30.0: Prelude to Plant Form and Physiology - Biology

30.0: Prelude to Plant Form and Physiology - Biology

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Plants are as essential to human existence as land, water, and air. Without plants, our day-to-day lives would be impossible because without oxygen from photosynthesis, aerobic life cannot be sustained. From providing food and shelter to serving as a source of medicines, oils, perfumes, and industrial products, plants provide humans with numerous valuable resources.

When you think of plants, most of the organisms that come to mind are vascular plants. These plants have tissues that conduct food and water, and they have seeds. Seed plants are divided into gymnosperms and angiosperms. Gymnosperms include the needle-leaved conifers—spruce, fir, and pine—as well as less familiar plants, such as ginkgos and cycads. Their seeds are not enclosed by a fleshy fruit. Angiosperms, also called flowering plants, constitute the majority of seed plants. They include broadleaved trees (such as maple, oak, and elm), vegetables (such as potatoes, lettuce, and carrots), grasses, and plants known for the beauty of their flowers (roses, irises, and daffodils, for example).

While individual plant species are unique, all share a common structure: a plant body consisting of stems, roots, and leaves. They all transport water, minerals, and sugars produced through photosynthesis through the plant body in a similar manner. All plant species also respond to environmental factors, such as light, gravity, competition, temperature, and predation.

30.3 Roots

By the end of this section, you will be able to do the following:

  • Identify the two types of root systems
  • Describe the three zones of the root tip and summarize the role of each zone in root growth
  • Describe the structure of the root
  • List and describe examples of modified roots

The roots of seed plants have three major functions: anchoring the plant to the soil, absorbing water and minerals and transporting them upwards, and storing the products of photosynthesis. Some roots are modified to absorb moisture and exchange gases. Most roots are underground. Some plants, however, also have adventitious roots , which emerge above the ground from the shoot.

Types of Root Systems

Root systems are mainly of two types (Figure 30.15). Dicots have a tap root system, while monocots have a fibrous root system. A tap root system has a main root that grows down vertically, and from which many smaller lateral roots arise. Dandelions are a good example their tap roots usually break off when trying to pull these weeds, and they can regrow another shoot from the remaining root. A tap root system penetrates deep into the soil. In contrast, a fibrous root system is located closer to the soil surface, and forms a dense network of roots that also helps prevent soil erosion (lawn grasses are a good example, as are wheat, rice, and corn). Some plants have a combination of tap roots and fibrous roots. Plants that grow in dry areas often have deep root systems, whereas plants growing in areas with abundant water are likely to have shallower root systems.

Root Growth and Anatomy

Root growth begins with seed germination. When the plant embryo emerges from the seed, the radicle of the embryo forms the root system. The tip of the root is protected by the root cap , a structure exclusive to roots and unlike any other plant structure. The root cap is continuously replaced because it gets damaged easily as the root pushes through soil. The root tip can be divided into three zones: a zone of cell division, a zone of elongation, and a zone of maturation and differentiation (Figure 30.16). The zone of cell division is closest to the root tip it is made up of the actively dividing cells of the root meristem. The zone of elongation is where the newly formed cells increase in length, thereby lengthening the root. Beginning at the first root hair is the zone of cell maturation where the root cells begin to differentiate into special cell types. All three zones are in the first centimeter or so of the root tip.

The root has an outer layer of cells called the epidermis, which surrounds areas of ground tissue and vascular tissue. The epidermis provides protection and helps in absorption. Root hairs , which are extensions of root epidermal cells, increase the surface area of the root, greatly contributing to the absorption of water and minerals.

Inside the root, the ground tissue forms two regions: the cortex and the pith (Figure 30.17). Compared to stems, roots have lots of cortex and little pith. Both regions include cells that store photosynthetic products. The cortex is between the epidermis and the vascular tissue, whereas the pith lies between the vascular tissue and the center of the root.

The vascular tissue in the root is arranged in the inner portion of the root, which is called the stele (Figure 30.18). A layer of cells known as the endodermis separates the stele from the ground tissue in the outer portion of the root. The endodermis is exclusive to roots, and serves as a checkpoint for materials entering the root’s vascular system. A waxy substance called suberin is present on the walls of the endodermal cells. This waxy region, known as the Casparian strip , forces water and solutes to cross the plasma membranes of endodermal cells instead of slipping between the cells. This ensures that only materials required by the root pass through the endodermis, while toxic substances and pathogens are generally excluded. The outermost cell layer of the root’s vascular tissue is the pericycle , an area that can give rise to lateral roots. In dicot roots, the xylem and phloem of the stele are arranged alternately in an X shape, whereas in monocot roots, the vascular tissue is arranged in a ring around the pith.

Root Modifications

Root structures may be modified for specific purposes. For example, some roots are bulbous and store starch. Aerial roots and prop roots are two forms of aboveground roots that provide additional support to anchor the plant. Tap roots, such as carrots, turnips, and beets, are examples of roots that are modified for food storage (Figure 30.19).

Epiphytic roots enable a plant to grow on another plant. For example, the epiphytic roots of orchids develop a spongy tissue to absorb moisture. The banyan tree (Ficus sp.) begins as an epiphyte, germinating in the branches of a host tree aerial roots develop from the branches and eventually reach the ground, providing additional support (Figure 30.20). In screwpine (Pandanus sp.), a palm-like tree that grows in sandy tropical soils, aboveground prop roots develop from the nodes to provide additional support.

Students select one of five concentration and fulfill the requirements, as outlined below.

1. The Cell/Molecular/Genetics/Biochemistry (CMGB) Concentration

This concentration provides exposure to several vital disciplines within Biology, and will prepare students for a diversity of careers in research, medicine, and industry. Students interested in tailoring their studies more specifically may follow the suggested "focus areas" when selecting their two CMGB Concentration electives.

Cell/Molecular/Genetics/Biochemistry (CMGB) Concentration Requirements
BIO 244Genetics I3.0
or BIO 444 Human Genetics
BIO 314Pharmacology3.0
or BIO 404 Structure and Function of Biomolecules
or BIO 416 Biochemistry of Major Diseases
BIO 318Biology of Cancer3.0
or BIO 430 Cell Biology of Disease
BIO 410Advanced Molecular Biology3.0
Cell/Molecular/Genetics/Biochemistry (CMGB) Concentration Electives (See Lists Below)
Two Cell/Molecular/Genetics/Biochemistry (CMGB) Electives (see list below) 6.0
Organismal/Physiology Elective (see list below) 3.0
Ecology/Evolution/Genomics Elective (see list below) 3.0
Concentration Laboratory Courses
Two Laboratory Electives (see list below) 4.0
Total Credits28.0

Students interested in pursuing a focus area in Neurobiology, Pharmaceutics, Cell Biology, Biochemistry, Molecular Biology or Genetics should contact the academic advisor in the Biology Department for specific focus recommendations.

2. The Organismal Biology/Physiology Concentration

This concentration combines courses in organismal biology and physiology with an opportunity to focus on human physiology. The concentration is designed to appeal to students interested in health and medicine, but also accommodates students seeking a wider breadth of knowledge in organismal diversity. Students can focus their electives in human physiology or can choose courses that study non-human organisms.

Organismal Biology/Physiology Concentration Requirements
BIO 201Human Physiology I4.0
or ENVS 254 Invertebrate Morphology and Physiology
BIO 203Human Physiology II4.0
or BIO 256 Vertebrate Morphology and Physiology
BIO 373Developmental Biology3.0
Select one of the following:
BIO 412Biology of Aging3.0
or BIO 284 Biology of Stress
or BIO 466 Endocrinology
or BIO 468 Pathophysiology
Organismal Biology/Physiology Concentration Concentration Electives (See List Below)
Cell/Molecular/Genetics/Biochemistry (CMGB) Elective 3.0
Two Organismal/Physiology Electives 6.0
Ecology/Evolution/Genomics Elective 3.0
Concentration Laboratory Courses
Two Laboratory Electives 4.0
Total Credits30.0

Students interesting in pursuing a focus area in Human Physiology or Organismal Biology should contact the academic advisor in the Biology Department for specific focus recommendations.

3. The Ecology/Evolution/Genomics Concentration

This concentration focuses on ecological and evolutionary aspects of biology for biology majors who also have specific interests in ecology, evolution or genomics. This concentration is designed to maintain a breadth of knowledge in biology, but also allows students to tailor their course work more specifically to reflect their specific area of interest.

Students interested in pursuing a focus area in Ecology, Evolutionary Biology or Genomics should contact the academic advisor in the Biology Department for specific focus recommendations.

4. The Pathobiology Concentration

The Pathobiology concentration focuses on pathogenesis, and provides a unique option for students that differs from the more traditional disciplines in cell/molecular/genetics/biochemistry. This concentration is designed to appeal to students with an interest in pursuing careers in areas of public and allied health.

BIO 221Microbiology3.0
BIO 320Microbial Pathogenesis3.0
BIO 323Parasitology3.0
or BIO 420 Virology
or BIO 435 Immunobiology of Disease
BIO 426Immunology3.0
Select one Cell/Molecular/Genetics/Biochemistry (CMGB) elective (see list below) 3.0
Select two Organismal/Physiology electives (see list below) 6.0
Select one Evolutionary Bio/Ecology elective (see list below) 3.0
Concentration Laboratory Courses
Two Laboratory electives (see list below) 4.0
Total Credits28.0
Cell/Molecular/Genetics/Biochemistry (CMGB) electives
BIO 244Genetics I3.0
BIO 285Forensic Biology3.0
BIO 311Biochemistry4.0
BIO 314Pharmacology3.0
BIO 318Biology of Cancer3.0
BIO 346Stem Cell Research3.0
BIO 348Neuroscience: From Cells to Circuits3.0
BIO 404Structure and Function of Biomolecules4.0
BIO 410Advanced Molecular Biology3.0
BIO 414Behavioral Genetics3.0
BIO 415Proteins3.0
BIO 416Biochemistry of Major Diseases3.0
BIO 421Biomembranes3.0
BIO 430Cell Biology of Disease3.0
BIO 433Advanced Cell Biology3.0
BIO 444Human Genetics3.0
BIO 453Protein Dysfunction in Disease3.0
BIO 462Biology of Neuron Function3.0
BIO 463Molecular Mechanisms of Neurodegeneration3.0
ENVS 326Molecular Ecology3.0
Organismal/Physiology electives
BIO 201Human Physiology I4.0
BIO 203Human Physiology II4.0
BIO 221Microbiology3.0
BIO 256Vertebrate Morphology and Physiology3.0
BIO 284Biology of Stress3.0
BIO 286Forensic Toxicology3.0
BIO 323Parasitology3.0
BIO 349Behavioral Neuroscience3.0
BIO 368Embryology4.0
BIO 372Histology4.0
BIO 373Developmental Biology3.0
BIO 386Gross Anatomy I2.0
BIO 388Gross Anatomy II2.0
BIO 412Biology of Aging3.0
BIO 420Virology3.0
BIO 435Immunobiology of Disease3.0
BIO 461Neurobiology of Autism Disorders3.0
BIO 466Endocrinology4.0
BIO 468Pathophysiology4.0
ENVS 254Invertebrate Morphology and Physiology3.0
Ecology/Evolution/Genomics electives
BIO 228Evolutionary Biology & Human Health3.0
BIO 331Bioinformatics I3.0
BIO 413Genomics3.0
BIO 436Population Genetics4.0
ENVS 230General Ecology3.0
ENVS 247Native Plants and Sustainability3.0
ENVS 323Tropical Field Studies3.0
ENVS 328Conservation Biology3.0
ENVS 333Wetland Ecology3.0
ENVS 343Equatorial Guinea: Field Methods3.0
ENVS 352Ornithology3.0
ENVS 354Ichthyology3.0
ENVS 355Biogeography3.0
ENVS 360Evolutionary Developmental Biology3.0
ENVS 364Animal Behavior3.0
ENVS 382Field Botany of the New Jersey Pine Barrens4.0
ENVS 383Ecology of the New Jersey Pine Barrens4.0
ENVS 391Freshwater and Marine Algae3.0
ENVS 438Biodiversity3.0
ENVS 470Advanced Topics in Evolution3.0
Laboratory electives
BIO 202Human Physiology Laboratory2.0
BIO 213Drosophila Neural Research3.0
BIO 215Techniques in Cell Biology3.0
BIO 222Microbiology Laboratory2.0
BIO 232Discovering Antibiotics3.0
BIO 257Vertebrate Morphology & Physiology Lab2.0
BIO 306Biochemistry Laboratory2.0
BIO 329Dictyostelium Research3.0
BIO 333Bioinformatics Laboratory2.0
BIO 374Developmental Biology Lab2.0
BIO 387Gross Anatomy I Laboratory2.0
BIO 389Gross Anatomy II Lab2.0
BIO 427Immunology Laboratory2.0
BIO 497Research (by permission of the department)0.5-12.0
ENVS 255Invertebrate Morphology and Physiology Lab2.0
ENVS 344Equatorial Guinea: Field Research6.0
ENVS 353Field Ornithology Lab2.0
ENVS 365Animal Behavior Laboratory2.0

