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1 a. What is natural selection?

(Theory put forward by Charles Darwin)It explains that nature selects for individuals that are well adapted to a particular environment; and against those that are less adapted

b. Discuss three examples of natural selection in action

Melanic forms of peppered moths; in Europe, there are two forms of peppered moths; white and black; before industrialization, the tree trunks were white; therefore the white peppered moths were white; hence were camouflaged; the black varieties were easily noticed and fed upon by predatory birds; the white form therefore reproduced and increased in number; during industrialization, the smoke from industries coated tree trunks black; the black variety became camouflaged; reproduced and increased in population; the white variety were easily noticed and fed upon by predators; they reduced in population;

Resistance against drugs and antibiotics; where microorganisms are continually exposed to a certain drug; their cells synthesise specific proteins; which counter the drug; this ability to synthesize the protein is passed onto the offspring;

Resistance to pesticides by insects; insects such as mosquitoes when continually exposed to a particular pesticide; synthesize a specific protein which make them resistant to the pesticide; this is then inherited by their offspring;

2. Discuss Lamarck’s and Darwin’s theories of evolution

Larmarck’s theory states that when the environment demands the need or use of a particular structure in the body; the body develops it in response; for example giraffes used to have short necks; when all the grass was exhausted, they started stretching their necks in search of leaves on trees; therefore they developed long necks; which then were inherited by their offspring;

However, when a structure is not continually used, it reduces in size and becomes dysfunctional; this theory fails to explain how acquired characteristics become inherited;

Darwin’s theory suggests that in nature there occur struggle for existence; only those individuals with the desired adaptations survive; those poorly adapted fail to compete; and become extinct;

There also occurs variation in nature; where organisms with desired adaptations pass on their characteristics to offspring during reproduction; those poorly adapted fail to reach maturity; and do not reproduce; therefore,nature selects for individuals best suited to an environment; and against those poorly adapted (natural selection); as there occurs survival of the fittest;

3. Describe how the following vertebrae are adapted to their functions

a. Atlas

Has a wide neural canal; to accommodate the large spinal cord at the neck region;

Has large/broad wing-like cervical ribs; to increase the surface area for attachment of the neck muscles;

Has facets on the anterior side; for articulation with the occipital condyles of the skull; allowing up and down movement/nodding of the head;

Has posterior facets for articulation with the anterior facets of the axis; forming a joint that allows sideways movement of the head;

b. Axis

Has a broad centrum; that projects to form the odontoid process; for articulation with the neural canal of the atlas; a joint that allows turning of the head;

Has a large and broad/flattened neural spine; and flat cervical ribs; to increase the surface area for attachment of neck muscles;

c. Lumbar

Has many transverse processes; and additional projections (metapophyses, hypapophyses,anapophyses); to offer a large surface area for attachment of abdominal muscles;

Broad neural canal; to allow passage of the large spinal cord at the upper abdominal area;

Large/thick centrum; to support the weight of the body; and withstand strains/upthrust force due to movement;

d. Thoracic

Long/elongated neural spine; to offer a large surface area for attachment of the large back muscles;

Have a large centrum and neural canal; to offer support to the thoracic cage;

Has tubercular facet on the transverse processes; to articulate with the tuberculum of the ribs; while the capitular demifacets on the centrum; articulates with the capitula of the ribs;

Together with the ribs and the sternum form the thoracic/rib cage; for protection of heart and lungs; and for breathing process;

4a. Why is locomotion necessary in higher animals?

Animals move in order to look for food; mates; escape danger/predators; look for shelter/ suitable environmental conditions;

b. Explain how bony fish are adapted to their habitats

Have streamlined bodies; to reduce friction;

Body is covered with scales; which overlap backwards; to reduce friction;

Skin produces mucus; which covers the body making it slippery; reducing friction;

Have swim bladder; which stores air; for buoyancy hence make the fish float;

Myotomes/muscle blocks; that contract alternately; for forward thrust in water;Lateral line system; on either side of the body which is sensitive to pressure and water currents;

Possess fins; that are used for locomotion: tail/caudal fins; for propulsion; dorsal; and anal fins; prevent rolling; pectoral fin; used for breaking/steering; prevents yawing/side to side movement; controls pitching; pelvic fins; for steering/pitching;

