K.C.S.E Biology Revision Eassays.

K.C.S.E Biology Revision Eassays.

1.How are mammalian teeth adapted to their functions (20mks)

Incisors
Sharp; chisel-shaped; for biting; and cutting food.
Have one root for support in the jaw bone;

Canines
They are Long and sharp pointed; for holding prey; piercing; and tearing flesh from prey.
Have a single root; for support in the jaw bone;

Premolars
Are large and wide; to increase surface area for grinding food.
Highly cusped; to increase surface area for grinding food
Two roots; for firm support in the jaw bone;Biology questions and answer form 2

Molars
Are large and wide; to increase surface area for grinding food.
Highly cusped; to increase surface area for grinding food.

2.How are small intestines in mammals adapted to their functions.(20mks)

The Small intestines consists of the duodenum and the ileum;
most digestion of food occurs in the duodenum;

The Duodenum.

♣The gall bladder of the liver secretes bile through the bile ducts; which function to;

≅Emulsify fat particles into tiny droplets; to increase the surface area for enzyme action;

♣The pancrease secretes pancreatic juice to the duodenum; the juice contains

≅Pancreatic amylase; that helps to breakdown the remaining starch into maltose.

≅Trypsin; (that is secreted in its inactive form, trypsinogen, and activated by enterokinase enzyme); hydrolyses proteins into shorter peptides;

≅Pancreatic lipase; converts lipids into fatty acids and glycerol;

≈Sodium hydrogen carbonate is also produced; to neutralize the acidic chyme from the stomach; and provide a suitable alkaline medium for pancreatic and other intestinal enzymes;

The ileum.K.C.S.E Biology Quick Revision

It is long; and narrow.

To increase the surface area for complete digestion of food; and maximum absorption of digested food.

Highly-coiled;

To reduce speed of food flow; to allow more time for maximum digestion; and absorption;

Presence of villi; and microvilli;

To increase surface area; for maximum absorption;

Dense network of capillaries;

To transport blood; for efficient transport of absorbed food;

Presence of lacteals in the villi;

For absorption of fatty acids and glycerol molecules;

Presence of enzymes:

Lipase; for digestion of lipids into fatty acids and glycerol;

Maltase for digestion of maltose to glucose molecules

Peptidase; for breakdown of peptides into amino acids.

Sucrase; for digestion of sucrose into glucose and fructose

Lactase;for digestion of lactose into glucose and galactose;

Goblet cells;

They produce mucus; which lubricate the walls of the ileum; for smooth flow of food; coats the walls of ileum to prevent digestion by peptidase enzyme;

3(a) Explain how blood is involved in transport, stating the constituents of blood involved.(6mks)

Red blood cells;

√Transport oxygen from the lungs to body tissue; (in the form of oxyhaemoglobin)

√Transport carbon IV oxide; from body tissue to the lungs; (in the form of bicarbonate)

Plasma;

√Transport dissolved food nutrients/glucose/amino acids; from the small intestines to the liver and other  body tissues;

√Transport hormones/enzymes; from secretory glands to tissues where required; transport urea; from tissues to the kidneys for excretion; distribute heat.

b)Describe how seeds and fruits are adapted to different modes of dispersal. (14marks) .

Wind dispersal;

Small and light; to float in air to be blown by air.

Have wings; to increase buoyancy

Have hairs/parachute shaped; to increase buoyancy in air.

Animal dispersal;

Are succulent; to attract animals; Scented; to attract animals.

Have small and hard seeds resistant to digestive enzymes;to prevent digestion once  swallowed;

Have hooks; to attach to fur/hair of animals;

Brightly coloured; to attract animals;

Water dispersal

Water proof epicarp; to prevent entry of water  or soaking;

Fibrous mesocarp; with air spaces to increase buoyancy in water.

Self-explosive mechanism;

Have lines of weakness; where  they break  to release seeds;

Have rings of pores; through which seeds are released.

4.Describe how the mammalian male reproductive system is adapted to perform its functions.(20marks)

≅Penis; Highly vacularised/spongy, Long to allow entry into the vagina; becomes erect  when  blood  flows to the blood  spaces,

≅Testis contains numerous seminiferous tubules; containing premedical germ  cells for  spermatogenesis takes place; the  process is favored by slightly lower temperature than  that  of the  body, contain sertoli cells which  nourish sperms until they are  mature;

≅Long coiled  Epididymis; for storage of sperms;

≅A muscular Vasdeferens;  that   upon   contraction  pushes  sperms  out  and   allows  ejaculation;  to  increase chances of fertilization,

≅Sperms have a tail and a head  with a large number of mitochondria; to provide energy  for swimming to each the egg/ovum.

≅Seminal  vesicle/cowpers glands/prostate gland; produce seminal fluid to provide a medium for sperms to swim.

 

5.Describe how water  moves from soil to the leaves                                         (20mks)

≅The cell sap of the root hair cell is highly concentrated due to the presence of the food component of the plant root such as starch. Water and mineral  salts in the soil is in dilute form and therefore has lower concentration as compared to the cell sap of the root hairs.

≅Water and dissolved mineral  salts therefore moves from hypotonic solution in the soil into the cell sap of the  root hairs which is hypertonic by osmosis.  This process makes the content of the root hair cell sap to form a mixture of diluted molecule of low concentration compared to that of the piliferous layer of the root.

≅Water and dissolved mineral  salts move from the cell sap of the root hairs by osmosis into the piliferous layer which is of higher concentration.  Movement of water  and dissolved mineral  salts into the piliferous layer then makes it of lower concentrated compared to the adjacent cortex  cell concentration. Water then moves by osmosis into the cortex  cells from the piliferous layer which is of lower concentration.

≅This makes cortex  cells become hypotonic by diluting the cell content compared to the adjacent endodermis.

Dissolve mineral  salts and water  molecules from the cortex  into the endodermis cells by osmosis.

≅The endodermis cell sap becomes less concentrated due to dilution  with water  molecules compared to the adjacent pericycle  cell sap.

≅As more  water  enters the pericycle its content become lowly concentrated compared to the adjacent xylem vessels.

This leads to movement of water  by osmosis in to the xylem vessels.

≅Through  the xylem, water  is conducted up by various mechanism of transpiration such as root pressure, capillary, adhesive and cohesive forces and transpiration pull.

6.(a)How are arthropods is adapted for gaseous exchange (10mks)

≅Have a muscular valve that controls opeing  and closing of spiracles to allow entry of air and prevents excessive loss of water  from the body tissues by evaporation

≅Has spiral bands of chitin to keep it open  to maintain its shape, prevent it from collapsing hence permitting gaseous exchange

≅Tracheoles lack spiral bands of chitin so as to permit  more  gaseous exchange through them as chitin would have hindered gaseous exchange.