5. The General Biology Concentration

This concentration will allow maximum flexibility for students who want to develop their own unique plan of study. The concentration is designed for students who may not have one specific area of interest, but who are looking to be well-rounded in the biological sciences. Students pursuing careers in education, where a wider breadth of knowledge in biology is desirable, may choose to select this concentration.

General Biology Concentration Electives 24.0
2 or 3 Cell/Molecular/Genetics/Biochemistry (CMGB) electives (see list below)
2 or 3 Organismal/Physiology electives (see list below)
2 or 3 Ecology/Evolution/Genomics electives (see list below)
Concentration Laboratory Courses
Two Laboratory electives (see list below) 4.0
Total Credits28.0
Cell/Molecular/Genetics/Biochemistry (CMGB) electives
BIO 244Genetics I3.0
BIO 285Forensic Biology3.0
BIO 311Biochemistry4.0
BIO 314Pharmacology3.0
BIO 318Biology of Cancer3.0
BIO 331Bioinformatics I3.0
BIO 332Bioinformatics II3.0
BIO 346Stem Cell Research3.0
BIO 348Neuroscience: From Cells to Circuits3.0
BIO 404Structure and Function of Biomolecules4.0
BIO 413Genomics3.0
BIO 415Proteins3.0
BIO 421Biomembranes3.0
BIO 430Cell Biology of Disease3.0
BIO 433Advanced Cell Biology3.0
BIO 444Human Genetics3.0
BIO 447Advanced Genetics and Molecular Biology3.0
BIO 451Genetic Reg Development3.0
BIO 453Protein Dysfunction in Disease3.0
BIO 462Biology of Neuron Function3.0
BIO 465Neurobiology of Disease3.0
ENVS 326Molecular Ecology3.0
Organismal/Physiology electives
BIO 201Human Physiology I4.0
BIO 203Human Physiology II4.0
BIO 221Microbiology3.0
BIO 256Vertebrate Morphology and Physiology3.0
BIO 264Ethnobotany3.0
BIO 284Biology of Stress3.0
BIO 286Forensic Toxicology3.0
BIO 320Microbial Pathogenesis3.0
BIO 323Parasitology3.0
BIO 349Behavioral Neuroscience3.0
BIO 368Embryology4.0
BIO 372Histology4.0
BIO 373Developmental Biology3.0
BIO 386Gross Anatomy I2.0
BIO 388Gross Anatomy II2.0
BIO 412Biology of Aging3.0
BIO 420Virology3.0
BIO 426Immunology3.0
BIO 435Immunobiology of Disease3.0
BIO 461Neurobiology of Autism Disorders3.0
BIO 466Endocrinology4.0
BIO 468Pathophysiology4.0
ENVS 254Invertebrate Morphology and Physiology3.0
ENVS 392Ichthyology and Herpetology3.0
ENVS 393Entomology3.0
Ecology/Evolution/Genomics electives
BIO 228Evolutionary Biology & Human Health3.0
BIO 331Bioinformatics I3.0
BIO 332Bioinformatics II3.0
BIO 413Genomics3.0
ENVS 230General Ecology3.0
ENVS 247Native Plants and Sustainability3.0
ENVS 284Physiological and Population Ecology3.0
ENVS 286Community and Ecosystem Ecology3.0
ENVS 315Plant Animal Interactions3.0
ENVS 322Tropical Ecology3.0
ENVS 323Tropical Field Studies3.0
ENVS 328Conservation Biology3.0
ENVS 330Aquatic Ecology3.0
ENVS 333Wetland Ecology3.0
ENVS 336Terrestrial Ecology5.0
ENVS 343Equatorial Guinea: Field Methods3.0
ENVS 352Ornithology3.0
ENVS 354Ichthyology3.0
ENVS 355Biogeography3.0
ENVS 360Evolutionary Developmental Biology3.0
ENVS 364Animal Behavior3.0
ENVS 382Field Botany of the New Jersey Pine Barrens4.0
ENVS 383Ecology of the New Jersey Pine Barrens4.0
ENVS 388Marine Field Methods4.0
ENVS 390Marine Ecology3.0
ENVS 391Freshwater and Marine Algae3.0
ENVS 410Physiological Ecology3.0
ENVS 412Biophysical Ecology3.0
ENVS 413Advanced Population Ecology3.0
ENVS 414Advanced Community Ecology3.0
ENVS 438Biodiversity3.0
ENVS 470Advanced Topics in Evolution3.0
Laboratory electives
BIO 202Human Physiology Laboratory2.0
BIO 213Drosophila Neural Research3.0
BIO 215Techniques in Cell Biology3.0
BIO 222Microbiology Laboratory2.0
BIO 232Discovering Antibiotics3.0
BIO 257Vertebrate Morphology & Physiology Lab2.0
BIO 306Biochemistry Laboratory2.0
BIO 329Dictyostelium Research3.0
BIO 333Bioinformatics Laboratory2.0
BIO 374Developmental Biology Lab2.0
BIO 387Gross Anatomy I Laboratory2.0
BIO 389Gross Anatomy II Lab2.0
BIO 427Immunology Laboratory2.0
BIO 497Research (by permission of the department)0.5-12.0
ENVS 255Invertebrate Morphology and Physiology Lab2.0
ENVS 327Molecular Ecology Laboratory2.0
ENVS 344Equatorial Guinea: Field Research6.0
ENVS 353Field Ornithology Lab2.0
ENVS 365Animal Behavior Laboratory2.0
ENVS 382Field Botany of the New Jersey Pine Barrens4.0
ENVS 383Ecology of the New Jersey Pine Barrens4.0
ENVS 388Marine Field Methods4.0
ENVS 394Entomology Laboratory2.0

Note about laboratory credits: ENVS 336 , ENVS 382 and ENVS 388 have both a lecture and laboratory component.

32. The cell of the unicellular algae Ventricaria ventricosa is one of the largest known, reaching one to five centimeters in diameter. Like all single-celled organisms, V. ventricosa exchanges gases .

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This text is based on Openstax Biology for AP Courses, Senior Contributing Authors Julianne Zedalis, The Bishop's School in La Jolla, CA, John Eggebrecht, Cornell University Contributing Authors Yael Avissar, Rhode Island College, Jung Choi, Georgia Institute of Technology, Jean DeSaix, University of North Carolina at Chapel Hill, Vladimir Jurukovski, Suffolk County Community College, Connie Rye, East Mississippi Community College, Robert Wise, University of Wisconsin, Oshkosh

This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 Unported License, with no additional restrictions

Author information


Department of Biological Sciences, Lehman College, City University of New York, New York, NY, USA

Graduate School and University Center-CUNY, New York, NY, USA

CSIRO Synthetic Biology Future Science Platform, Canberra, Australia

Australian Institute for Bioengineering & Nanotechnology, University of Queensland, Brisbane, Queensland, Australia

Horticultural Sciences Department, University of Florida, Gainesville, FL, USA

ARC Centre of Excellence in Plant Energy Biology, School of Molecular Sciences, University of Western Australia, Crawley, Western Australia, Australia

Queensland Alliance for Agriculture & Food Innovation, University of Queensland, St. Lucia, Queensland, Australia

Mark Cooper & Kai P. Voss-Fels

Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Kgs Lyngby, Denmark

Max-Planck-Institute for Terrestrial Microbiology, Department of Biochemistry & Synthetic Metabolism, Marburg, Germany

LOEWE Center for Synthetic Microbiology, Marburg, Germany

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A.D.H., E.T.W., and C.E.V. led the writing of the paper, to which A.H.M., P.I.N., T.J.E., M.C. and K.P.V.-F. contributed in addition, T.J.E. conceived of and composed Fig. 1, and M.C. and K.P.V.-F. performed evolutionary modelling.

Corresponding authors

Biology Notes Form 1

Click Here - Free KCSE Past Papers » KNEC Past Exams » Free Downloads » KCSE Papers & Marking Schemes

Biology Notes Form One Syllabus

By the end of form one work, the learner should be able to:

• Carbon (IV) oxide is necessary for photosynthesis

• Oxygen is produced during photosynthesis

• Effect of temperature on enzymes

• Effects of enzyme concentration on the rate of a reaction

• Effect of PH on enzyme activities

Biology Notes Form 1 - Form One Biology

• Biology derived from Greek words - BIOS meaning LIFE and LOGOS meaning STUDY or KNOWLEDGE

• Biology means "life knowledge"

• It is the study of living things/organisms

• Zoology - study of animals

• Microbiology - study' of microscopic organisms

• Morphology - study of external structure of organisms

• Anatomy - study of internal structure of organisms

• Physiology - study of the functioning or working of the cells or body

• Biochemistry - study of the chemistry of materials in living organisms

• Genetics - study of inheritance

• Ecology- study of the relationship between organisms and their environment

• Taxonomy - sorting out of organisms into groups

• Histology - study of fine structure of tissues

• Virology - study of viruses

• Bacteriology - study of bacteria

• Entomology - study of insects

• Ichthyology - study of fish

Importance of Biology

• One learns about the functioning of the human body

• One understands the developmental changes that take place in the body

• It contributes immensely to improved life

• It enables one to enter careers such as:

Characteristics of Living Things

Life defined through observations of activities carried out by living things

• Gaseous Exchange – Process throw which respiratory gases (CO2 & O2) are taken in and out through a respiratory surface

Growth and Development

• Reproduction-Reproduction is the formation of new individuals of a species to ensure continued existence of a species and growth of its population

This is of great survival value to the organism

Collection and Observation of Organisms Biology as a practical subject is learnt through humane handling of organisms

Materials needed for collection of organisms

• Knives to cut portions of plant stem/root or uproot

• Polythene bags to put the collected plant or specimens

Observation of Organisms

• Observe the plant/animal in its natural habitat before collecting

• Identify the exact place -on surface, under rock, on tree trunk, on branches

• How does it interact with other animals and the environment?