5. Describe how the various supportive tissues in plants adapt them to their


Sclerenchyma tissue; Long, slender cells with tapering ends; with walls thickened with lignin; provide support and protection to the more delicate tissues; and resistance to storms and strong winds; main constituent of wood;

Xylem vessels; longitudinally-elongated cells; with perforated end walls; with heavily lignified walls; to increase rigidity and strength to the plant; a main constituent of wood;

Tracheids; mainly found in angiosperms; made up of long tapering dead cells; cell walls are highly lignified;and pitted; cells lie in large overlapping groups; to offer extra support;

Collenchyma tissue; longitudinally elongated living cells; located beneath the epidermis and mid rib of leaf veins; thickened at the corners by cellulose and pectin compounds; to provide support in leaves, herbaceous plants and young woody plants;

Parenchyma tissue; large; spherical cells; with thin cellulose walls; forming the bulk of cortex and pith of most plants; become tightly packed and rigid when turgid; to attain and maintain an erect posture of plants; main support structures in herbaceous stems/plants;

6.a. What is a reflex action?

Rapid and automatic; response to a particular stimulus;

b. Outline the activities that occur in the body when one touches a hot object

When the hot object is touched, the pain receptors; in the skin of the finger are stimulated;

Nerve impulses are initiated and transmitted through the sensory neurone; to the grey matter; of the spinal cord to the brain; for interpretation; the impulses are then transmitted through the relay neurone;via a synapse; the impulses from the relay neurone are transmitted via the motor neurone; throughanother synapse; to the effector; which are the biceps muscles of the upper arm; making musclesto contract; straightening the arm; and the arm is withdrawn from the hot object;

7. Describe the nitrogen cycle

This is the cycling of nitrogen and its compounds in nature;

Plants absorb nitrogen in form of nitrates and then assimilate it into plant proteins; animals obtain this nitrogen in plant proteins through feeding on plants;

When the animals die and decompose, they release the nitrogen in form of ammonia to the soil; free atmospheric nitrogen is converted into nitrates through a process known as nitrogen fixation; the process occurs in two ways: Biological and nonbiological;

Biological fixation of nitrogen is done by nitrogen-fixing bacteria; which are either free-living or symbiotic;symbiotic bacteria are of the genus Rhizobium; and are found in root nodules of legumes (such as pea, clover and alfalfa); the bacteria convert atmospheric nitrogen into ammonia; that is used directly by the leguminous plants to form nitrogen containing organic compounds (amino acids, nucleic acids, proteins);

When plants die, the nodules release ammonium compounds into the soil; which are then converted to nitrites;by nitrifying bacteria of genus Nitrosomonas and Nitrococcus (nitrite bacteria) and then to nitrates by

Nitrobacter (nitrate) bacteria; free-living micro-organisms that fix nitrogen include putrefying/saprophytic bacteria; (such as Azobacter spp, Clostridium and some algae such as Anabaena, Chlorella and Nostoc);

The organisms fix nitrogen into ammonia by break down of protein material in dead organisms; the ammonia is converted to nitrites; then to nitrates; However, denitrifying bacteria (e.g. Pseudomonas denitrificans and Thiobacillus denitrificans); break down/reduce nitrates to nitrites,ammonium compounds and even gaseous nitrogen; a process known as denitrification; the process helps to release free nitrogen into the air for recycling; nonbiological nitrogen fixing is carried out by lightning during thunderstorms; the lightning energy, causes atmospheric nitrogen and oxygen to combine forming oxides of nitrogen; which dissolve in rain water to form nitrous acid/nitric acid; that is washed down into the soil; the nitric acid formed reacts with other chemical compounds dissolved in soil water; to form nitrates; the nitrates are then utilized by plants;

8. Discuss how the various tropisms adapt plants to their habitats

Phototropism; growth curvature in response to direction of light; enables plant shoots to grow and get light for maximum photosynthesis; allows for leaf mosaic;

Thigmotropism; growth curvature in response to contact/hard surface; makes plants with weak stems to get support on large plant/trees; this makes them to reach and get light for maximum photosynthesis;

Geotropism; growth curvature in response to gravity; enables plant roots to grow deep into the soil for maximum support/anchorage;

Hydrotropism; growth curvature in response to moisture/water; water is then used as a raw material during photolysis stage of photosynthesis;

Chemotropism; growth curvature in response to chemical concentration gradient; enables pollen tubes to grow down the style and into the ovary for fertilization to occur in plant flowers;