≅At the end of the tracheoles is a thin film of moisture that facilitates dissolution of gases.

≅Each tracheole moves as closer to the cells as possible to minimize  diffusion distance, hence faster exchange of respiratory gases

≅Opening of spiracles is surrounded by a tuff of hairs to trap dust particles and microorganism and prevent excessive water  toss by evaporation

 

(b) What are the possible causes of incomplete fossil records?                     (10 marks)

-Whole organisms or their parts have decomposed.

-Body parts may have been  scavenged upon.

-Poor environmental conditions did not such their fossilization.

-Fossils might have been  destroyed by geological activities such as earthquakes, faulty and mass movement.

-Distortion or destruction by parts of an organism during fossilization/            sedimentation which may give wrong impression of the structures.

-The body may be too soft for fertilization.

-the probability  of fossilization in generally  low.

7.Describe the methods by which plants get rid of their waste products.  (20 marks)

Diffusion;

Gaseous waste products such as carbon (IV) oxide; oxygen and water  vapour; diffuse through the stomata/cuticle/lenticels; into the environment;

Transpiration;

Excess water  vapour; is excreted through transpiration;

Deposition;

Some  toxic wastes such as alkaloids and nitrogenous compounds e.g. nicotinic,     caffeine, quinine, cocaine and glycosides/sugar compounds such as colchicines (any two examples); are converted into  non-tonic insoluble forms; and deposited in certain tissues of the plant or aging structures;  Those deposited in aging structures are lost when these structures die or drop during leaf fall or fruit fall;

Exudation;

Resins, tannins, gums latex, rubber, oils, mucilage and oxalates are released in fluid form at a slow rate/exuded through the bark a the stem, pores of fruit;

Guttation;

In conditions of high humidity; some plants particular hydrophytes; excrete excess water;

through specialized tissue called hydathodes; water  is secreted in form of droplets;

Recycling

Substances such as carbon (IV) oxide and metabolic water  from respiration are used in photosynthesis; while oxygen from photosynthesis is used in respiration;

8(a)Explain five milestones in the evolution  of man that have made him the most dominant species on earth.   (10marks)

≅Man has a larger brain giving him move intellectual capacity and this has enabled him to exploit the environment fully.

≅Ability to speak/use language to communicate clearly with his fellow men.

≅ Bipedal locomotion, upright posture that frees the hands and rises them  to manipulate the environment and carry objects.

≅ A prehensile/grasping hand  that enables him to handle things with a high degree of precision.

≅Forward  facing  eyes which gives him a three  dimensional view for the    purpose of judging distances and have wider angle  of view.

 

b)Describe how Mesophyll plant is adapted to its habitats:              (10mks) .

– Trees may grow very tall in forests ecosystem due to competition for light as vegetation is very dense

– Some  plants are climbers which support themselves on large tree in an attempt to reach light

– Some  plants are epiphytes growing on tree branches to reach light

– Some  undergrowth plants have numerous chloroplasts which are sensitive to low light intensity to enable them  carry out photosynthesis in low light intensity

– Many plants have leaf mosaic that minimise overlapping and overshadowing and increase exposure of leaves to light

– Those in areas with adequate water  supply posses broad  leaves with thin cuticle  and many stomata on both sides of the leaf to increase transpiration

– Those in dryer areas have fewer stomata which are mainly located on the lower surface to reduce transpiration.

– Some  which leave in wet areas have shallow roots to absorb less water

– Large tall trees have developed butress roots or prop roots for extra support.

– Those in dryer areas have deep  roots to absorb water  from water  table

– Some  have waxy and glossy surface to reflect  light to reduce absorption of light hence reduce transpiration also to drip off rain water.

9.Discuss the adaptations of the human eye to its functions                                        (20mks) .

-The sclerotic layer which contains tough  connective tissue fibres which helps it to support and protect the other  parts of the eye ball.

-The choroids which contain many blood capillaries which supply oxygen and nutrients of the retina and removes metabolic wastes from eye.

-Its highly pigmented, to reflection of light within the posterior chamber of the eye ball.

-The retina which contains photoreceptor cells I.e cones and rods. It is the light sensitive part of the eye. Cones are adapted for bright light and colour vision while rods are adapted for dim light vision.

-The vitreous humour-Which is under turgor pressure. It helps to maintain the shape of the posterior chamber of the eye ball. It also plays an important part in the refraction of light rays enabling them  to be focused on the retina.

-The cornea, transparent and curved  which helps to play an important role in focusing of the image  on the retina.  It accounts for the largest refraction of light rays.

-The aqueous humour –Contains oxygen and nutrients, which nourish the cornea and the lens. It is under pressure thus helping to maintain the shape of the anterior chambers of the eye. It also plays a part in the refraction of light rays enabling them  to be focused on the retina.

-The Iris is highly pigmented region, to prevent entry of light into the eye except through its central aperture called the pupil. It contains circular and radial muscles which constrict or dilate the pupil depending on the intensity of light.

-The Iens is elastic, therefore allows changes in its shape depending on the tension exerted through the suspensory ligaments. This enables it to bring light rays coming from either near or far objects into sharp focus on the fovea.

-The ciliary’s body Contains the ciliary muscles whose contraction and relaxation alters the tension exerted on the suspensory ligaments.

-This in turn alters the shape of the lens enabling it to focus for both near and distant objects.

-The eyelids which are movable and opaque structures can be closed through a reflex action to protect the eye from too much  light or from foreign objects.

– The eye muscles help to move the eye ball within the orbit. The lateral rectus muscles move the eye up and down whole the oblique muscles, move  the eyeball in its up and down movement.

-The lachrymal gland which continuously secretes a watery, saline and antiseptic fluid called tears. The tears moisten the cornea and wash foreign particles out of the eye.

-The eyelashes, which are many hairs, protect the eye from the entry of small foreign particles.

-The eyebrows raised portion  of the skin above  the eye, thickly covered with hair, whose functions are to prevent sweat and dust from entering the eye.

 

10.a) Describe how the heart  beat  is controlled and maintained.                  (10 marks)

-The sino atrial node  initiates and maintains the heartbeat; by generating a wave of electrical signals that spreads through both atria; making  them  contract simultaneously; the signal then spreads to the autria- ventricular node  (AVN);

-Atria- ventricular node  (AVN); during which the atria empty into the ventricles; the signals spreads to the purkinje fibres; then conduct signals to the apex of the heart; and through the ventricular walls; these signals triggers a wave of powerful  contraction of both ventricles; from the apex towards the atria driving blood in large arteries; the cardiac muscles are myogenic hence not controlled by nervous stimulation.