• How many of that kind of plant or animal are in a particular place?

• Plant specimens placed on the bench and sorted out into-

• Animal specimens may be left inside polythene bags if transparent

• Others (killed ones) are put in petri dishes

• Use hand lens to observe the external features of small animals

Presenting the Results of Observations

• Organisms are observed and important features noted down: colour, texture hard or soft if hairy or not

Size is measured or estimated

• Biological Drawings - It is necessary to draw some of the organisms

• In making a biological drawing, magnification (enlargement) is noted

• Indicate the magnification of your drawing

• ie how many times the drawing is larger/smaller than the actual specimen MG=length of drawing/length specimen

How does it interact with other animals and the environment

• Several drawings of one organism may be necessary to represent all features observed, eg

• Anterior view of grasshopper shows all mouth parts properly, but not all limbs

• Lateral (side) view shows all the legs

Collection, Observation and Recording of Organisms

• Plants and animals collected from the environment, near school or within school compound using nets, bottles and gloves

• Animals collected include:-arthropods, earthworms and small vertebrates like lizards/chameleons/ rodents

• Place in polythene bags and take to the laboratory

• Stinging/poisonous insects killed using ether

• Other animals are observed live and returned to their natural habitat

• Plant specimen collected include:- leaves, flowers and whole plants

The differences between animals and plants collected

Comparison Between Plants And Animals

• Classification is putting organisms into groups

• Classification is based on the study of external characteristics of organisms

• It involves detailed observation of structure and functions of organisms

• Organisms with similar characteristics are put in one group

• Differences in structure are used to distinguish one group from another

• The magnifying lens is an instrument that assists in the observation of fine structure eg hairs by enlarging them

• A specimen is placed on the bench or held by hand,

• Then the magnifying lens is moved towards the eye until the object is dearly focused and an enlarged image is seen

The magnification can be worked out as follows:

Magnification = length of the drawing/ length of the specimen

Note: magnification has no units

Nececity/need for Classification

• To be able to identify organisms into their taxonomic groups

• To enable easier and systematic study of organisms

• To show evolutionary relationships in organisms

Major Units of Classification (Taxonomic Groups)

• Taxonomy is the study of the characteristics of organisms for the purpose of classifying them

• The groups are Taxa (singular Taxon)

The taxonomic groups include:

Species: This is the smallest unit of classification

Organisms of the same species resemble each other

The number of chromosomes in their cells is the same

Members of a species interbreed to produce fertile offspring

Genus (plural genera): A genus is made up of a number of species that share several characteristics

Members of a genus cannot interbreed and if they do, the offspring are infertile

Family: A family is made up of a number of genera that share several characteristics

Order: A number of families with common characteristics make an order

Class: Orders that share a number of characteristics make up a class

Phylum/Division: A number of classes with similar characteristics make up a phylum (plural phyla) in animals

In plants this is called a division

Kingdom: This is made up of several phyla (in animals) or divisions (in plants)

It is the largest taxonomic unit in classification

Living organisms are classified into five kingdoms

• Some are unicellular while others are multicellular

• Most are saprophytic eg yeasts, moulds and mushrooms

• A few are parasitic eg Puccinia graminae

• These are very small unicellular organisms

• They lack a nuclear membrane

• Do not have any bound membrane organelles

• Hence the name Prokaryota

• They are mainly bacteria, eg Vibrio cholerae

• They are unicellular organisms

• Their nucleus and organelles are surrounded by membranes (eukaryotic)

• They include algae, slime moulds - fungi-like and protozoa

• They are all multicellular

• They contain chlorophyll and are all autotrophic

• They include Bryophyta (mossplant), Pteridophyta (ferns) and Spermatophyta (seed bearing plants)

• These are all multicellular and heterotrophic

• Examples are annelida (earthworms), mollusca (snails),athropoda, chordata

• Example of Arthropods are ticks, butterflies

• Members of Chordata are fish, frogs and humans

External Features of Organisms

In plants we should look for:

• Spore capsule and rhizoids in moss plants

• Stem, leaves, roots, flowers, fruits and seeds in plants

In animals, some important features to look for are:

• Segmentation, presence of limbs and, number of body parts, presence and number of antennae

These are found in phylum arthropoda:

• Visceral clefts, notochord, nerve tube, fur or hair, scales, fins, mammary glands, feathers and wings

• These are found in chordata

Binomial Nomenclature

• Organisms are known by their local names

• Scientists use scientific names to be able to communicate easily among themselves

• This method of naming uses two names, and is called Binomial nomenclature

• The first name is the name of the genus: (generic name) which starts with a capital letter

• The second name is the name of the species (specific name) which starts with a small letter

• The two names are underlined or written in italics

• Man belongs to the genus Homo, and the species, sapiens

• The scientific name of man is therefore Homo sapiens

• Maize belongs to the genus Zea, and the species mays

• The scientific name of maize is Zea mays

• Use of Collecting Nets, Cutting Instruments and Hand Lens

• Forceps are used to collect crawling and slow moving animals

• Sweep nets are used to catch flying insects

• Cutting instrument like scapel is used to cut specimen e.g. making sections

• Hand lens is used to magnify small plants and animals

• Drawing of the magnified organism are made and the linear magnification of each calculated

Collection and Detailed Observation of Small Plants and Animals

Look for the following:

• Moss plants: Rhizoids and spore capsules

• Fern plants: Rhizomes with adventitious roots large leaves (fronds) with Sori (clusters of sporangia)

• Seed plants: Tree/shrub (woody) or non-woody (herbs) e.g. bean

• Root system - fibrous, adventitious and tap root

• Stem - position and length of interrnodes

• Type of leaves - simple or compound arranged as alternate, opposite or whorled

• Flower - colour, number of parts, size and relative position of each:

• Fruits - freshy or dry edible or not edible

• Seeds - monocotyledonous or dicotyledonous

Small animals e.g. earthworms, tick, grasshopper, butterfly, beetles

Observe these animals to see:

• Presence or absence of wings

• The cell is the basic unit of an organism

• All living organisms are made up of cells

• Some organisms are made up of one cell and others are said to be multicellular

• Other organisms are made of many cells and are said to be multicellular

• Cells are too little to see with the naked eye

• They can only be seen with the aid of a microscope

The microscope is used to magnify objects

• The magnifying power is usually inscribed on the lens

• To find out how many times a specimen is magnified, the magnifying power of the objective lens is multiplied by that of the eye piece lens

• If the eye piece magnification lens is x10 and the objective lens is x4, the total magnification is x40

• Magnification has no units

• It should always have the multiplication sign

• Turn the low power objective lens until it clicks into position

• Looking through the eye piece, ensure that enough light is passing through by adjusting the mirror

• This is indicated by a bright circular area known as the field of view

• Place the slide containing the specimen on stage and clip it into position

• Make sure that the specimen is in the centre of the field of view

• Using the coarse adjustment knob, bring the low power objective lens to the lowest point

• Turn the knob gently until the specimen comes into focus

• If finer details are required, use the fine adjustment knob

• When using high power objective always move the fine adjustment knob upwards

• Great care should be taken when handling it

• Keep it away from the edge of the bench when using it

• Always hold it with both hands when moving it in the laboratory

• Clean the lenses with special lens cleaning paper

• Make sure that the low power objective clicks in position in line with eye piece lens before and after use

• Store the microscope in a dust-proof place free of moisture

Cell Structure as Seen Through the Light Microscope

Cell membrane (Plasma membrane):

• This is a thin membrane enclosing cell contents

• It controls the movement of substances into and out of the cell

• This is a jelly-like substance in which chemical processes are carried out

• Scattered all over the cytoplasm are small structures called organelles

• Like an animal cell, the plant cell has a cell membrane, cytoplasm and a nucleus

• Plant cells have permanent, central vacuole

It contains cell sap where sugars and salts are stored

• This is the outermost boundary of a plant cell

• Between the cells is a middle lamella made of calcium pectate

• With special staining techniques it is possible to observe chloroplasts

• These are structures which contain chlorophyll, the green pigment responsible for trapping light for photosynthesis

The Electron Microscope (EM)

• Capable of magnifying up to 500,000 times

• The specimen is mounted in vacuum chamber through which an electron beam is directed

• The image is projected on to a photographic plate

• The major disadvantage of the electron microscope is that it cannot be used to observe living objects

• However, it provides a higher magnification and resolution (ability to see close points as separate) than the light microscope so that specimen can be observed in more detail

Cell Structure as Seen Through Electron Microscope

• Under the electron microscope, the plasma membrane is seen as a double layer

• This consists of a lipid layer sandwiched between two protein layers

• This arrangement is known as the unit membrane and the shows two lipid layers with proteins within

• Substances are transported across the membrane by active transport and diffusion

• This is a network of tubular structures extending throughout the cytoplasm of the cell

• It serves as a network of pathways through which materials are transported from one part of the cell to the other

• An ER encrusted with ribosomes it is referred to as rough endoplasmic reticulum

• An ER that lacks ribosomes is referred to as smooth endoplasmic reticulum

• The rough endoplasmic reticulum transports proteins while the smooth endoplasmic reticulum transports lipids

• These are small spherical structures attached to the ER

• They consist of protein and ribonucleic acid (RNA)

• They act as sites for the synthesis of proteins

• Golgi bodies are thin, plate-like sacs arranged in stacks and distributed randomly in the cytoplasm

• Their function is packaging and transportation of glycol-proteins

• They also produce lysosomes

• Each mitochondrion is a rod-shaped organelle

• Made up of a smooth outer membrane and a folded inner membrane

• The foldings of the inner membrane are called cristae

• They increase the surface area for respiration

• The inner compartments called the matrix

• Mitochondria are the sites of cellular respiration, where energy is produced

• These are vesicles containing hydrolytic enzymes

• They are involved in the breakdown of micro-organisms, foreign macromolecules and damaged or worn-out cells and organelles

• The nucle s is surrounded by a nuclear membrane which is a unit membrane

• The nuclear membrane has pores through which materials can move to the surrounding cytoplasm

• The nucleus contains proteins and nucleic acid deoxyribonucleic acid (DNA) and RNA

• The chromosomes are found in the nucleus

• They are the carriers of the genetic information of the cell

• The nucleolus is also located in the nucleus but it is only visible during the non-dividing phase of the cell

• These are found only in photosynthetic cells

• Each chloroplast consists of an outer unit

membrane enclosing a series of interconnected membranes called lamellae

• At various points along their length the lamellae form stacks of disc like structures called grana

• The lamellae are embedded in a granular material called the stroma

• The chloroplasts are sites of photosynthesis

• The light reaction takes place in the lamellae while the dark reactions take place in the stroma

Comparison between animal cell and plant cell

Cells are specialised to perform different functions in both plants and animals

• Palisade cells have many chloroplasts for photosynthesis

• Root hair cells are long and thin to absorb water from the soil

• Red blood cells have haemoglobin which transports oxygen

• Sperm cells have a tail to swim to the egg

• Multicellular organisms cells that perform the same function are grouped together to form a tissue

• Each tissue is therefore made up of cells that are specialised to carry out a particular function

Animal Tissues- Examples of animal tissues

• An organ is made up of different tissues

• e.g the heart, lungs, kidneys and the brain in animals and roots, stems and leaves in plants

• Organs which work together form an organ system

• Digestive, excretory, nervous and circulatory in animals and transport and support system in plants