Thermotropism; growth curvature in response to temperature changes; enables plants to grow to where they can acquire optimum temperature for effective plant process (e.g.sunflower orientates towards the direction of the sun);

9. Discuss the various evidences of organic evolution

Comparative anatomy/taxonomy;

Members of a phylum/group show similarities; organs have similar structure/organs performing the same function such as the digestive system, urinary system, vertebrate heart; homologous structures are structureswith the same embryonic origin but have been modified to perform different and specific functions; show a form of divergent evolution; e.g. the pentadactyl limb in vertebrates which has been modified for racing;swimming and flight or beaks of finches and birds; while analogous structures are those with different embryonic origin but have been modified to perform the same function e.g. wings of insects, bats and birds;eyes in octopuses and humans; show a form of convergent evolution; Vestigial structures; have been reduced in size and become functionless; in the course of evolution; e.g. limbs in snakes, human hair and tail;

Cell biology/cytology;

Occurrence of similar organelles such as the mitochondria and the endoplasmic reticula point to common ancestry;

Fossil records/Paleontology;

Remains of organisms preserved in naturally-occurring materials for many years; fossil records show morphological changes of organisms over a long period of time e.g. skull of humans and horse; they provide a direct evidence of existence of organisms at a particular ecological era; however, since only hard parts are preserved, no evidence is available for existence of soft-bodied organisms; and there are many missing links; since remains are accidentally preserved in rudimentary rocks and resins;

Comparative embryology;

Vertebrate embryos are morphologically similar during the early stages of development; suggesting that the organisms had a common ancestry/origin e.g. larvae of mollusks/annelids, embryos of chicken, humans, sheep; the closer the semblance between embryos, the closer their ancestral backgrounds;

Geographical distribution;

Present continents are thought to have been a large land mass joined together; as a result of continental drift; isolation occurred bringing about different patterns of evolution; where plants and animals from different continents yet with common ancestry can no longer interbreed; because they evolved into different species; examples of animals that moved to different areas are the jaguars and Llamas in south America, lions in Africa, Tigers in Asia, marsupials in Australia;

Comparative serology/physiology;

Semblance in blood components such as blood proteins, antigen-antibody reactions, structure of haemoglobin in all vertebrates; reveal some phylogenic relationship among organisms/show common ancestry;

10 Describe the structure and functions of the various parts of the mammalian

Ear Pinna; is wide/funnel-shaped to collect/gather sound waves; and direct them to the auditory canal into the ear;

Eardrum/tympanic membrane is thin and light; to convert sound waves into vibrations;

Ear ossicles/maleus, incus and stapes are of high density; to magnify/amplify sound waves;

Oval window is smaller than eardrum; to magnify the sound waves; and direct them to the inner ear;

Cochlea is long and coiled; to increase surface area; for attachment of receptor cells/sensory hairs; cochlea has many sensory hairs; which receive sound vibrations and generate impulses;

Liquid or fluid/endolymph in cochlea; transmit sound vibrations;

Auditory nerve; transmit impulses to the brain for interpretation;

Eustachian tube; link the mouth and middle ear to equalise pressure; between middle and outer ear to prevent damage to delicate eardrum;

Round window; lose excess vibrations; to avoid continuous stimulation;

Semicircular canals; contain receptors for body balance and posture;

External auditory canal cells produce/secrete wax; to trap dust particles/solid/micro-organisms that can damage eardrum;

11. Discuss the various ways employed by preys to avoid the predators

-Some preys resemble inedible inanimate and animate objects; this is called mimicry; e.g. walking stick insect resembles dry twigs of plants, some moths look like bees or flowers of some plants; this prevents birds from easily noticing and eating them;

-Many have the ability to run very fast; because of having muscular bodies; and long legs; enabling them to escape predators e.g. antelopes, zebras;

-Some have a body colour that resembles the surrounding; which helps them to camouflage or conceal in the background environment; e.g. zebras, giraffes;

-Some graze in large herds; this enables them to fight off predators; e.g. wildebeests and buffaloes;

-Some have evolved tough skin or coverings like shells; which can not be broken by some predators e.g.snails, tortoises, armadillo;

-Production of foul smell e.g. in skunks; that discourages the predators;

-Confrontational display that can scare away the predator e.g. porcupine;

-Large eyes on both sides of the head give animals such as zebra a wide field of vision; enabling them to keep track of their enemies from far; and take precautions;

12 a. What is meant by the term symbiosis?