 

b)Describe the structure and function of thrombocytes                              (10 marks)

The structure of thrombocytes.

Thrombocytes are blood fragments that are irregularly shaped; they lack a nuclear  and they play a major role in blood clotting  process.

Clotting process.

≅When a blood vessel is damaged the platelets are exposed to air; the inactive  enzyme prothrombin is then converted to active enzyme thrombin; under influence of thromboplastin /thrombokinese in presence of factors like Ca2+; thrombin the converts soluble plasma proteins fibrinogen; into insoluble protein  fibres fibrin;

≅Fibrin forms a fine mesh over the wound trapping blood cells; and large proteins to form a soft fibrin clot; serum oozes out through the clot; and due to exposure to air it dries up and hardens to form a scab; which serves to protect soft underlying and allow it to heal quickly.

 

11. a)  Define the term secondary thickening                                                             (2mrks)

. Secondary thickening is the increase in girth width / circumference of the stem branches and roots of woody plants

b) Briefly describe how secondary thickening occurs in woody plants                                 (18mrks)

.Secondary thickening is facilitated by meristematic cells / cambium; located between phloem and xylem tissue in the vascular bundles of the plants;

Cambium cells divide radially; to form a ring  ofcambium tissue; with xylem inside the ring; and phloem outside the ring;

The cells of the cambium divide to form secondary phloem outside ;Later vascular cambium / cambium between the vascular bundles divide to form secondary parenchyma; thereby  increasing the growth  of the medullary  rays; much  more  xylem cells are formed than those of the phloem; thus pushing the phloem and the cambium ring outwards;

The rate of growth  is dependent on the seasons / rains ; resulting in annual rings;

cork cambium divides to form new cork/bark to accommodate the expending tissue and secondary cortex  inside

12. )  i) State two ways in which growth  in plants is different from that in animals                     (2mrks)

– Growth in plants is continous throughout plant life while in animals it stops at adulthood.

ii)Discuss the application of anaerobic respiration in industry and at home       (18mks) . 

–Sewage   Treatment;

The micro-organisms present in sewage breakdown the contents of the sewage  anaerobically into less toxic forms.

–Brewing industry.

Manufacture of alcoholic drinks (wines, beer and spirits) are produced by fermentation  (using Yeast);

≅Beer is produced by fermentation of maltose found in grains/ wines are produced by fermentation of fruit sugar

Dairy industry;

e.g. Yoghurt is made by fermenting sugar in milk;

Production of power alcohol  / gasohol /methanol; for driving machines and engines.

Production of Biogas from plant and animal  waste ;The organic matter in cow dung broken   into gases like methane;

Baking industry;

Yeast is added to dough  mixture causing it to rise ; due to production of carbon (iv) oxide bubbles arising from fermentation;

Commercial production of organic acids;

For example citric acid and vinegar used for food preservation;

Making of compost manure;

Organic matter in plant material is broken  down anaerobically  to form organic manure

 making Silage;

Fresh green  plant materials are partially fermented to form silage ; used as animal feed.

I3 a)Give four effects of hypothyroidism                                                                 (4marks) .

–     Muyodedema in adults

–      Reduced heartbeat rate

–      Reduced breathing rate

–      Low body temperature

–      Mental and physical sluggishness

–      Weigh gain

 

(b)Briefly describe the process of hearing in man                                                     (16 marks)

.The pinna’ collects and concentrates sound waves; directing them  into their auditory  meatus; from where  they strike the ear drum; causing it to vibrate; and transform sound waves into sound vibrations;

The vibrations from the eardrum are transmitted to  the ear ossicles which amplify sound vibrations; as they transmit them  to the oval window;

From the oval window vibrations are transmitted to the perilymph; of the cochlea; in the cochlea the vibrations stimulate sensory cell hairs; to generate nerve impulses;

Which are transmitted to the brains; via the auditory  nerve; for interpretation; the brain interprets the impulses as sound; of specific pitch and loudness.

14.Explain the adaptations of xerophytes to their habitat  .  (  20mks) 

–  Leaves are reduced in size to reduce surface area  over which transpiration occurs;

– Shedding of leaves during drought/hot conditions to reduce S.A thick waxy cuticle  to minimize  the rate of cuticular transpiration;

– Leaves have thick waxy cuticle  to minimize  the rate of cuticular transpiration;

– Some  leaves are folded to reduce S.A exposed to sun’s rays hence reducing rate of transpiration;

– Some  have sunken stomata which accumulate water  vapor in deep  pits; reducing saturation deficit hence reducing rate of transpiration;

– Most of them  have reduced number of stomata to reduce the rate of transpiration;

–  Some  experience reversed stomatal rhythm to reduce transpiration rate;

– Some  have deep  roots to absorb water  form deep  the soil; // other  shave superficial roots to absorb water  after short/light shower of rain;

– Some  plants store water  in large parenchyma cells contained in succulent stems and leaves;

-Some  are drought evaders i.e. germinate. Flower and produce seeds during short rainy season before drought sets in;

15.Describe the process of fertilization in flowering plants.             (20mrks)

Fertilization  is the fusion of the male and female nuclei in the embryo  sac;

The male gamete is contained in the pollen grain; produced in the anthers;

The female gamete is found in ovules; within the embryo sac; After pollination, the pollen grain absorbs nutrients from the stigma; and develops an outgrowth called the pollen tube; which grows down the style to the embryo  sac taking along the male gametes with it; The pollen grains usually adhere to the stigma as a result of the stigma cells secreting a sticky substance; which also stimulates the pollen grain to germinate sending down its pollen tube; The growth  of the pollen tube into the stigma, through the style to the ovary, is by pushing its way between the cells where  it gets its nourishment from the surrounding tissues;

As the pollen grain germinates; the tube nucleus occupies a position at the tip of the growing pollen tube; The generative nucleus divides by mitosis; into two male gamete nuclei; which follow behind  the tube nucleus as the pollen tube grows down the style. The pollen tube enters an ovule through the micropyle; and when it reaches the centre of the ovule it penetrates the wall of the embryo  sac and bursts open; the tube nucleus disintegrates leaving a clear way for the entry of the male nuclei; One of the male nuclei fuses with the egg cell nucleus; to form a diploid zygote; which develops into an embryo; while the other  male nucleus fuses with the polar nucleus form a triploid nucleus; This gives the double  fertilization in flowering plants;

16(a) State characteristics of gaseous exchange surface.                                                       (4mrks)

i) They are densely supplied with blood capillaries highly vascularised for transportation of gases

ii) They are thin wailed facilitate easy diffusion of gases and also to reduce the distance covere)y  the diffusing gases.

iii) They are moist dissolve gas

iv) They have a large surface area  for gaseous exchange.