• Different organ systems form an organism

Observation and Identification of parts of a light microscope and their functions

• A light microscope is provided

• Various parts are identified and observed

• Drawing and labelling of the microscope is done

• Functions of the parts of the mircroscope are stated

• Calculations of total magnification done using the formula

• Eye piece lens maginification x objective lens maginification

Preparation and Observation of Temporary Slides of Plant Cells

• A piece of epidermis is made from the fleshy leaf of an onion bulb

It is placed on a microscope slide and a drop of water added

• A drop of iodine is added and a cover slip placed on top

• Observations are made, under low and medium power objective

• The cell wall and nucleus stain darker than other parts

• A labelled drawing is made

• The following are noted: Nucleus, cell wall, cytoplasm and cell membrane

Observation of permanent slides of animal cells

• Permanent slides of animal cells are obtained e.g, of cheek cells, nerve cells and muscle cells

• The slide is mounted on the microscope and observations made under low power and medium power objectives

• Labelled drawings of the cells are made

• A comparison between plant and animal cell is made

Observation and Estimation of Cell Size and Calculation of Magnification of Plant Cells

• Using the low power objective, a transparent ruler is placed on the stage of the microscope

• An estimation of the diameter of the field of view is made in millimeters

• This is converted into micrometres (1mm=1000u)

• A prepared slide of onion epidermal cells is mounted

• The cells across the centre of the field of view are counted from left and right and top to bottom

• The diameter of field of view is divided by the number of cells lying lengthwise to give an estimate of the length and width of each cell

Meaning of cell physiology

• The term physiology refers to the functions that occur in living organisms

• Cell physiology refers to the process through which substances move across the cell membrane

• Several physiological processes take place inside the cell e.g respiration

• Oxygen and glucose required enter the cell while carbon (IV) oxide and water produced leave the cell through the cell membrane

Structure and properties of cell membrane

• The cell membrane is the protective barrier that shelter cellular contents

• Movement of all substances into and out of the cells takes place across the cell membrane

• It is made up of protein and lipid molecules

• Lipid molecules have phosphate group attached to it on one end

• They are then referred to phospholipids

• The phospholipids are arranged to form a double layer

• The ends with phosphate group face outwards

• the proteins are scattered throughout the lipid double layer

• Some of these proteins act as carrier molecules that channel some material in and outside the cells

• The cell membrane allows certain molecules to pass through freely while others move through with difficulty and still others do not pass through at all

• This is selective permeability and the cell membrane is described as semi-permeable

Properties of cell membrane

• The cell membrane is semi-permeable

• it allows small molecules that are soluble in lipid to pass through with more ease than water soluble molecules

• this is due to the presence of the phospholipids double layer Polarlity

• The cell membrane has electrical charges across its surface

it has positive charged ions on the outside and negatively charged ions on the inside

this property contributes to electrical impulses sent along nerve cells

• Sensitivity to changes in temperature and pH

• Very high temperatures destroy the semi-permeability nature of the cell membrane because the proteins are denatured by extreme pH values have the same effect on the membrane permeability

• Some of the physiological processes include diffusion, osmosis and active transport

• Diffusion is the movement of molecules or ions from a region of high concentration to a region of low concentration aided by a concentration gradient

• diffusion continues to occur as long as there is a difference in concentration between two regions (concentration gradient)

• Stops when an equilibrium is reached i.e

, when the concentration of molecules is the same in both regions

• Diffusion is a process that occurs inside living organisms as well as the external environment

Factors Affecting Diffusion

Concentration Gradient

An increase in the concentration of molecules at one region results in a steeper concentration gradient which in turn increases the rate of diffusion

High temperature increases kinetic energy of molecules

They move faster hence resulting in an increase in rate of diffusion, and vice versa

Size of Molecules or Ions

The smaller the size of molecules or ions, the faster their movement hence higher rate of diffusion

The denser the molecules or ions diffusing, the slower the rate of diffusion, and vice versa

The medium through which diffusion occurs also affects diffusion of molecules or ions

For example, diffusion of molecules through gas and liquid media is faster than through a solid medium

This refers to the thickness or thinness of surface across which diffusion occurs

Rate of diffusion is faster when the distance is small i.e, thin surface

Surface Area to Volume Ratio

The larger the surface area to volume ratio, the faster the rate of diffusion

For example, in small organisms such as Amoeba the surface area to volume ratio, is greater hence faster diffusion than in larger organisms

Role of Diffusion in Living Organisms

Some processes that depend on diffusion include the following:

• Gaseous exchange: Movement of gases through respiratory surfaces is by diffusion

• Absorption of materials into cells Cells obtain raw materials and nutrients from the surrounding tissue fluid and blood through diffusion, e.g, glucose needed for respiration diffuses from blood and tissue fluid into cells

• Excretion: Removal of metabolic waste products like carbon (IV) oxide, and ammonia out of cells is by diffusion

• Absorption of the end-products of digestion from the intestines is by diffusion

• Osmosis is the movement of water molecules from a region of high water concentration to a region of low water concentration through a semi-permeable membrane

• Osmosis is a special type of diffusion that involves the movement of water molecules only and not solute molecules

• Osmosis takes place in cells across the cell membrane as well as across non-living membranes

• e.g cellophane or visking tubing which are also semi-permeable

• It is purely a physical process

Factors Affecting Osmosis

Size of solute molecules

Osmosis' occurs only when solute molecules are too large to pass through a semi-permeable membrane

Concentration Gradient

Osmosis occurs when two solutions of unequal solute concentration are separated by a semi-permeable membrane

High temperatures increase movement of water molecules hence influence osmosis

However, too high temperatures denature proteins in cell membrane and osmosis stops

Increase in pressure affects movement of water molecules

As pressure increases inside a plant cell, osmosis decreases

Roles of Osmosis in Living Organisms

The following processes depend on osmosis in living organisms:

• Movement of water into cells from the surrounding tissue fluid and also from cell to cell

• Absorption of water from the soil and into the roots of plants

• Support in plants especially herbaceous ones, is provided by turgor pressure, which results from intake of water by osmosis

• Absorption of water from the alimentary canal in mammals

• Re-absorption of water in the kidney tubules

• Opening and closing stomata

Water Relations in Plant and Animal Cells

• The medium (solution) surrounding cells or organisms is described by the terms hypotonic, hypertonic and isotonic

• A solution whose solute concentration is more than that of the cell sap is said to be hypertonic

A cell placed in such a solution loses water to the surroundings by osmosis

• A solution whose solute concentration is less than that of the cell sap is said to be hypotonic

A cell placed in such a solution gains water from the surroundings by osmosis

• A solution which has the same solute concentration as the cell sap is said to be isotonic

When a cell is placed in such a solution there will be no net movement of water either into or out of the cell

• The term osmotic pressure describes the tendency of the solution with a high solute concentration to draw water into itself when it is separated from distilled water or dilute solution by a semi-permeable membrane

• Osmotic pressure is measured by an osmometer

• When plant cells are placed in distilled water or in a hypotonic solution, the osmotic pressure in the cells is higher than the osmotic pressure of the medium

• This causes the water to enter the cells by osmosis

• The water collects in the vacuole which increases in size

• As a result the cytoplasm is pushed outwards and it in turn presses the cell membrane next to the cell wall

• This builds up water pressure (hydrostatic pressure) inside the cell

• When the cell is stretched to the maximum, the cell wall prevents further entry of water into the cell

• Then the cell is said to be fully turgid

• The hydrostatic pressure developed is known as turgor pressure

• When a plant cell is placed in a hypertonic medium, it loses water by osmosis

• The osmotic pressure of the cell is lower than that of the medium

• The vacuole decreases in size and the cytoplasm shrinks as a result of which the cell membrane loses contact with the cell wall

The whole process is described as plasmolysis

• Incipient plasmolysis is when a cell membrane just begins to lose contact with the cell wall

• Plasmolysis can be reversed by placing the cell in distilled water or hypotonic solution

• However, full plasmolysis may not be reversed if cell stays in that state for long

• The term wilting describes the drooping of leaves and stems of herbaceous plants after considerable amounts of water have been lost through transpiration

• It is observed in hot dry afternoons or in dry weather

• This is when the amount of water lost through transpiration exceeds the amount absorbed through the roots

• Individual cells lose turgor and become plasmolysed and the leaves and stems droop

• The condition is corrected at night when absorption of water by the roots continue while transpiration is absent

• Eventually, wilting plants may die if the soil water is not increased through rainfall or watering

Water Relations in Plants and Animals

• Haemolysis is the bursting of cell membrane of red blood cells releasing their haemoglobin

• It occurs when red blood cells are placed in distilled water or hypotonic solution

• This is because the cell membrane does not resist further entry of water by osmosis after maximum water intake

• Takes place when red blood cells are placed in hypertonic solution

• They lose water by osmosis, shrink and their shape gets distorted

• Animal cells have mechanisms that regulate their salt water balance (osmoregulation) to prevent above processes that lead to death of cells

• An Amoeba placed in distilled water, i.e

hypotonic solution, removes excess water using a contractile vacuole

• The rate of formation of contractile vacuoles increases

• Active transport is the movement of solutes such as

glucose, amino acids and mineral ions

• From an area of their low concentration to an area of high concentration

• It is movement against a concentration gradient and therefore energy is required

• As such it only takes place in living organisms

• The energy needed comes from respiration

• Certain proteins in the cell surface membrane responsible for this movement are referred to as carrier proteins or channel proteins

• The shape of each type of carrier protein is specific to the type of substances conveyed through it

• It has been shown that the substance fits into a particular slot on the protein molecule,

• As the protein changes from one form of shape to another the substance is moved across and energy is expended

Factors Affecting Active Transport

• Energy needed for active transport is provided through respiration

• An increase in the amount of oxygen results in a higher rate of respiration

• If a cell is deprived of oxygen active transport stops

• Optimum temperature is required for respiration, hence for active transport

• Very high temperatures denature respiratory enzymes

• Very low temperatures inactivate enzymes too and active transport stops

Availability of carbohydrates

• Carbohydrates are the main substrates for respiration

• Increase in amount of carbohydrate results in more energy production during respiration and hence more active transport

• Lack of carbohydrates causes active transport to stop

• Metabolic poisons e.g. cyanide inhibit respiration and stops active transport due to lack of energy

Role of Active Transport in Living Organisms

Processes requiring active transport:

• Absorption of mineral salts from the soil into plant roots

• Absorption of end products of digestion e.g. glucose and amino acids from the digestive tract into blood stream

• Excretion of metabolic products e.g.urea from the cells

• Re-absorption of useful substances and mineral salts back into blood capillaries from the kidney tubules

• Sodium-pump mechanism in nerve cells

• Re-absorption of useful materials from tissue fluid into the blood stream

1.Experiment to Demonstrate Diffusion

• Various coloured substances such as: dyes, plant extracts and chemicals like potassium pennanganate are used

• Potassium manganate (VII) crystals are introduced to the bottom of a beaker filled with water using a glass tubing or drinking straw which is then removed

• Observations are made and the disappearance of the crystals and subsequent uniform colouring of water noted

2.Experiment to Demonstrate Osmosis Using a Visking Thbing

• A strip of visking tubing 8-10 cm is cut and tied at one end using strong thread

• About 2 ml of 25% sucrose solution is put inside and the other end tied with thread

• The tubing is washed under running water and then blotted to dry

• It is immersed in a beaker containing distilled water and left for at least one hour or overnight

• It will then be observed that the visking tubing has greatly increased in size and has become firm