Nutritional association of two different organisms (2 plants or between an animal and plant); for mutual benefit; the relationship enables the composite organism to survive where neither can live on its own;

b. Describe five types of symbiotic relationships in a natural ecosystem

Lichens; these are composite plants consisting of blue-green algae; within a mycelial mass of a fungus;algal cells are provided with support, obtain water, carbon (IV) oxide and minerals and protection from fungus; while the fungus obtains oxygen and the carbohydrates made by algae; this enables the plants to survive on hard bare rocks in high attitudes and polar regions;

Leguminous plants and nitrogen-fixing bacteria; the bacteria multiply and fix nitrogen from air into nitrates for the benefit of the plant; bacteria are protected and obtain nutrients from the plants;

Ruminants and bacteria; the rumen has bacteria that secrete cellulose; that digests cellulose in the food/vegetation consumed by the animal to glucose for the animal; while the bacteria get shelter and use part of digested food;

Mycorrhizal fungi and higher plants; the fungi found on forest trees gain photosynthetic organic products made by the trees; while the trees get nutrients/minerals absorbed by the fungus from the soil;

Tryconympha and termites; the former is a protozoan living in gut of termites; and produce cellulose enzyme; that digests cellulose from the plant into digestible products for the benefit of the termite; the termite on the other hand provides shelter and protection; and absorbs some of the food for its use;

13 a. Describe the adaptations of Schistosoma spp to their parasitic mode of life

The parasite utilizes two hosts; the snail and humans; to increase chances of transfer of the parasite from one place to another;

Have suckers for attachment to host walls; to prevent them from being dislodged;

The parasite produces many larval forms (e.g. miracidia, cercariae and redia) in snails; to increase chances of transmission and survival; as this feature poses barriers/difficulties in efforts aimed at eradicating the parasite;

Cercariae larvae and eggs of the parasite have glands that secrete lytic enzymes; which soften the tissues of humans/snails; to allow for penetration;

Chemical substances produced by the adult worm; protects the parasite from the action of the hosts; defense mechanisms;

They exist as separate sexes; with the male carrying the female; this ensures that eggs produced by the female are fertilized before being shed into the blood stream;

b. Outline five measures that can be employed to prevent and control the spread of the parasite

-Proper disposal of human waste; urine and faecal material should not be disposed in water bodies to avoid contamination by the eggs or adult worms;

-Drainage of stagnant water pools and use of molluscides to kill the intermediate hosts (snails);

-Avoid swimming/bathing in snail-infested water bodies;

-Wearing protective clothing such as gloves and gumboots when working or walking in swampy areas;

-Personal hygiene that includes washing hands after visiting the toilet and drinking of boiled or chemically treated water to kill the eggs and the larval forms in the water;proper treatment of infected persons;

14. Describe the process of mitosis

Occurs in somatic/body cells; through five main stages/phases:

Interphase/Resting stage;intense internal activities occur in the cell at this stage in preparation for the division; the activities include;replication of each chromosome to multiply genetic material to retain chromosomal number in daughter cells;chromosomes appear as a diffuse tangle of threads (chromatin); synthesis of new cellular organelles; build-up of energy stores (ATP) to drive the entire cell division process;

Prophase; chromosomes become visible; as they shorten and thicken appearing as discrete strands (chromatids) lying parallel to each other; in animal cells, centrioles separate and move to opposite ends (poles) of the cell; they radiate from each of the ends forming spindle fibres; nuclear membrane begins tobreakdown; nucleolus disappear;

Metaphase; Chromosomes migrate/move to the centre of the cell; and align themselves along the equatorial plane of the spindle; they get attached to the chromosomes, by their centromeres; nuclear membrane breaks down and disappears; spindle fibres lengthen; and attach to the centrioles at both poles forming asters;

Anaphase; chromatids separate at the centromere; shortening of the spindle fibres occurs; resulting in the chromatids migrating to opposite poles of the cell; spindle apparatus begins to disappear;

Telophase; final stage where chromatids reach the poles; become densely packed together and uncoil; a nuclear membrane forms around each mass/set of chromatids (now referred to as chromosomes); cytoplasm divides into two (cytokinesis); in animal cells, the cytoplasm divides by constriction of the cell membrane; while in plant cells, a cell plate forms within the cytoplasm and grows to separate the cell into two; spindle fibres disappear within the cytoplasm; and nucleoli reappear in the nuclei; of the two daughter cells formed at the end of telophase;