(b)  Describe the mechanics of gaseous exchange in mammals.                               (16mrks)

-During inhalation/inspiration; the external intercostals muscles contract; while the internal  intercostal muscles relax; raising the rib cage upwards and outwards; muscles of the diaphragm contract; making  it to flatten; the volume of the thoracic cavity increases; as pressure decreases; higher pressure in the atmosphere forces air into the lungs inflating it;

-During exhalation; the external intercostals muscles relax while the internal  intercostals muscles contract; moving the rib cage downward and inwards; the diaphragm muscles relax; diaphragm retains its dome shape; volume of the thoracic cavity reduces; increasing pressure; higher pressure forces air out of the lungs.

17a) Describe how the following evidences support the theory of organic evolution:(10mks)

Geographical distribution, fossil records and comparative anatomy

Fossil records//Palaeontology;

These are remains of organisms which were accidentally preserved in some naturally occurring materials e.g. sedimentary rocks for many years; They give direct evidence of the type of organisms that existed at a certain geological time//show a gradual increase in complexity/morphological changes of organisms over a long period of time e.g. skull of man

Geographical distribution;

The present day continents are thought to have been  a large land mass joined together called pangea; continental drift led to isolation that lead to different  patterns of evolution; e.g. camels of Africa resemble  the Ilamas of S. America// tiger of  Asia resemble jaguars of S. America // unique  Marsupials of Australia; (accept any valid example)

Comparative anatomy/taxonomy;     Members of a phylum show similarities indicating common ancestry; These organisms have similar functions e.g. presence of digestive, urinary, nervous systems e.t.c;

–   Homologous structures are structures that have a common embryonic origin but modified to perform different functions e.g pentadactyl limbs in different animals they show adaptive radiation//divergent evolution

-Vestigial are structures that have been greatly  reduced hence functionless e.g coccyx Appendix;

–  Analogous structures like wings of birds and wings of insects with different embryonic origin but adapted to perform same function they show convergent evolution.

 

b)Explain the role of osmosis in organisms                                                                               (10mks)

√Absorption of water  from the soil;

Root hair cells of plants absorb water  from the soil by osmosis; also helps in water  distribution from cell to cell in the body.

√Support;

Water taken  into the cells increase cell turgor hence cells become firm /rigid/turgid; and therefore turgidity in the cells provide support to plant organs;

Opening and closing of stomata;

Guard cells become turgid; when they take in water  by osmosis; Turgid guard  cells cause the stomata to open;

when the guard  cells lose water  by osmosis they become flaccid  leading  to the closure of the stomata;

Feeding  of insectivorous plants;

The plants trap insects using special structures that suddenly change there  turgor pressures when disturbed; the change in turgor pressure enables the special structures/ leaves to close trapping the insect which are then digested to provide amino  acids;

Osmoregulation;

In kidney tubules of animals; water  is withdrawn from the tubules through the tubular  walls through osmosis; the water  then enter  the surrounding blood capillaries, this helps the animal  to regulate its body osmotic pressure;

18.Describe the structure and functions of various organelles in a mature animal  cell.  (20marks)

.Mitochondria is a double  membrane with inner  folded to form cristae which increases the surface area  for attachment of respiratory

. Golgi apparatus stack of membrane bound  like sac/is a system of membranes sacs/hollow spaces; that  transports glycoproteins/carbohydrates and proteins; They package glycoproteins; secrete mucus/enzymes/synthesized proteins

Lysosomes

Are spherical in shape and enclosed by a single membrane; contain hydrolytic enzyme which destroy worn out organelles, micro-organism/ingest food/breakdown large molecules.

Endopasmic reticulum

Are  membrane bound   cavities  in  cytoplasm;  smooth endoplasmic  reticulum  site  for  lipid/sterot transport.

Rough endoplasmic reticulum

Has ribosome on its surface; and transport proteins.

Centrioles

Rod shaped; located outside the nuclear membrane, for formation of fibs and cilia

Cytoplasm

It’s a fluid medium; where  chemical reaction occurs, contains organelles and inclusions

(e.g. glycogen granules, fat droplets and dissolved substances).

Cell membrane

Encloses all cell organelles; has phosplipid layer between two protein  layers/it’s a lipoprotein layer has pores that selectively allows substances to pass in and out of the cell/its semi permeable.

Nucleus.

Has a double  membrane/nuclear membrane around it, which has pores to allow substances in and out of the nucleus; Has nucleoplasm, which contain nucleolus/chromatin, nucleus controls all cell activities, Nucleolus manufactures ribosomes and centrioles.

Ribosomes

Are spherical in shape and suspended in cytoplasm and attached on endoplasmic reticulum;synthesis proteins.

19(a)A dicotyledonous stem offer support to the plant. Give three  necessities for this support(3mks)

_    To expose the leaves to sunlight for photosynthesis;

_    Expose flowers to agents of pollination;

_    Expose fruits and seeds to agents of dispersal

 b)Describe the adaptation of the stem of a dicotyledonous plant to its function  (17mks)

. The stem has several strengthening tissue; that provide support i.e. collenchyma and schlerenchyma;

These tissue; are strengened by lignin;

-Xylem tissue; made up of xylem vessels and tracheids. The xylem tissues have thickened walls by lignin; to prevent walls from collapsing during transpiration;

– Xylem vessels are narrower; to facilitate upward  movement of water  by capillarity;

-Xylem vessels have boardened pits; lateral  movement of water  and mineral  salt;

– Phloem tissue contain contractile cytoplasmic strands ; to  push organic food substance from one sieve tube to the next;

– Phloem tissue contain plasmodesmata; that joins companion cells to sieve elements; allowing for passage of protein  and ATP to be used in translocation of substances;

– Cambium tissue for secondary growth  within the vascular bundles;

– Parenchyma tissue /cells stores water  and food hence support through turgidly;

-Suberin in the stem prevents excess loss of water  and entry to pathogens;

-Lenticels that facilitate gaseous exchange ;

-Some stems have parenchyma cells with chlorophyll for photosynthesis;

20(a)Describe the dentition of carnivorous mammals and their adaptation to the mode of  Feeding(10mks)

_    Have sharp pointed incisors ;  for tearing and stripping flesh from bones

_    Have canines that are  long / curved  / pointed; for piercing  , grasping and holding the prey;

_    Have got the carnassial teeth (upper  fourth premolar and lower first molar) with smooth sides;

sharp edges to shear and slice flesh from tendons and crush the bones;.

