists and governments. [64] He also coined the term stressor to refer to the causative event or stimulus, as opposed to the resulting state of stress.

Selye was in contact with the tobacco industry from 1958 and they were undeclared allies in litigation and the promotion of the concept of stress, clouding the link between smoking and cancer, and portraying smoking as a "diversion", or in Selye's concept a "deviation", from environmental stress. [65]

From the late 1960s, academic psychologists started to adopt Selye's concept they sought to quantify "life stress" by scoring "significant life events", and a large amount of research was undertaken to examine links between stress and disease of all kinds. By the late 1970s, stress had become the medical area of greatest concern to the general population, and more basic research was called for to better address the issue. There was also renewed laboratory research into the neuroendocrine, molecular, and immunological bases of stress, conceived as a useful heuristic not necessarily tied to Selye's original hypotheses. The US military became a key center of stress research, attempting to understand and reduce combat neurosis and psychiatric casualties. [64]

The psychiatric diagnosis post-traumatic stress disorder (PTSD) was coined in the mid-1970s, in part through the efforts of anti-Vietnam War activists and the Vietnam Veterans Against the War, and Chaim F. Shatan. The condition was added to the Diagnostic and Statistical Manual of Mental Disorders as posttraumatic stress disorder in 1980. [66] PTSD was considered a severe and ongoing emotional reaction to an extreme psychological trauma, and as such often associated with soldiers, police officers, and other emergency personnel. The stressor may involve threat to life (or viewing the actual death of someone else), serious physical injury, or threat to physical or psychological integrity. In some cases, it can also be from profound psychological and emotional trauma, apart from any actual physical harm or threat. Often, however, the two are combined.

By the 1990s, "stress" had become an integral part of modern scientific understanding in all areas of physiology and human functioning, and one of the great metaphors of Western life. Focus grew on stress in certain settings, such as workplace stress, and stress management techniques were developed. The term also became a euphemism, a way of referring to problems and eliciting sympathy without being explicitly confessional, just "stressed out". It came to cover a huge range of phenomena from mild irritation to the kind of severe problems that might result in a real breakdown of health. In popular usage, almost any event or situation between these extremes could be described as stressful. [14] [64]

The American Psychological Association's 2015 Stress In America Study [67] found that nationwide stress is on the rise and that the three leading sources of stress were "money", "family responsibility", and "work".

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The Galapagos Finches and Natural Selection

The differences in shape and size of beaks in Darwin’s finches illustrate ongoing evolutionary change.

Learning Objectives

Describe how finches provide visible evidence of evolution

Key Takeaways

Key Points

  • Darwin observed the Galapagos finches had a graded series of beak sizes and shapes and predicted these species were modified from one original mainland species.
  • Darwin called differences among species natural selection, which is caused by the inheritance of traits, competition between individuals, and the variation of traits.
  • Offspring with inherited characteristics that allow them to best compete will survive and have more offspring than those individuals with variations that are less able to compete.
  • Large-billed finches feed more efficiently on large, hard seeds, whereas smaller billed finches feed more efficiently on small, soft seeds.
  • When small, soft seeds become rare, large-billed finches will survive better, and there will be more larger-billed birds in the following generation when large, hard seeds become rare, the opposite will occur.

Key Terms

  • natural selection: a process in which individual organisms or phenotypes that possess favorable traits are more likely to survive and reproduce
  • evolution: the change in the genetic composition of a population over successive generations

Visible Evidence of Ongoing Evolution: Darwin’s Finches

From 1831 to 1836, Darwin traveled around the world, observing animals on different continents and islands. On the Galapagos Islands, Darwin observed several species of finches with unique beak shapes. He observed these finches closely resembled another finch species on the mainland of South America and that the group of species in the Galápagos formed a graded series of beak sizes and shapes, with very small differences between the most similar. Darwin imagined that the island species might be all species modified from one original mainland species. In 1860, he wrote, “seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.”

Darwin’s Finches: Darwin observed that beak shape varies among finch species. He postulated that the beak of an ancestral species had adapted over time to equip the finches to acquire different food sources. This illustration shows the beak shapes for four species of ground finch: 1. Geospiza magnirostris (the large ground finch), 2. G. fortis (the medium ground finch), 3. G. parvula (the small tree finch), and 4. Certhidea olivacea (the green-warbler finch).

Natural Selection

Darwin called this mechanism of change natural selection. Natural selection, Darwin argued, was an inevitable outcome of three principles that operated in nature. First, the characteristics of organisms are inherited, or passed from parent to offspring. Second, more offspring are produced than are able to survive in other words, resources for survival and reproduction are limited. The capacity for reproduction in all organisms exceeds the availability of resources to support their numbers. Thus, there is a competition for those resources in each generation. Third, offspring vary among each other in regard to their characteristics and those variations are inherited. Out of these three principles, Darwin reasoned that offspring with inherited characteristics that allow them to best compete for limited resources will survive and have more offspring than those individuals with variations that are less able to compete. Because characteristics are inherited, these traits will be better represented in the next generation. This will lead to change in populations over generations in a process that Darwin called “descent with modification,” or evolution.

Studies of Natural Selection After Darwin

Demonstrations of evolution by natural selection can be time consuming. Peter and Rosemary Grant and their colleagues have studied Galápagos finch populations every year since 1976 and have provided important demonstrations of the operation of natural selection. The Grants found changes from one generation to the next in the beak shapes of the medium ground finches on the Galápagos island of Daphne Major.