15. Discuss the various mechanisms that hinder self-pollination and self fertilization in plants

Protandry and protogyny; these are mechanisms where either the male or female parts of the reproductive organs ripen at different times in some flowers; Protandry is a case where stamens ripen earlier; and anthers release their pollen grains before the stigma is mature; while protogyny refers to a case where the stigma matures earlier; and hence becomes ready to receive pollen grains before the anthers are ready/ripe to shed the pollen grains; common in plants of the grass family;

Self-sterility or incompatibility; is a case where pollen grains cannot germinate on stigma of the same plant;but only germinate on a different plant of the same species; hindering self-pollination;

Heterostyly; condition of having different arrangements of style and stigma; for instance flowers could have shorter stamens than pistils; hence becomes impossible for the pollen to land, germinate and fertilise the ovules of the same flower; pistils on some flowers could also be shorter than the stamens therefore other mechanisms that hinder self-pollination are utilized;

Dioecius and monoecius plants; dioecius plants have reproductive parts located separately on different plants of the same species; discouraging self-pollination; while monoecius plants have the parts located at different parts of the same plant body; encouraging cross-pollination;

16 How are seeds and fruits of plants adapted to their mode of dispersal?


Fruit mesocarp/seed testa has air spaces; thus light/buoyant to float; carried away by water;

Fruits/seeds protected from soaking by waterproof pericarp/testa;


Have hooks for attachment to animals; thus carried to other places;

Fruits are brightly coloured;succulent/fleshy; aromatic/scented, to attract animals; which feed on them;

The seed coats/hard seeds are resistant to digestive enzymes; thus are unaffected; seeds dropped away from parent in faeces/droppings;


Have hairs/wing-like structures/floss/extensions; which increase surface area/for buoyancy; making it easy to be blown away;

Fruits/seeds are light due to small size; therefore easily carried away by wind;

Censor mechanism;perforated/open/split/capsule; usually loosely attached to the stalk/long stalk; is swayed by wind; scattering seeds;

Selfdispersal/Explosive mechanism;Tension/pressure is created inside a dry pod; pod opens (violently) along lines of weaknesses; the two halves curl outwards; scattering the seeds;

17 a. Distinguish between mutations, mutants and mutagens

Mutations are sudden, spontaneous and permanent changes; in an individual’s genetic material;

Mutants are individuals who develop and exhibit unusual characteristics that were not previously present in the population; due to mutations;

Mutagens are factors in the environment;that cause mutations to occur;

b. Give two causes of mutations

Irradiations such as gamma rays and ultra violet rays; chemical substances such as mustard gas and other heavy metals (mercury, lead, asbestos); sudden extreme (high or low) temperatures;

c. Describe the causes and effects of chromosomal mutations

Deletion; refers to the absence of a portion of a chromosome; it results from breakage and falling off of a portion of a chromosome; leading to loss of a group of genes that may have a disastrous effect on the development of an organism;

Inversion; refers to reversal of normal sequence of genes in portion of a chromosome; occurs when a middle portion of a chromosome breaks, turns or rotates (inverts) through 180o and joins up again; this does not change the genetic constitution of the organism; but may bring into close proximity genes whose combined effects to an organism produce a beneficial effect to an organism; or cause disadvantages to the organism;

Translocation; attachment of a portion of a chromosome to a non-homologous chromosome; occurs when a chromosome breaks and the portion joins another non-homologous chromosome; this may lead to serious consequences, even death depending on what genes are missing;

Duplication; situation where a set of genes is represented twice in a chromosome; a part of a chromatid formed during cell division may replicate further to form an extra piece; which may attach onto the same or another chromatid; resulting to traits controlled by some genes being excessively expressed;

Non-disjunction; this is failure of a pair of homologous chromosomes to separate during the first stage of meiosis; resulting in one of the daughter cells formed after division of the cell having two of one kind of a chromosome; while the other cell has less or none; diseases or disorders known as syndromes are known to result from this aberration e.g. Down’s Syndrome (Mongolism),Turner Syndrome, Klinefelter Syndrome;

Polyploidy; this is the presence of more than two sets of chromosomes in a cell; occurs due to a failure of a cell to divide after the first stage of meiosis or after the chromosomes have replicated in mitosis; common in plants than animals; in plants, it causes some improvements such as resistance to drought, certain diseases and pests, improved yields and early maturity;