–     Have powerful  jaw bones for powerful  muscle attached ; This prevents dislocation of jaws for cutting  and shearing of flesh;

_    Have sharp and curved  claws ; for holding and grasping  prey;

b) Explain the different forms of chromosomal mutation                 (10mks)

Chromosomal mutation change involves number or structure chromosome i.e.

– Deletion; Part of chromosome break  away and does not rejoin to the original chromosome. Leads to loss of some genes;

– Duplication; chromosome replicate itself either in whole as a portion  of itself. This causes extra

– homologous chromosome;

– Inversion; a part of chromosome gets detached, rotates at 180 then rejoins to the original chromosome;

– Non disjunction chromosomes i.e. polyploidy;.

– Translocation; A part of the chromosome detatches itself  from one chromosome and attaches to another  non; this is failure to segregate in a pair of homologous chromosome during meiosis ; leading  to some cells  having extra set of chromosome and others without chromosome;

21.Explain the mechanism of opening and closing of the stomata using photosynthetic theory(20mks)

During the day the guard  cells have chloroplast and they carry out photosynthesis producing sugars

– The sugars increase the osmotic pressure of cell sap of guard  cells

– The cells draw water  from neighboring epidermal cells by osmosis, there  is expansion of guard  cells and increase turgidity

– The guard  cells swell and bulge outwards causing stomata to open

– During night there  is no light and photosynthesis stops, sugars manufactured during the day is converted to starch lowering the osmotic pressure in guard  cells

– The guard  cells lose water  to neighboring epidermal cells by osmosis and become flaccid  and shrink towards each other  cloving the stomata

. The stem has several strengthening tissue; that provide support i.e. collenchyma and schlerenchyma;

These tissue; are strengened by lignin;

-Xylem tissue; made up of xylem vessels and tracheids. The xylem tissues have thickened walls by lignin; to prevent walls from collapsing during transpiration;

– Xylem vessels are narrower; to facilitate upward  movement of water  by capillarity;

-Xylem vessels have boardened pits; lateral  movement of water  and mineral  salt;

– Phloem tissue contain contractile cytoplasmic strands ; to  push organic food substance from one sieve tube to the next;

– Phloem tissue contain plasmodesmata; that joins companion cells to sieve elements; allowing for passage of protein  and ATP to be used in translocation of substances;

– Cambium tissue for secondary growth  within the vascular bundles;

– Parenchyma tissue /cells stores water  and food hence support through turgidly;

-Suberin in the stem prevents excess loss of water  and entry to pathogens;

-Lenticels that facilitate gaseous exchange ;

-Some stems have parenchyma cells with chlorophyll for photosynthesis;

22(a)Explain the conditions necessary for germination in seeds.               (12 marks) .

i) Water (moisture);

–      Activates germination enzymes;/ breaks seed dormancy

–      Provides medium for enzymes to act;

–      Is a medium for transportation of dissolved food;

–      Softens seeds coat, which burst open  to allow emergence of radicle  and plumule;

–      Hydrolysis of food during germination;

ii)   Oxygen

Oxidation of food during respiration to provide energy for germination;/cell division and formation of new

tissues ;

iii) Optimum  temperature

–       Suitable  for action of germination enzymes which hydrolyse stored food;

–      Low temperature below 00c inactivates germination enzymes slowing down germination rate;

–       High temperature above  400c denatures germination enzymes stopping germination;

iv)  Enzymes

–    Breaks down food by oxidation

–    Food stored are in insoluble form e.g. carbohydrates fats and proteins and hence must be acted upon by the enzymes ;

Example

Starch   amylase   maltose  maltase   glucose; Lipids    lipase   fatty acids and glycerol; Proteins protease amino  acids;

v)   Viability;

–       Refers to percentage change that a seed will germinate and when planted;

–      Only seeds with live and healthy  embryos will germinate and grow;

–      Seeds stored for a long time lose their viability;

vi)  Hormones

–      These stimulate certain metabolic pathways in the germination process;

b)Describe the role of the following hormones in growth  and development of plants.

i)    Auxins

.- Promotes cell division /cell elongation /influence tropic response;

–       Promote fruit formation (parthonocarpy);

–      Promotes formation of abscission layer /brings about; leaf fall;

–      Promotes cell differentiation of vascular tissue;

–      Causes apical  dominance /inhibits growth  and development of lateral  duds;

–      Promotes growth  of adventitious roots on stems;

–      IAA and cytokinins induces healing  of wounds;

ii)   Gibberellins               

. -Promotes cell division /cell elongation in dwarf plants;

–      Parthenocarpy /initiating formation of fruits without  fertilization.

–      Formation of side branches of stem /end apical  dominance;

–      Inhibit growth  of adventitious roots;

–      Activates hydrolytic enzymes during germination /promotes germination of seeds /breaks seed dormancy;

-Affects leaf expansion and retards leaf abscission;

23(a)what is meant by the following terms

i)    Excretion

It is the removal of waste products of metabolism from the body;

ii Secretion

.- It is the release of useful substances by the body  e.g hormones.                                                                                    (1mk)

iii) Egestion

– The removal  of indigestible and undigested substances from the body.( 1mk )

Homeostasis

. It’s is a self adjusting mechanism that is ment to maintain a constant internal  environment in an organism;     (1mk)

(b) Explain how the osmotic pressure in the human blood is maintained at normal  level. (12marks)

. an impulse to the pituitary gland; The pituitary gland is stimulated to produce more  ADH; Which make kidney tubules more  permeable to water; and more  water  is reabsorbed into the blood lowering the osmotic pressure to normal  ;

when osmotic pressure of blood decreases; (osmoreceptors in) hypothalamus and pituitary gland are less stimulated; less ADH is produced ;which make  the kidney tubules less permeable to water  ;less water  is reabsorbed into When osmotic pressure of blood increases above  the normal  level;( osmoreceptors in) hypothalamus is stimulated to sent the blood raising the osmotic pressure to normal;

(c) Describe how the oxygen in the alveolus reaches the red cells.                     (4 marks)

. Inhaled oxygen dissolves in the moisture in the alveolus; the oxygen concentration in the blood is lower than the alveolus; oxygen diffuses; through the alveolus epithelium, capillary walls into the red blood cell;

24(a) How are lungs adapted to their function?