• A control experiment can be set up using distilled water inside the visking tubing in place of sucrose solution

3.xperiment to Show Osmosis using Living Tissue

• Irish potato tubers are peeled and scooped out to make hollow space at the centre

• Sucrose solution is placed inside the hollow, and the potato tuber placed in a beaker or petri-dish with distilled water

A conttrol is set using a boiled potato

• Another one using distilled water inside hollow in place of sugar solution

• The experiment is left for 3 hours to 24 hours

4.Experiment to Demonstrate Turgor and Plasmolysis in Onion Epidermal Cells

• Two strips of onion epidermis are obtained

• One is placed on a slide with distilled water while the other is placed on a slide with 25% sucrose solution and a coverslip placed on top of each

• The mounted epidermis is observed under low power microscope and then left for 30 minutes

• After 30 minutes, observations are made again

The cells in distilled water have greatly enlarged

Cells in 25% sucrose have shrunk

Nutrition in Plants and Animals

• The external structure of the leaf consists of a leaf stalk or petiole and a broad leaf blade or lamina

• The lamina has a main vein midrib from which smaller veins originate

• The outline of the leaf is the margin and the tip forms the apex

• This is the outer layer of cells, normally one cell thick

• It is found in both the upper and lower leaf surfaces

• The cells are arranged end to end

• The epidermis offers protection and maintains the shape of the leaf

• It is covered by a layer of cuticle which reduces evaporation

Leaf Mesophyll Consists of the palisade layer, next to upper epidermis, and the spongy layer next to the lower epidermis

Palisade Mesophyll Layer The cells are elongated and arranged close to each other leaving narrow air spaces

These contain numerous chloroplasts and are the main photosynthetic cells

In most plants, the chloroplast are distributed fairly uniformly throughout the cytoplasm

In certain plants growing in shaded habitats in dim light, most chloroplasts migrate to the upper region of the palisade cells in order to maximise absorption of the limited light available

Spongy Mesophyll Layer

• The cells are spherical in shape

• They are loosely arranged, with large intercellular spaces between them

• The spaces are air¬filled and are linked to the stomatal pores

• The spongy mesophyll cells have fewer chloroplasts than the palisade mesophyll cells

• These are made up of the xylem and the phloem tissues

• The xylem transports water and mineral salts to the leaves

• The phloem transports food manufactured in the leaf to the other parts of the plant and from storage organs to other parts

Adaptations of Leaf for Photosynthesis

• Presence of veins with vascular bundles

Xylem vessels transport water for photosynthesis

• Phloem transports manufactured food from leaves to other parts of the plant

• Leaf lamina is thin to allow for penetration of light over short distance to reach photosynthetic cells

• Broad lamina provides a large surface area for absorption of light and carbon (IV) oxide

• Transparent cuticle and epidermal layer allow light to penetrate to mesophyll cells

• Palisade cells are close to the upper epidermis for maximum light absorption

• Presence of numerous chloroplasts in palisade mesophyll traps maximum light

• Chloroplast contain chlorophyll that traps light energy

• Spongy mesophyll layer has large intercellular air spaces allowing for gaseous exchange

• Presence of stomata for efficient gaseous exchange (entry of carbon (IV) oxide into leaf and exit of oxygen)

• Mosaic arrangement of leaves to ensure no overlapping of leaves hence every leaf is exposed to light

Structure and Function of Chloroplasts

• Chloroplasts are large organelles (5 um in diameter) found in the cytoplasm of green plant cells

• They are visible under the light microscope

• They contain chlorophyll, a green pigment and other carotenoids which are yellow, orange and red in colour

• Certain plants have red or purple leaves due to abundance of these other pigments

• Chlorophyll absorbs light energy and transforms it into chemical energy

• The other pigments absorb light but only to pass it onto chlorophyll

• The two make up the chloroplast envelop

• Inner membrane encloses a system of membranes called lamellae

• At intervals, the membranes form stacks of fluid filed sacs known as grana (singular granum)

• Chloroplast and other pigments are attached to the grana

• In between the lamellae is a gel-like stroma, that contains starch grains and lipid droplets

• Enzymes for the dark stage reaction (light independent stage) are embedded in the stroma

• Enzymes for the light dependent stage occur in the grana

• Absorption of light by chlorophyll and other pigments

• Light stage of photosynthesis occurs on the grana

(transformation of light energy to chemical energy

) • Carbon fixation to form carbohydrate takes place in the stroma which has enzymes for dark stage of photosynthesis

Process of Photosynthesis

• Photosynthesis involves a series of chemical reactions, all of which take place inside chloroplasts

• A general equation for photosynthesis is:

Carbon (IV)Oxide+Water light energy---Glucose+Oxygen chlorophyll

• The reaction occurs in two main phases or stages

• The initial state requires light and it is called the light dependent stage or simply light stage

• It takes place on the lamellae surfaces

• Its products are used in the dark stage

• The dark stage does not require light although it occurs in the light and is called light independent stage

• Two reactions take place that produce raw materials for the dark stage:

• Light energy splits the water molecules into hydrogen and oxygen

• This process is called photolysis

• The hydrogen is taken up by a hydrogen acceptor called Nicotinamide adenine dinucleotide phosphate (NADP) while oxygen is released as a by-product

2H2O(l) light energy4H+O2 photolysis

• Light energy strikes the chlorophyll molecules and sets in motion a series of reactions resulting in the production of a high energy molecule called adenosine triphophate (ATP)

• This stage involves the fixation of carbon i.e

the reduction of carbon (IV) oxide by addition of hydrogen to form carbohydrate

• It uses the products formed during the light stage

Carbon (IV) oxide + Hydrogen --- Carbohydrates

• The synthesis of carbohydrates does not take place in a simple straight line reaction as shown in the equation above

• It involves a series of steps that constitute what is known as the Calvin cycle

• Carbon (IV) oxide is taken up by a compound described as a carbon (IV) oxide acceptor

• This is a 5-carbon compound known as ribulose biphosphate and a six carbon compound is formed which is unstable and splits into two three-carbon compounds

• Hydrogen from the light reaction is added to the three carbon compound using energy (ATP) from the light reaction

• The result is a three carbon (triose) sugar, (phosphoglycerate or PGA)

• This is the first product of photosynthesis

• Glucose, other sugars as well as starch are made from condensation of the triose sugar molecules

• The first product is a 3-carbon sugar which condenses to form glucose (6-C sugar)

• From glucose, sucrose and eventually starch is made

• Sucrose is the form in which carbohydrate is transported from the leaves to other parts of the plant

• Starch is the storage product

• Other substances like oils and proteins are made from sugars

• This involves incorporation of other elements e.g. nitrogen, phosphorus and sulphur

Factors Influencing Photosynthesis

• Certain factors must be provided for before photosynthesis can take place

• The rate or amount of photosynthesis is also influenced by the quantity or quality of these same factors

Carbon(IV) Oxide Concentration

• Carbon (IV) oxide is one of the raw materials for photosynthesis

• No starch is formed when leaves are enclosed in an atmosphere without carbon (IV) oxide

• The concentration of carbon (IV) oxide in the atmosphere remains fairly constant at about 0.03% by volume

• However, it is possible to vary the carbon (IV) oxide concentration under experimental conditions

• Increasing the carbon (IV) oxide concentration up to 0.1 % increases the rate of photosynthesis

• Further increase reduces the rate

• Light supplies the energy for photosynthesis

• Plants kept in the dark do not form starch

• Generally, increase in light intensity up to a certain optimum, increases the rate of photosynthesis

• The optimum depends on the habitat of the plant

• Plants that grow in shady places have a lower optimum than those that grow in sunny places

• Water is necessary as a raw material for photosynthesis

• The amount of water available greatly affects the rate of photosynthesis

• The more water available, the more the photosynthetic rate, hence amount of food made

• Effect of water on photosynthesis can only be inferred from the yield of crops

• It is the main determinant of yield (limiting factor in the tropics)

• The reactions involved in photosynthesis are catalysed by a series of enzymes

• A suitable temperature is therefore necessary

• The optimum temperature for photosynthesis in most plants is around 30"C

• This depends on the natural habitat of the plant

• Some plants in temperate regions have 20°C as their optimum while others in the tropics have 45°C as their optimum temperature

• The rate of photosynthesis decreases with a decrease in temperature below the optimum

• In most plants, photosynthesis stops when temperatures approach O°C although some arctic plant species can photosynthesise at -2°C or even -3°C

• Likewise, increase in temperature above the optimum decreases the rate and finally the reactions stop at temperatures above 40°c due to enzyme denaturation

• However, certain algae that live in hot springs e.g. Oscilatoria can photosynthesise at 75°C

• Chlorophyll traps or harnesses the energy from light

• Leaves without chlorophyll do not form starch

Chemical Compounds Which Constitute Living Organisms

• All matter is made up of chemical elements, each of which exists in the form of smaller units called atoms

• Some of the elements occur in large amounts in living things

• These include carbon, oxygen, hydrogen, nitrogen, sulphur and phosphorus

• Elements combine together to form compounds

• Some of these compounds are organic

• Organic compounds contain atoms of carbon combined with hydrogen and they are usually complex

• Other compounds are inorganic

• Most inorganic compounds do not contain carbon and hydrogen and they are usually less complex

• Cells contain hundreds of different classes of organic compounds

• However, there are four classes of organic compounds found in all cells

• These are: carbohydrates, lipids, proteins and nucleic acids

• Carbohydrates are compounds of carbon, hydrogen and oxygen

• Hydrogen and oxygen occur in the ratio of 2: 1 as in water

• Carbohydrates are classified into three main groups: monosaccharides, disaccharides and polysaccharides

• The carbon atoms in these sugars form a chain to which hydrogen and oxygen atoms are attached

• Monosaccharides are classified according to the number of carbon atoms they possess

• The general formula for these monosaccharides is (CH2O)n where n is 6

• They have the same number of carbon, hydrogen and oxygen molecules i.e

Properties of Monosaccharides

• They are soluble in water

• The are all reducing sugars

• This is because they reduce blue copper (II) sulphate solution when heated to copper oxide which is red in colour and insoluble

Functions of Monosaccharides

• They are oxidised in the cells to produce energy during respiration

• Formation of important biological molecules e.g. deoxyribonucleic acid (DNA) and ribonucleic acid (RNA)

• Some monosaccharides are important metabolic intermediates e.g. in photosynthesis and in respiration

• Monosaccharides are the units from which other more complex sugars are formed through condensation

• These contain two monosaccharide units

• The chemical process through which a large molecule (e.g a disaccharide) is formed from smaller molecules is called condensation and it involves loss of water

Common examples of disaccharides include sucrose, maltose and lactose

• This is known as hydrolysis and involves addition of water molecules

• The same process takes place inside cells through enzymes

Sucrose+water_--hydrolysis-----------------glucose+fructose Properties of Disaccharides

• Maltose and lactose are reducing sugars while sucrose is non-reducing sugar

• Sucrose is the form in which carbohydrate is transported in plants:

• This is because it is soluble andjchernically stable

• Sucrose is a storage carbohydrate in some plants e.g sugar-cane and sugar-beet

• Disaccharides are hydrolysed to produce monosaccharide units which are readily metabolised by cell to provide energy

• If many monosaccharides are joined together through condensation, a polysaccharide is formed

• Polysaccharides may consist of hundreds or even thousands of monosaccharide units

• Examples of polysaccharides:

Importance and Functions of Polysaccharides

• They are storage carbohydrates - starch in plants glycogen in animals

• They are hydrolysed to their contituent monosaccharide units and used for respiration

• They form structural material e.g. cellulose makes cell walls

• Carbohydrates combine with other molecules to form important structural compounds in living organisms

Pectins: Combine with calcium ions to form calcium pectate

Chitin: Combine with (NH) group

Makes the exoskeleton of arthropods, and walls of fungi

• Fats are solid at room temperature while oils are liquid

• They are made up of carbon, oxygen and hydrogen atoms

• The structural units of lipids are fatty acids and glycerol

• Fatty acids are made up of hydrocarbon chain molecules with a carboxyl group (-COOH) at one end

• In the synthesis of a lipid, three fatty acid molecules combine with one glycerol molecule to form a triglyceride

• Three molecules of water are lost in the process

• This is a condensation reaction and water is given off

• Lipids are hydrolysed e.g. during digestion to fatty acids and glycerol, water is added

Glycerol + 3 Fatty hydrolysis Lipid + Water acids

• Fats are insoluble in water but dissolve in organic solvents e.g. in alcohols

• They are chemically inactive, hence used as food storage compounds

• Structural materials - as structural material they make up the cell membrane

• Source of energy - they are energy rich molecules

One molecule of lipid provides more energy than a carbohydrate molecule

• Storage compound - They are stored as food reserves in plants

• In animals e.g. mammals, all excess food taken is converted to fats which are stored in adipose tissue, and around internal organs such as the heart and kidneys

• Insulation - They provide insulation in animals living in cold climates

A lot of fat is stored under the skin e.g blubber in seals

• Protection - Complex lipids e.g wax on leaf surfaces protects the plant against water-loss and overheating

• Fats stored around some internal organs acts as shock absorbers, thus protecting the organs

• Source of Metabolic Water - lipids when oxidised produce metabolic water which supplements water requirements in the body

Desert animals e.g the camel accumulate large quantities of fat in the hump which when oxidised releases metabolic water

• Proteins are the most abundant organic compounds in cells and constitute 50% of total dry weight

• Proteins are compounds which are made up of carbon, hydrogen, nitrogen, oxygen and sometimes sulphur and phosphorus

• The structural units of proteins are amino acids

• The nature of a protein is determined by the types of amino acids it is made of

• There are about 20 common amino acids that make up proteins

Essential and Non-Essential Amino Acids

• Essential amino acids are those which cannot be synthesised in the body of an organism and must therefore be provided in the diet

• There are ten amino acids which are essential for humans

• These are valine, leucine, phenylalanine, lysine, tryptophan, isoleucine, methionine, threonine, histidine and arginine

• Non-essential amino acids are those which the body can synthesise and therefore need not be available in the diet

• These are glycine, alanine, glutamic acid, aspartic acid, serine, tyrosine, proline, glutamine, arginine and cysteine

• Proteins are essential in the diet because they are not stored in the body

• Excess amino acids are deaminated

Formation of Proteins

• Proteins are made up of many amino acid units joined together through peptide bonds

• When two amino acids are joined together a dipeptide is formed

• The chemical process involved is called condensation and a molecule of water is eliminated

• When many amino acids are joined together a polypeptide chain is formed

• The nature of a particular protein depends on the types, number and sequence of amino acids from which it is made

Functions of Proteins As structural materials proteins

Examples of structural proteins include:

As functional chemical compounds

• Enzymes are biological catalysts that increase the rate of chemical reaction in the body

• They are all produced inside cells

• Some are intracellular and they catalyse reactions within the cells

• Others are extracellular and are secreted out of the cells where they work e.g. digestive enzymes

Properties of Enzymes

• Enzymes are protein in nature

• Enzymes are specific to the type of reaction they catalyse

• This is referred to as substrate specificity

• Enzymes work in very small amounts

• They remain unchanged after the reaction

• They catalyse reversible reactions

• They work very fast (high turnover numbers) e.g. the enzyme catalase works on 600 thousand molecules of hydrogen peroxide in one second

Enzymes are named by adding the suffix -ase to:

Factors Affecting Enzyme Action

• Enzymes are sensitive to temperature changes

• Generally, the rate of an enzyme¬controlled reaction doubles with every 10OC increase in temperature

• However, temperatures above 40°C do not favour enzyme reaction

• This is because enzymes are denatured by high temperatures

• Every enzyme has a particular pH range over which it works best

• Some enzymes work best in acidic media while others function better in alkaline media

• Many enzymes function well under neutral conditions

• Under conditions where the substrate is in excess, the rate of an enzyme-controlled reaction increases as the enzyme concentration is increased

Substrate Concentration

• If the concentration of the substrate is increased while that of the enzyme remains constant, the rate of the reaction will increase for sometime and then become constant

• Any further increase in substrate concentration will not result in corresponding increase in the rate of the reaction

• These are substances that either compete with substrates for enzyme active sites or combine with enzymes and hence they inhibit the enzyme reaction

• e.g. certain drugs, cyanide and nerve gas

• Most enzymes require the presence of other compounds known as co-factors which are non-proteins

• There are three groups of co-factors

• Inorganic ions - e.g. iron, magnesium, copper and zinc

• Complex organic molecules known as prosthetic groups are attached to the enzyme e.g. flavin adenine dinucleotide (FAD) derived from vitamin B2 (riboflavin)

• Co-enzymes e.g. co¬enzyme A is involved in respiration

• All co-enzymes are derived from vitamins

Nutrition in Animals=Heterotrophism

Meaning and Types of Heterotrophism

• This is a mode of nutrition whereby organisms feed on complex organic matter from other plants or animals

• All animals are heterotrophs

• Their mode of feeding is also said to be holozoic to distinguish it from other special types of heterotrophic nutrition namely:

• Saprophytism/saprotrophysim- occurs in most fungi and some forms of bacteria

• Saprophytes feed on dead organic matter and cause its decomposition or decay

• Parasitism is a mode of feeding whereby one organism called the parasite feeds on or lives in another organism called the host and harms it

Modes of Feeding in Animals

• Animals have developed various structures to capture and ingest food

• The type of structures present depend on the method of feeding and the type of food

• Carnivorous animals feed on whole animals or portions of their flesh

• Herbiverous animals feed on plant material

• Omnivorous animals feed on both plants and animal materials

• The jaws and teeth of mammals are modified according to the type of food eaten

• Mammals have different kinds of teeth

• Each type of teeth has a particular role to play in the feeding process

• The jaws and teeth of mammals are modified according to the type of food eaten

• Mammals have different kinds of teeth

• Each type of teeth has a particular role to play in the feeding process

• This condition is described as heterodont

• The teeth of reptiles and amphibians are all similar in shape and carry out the same function

• They are said to be homodont

Types of Mammalian Teeth

• Mammals have four kinds of teeth

• The incisors are found at the front of the jaw

• They are sharp-edged and are used for biting

• The canines are located at the sides of the jaw

• They are pointed and are used for tearing and piercing

• The premolars are next to the canines and the molars are at the back of the jaw

• Both premolars and molars are used for crushing and grinding

• Teeth are replaced only once in a lifetime

• The first set is the milk or deciduous teeth

• These are replaced by the second set or the permanent teeth

• A dental formula shows the type and number of teeth in each half of the jaw

• The number of teeth in half of the upper jaw is represented above a line and those on the lower jaw below the line

• The first letter of each type of teeth is used in the formula i.e

i = incisors, c = canines, pm = premolars and m = molars

• The total number is obtained by multiplying by two (for the two halves of each jaw)

Adaptation of Teeth to Feeding

• In general, incisors are for cutting, canines for tearing while premolars and molars are for grinding

• However, specific modifications are observed in different mammals as an adaptation to the type of food they eat

• Incisors are long and flat with a sharp chisel¬like edge for cutting

• The enamel coating is thicker in front than at the back so that as the tooth wears out, a sharp edge is maintained

• Canines are reduced or absent

• If absent, the space left is called the diastema

• The diastema allows the tongue to hold food and push it to the grinding teeth at the back of the mouth

• These are transversely ridged

• The ridges on the upper teeth fit into grooves on the lower ones

• This gives a sideways grinding surface

• The teeth of herbivores have open roots i.e

, wide opening into the pulp cavity

• This ensures a continued adequate supply of food and oxygen to the tooth

• In some herbivores, such as rabbits and elephants, the incisors continue to grow throughout life

• Incisors are reduced in size and pointed

• They are well suited for grasping food and holding prey

• Canines are long, pointed and curved

• They are used for piercing and tearing flesh as well as for attack and defence

Premolars and molars: In general, they are long and longitudinally ridged to increase surface area for crushing

Carnassial Teeth: These are the last premolars on the upper jaw and the first molars on the lower one

• They are enlarged for cutting flesh

• They act as a pair of shears

• The teeth of carnivores have closed roots i.e

, only a very small opening of the pulp cavity to allow food and oxygen to keep teeth alive

• Once broken, no re-growth can take place

• Incisors have a wide surface for cutting

• Canines are bluntly pointed for tearing

• Premolars and molars have cusps for crushing and grinding

• The premolars have two blunt cusps while the molars have three to four

Internal Structure of tooth

Crown: The portion above the gum it is covered by the enamel

Root: The portion below the gum it is covered by the cement

Neck: Is the region at the same level with the gum

• It forms the junction between the crown and the root

Incisors and canines have one root only

• Premolars have one or two roots while molars have two to three roots each

• Internally, the bulk of the tooth is made up of dentine which consists of living cells and extends to the root

• It is composed of calcium salts, collagen and water

• It is harder than bone but wears out with use

• This is why it is covered by enamel which is the hardest substance in a mammal's body

Pulp Cavity: Contains blood vessels which provide nutrients to the dentine and remove waste products

• It also contains nerve endings which detect heat, cold and pain

Cement: Fixes the tooth firmly to the jaw bone

• Dental carries are the holes or cavities that are formed as acid corrodes enamel and eventually the dentine

• These are diseases of the gum

• The gum becomes inflamed, and starts bleeding

• Progression of the disease leads to infection of the fibres in the periodontal membranes and the tooth becomes loose

• This condition is known as pyorrhoea

• The diseases are caused by poor cleaning of the teeth

• The accumulation of food particles leading to formation of plaque, lack of adequate vitamin A and C in the diet

• Nutrition - by taking adequate balanced diet rich in vitamins A and C

• Antibiotics are used to kill bacteria

• Anti-inflamatory drugs are given

• Antiseptic is prescribed to use in cleaning the mouth daily to prevent further proliferation of bacteria

• The plaque is removed-drilled away - a procedure known as scaling

In order to maintain healthy teeth the following points should be observed:

• A proper diet that includes calcium and vitamins, particularly vitamin D is essential

• The diet should also contain very small quantities of fluorine to strengthen the enamel

• Large quantities of fluorine are harmful

• The enamel becomes brown, a condition known as dental flourosis

• Chewing of hard fibrous foods like carrots and sugar cane to strengthen and cleanse the teeth

• Proper use of teeth e.g. not using teeth to open bottles and cut thread

• Regular and thorough brushing of teeth after meals

• Dental floss can be used to clean between the teeth

• Not eating sweets and sugary foods between meals

• Regular visits to the dentist for check¬up

• Washing the mouth with strong salt solution or with any other mouth wash with antiseptic properties

Digestive System and Digestion in Humans

• Organs that are involved with feeding in humans constitute the digestive system