18. How is the mammalian eye adapted to its functions?

Sclera/sclerotic layer; white fibrous layer; made up of thick connective tissue; protects the eye; maintains shape of eyeball;

Cornea; transparent; disc-shaped layer; that allows light to enter the eye; refracts light towards the retina;

Conjunctiva; delicate membrane; lining the inside of the eyelid; protects the cornea/eye;

Eyelids and eye lashes; thin muscle with hairs; protects the cornea/eye from mechanical/chemical damage/protects the eye from entry of foreign particles; protects retina from bright light;

Choroid; dark pigmented and membranous layer; that prevents light reflection within the eye/absorbs light; to prevent distortion of the image; has blood vessels; that nourish eye/retina/supply oxygen/remove carbon (IV) oxide and wastes; extends to form the ciliary body and iris;

Ciliary muscles; have elastic muscles that contract and relax; to alter shape/curvature of lens during accommodation;

Ciliary body; thickened front edge of the choroids layer; that produces aqueous humour;

Suspensory ligaments; made up of elastic connective tissue whose contraction and relaxation helps to adjust the shape of lens during accommodation/holds lens in position;

Lens; transparent; biconvex; balloon-like; it refracts light rays/focus light onto the retina;

Vitreous humour; nourishes cornea/lens; refraction of light; maintains eyeball shape;

Iris; thin circular ring; with circular and radial muscles; it gives eye colour/absorbs light; controls the amount of light entering the eye/adjusts size of pupil;

Pupil; an aperture through which light enters the eye;

Retina; has photoreceptor cells/rods/cones for image formation; generates impulses to the brain for interpretation;

Fovea/Yellow spot; with only cones; for high visual acuity/most sensitive part of the retina;

Blind spot; point where nerve fibres emerge from the optic nerve/where optic nerve leaves eye/point where nerve fibres and blood vessels enter the eye;

Optic nerve; transmits impulses to the brain;

Muscles; inferior and superior oblique muscles; move eye from left to right; superior and inferior rectus muscles; move the eye up and down; external and internal rectus muscles steady the eye in its up and down movement;

Tear/Lachrymal glands; secrete a watery and saline fluid containing lysozymes/lytic enzymes/is antiseptic (tears); that moisten the conjunctiva and cornea; washes away dust and other foreign objects; kills microorganisms entering the eye;

19. Explain how the process of evolution may result to the formation of a new Species.

For a new species to be formed, a population of organisms must become completely isolated or separated from others; over long periods of time so that any new variations that arise will not therefore flow to the other population; there are various isolation mechanisms:

Geographical isolation; this is due to physical barriers such as oceans/seas/deserts;

Ecological isolation; a barrier resulting from the occupation of different types of habitats from the original type; it may be due to isolation for reasons of feeding/predation/breeding; as well as environmental changes such as climate and vegetation; which may result in a population living in different habitats; to become ecologically separated from one another;

Behavioural isolation; alteration of behaviour proceeding mating; which include courtship behaviour/lack of attraction between males and females in different populations; due to production of different chemicals or pheromones or colouration/songs;

Reproduction isolation; a barrier to successful mating between individuals of a population; due to structural differences in reproductive organs; as well as failure in fertilization/incompatibility;

Genetic isolation; even if fertilization takes place; the zygote may be inferior/fails to develop; however if the zygote develops, the offspring may be inferior or infertile/sterile;

19. Discuss the structure and functions of the various muscle tissues found in humans

Smooth/Visceral Muscle; consists of spindle-shaped cells; made up of long filaments or myofibrils; the cells lack cross striations and sarcolemma; they are uninucleate/with one cell; they contract and fatigue slowly; to bring about contraction and relaxation of the walls of blood vessels,

Urino-genital tract and the gut; which aids in blood flow, urine and sperm flow and peristalsis of food respectively;

Skeletal/Striated muscles; made up of long cylindrical cells; with long myofibrils running parallel to each other; the cells have cross striations/stripes; are multinucleated; they form bundles of long fibres attached to bones by tendons; they contract and fatigue rapidly; to bring about movement of bones; (on the body) they contain contractile protein myosin and actin;

Cardiac/Heart muscle; this is the muscle of the heart; is made up of short cylindrical cells; with parallel myofibrils; the ends of each all are thickened into intercalated discs; that connect adjacent cells; the myofibrils have cross striations; each cell is uninucleate; the myofibrils contract without fatigue;