·   Has numerous alveoli; that provide large surface area  for efficient  gaseous exchange;

·  Epithelial lining between alveoli wall and  blood  capillaries is thin; to provide  a shorter diffusion distance for easy gaseous exchange;

. It is highly supplied with blood  capillaries; that  transport oxygen  and  carbon (IV) oxide  to and from the body tissues respectively;

. Lungs are  covered with pleural  membrane; which  is gas tight  thus changes in pressure within the lungs can occur  without  external interference;

.  Lungs is spongy & has numerous alveoli; that accumulate large volume of gases.

(b)Describe the mechanism of opening and closing of the stomata using the photosynthesis theory.

Opening

In the guard  cells there  are chloroplasts; which carry out photosynthesis in the presence of light;

During the day glucose is produced in the guard  cells; this increases osmotic pressure; compared to the neighbouring epidermal; water  is drawn from the epidermal cell cells into the guard  cells by osmosis; their turgidity increases;

The inner walls of guards cells are thicker  than  the other  wall; so outer

Highly coiled distal and proximal  can heated  tubules slow down movement of  filtration to allow more  time for  reabsorption .

·  The loop of hence has a counter-current flow system of the blood and glomerular filtrate to maintain a steep concentration gradient for the diffusion of reabsorbed products

(c) Describe the role of the pituitary gland in the female reproductive system.   (10mks)

Follicle Stimulating Hormone – which stimulates the development of Graafian follicle ;

Stimulates the  corpus luteum to secret progesterone;

Luteinizing Hormone- Stimulates maturation of Graafian follicle and ovulation

–     Stimulates the corpus luteum to secrete progesterone;

–   Oxytocin– stimulates the constriction of the   uterus wall to bring about parturition

–   stimulates the production of milt of the mammary gland (melt let down)

26  . Discuss the economic importance of fungi                            (20mks)

•    Some  fungi are used as food e.g mushrooms

•    Some  fungi are used for fermentation in baking and brewing  industries

•    Some  fungi  are used in the production of organic acids like citric acid;

•    Some are used in the production of antibiotics; e.g penicillium; for the production of penicillin.

•    Saprophytic fungi decompose dead and decaying organic matter; releasing nutrients to the soil;

•    Some  fungi are used in scientific research e.g Neurospora crassa is used in genetic research;

•    Some  fungi cause human diseases such as ringworm, candidiasis;

•    Some  cause plant diseases like coffee berry disease, late blight

•    Some  cause food spoilage

•    Some  cause food poisoning  e.g Aspergillus niger which produces aflatoxin

27. Describe the process of fertilization in a flowering plant.                   (15mks)

. Pollen grains stick in the stigma surface; that surface of stigma produces a chemical substance ;

which stimulates the pollen grain to produce a pollen tube/germinate. The pollen tube grows down ( into the tissue of the style) from where it derives nutrients; the generative nucleus divides to give rise to two male nuclei and the embryo sac contains eight nuclei, 2 synergids, ovum two polar nuclei, three antipodal cells when pollen tube reaches the micropile the vegetative nucleus/pollen tube nucleus in the pollen tube disintegrates and make nucleus fuses with the egg cell and form the zygote.

The other male nucleus fuses with the two polar nuclei to form a tripod nucleus. The process involves double fertilization.

(b) State the changes that take place in a flower after fertilization. .(5mks)

Integument changes into seed coat/testa

Zygote into embryo Ovary wall into pericarp Ovary into fruit

Ovule into seed

Triploid into endosperm

Style dries up/fall of leaving a scar/corolla dries up (falls off) stamen dry up

(disinergrates)

28 (a) Discuss eye accommodation                                                               (10mks).

Accommodation is the ability of the eye to focus both far and near objects;

For accommodation of a distant object away Muscles relax; creating tension on suspensory ligaments /suspensory  ligaments contract; the lens becomes flattened less conveys; minimizing  the refractive power of lens; bringing light rays from afar object to focus on the retina;

For accommodation of a neat object alimony muscles contracts relaxing lesion on suspensory ligaments/sensory ligaments spherical in shape; this increase the  refractive power of the lens; that brings light rays from a near object to focus on the retina;

29. Describe the structure and function of various parts of the skin                       (20mks)

a)   Epidermis has three

I)Cornified layer; Made of dead cells that protect against desiccation/mechanical damages;

ii)Granular layer; made of living cells that replace worn-out cells of cornified  layer;

iii)Malpighian  layer; which actively divides to give rise to new epidermal cells

– Has melanin which screens against UV light; cells producing melanin synthesise vitamin D

b) Dermis cells

(i)Has blood capillaries that supply food/and oxygen/remove excretory products; or arteries that validate when temperatures are low

(ii) Has sweat glands; that produce sweat which consists of water  and salts/sodium chloride  /urea and lactic acid; as sweat evaporates, latent  heat  of vaporization is taken  away from the body, therefore, reducing the body temperatures; under cold conditions, little sweat is produced hence little latent  heat  of vaporization is taken  away from the body, therefore, conserving heat;

(iii)Has hair follicles which have hair; which insulates the body against heat loss/hair stand erect to trap air when the temperature is low; hair lies flat to allow heat loss when the temperature is high; through this, the skin acts as a temperature regulator.

(iv) Nerve endings; which are sensitive to various stimuli; the skin, therefore, acts as a sensory organ.

(v) Sebaceous gland; which produce oily substance sebum which is water  repellant/antiseptic;

prevents drying and cracking of the skin.

(vi)Subcutaneous fat; which insulates the body against heat loss.

30. (i) Identify each of the following responses described below.

(a) A person coughs whenever a foreign body irritates the respiratory tract – – Simple Reflex action;                                                                                                          (1mk)

(b) Whenever a bell is rung, a dog is presented with a meal. After several days of practice, the dog salivates once the bell is rung even if food is not available. — Conditioned reflex;                                                                                  (1m

b) Differentiate between Homologous and Analogous structures.                           (4 mks) . –

Homologous structures;

Structures of the same embryonic origin; that become modified in the course of evolution  to perform different functions in different ecological niches;

–  Analogous structures;

Structures of different embryonic origin; that become modified in the course of evolution to perform similar functions in the same ecological niches;

 

c) Describe how natural selection brings about the adaptation of a species to its environment

( 16marks)

.  Organisms in the same environment are always competing  for resources such as food, mates, shelter etc;

·  There follow struggle for existence  and that organism that is well/best  adapted to survive and breed  in the prevailing environmental condition survive to the reproductive maturity  and give rise to offspring of the next generation;

· The less/poorly adapted die young hence leading  to survival for the fittest ;

· The favourable characteristics possessed by the fittest organism are genetic hence are passed on to the offspring ;