The medium ground finch feeds on seeds. The birds have inherited variation in the bill shape with some individuals having wide, deep bills and others having thinner bills. Large-billed birds feed more efficiently on large, hard seeds, whereas smaller billed birds feed more efficiently on small, soft seeds. During 1977, a drought period altered vegetation on the island. After this period, the number of seeds declined dramatically the decline in small, soft seeds was greater than the decline in large, hard seeds. The large-billed birds were able to survive better than the small-billed birds the following year.

The year following the drought when the Grants measured beak sizes in the much-reduced population, they found that the average bill size was larger. This was clear evidence for natural selection of bill size caused by the availability of seeds. The Grants had studied the inheritance of bill sizes and knew that the surviving large-billed birds would tend to produce offspring with larger bills, so the selection would lead to evolution of bill size. Subsequent studies by the Grants have demonstrated selection on and evolution of bill size in this species in response to other changing conditions on the island. The evolution has occurred both to larger bills, as in this case, and to smaller bills when large seeds became rare.

Finches of Daphne Major: A drought on the Galápagos island of Daphne Major in 1977 reduced the number of small seeds available to finches, causing many of the small-beaked finches to die. This caused an increase in the finches’ average beak size between 1976 and 1978.

How to Study Biology: Top 5 Study Techniques

#1 Learn the Terminology

One of the hardest parts of studying biology is remembering the many different terms. If you want to understand what you are studying, then you need to familiarize yourself with all these terms first. A good method for this is to try and break down complex words to identify their root.

It is highly recommended that whenever you encounter unfamiliar words while studying biology you should take note of them, find it’s definition and then take the time to understand its roots.

Glossary of Task Words

Understanding the meaning of words, especially task words, helps you to know exactly what is being asked of you. It takes you halfway towards narrowing down your material and selecting your answer.

Task words direct you and tell you how to go about answering a question. Here is a list of such words and others that you are most likely to come across frequently in your course.

Table of task words
WordsWhat they (might) mean.
Account forExplain, clarify, give reasons for. (Quite different from "Give an account of which is more like 'describe in detail').
AnalyseBreak an issue down into its component parts, discuss them and show how they interrelate.
AssessConsider the value or importance of something, paying due attention to positive, negative and disputable aspects, and citing the judgements of any known authorities as well as your own.
ArgueMake a case based on appropriate evidence for and/or against some given point of view.
Comment onToo vague to be sure, but safe to assume it means something more than 'describe' or 'summarise' and more likely implies 'analyse' or 'assess'.
CompareIdentify the characteristics or qualities two or more things have in common (but probably pointing out their differences as well).
ContrastPoint out the difference between two things (but probably point out their similarities as well).
CriticiseSpell out your judgement as to the value or truth of something, indicating the criteria on which you base your judgement and citing specific instances of how the criteria apply in this case.
DefineMake a statement as to the meaning or interpretation of something, giving sufficient detail as to allow it to be distinguished from similar things.
DescribeSpell out the main aspects of an idea or topic or the sequence in which a series of things happened.
DiscussInvestigate or examine by argument. Examine key points and possible interpretations, sift and debate, giving reasons for and against. Draw a conclusion.
EvaluateMake an appraisal of the worth of something, in the light of its apparent truth include your personal opinion. Like 'assess'.
EnumerateList some relevant items, possibly in continuous prose (rather than note form) and perhaps 'describe' them (see above) as well.
ExaminePresent in depth and investigate the implications.
ExplainTell how things work or how they came to be the way they are, including perhaps some need to 'describe' and to 'analyse' (see above).
To what extent. Explore the case for a stated proposition or explanation, much in the manner of 'assess' and 'criticise' (see above), probably arguing for a less than total acceptance of the proposition.
How far Similar to 'to what extent. ' (see above)
Identify Pick out what you regard as the key features of something, perhaps making clear the criteria you use.
Illustrate Similar to 'explain' (see above), but probably asking for the quoting of specific examples or statistics or possibly the drawing of maps, graphs, sketches etc.
InterpretClarify something or 'explain' (see above), perhaps indicating how the thing relates to some other thing or perspective.
JustifyExpress valid reasons for accepting a particular interpretation or conclusion, probably including the need to 'argue' (see above) a case.
OutlineIndicate the main features of a topic or sequence of events, possibly setting them within a clear structure or framework to show how they interrelate.
ProveDemonstrate the truth of something by offering irrefutable evidence and/or logical sequence of statements leading from evidence to conclusion.
ReconcileShow how two apparently opposed or mutually exclusive ideas or propositions can be seen to be similar in important respects, if not identical. Involves need to 'analyse' and 'justify' (see above).
RelateEither 'explain' (see above) how things happened or are connected in a cause-and-effect sense, or may imply 'compare' and 'contrast' (see above).
Review Survey a topic, with the emphasis on 'assess' rather than 'describe' (see above).
StateExpress the main points of an idea or topic, perhaps in the manner of 'describe' or 'enumerate' (see above).
Summarise'State' (see above) the main features of an argument, omitting all superfluous detail and side-issues.
TraceIdentify the connection between one thing and another either in a developmental sense over a period of time, or else in a cause and effect sense. May imply both 'describe' and 'explain' (see above).
Other useful definitions
WordsWhat they (might) mean.
AssumptionSomething which is accepted as being true for the purpose of an argument.
IssueAn important topic for discussion something worth thinking and raising questions about.
MethodologyA system of methods and principles for doing something. Often used to explain methods for carrying out research.
ObjectiveIt is the point, or the thing aimed at. It is what you want to achieve by a particular activity.


Maddox, H 1967, How to Study, 2nd ed, Pan Books, London.

Marshall, L., & Rowland, F 1998, A guide to learning independently, Addison Wesley Longman, Melbourne.

Northedge, A 1997, The good study guide, Open University, Milton Keynes, UK.

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