20.Describe the adaptations of the nervous system to its functions

The central nervous system consists of the brain; and the spinal cord; and nerve fibres; that serve the sensory organs ; and the effector organs and glands; the brain is a collection of millions/billions/109 neurones; that form the biggest ganglion;

It is highly convoluted; to provide a large surface area for impulse reception, processing and transmission;

The brain and the spinal cord are protected by the meninges; the brain and the spinal cord have spaces/canals and ventricles; filled with a cerebrospinal fluid; which acts as a bridge/supply medium for oxygen and nutrients; and the removal of metabolic waste;

The brain has centres for the storage; retrieval and processing of impulses; the cerebrum processes and stores information; the cerebellum; sends impulses to joints and muscles; to correct balance; the medulla oblongata sends impulses to the cardiovascular; and breathing/ventilation systems; to regulate them;

The brain has the hypothalamus that secretes a neurosecretion to influence a pituitary gland that secretes hormones; involved in reproduction; and homeostatic functions; the hypothalamus; detects changes in temperature; and osmotic pressure; and sends impulses to relevant effector organs for their regulation; the thalamus; receives majority of the impulses and channels them to the relevant areas of the brain;

Both the brain and the spinal cord have regions of the grey matter; that enable very rapid processing/transmission of impulses;

The nervous system has neurones (relay/intermediate, motor and sensory); that transmit impulses at a very rapid note/speed (100 ms-1) to and from the central nervous system to effect suitable responses;

There exists in the central nervous system an electrochemical gradient/concentration gradient; that allows for the generation of electrical impulses;

They have numerous mitochondria; for generating energy for the function of the sodium pump; which enables polarization and repolarisation; during impulse transmission and refractory/recovery periods;

The spinal cord has no integration/association functions and is therefore suited for reflex actions; needed in emergencies; the spinal cord is long; and connects nerve fibres of the peripheral nerves with the brain for storage of information; the spinal cord has a dorsal root for sensory fibres/neurones; and a ventral root; for motor neurones/fibres;

21. Describe the defects that affect the mammalian eye and how they could be


Short-sightedness (myopia);

A condition where light rays from a distant object are focused in front of the retina; while those from a near object are clearly focused on the retina; it is caused by an abnormally elongated eyeball; or too much refractive power of the eye lens;

-It is corrected by wearing concave/diverging lenses; which help to diverge light rays; or reduce the refractive power of the eye before they reach the eye lens;

Long-sightedness (Hypermetropia); light rays from a near object are not focused by the time they reach the retina; or may be focused behind the retina; while the rays from a distant object are sharply focused; the defect is caused by an eyeball that is too short; or a weak lens system (distance between lens and the retina isshort);

-Corrected by wearing a convex/converging lens; which refracts light rays before reaching the eye lens;this enhances refraction resulting in rays being sharply focused onto the retina;

Astigmatism; rays from an object are brought to focus on different planes; due to unequal curvature of the cornea/lens; causing unequal refraction of light entering the eye; this defect is corrected by wearing special cylindrical lens in front of the eye; the lens corrects the focus in the defective planes;

Colour-blindness; a genetic defect; in which an animal is unable to distinguish between colours particularly within the red-green spectrum; the retina lacks cones; pigments that respond to colour vision;

Squintedness; an eye defect in which extrinsic muscles of the eye; that controls the turning of the eyeball do not co-ordinate accordingly on stimulation; it affects the paired rectus muscles that move the eyeball up and down; and the lateral rectus muscles that move the eyeball left to right; the eyeballs therefore face different directions;making focusing and accommodation difficult to achieve; corrected by specialized surgery;

Old sight (Presbyopia); caused by old age; when supplies of nutrients and oxygen to the lens is far much reduced; hence the cells of the lens die; the lens’ elasticity is reduced; and hence cannot change shape; and becomes fixed into a shape that is not suitable for distant vision; managed by use of reading glasses that have converging lenses; to give the eyes an extra power to manage close work;

Cataracts; associated with old age; but may also be caused by an eye injury due to a blow; or complications of diabetes mellitus; the eye lens become cloudy; blocking transmission of light rays; protein fibres become denatured; and clump together making the lens opaque; corrected by surgery; to replace the defective lens with a normal one from a donor; or use of artificial lens;