Digestive System and Associated Glands

• Human digestive system starts at the mouth and ends at the anus

• This is the alimentary canal

• Digestion takes place inside the lumen of the alimentary canal

• The epithelial wall that faces the lumen has mucus glands (goblet cells)

• These secrete mucus that lubricate food and prevent the wall from being digested by digestive enzymes

• Present at specific regions are glands that secrete digestive enzymes

• The liver and pancreas are organs that are closely associated with the alimentary canal

• Their secretions get into the lumen and assist in digestions

Digestive system consists of:

- consist of duodenum, the first part next to the stomach, ileum - the last part that ends up in a vestigial caecum and appendix which are non-functional

consist of: colon and rectum that ends in the anus

Ingestion, Digestion and Absorption

• Feeding in humans involves the following processes:

• Ingestion: This is the introduction of the food into the mouth

• Digestion: This is the mechanical and chemical breakdown of the food into simpler, soluble and absorbable units

• Absorption: Taking into blood the digested products

• Assimilation: Use of food in body cells

• Mechanical breakdown of the food takes place with the help of the teeth

• Chemical digestion involves enzymes

Digestion in the Mouth

• In the mouth, both mechanical and chemical digestion takes place

• Food is mixed with saliva and is broken into smaller particles by the action of teeth

• Saliva contains the enzyme amylase

• It also contains water and mucus which lubricate and soften food in order to make swallowing easy

• Saliva is slightly alkaline and thus provides a suitable pH for amylase to act on cooked starch, changing it to maltose

• The food is then swallowed in the form of semisolid balls known as boluses

• Each bolus moves down the oesophagus by a process known as peristalsis

• Circular and longitudinal muscles along the wall of the alimentary canal contract and relax pushing the food along

Digestion in the Stomach

• In the stomach, the food is mixed with gastric juice secreted by gastric glands in the stomach wall

• Gastric juice contains pepsin, rennin and hydrochloric acid

• The acid provides a low pH of 1.5-2.0 suitable for the action of pepsin

• Pepsin breaks down protein into peptides

• Rennin coagulates the milk protein casein

• The stomach wall has strong circular and longitudinal muscles whose contraction mixes the food with digestive juices in the stomach

Digestion in the Duodenum

• In the duodenum the food is mixed with bile and pancreatic juice

• Bile contains bile salts and bile pigments

• The salts emulsify fats, thus providing a large surface area for action of lipase

• Pancreatic juice contains three enzymes:

• These enzymes act best in an alkaline medium which is provided for by the bile

• Epithelial cells in ileum secrete intestinal juice, also known as succus entericus

• This contains enzymes which complete the digestion of protein into amino acids, carbohydrates into monosaccharides and lipids into fatty acids and glycerol

• This is the diffusion of the products of digestion into the blood of the animal

• It takes place mainly in the small intestines though alcohol and some glucose are absorbed in the stomach

The ileum is adapted for absorption in the following ways:

• The coiling ensures that food moves along slowly to allow time for its digestion and absorption

• It is long to provide a large surface area for absorption

• The epithelium has many finger-like projections called villi (singular villus)

• They greatly increase the surface area for absorption

• Villi have microvilli that further increase the surface area for absorption

• The wall of villi has thin epithelial lining to facilitate fast diffusion of products of digestion

• Has numerous blood vessels for transport of the end products of digestion

• Has lacteal vessels for absorption of fatty acids and glycerol and transport of lipids

Absorption of Glucose and Amino Acids

• Glucose and other monosaccharides as well as amino acids are absorbed through the villi epithelium and directly into the blood capillaries

• First they are carried to the liver through the hepatic portal vein, then taken to all organs via circulatory system

Absorption of Fatty Acids and Glycerol

• Fatty acids and glycerol diffuse through the epithelial cells of villi and into the lacteal

• When inside the villi epithelial cells, the fatty acids combine with glycerol to make tiny fat droplets which give the lacteal a milky appearance

• The lacteals join the main lymph vessel that empties its contents into the bloodstream in the thoracic region

• Once inside the blood, the lipid droplets are hydrolysed to fatty acids and glycerol

Absorption of Vitamins and Mineral Salts

• Vitamins and mineral salts are absorbed into the blood capillaries in' the villi

Water is mainly absorbed in the colon

• As a result the undigested food is in a semi-solid form (faeces) when it reaches the rectum

Egestion: This is removal of undigested or indigestible material from the body

Faeces are temporarily stored in the rectum then voided through the anus

Opening of the anus is controlled by sphincter muscles

Assimilation: This is the incorporation of the food into the cells where it is used for various chemical processes

• used to provide energy for the body

• Excess glucose is converted to glycogen and stored in the liver and muscles

• Some of the excess carbohydrates are also converted into fat in the liver and stored in the adipose tissue' (fat storage tissue), in the mesenteries and in the connective tissue under the skin, around the heart and other internal organs

• Amino acids are used to build new cells and repair worn out ones

• They are also used for the synthesis of protein compounds

• Excess amino acids are de-aminated in the liver

• Urea is formed from the nitrogen part

• The remaining carbohydrate portion is used for energy or it is converted to glycogen or fat and stored

• Fats are primarily stored in the fat storage tissues

• When carbohydrates intake is low in the body, fats are oxidised to provide energy

• They are also used as structural materials e.g. phospholipids in cell membrane

They act as cushion, protecting delicate organs like the heart

• Stored fats under the skin act as heat insulators

Summary of digestion in humans

• These are organic compounds that are essential for proper growth, development and functioning of the body

• Vitamins are required in very small quantities

• They are not stored and must be included in the diet

• Vitamins Band C are soluble in water, the rest are soluble in fat

• Various vitamins are used in different ways

• Mineral ions are needed in the human body

• Some are needed in small amounts while others are needed in very small amounts (trace)

• All are vital to human health

• Nevertheless, their absence results in noticeable mulfunction of the body processes

• Water is a constituent of blood and intercellular fluid

• It is also a constituent of cytoplasm

• Water makes up to 60-70% of total fresh weight in humans

• No life can exist without water

• Acts as a medium in which chemical reactions in the body takes place

• Acts as a solvent and it is used to transport materials within the body

• Acts as a coolant due to its high latent heat of vaporisation

• Hence, evaporation of sweat lowers body temperature

• Takes part in chemical reactions i.e

Vitamins, sources, uses and the deficiency disease resulting from their absence in diet

• Acts as a medium in which chemical reactions in the body takes place

• Acts as a solvent and it is used to transport materials within the body

• Acts as a coolant due to its high latent heat of vaporisation

Hence, evaporation of sweat lowers body temperature

• Takes part in chemical reactions ie hydrolysis

Vitamins, sources, uses and the deficiency disease resulting from their absence in diet

• Roughage is dietary fibre and it consists mainly of cellulose

• It adds bulk to the food and provides grip for the gut muscles to enhance peristalsis

• Roughage does not provide any nutritional value because humans and all animals not produce cellulase enzyme to digest cellulose

• In herbivores symbiotic bacteria in the gut produce cellulase that digests cellulose

Factors Determining Energy Requirements in Humans

• Age: Infants, for instance, need a greater proportion of protein than adults

• Sex: males generally require more carbohydrates than females

• The requirements of specific nutrients for females depends on the stage of development in the life cycle

• Adolescent girls require more iron in their diet expectant and nursing mothers require a lot of proteins and mineral salts

• State of Health: A sick individual requires more of certain nutrients eg proteins, than a healthy one

• Occupation: An office worker needs less nutrients than a manual worker

• A diet is balanced when it contains all the body's nutrient requirements and in the right amounts or proportions

A balanced diet should contain the following:

• Dietary fibre or roughage

• This is faulty or bad feeding where the intake of either less or more than the required amount of food or total lack of some food components

• Deficiency diseases result from prolonged absence of certain components in the diet

• Other deficiency diseases are due to lack of accessory food factors (vitamins and mineral salts)

Such diseases include rickets, goitre and anaemia

• Treatment of these deficiency diseases is by supplying the patient with the component missing in the diet

• Experiments to show that Carbon (IV) Oxide is necessary for Photosynthesis

• Experiment to Show Effect of Light on Photosynthesis

• Experiment to Show the Effect of Chlorophyll on Photosynthesis

• Experiment To Observe Stomata Distribution in Different Leaves

• Test for non-reducing sugar

• Test for Proteins -Biuret Test

• Experiment To Investigate Presence of Enzyme in Living Tissue

• Dissection of a Rabbit to show the Digestive System

KCSE Revision Notes Form 1 - Form 4 All Subjects

Movement of Water and Minerals in the Xylem

Transpiration aids in the movement of water and minerals in the xylem, but it must be controlled in order to prevent water loss.

Learning Objectives

Outline the movement of water and minerals in the xylem

Key Takeaways

Key Points

  • The cohesion – tension theory of sap ascent explains how how water is pulled up from the roots to the top of the plant.
  • Evaporation from mesophyll cells in the leaves produces a negative water potential gradient that causes water and minerals to move upwards from the roots through the xylem.
  • Gas bubbles in the xylem can interrupt the flow of water in the plant, so they must be reduced through small perforations between vessel elements.
  • Transpiration is controlled by the opening and closing of stomata in response to environmental cues.
  • Stomata must open for photosynthesis and respiration, but when stomata are open, water vapor is lost to the external environment, increasing the rate of transpiration.
  • Desert plants and plants with limited water access prevent transpiration and excess water loss by utilizing a thicker cuticle, trichomes, or multiple epidermal layers.

Key Terms

  • cohesion–tension theory of sap ascent: explains the process of water flow upwards (against the force of gravity) through the xylem of plants
  • cavitation: the formation, in a fluid, of vapor bubbles that can interrupt water flow through the plant
  • trichome: a hair- or scale-like extension of the epidermis of a plant

Movement of Water and Minerals in the Xylem

Most plants obtain the water and minerals they need through their roots. The path taken is: soil -> roots -> stems -> leaves. The minerals (e.g., K+, Ca2+) travel dissolved in the water (often accompanied by various organic molecules supplied by root cells). Water and minerals enter the root by separate paths which eventually converge in the stele, or central vascular bundle in roots.

Transpiration is the loss of water from the plant through evaporation at the leaf surface. It is the main driver of water movement in the xylem. Transpiration is caused by the evaporation of water at the leaf, or atmosphere interface it creates negative pressure (tension) equivalent to –2 MPa at the leaf surface. However, this value varies greatly depending on the vapor pressure deficit, which can be insignificant at high relative humidity (RH) and substantial at low RH. Water from the roots is pulled up by this tension. At night, when stomata close and transpiration stops, the water is held in the stem and leaf by the cohesion of water molecules to each other as well as the adhesion of water to the cell walls of the xylem vessels and tracheids. This is called the cohesion–tension theory of sap ascent.

The cohesion-tension theory explains how water moves up through the xylem. Inside the leaf at the cellular level, water on the surface of mesophyll cells saturates the cellulose microfibrils of the primary cell wall. The leaf contains many large intercellular air spaces for the exchange of oxygen for carbon dioxide, which is required for photosynthesis. The wet cell wall is exposed to the internal air space and the water on the surface of the cells evaporates into the air spaces. This decreases the thin film on the surface of the mesophyll cells. The decrease creates a greater tension on the water in the mesophyll cells, thereby increasing the pull on the water in the xylem vessels. The xylem vessels and tracheids are structurally adapted to cope with large changes in pressure. Small perforations between vessel elements reduce the number and size of gas bubbles that form via a process called cavitation. The formation of gas bubbles in the xylem is detrimental since it interrupts the continuous stream of water from the base to the top of the plant, causing a break (embolism) in the flow of xylem sap. The taller the tree, the greater the tension forces needed to pull water in a continuous column, increasing the number of cavitation events. In larger trees, the resulting embolisms can plug xylem vessels, making them non-functional.