· This lead to a natural  occurrence of variation  within

The genetic variations are passed on/transmitted to successive generations of offspring;

.  Consequently, there  is a gradual change in the characteristics of the species making  it better adapted to its environment;

· Accumulation  of small variation   over a long period leads to the emergence of new forms of life i.e. species;

·If suited to and well adapted to the new environment these new forms reproduce successfully and pass on their characteristics

If not suited these new forms are eliminated   by nature, leaving mutant forms which are better adapted to the environment;

· Through  this process  nature selects that organism with better adaptations;

·  While ensuring the elimination of those not able to adapt to the changing environment ;

·   Thus the changing environment forces an organism /species to adapt/be eliminated

31. A student sitting under a shade of a tree on a hot sunny day shifted her eyes from the shade to the sunlit jet in the sky and then looked back at a page on her book. Describe the changes that occurred in her eyes.                              (20mks)

 

Looking at the sunlight jet       Looking back at a page

•           Circular muscles in the iris contract; while the radial muscles in the iris relax

•    The pupil becomes small;

•           Less light passes through the pupil  to get into the eye;

•    Ciliary muscles in the ciliary bodies relax;

•           Suspensory ligaments become stot/tension increases in the suspensory ligaments;

•    The lens becomes long and thin;

•    The jet is brought to focus  •           Circular muscles in the iris relax while radial muscles contract;

•    The pupil becomes large;

•           More light  passes through the pupil to get into the eye

•    Ciliary muscles in the ciliary bodies contract

•           Suspensory ligaments loosen/tension is reduced or lost in the suspensory ligaments; the lens becomes short and thick;

•           The printed  words on the page are brought to focus

 

32. Describe the digestion of a starchy meal along the human alimentary canal.  (20mks)

 

Starch in food is first broken  down in the mouth by the action of teeth/ chewing; This increases the surface area  exposed enzyme action;

The food  is  then mixed with saliva which contains salivary amylase which breaks down some starch to maltose; saliva has a slightly alkaline pH which is optimum for the enzyme;

The food moves down to the oesophagus and stomach; where  the acidic pH, due presence of dilute Hcl, prevents further  action of salivary amylase;

In the duodenum, pancreatic amylase continues digestion of starch to maltose; Pancreatic amylase is produced in the pancreas and enters the duodenum through pancreatic ducts;

The acidic chyme  is neutralized by the sodium bicarbonate in bile/ pancreatic juice;

Maltose digestion continues in the ileum; whose walls secrete succus entericus/ intestinal juice;

which  contains enzyme maltase; which breaks down maltose to glucose;

(a) Describe how gaseous exchange occurs in terrestrial plants.               (13 marks)

 

The gaseous exchange takes place in a spongy mesophyll During the day air diffuses into large air spaces of spongy mesophyll; through stomata; the Carbon (IV) Oxide in the air diffuses into Photosynthetic cells; in solution form; during photosynthesis Carbon  (iv) Oxide is used while oxygen is produced. Oxygen diffuses out of the leaf; through stomata; During the night; air diffuses into the air spaces (of spongy mesophyll), the air dissolves into a film of moisture; then oxygen diffuses into the cells, and is used in respiration during which carbon (iv) oxide is produced, the Carbon  (iv) Oxide diffuses out of the leaf; through stomata; due to concentration/diffusion gradient; Gaseous exchange takes place  through the epidermis (of young leaves and stems); epidermis of the root carries out a gaseous exchange with air in the soil; some plants have pneumatophores/breathing roots; in which gaseous exchange occurs through lenticels; (found in older stems)

 

 

33(a) Distinguish between a community and a population.                                                     (2mks)

A community consists of all plants and animals (organisms of different species in a habitat)

interacting with each other; while a population consist of individuals of the same species in a habitat;

(b) Briefly describe how the population of grasshoppers in a given area can be estimated.   (8mks)

Use capture-recapture method; catch the grasshoppers and mark using permanent ink; records and release; to allow time to mix; recapture and count the marked and unmarked; the total population is equal to the number marked and unmarked in the second sample multiplied by several marked grasshoppers in the first sample; divide by the number of grasshoppers marled in the second sample that was recaptured.

 

(c) Explain how the various activities of man have caused pollution of air. (10mks)

 

Sulphur based chemicals; eg sulphur (iv) oxide gas, H2S, Cl2, Hcl gas produce by

(food processing ) industries/sewage matter; affect gaseous plants leaves;

-Aerosols; CFCs spray to control  ( plant) disease and pests also affect respiratory organs of animals; the chemicals are redounded and persistent ( not easily broken  down/ deplete the  ozone layers; smokes/ fumes produce in areas with ( heavy industries and ( high density of motor  vehicle/fire which burn fuel/oils, wood; reduce visibility fumes also settle on leaves and stop photosynthesis;

( excessive) production of carbon(iv) oxidcauses thegreenhousesee effect/temperature inversion as a result of heating in lower layers of the atmosphere; acc pesticides, herbicides, insecticides.

– Sound/ noise produce by machine/heavy vehicles/aircraft; affects hearing in animals; Dust; industrial production of (cement) generates dust; which finally settles on plants leaves limiting photosynthesis; removal  of vegetation/cutting of trees; interferes with the carbon cycle; radioactive emission; from nuclear reactors/mines/x-ray/machines, bombs cause mutation/cancer/death;

( 10mks)

34. Describe how the mammalian ear is adapted to its function.                                   (20mks)

The ear is an organ involved in perceiving sound and maintaining body balance and posture it is made up of the following sections:-

.   Pinna –Flap of skin that is funnel-shaped structure, made up of skin and cartilage; collects sound waves and concentrate them; to the auditory canal.

.  External auditory  meatus – a tubular canal  lined with hairs  and wax secreting cells; allows passage of sound waves to the middle ear; the hairs and wax trap dust particles that enter  the ear;

•   Tympanic  membrane- thin  flexible membrane; receives sound waves, vibrates transforming  the waves into vibrations transmitting them to the ossicles;

•    The Ossicles ( steps, mallets/anvil & incus) -; work as a system of the lever to amplify vibration from the tympanic membrane, and transmit them to the oval window.

•    Eustachian tube – connect pharynx and middle ear; it balances the pressure on both sides of the tympanic membrane/outer  and middle ear;

• Oval window- a thin flexible membrane that opens into the inner ear; it ( receives) and passes vibrations to the inner ear.

• Semi Circular canals arranged in planes at right angles to one another have swellings that contain sensory hair cells which are stimulated to generate impulses transmitted to the brain to bring about balance and postures; about body movement.