Cohesion–Tension Theory of Sap Ascent: The cohesion–tension theory of sap ascent is shown. Evaporation from the mesophyll cells produces a negative water potential gradient that causes water to move upwards from the roots through the xylem.

Control of Transpiration

Transpiration is a passive process: metabolic energy in the form of ATP is not required for water movement. The energy driving transpiration is the difference in energy between the water in the soil and the water in the atmosphere. However, transpiration is tightly controlled. The atmosphere to which the leaf is exposed drives transpiration, but it also causes massive water loss from the plant. Up to 90 percent of the water taken up by roots may be lost through transpiration.

Leaves are covered by a waxy cuticle on the outer surface that prevents the loss of water. Regulation of transpiration, therefore, is achieved primarily through the opening and closing of stomata on the leaf surface. Stomata are surrounded by two specialized cells called guard cells, which open and close in response to environmental cues such as light intensity and quality, leaf water status, and carbon dioxide concentrations. Stomata must open to allow air containing carbon dioxide and oxygen to diffuse into the leaf for photosynthesis and respiration. When stomata are open, however, water vapor is lost to the external environment, increasing the rate of transpiration. Therefore, plants must maintain a balance between efficient photosynthesis and water loss.

Plants have evolved over time to adapt to their local environment and reduce transpiration. Desert plant (xerophytes) and plants that grow on other plants ( epiphytes ) have limited access to water. Such plants usually have a much thicker waxy cuticle than those growing in more moderate, well-watered environments (mesophytes). Aquatic plants (hydrophytes) also have their own set of anatomical and morphological leaf adaptations.

Reducing Transpiration: Plants are suited to their local environment. (a) Xerophytes, like this prickly pear cactus (Opuntia sp.) and (b) epiphytes such as this tropical Aeschynanthus perrottetii have adapted to very limited water resources. The leaves of a prickly pear are modified into spines, which lowers the surface-to-volume ratio and reduces water loss. Photosynthesis takes place in the stem, which also stores water. (b) A. perrottetii leaves have a waxy cuticle that prevents water loss. (c) Goldenrod (Solidago sp.) is a mesophyte, well suited for moderate environments. (d) Hydrophytes, like this fragrant water lily (Nymphaea odorata), are adapted to thrive in aquatic environments.

Xerophytes and epiphytes often have a thick covering of trichomes or stomata that are sunken below the leaf’s surface. Trichomes are specialized hair-like epidermal cells that secrete oils and other substances. These adaptations impede air flow across the stomatal pore and reduce transpiration. Multiple epidermal layers are also commonly found in these types of plants.

Experiment on Plant Tissues

The chemical potential of water is referred to as water potential Ψ (psi) and is a property of great impor­tance to an understanding of water movement in the plant-soil-air system. Water potential (Ψ) is usually expressed in terms of pressure (e.g. bars). Absolute values of chemical potential of water potential (Ψ) are not easily measured, but differences in y can be measured with comparative ease.

The fundamental cell water potential Ψ is:

where Ψ cell = Water potential of a cell

Ψ p = Pressure potential (turgor pressure)

The water potential (Ψ) of pure water at normal atmospheric pressure is equal to zero hence the y of water in cells and solution is typically less than zero or negative.

According to one common method of measuring water potential in plant tissues, uniform sample pieces of tissues are placed in a series of solutions of a non-electrolyte like sucrose or mannitol. The object is to find that solution in which the weight and volume of the tissue does not change indicating neither a net loss nor a net gain in water.

Such a situation would mean that the tissue and the solution are in osmotic equilibrium to begin with, and so the Ψ of the tissue must equal the Ψ of the external solution. Thus, if one can calculate the Ψ of the external solution in which no change in weight or volume of the tissue occurs, one can calculate the Ψ of the tissue.

Materials and Equipments Required:

1. 12 beakers (250 ml) containing 100 ml of one of the following: distilled water, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50 and 0.60 molar sucrose solutions.

2. Potato slice freshly prepared from tubers by cork borer (approx. 1 cm in diameter).

4. Graph papers, blotting paper etc.


1. Using a cork-borer of approx. 1 cm diameter obtain from a single potato tuber 12 cylinders, each at least 3 cm — preferably 4 cm — long.

2. Cut all the 12 cylinders into measured and uniform length with a razor blade, bearing a clean transverse cut at the end of each cylinder.

3. Place the cylinders between the folds of a moist paper towel, on which the positions of the cylinders are denoted by the series of concentrations of sucrose to be used.

4. Using an analytical balance, weigh each cylinder to the nearest milligram.

5. Immediately after each cylinder is weighed, cut it into uniform slices, approximately 2 mm thick, and place all the slices obtained from one cylinder in one of the test solutions.

6. Do this for each cylinder, being sure that the initial weight of the cylinder placed in each test solution is accurately recorded.

7. After 1.5-2.0 hrs. of incubation, remove all the slices from one test solution, blot gently on paper towels and weigh.

8. Repeat this procedure until all the samples have been weighed in the chronological order, in which they were initially placed.

9. Present the data in a tabular form showing initial weight, final weight, change in weight and percentage change in weight

where percentage change in weight = Final weight – Initial weight/Initial weight

10. Then construct a graph (Fig. 3.3) plotting changes in weight or % change in weight (on ordinate) versus sucrose concentration (in molality, m) and osmotic potential (in bars) (on abscissa).

11. Calibrate the osmotic potential axis after first calculating the osmotic potential (Ψπ) for each sucrose solution.

Use the following formula:

where, m = Molality of the solution

i = ionization constant numerical value of 𔃱’ for sucrose

R = gas constant (0.083 liter bars/mole degree)

T = absolute temperature (= °C + 273)

12. Determine by interpolation from the graph the sucrose concentration in which no net change in weight has occurred. Calculate the Ψπ for this solution this value then equals the water potential (Ψ) of the tissue.

LAB 7- Chromatography - Lab report

Abstract— Chromatography is an analytical technique commonly used for separating a mixture of chemical substances into its individual components, so that the individual components can be thoroughly analyzed, and chromatography is thus a form of purification. Based on the ‘like dissolves like’ principle, the polarity of the mobile phase directly affects the distance each pigment will travel such that a polar mobile phase results in polar pigments moving up the strip the furthest and a non-polar mobile phase results in non-polar pigments moving up the furthest. Carotene changed from yellow to yellow-orange and moved 35.0 mm with an Rf factor of 0.34, xanthophyll stayed yellow and moved 30.0 mm with an Rf of 0.29, chlorophyll a changed from bright green to blue green and moved 15.0 mm with an Rf of 0.15, and chlorophyll b changed from yellow green to olive green and moved 25.0mm with an Rf of 0.24.

Introduction— There are two phases in chromatography, one is mobile phase, which is the moving solvent, and the other is stationary phase, which is the chromatography paper. In chromatography a mixture of two or more solutes are placed on a stationary material over which a moving fluid is passed. The solutes (different pigments of color) will have a competing tendency to be attracted to the stationary phase and also to be dissolved in the mobile phase. The competition will cause some pigments to move relatively quickly and some to move through more slowly, the different travel speeds cause them to separate. If pigments have a higher affinity for the mobile phase rather than the stationary phase, it will travel further up the paper (Rf value close to 1). If pigments have a higher affinity for the stationary phase rather than mobile phase, it won’t travel very far up the paper, and will remain closer to the original line (Rf value close to 0).

Materials and Equipment Spinach Leaves Chromatography Chamber

Procedure— In this experiment, paper chromatography will be applied to Spinach leaves and the components of the mixture characterized. We placed 10 leaves of Spinach, 6. grams of sand, 2.0 grams of anhydrous magnesium and 2.0 mL of acetone in a mortar and grinded the mixture to a pulp. After adding petroleum ether and acetone to the chromatography chamber, we drew a ‘start’ line on the chromatography paper with a pencil. We added small dots of spinach pigment to the start line and then placed the paper into the chamber and quickly closed it. We gave the pigment ample time to move up the paper in different shades of color, which we then measured. The experiment controls three variables in paper chromatography: pigment, paper, and distance pigment moves. The latter is difficult to repeat precisely and to compare experiments the ratio called the

representative fraction, Rf, is calculated. This value is invariably reported in manuscripts so that people who replicate the synthesis of a compound can verify that they too are getting the same Rf values for the same compounds. Rf is defined as the distance travelled by the individual pigment (Carotene 35.0 mm, Xanthophyll 30.0 mm, Chlorophyll a 15. mm, Chlorophyll b 25.0 mm) divided by the total distance travelled by the solvent (103. mm).

1) Data table Distance Travelled by Solvent: 103.0 mm

Band Color Plant Pigment Distance (mm) Rf (use formula)

Yellow Xanthophyll 30.0 mm 0.

Bright Green to Blue Green

Yellow Green to Olive Green

Ink is a liquid or paste that contains pigments or dyes that may dissolve in the solvent. The ink is likely to move during the Chromatography process and interfere with the components, hindering the interpretation of results. Pencil is made of graphite, which cannot dissolve in solvent.

  1. What other pigment mixtures might this technique be used for (HINT: black is a mixture of many colors)?

Chromatography can be used to distinguish the different pigments that make up a particular substance. For instance, this method can be used to distinguish the different colors that make up black ink since black is a mixture of various colors. Chromatography takes advantage of the differences in molecular characteristics, specifically solubility in water and rate of absorption by the paper used in order to separate colors in a mixture.

  1. The leaves of maple trees are green in the summer, but turn orange or red in the fall. Considering your results from the spinach leaf chromatography, why do you not see the orange and red maple leaf pigments in the summer? Why are they visible in the fall?

During the summer, the deep green color of chlorophyll hides any other color from the leaves. In the fall, trees break down their nutrients from the leaves. In the fall chlorophyll production slows down because of a lack of light and water, which allows the carotenoid colors (red, orange, and brown) to come through.

Mammals, Biodiversity of

I.B.1. Monotremata

Viviparity , or live birth of young, is so common among mammals that it is usually, wrongly, considered a defining character of the class. The three species of the order Monotremata all lay eggs. The platypus lays its eggs into a nest, similar to a bird's nest, while both species of the family Tachyglossidae, the echidna, or spiny anteaters, lay their eggs directly into a marsupial-like pouch. While this curiosity is the root of the common name for the monotremes—egg-laying mammals—the egg is actually a rather insignificant aspect of the monotreme's life history. Incubation is brief, under 2 weeks, following which monotreme development does not differ significantly from that of other mammals. Clearly mammals, they nurture their young with milk that is expressed from mammary glands that lack nipples. Like all mammals, they are endothermic, have hair, possess a single jaw bone, and have the diagnostic three-bone middle ear structure.

Divergence of the monotremes from other mammals occurred approximately 175 million years ago early in mammalian history. Fossil monotremes have only been found from Australasia, and all extant species share this distribution. Monotremes appear to be extremely primitive in their reproductive habits, with not only an egg-laying habit but also a single opening, or cloaca, into which both the excretory and reproductive tracts exit. The cloaca (or single exit) gives the order its name.

Watch the video: BISC132 - Lecture 3-1 - Part 1 of 3 - Plant Form and Physiology (July 2022).


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