• Cochlea – coiled tube filled with endolymph, it has sensory cells which are stimulated to generate nerve impulses which are transmitted by the auditory nerve to the brain; for interpretation.

 

35.  Describe how the human skin is adapted to its function.                                        (20mks)

 

– Cornified layer; made up of dead cells Rat protect against mechanical damage/desiccators/ entry of microbes.

– Glandular layer; made up of living cells that give rise to the cornified layer.

-The Malpighian layer, has actively living cells that give rise to new epidermal cells that contain melanin that protect the skin against ultraviolet rays.

-Has hair that stands erect  to trap air when cold low temperature to reduce heat  loss/ insulate/

lies flat to allow heat  loss when the temperature is high.

-Has nerve endings; which are sensitive to stimuli/touch/ heat/ cold/ poisonous/pain.

– Has subcutaneous fat/ adipose tissues; that insulate the body against heat loss.

–   Has arteries/ capillaries blood vessels; that supplies food/ oxygen/ remove excretory products.

-Arteries vasodilates when the temperature is high to lose heat  by radiation/ convection/

vasoconstriction when temperatures are low to conserve heat.

 

–  Has sebaceous gland;  which secretes sebum an antiseptic/ wastewater-repellanttance/ prevent drying/cracking of skin/makes skin supple.

 

 

36a) State three aspects of light that are important in photosynthesis.       (3mks)

 

–              Light intensity

 

–              Light duration

 

–              Light wavelength/ quality

 

b) Describe how the leaves of plants are adapted to carry out photosynthesis. (17mks)

–  Wide/ broad/ flat lamina; to provide large surface area for/absorptionfCo2 and light for photosynthesis.

– Thin to ensure a short distance for Co2 to reach photosynthesis cells(factor diffusion of gas

Thin transparent upper epidermis; to allow easier penetration of light for photosynthetic cells.

– Presence of stomata/ guard cells for efficient/ faster/ rapid diffusion of Co2 into the leaf/ O2 out/ gaseous exchange.

–  Palisade cells contain many chloroplasts; which is next to the upper epidermis to receive maximum light for photosynthesis.

-Chloroplasts have chlorophyll; to trap light.

-Leaves have leaf veins; xylem to conduct water to photosynthetic cells phloem to translocate products of photosynthesis to other parts of ptpotplant

-Large/ intercellular air spaces in the spongy mesophyll/ layer; for storage of Co2 and easier gaseous exchange

-Waxy watewaterprooficle; to reduce water loss and reflect excess light.

-Leaf mosaic/ non-oooverlappingaves for maximum exposure to light.

37. Describe the mechanism of natural selection based on industrial melanism. (20mks)

It explains that the peppered moth exists in two varieties, which are genetically controlled. The dark variety is found predominantly in industrial cities and the white variety is found predominantly in rural areas or non-industrial areas.

The peppered moth usually rests on trunks and branches of trees, during industrialization tree trunks and branches were normally dark in colour due to deposits of soot, smoke and other pollutants.

A white moth resting on such a trunk or branches is highly conspicuous and is easily picked and eaten by preying birds. A dark moth resting at the same places is effectively camouflaged by the dark background and is not easily seen by preying birds.
– In rural areas or non-industrial areas, tree trunks and branches are normally white due to the growth of lichens. A white moth resting on such a trunk or branch is effectively camouflaged by the white background and is not easily seen by preying birds. A dark moth resting at the same place is highly conspicuous and is easily picked and eaten by praying birds.
– Therefore, dark moths are adapted for survival in industrial areas. Here most of them reach maturity and reproduce more dark moths. On the other hand, only a few white moths survive to maturity and reproduce in industrial areas. In rural areas, most white moth survives to maturity and reproduces more white moths.
Here only a few dark moths survive to maturity and reproduce. rural areas, tree trunks and branches are normally white due to the growth of lichens. A white moth resting on such a trunk or branch is effectively camouflaged by the white background and is not easily seen by preying birds. A dark moth resting at the same place is highly conspicuous and is easily picked and eaten by praying birds.
– Therefore, dark moths are adapted for survival in industrial areas. Here most of them reach maturity

42. How is the mammalian heart adapted to its functions?

The heart is enclosed in a pericardial membrane/pericardium; that produces a fluid; to lubricate; the membrane and also to keep the heart in position; It is covered in a fatty layer; that acts as a shock absorber;
It is made up of cardiac muscles; which are interconnected hence contract and relax without fatigue or nervous stimulation/myogenic; for continuous pumping of blood throughout the lifespan of the animal; the muscles are supplied by nutrients and oxygen; by the coronary arteries; and the coronary veins take away wastes and carbon (IV) oxide; heart is divided into 4 chambers; for efficient double circulation/ avoid mixing of oxygenated and deoxygenated blood/carry large volume of blood; has interventricular septum; to separate oxygenated and deoxygenated blood; ventricles are thick/muscular; to generate high pressure to pump blood out of the heart; left ventricle has thick muscles/more muscular; to pump blood to all body tissues; heart has bicuspid; and tricuspid valves; to prevent back flow of blood to left auricle; and right auricle respectively; valves have tendinous cords/valve tendons; to prevent them from turning inside out; semi lunar valves located at the beginning of major arteries; prevent backflow of blood into the ventricles; has sino-artrio node located in the muscles of the right auricle; to initiate heart beat/contractions of heart muscles/cardiac muscles, rate of heart beat is controlled by nerves; vagus nerve; slows down heartbeat; while sympathetic nerve; speeds up the heartbeat; has aorta; to transport oxygenated blood to all body parts; has pulmonary artery; that transports deoxygenated blood from right ventricles to lungs for oxygenation; has pulmonary vein; that transports oxygenated blood from lungs to the left ventricles; for distribution to all body parts; has the venacava; that  receives deoxygenated blood from all body parts to right ventricles; Max. 20 mks
Describe double circulation in mammals

Deoxygenated blood from body tissues (except lungs); enters the heart via the right auricle; through the vena cava; it flows to the right ventricle; via the tricuspid valve; the right ventricle contracts; pumping blood; via the semilunar valves; through the pulmonary artery; to the lungs for oxygenation; the oxygenated blood from the lungs; flow through the pulmonary vein; to the left auricle; via the bicuspid valve; to the left ventricle; the left ventricle contracts; pumping blood via the semilunar valves; through the aorta; to the rest of the body tissues; Max. 20 mks

Describe the process of urine formation in the mammalian kidneys

The afferent arteriole which is a branch of the renal artery supplies blood to the glomerulus; the afferent arteriole has a wider lumen/diameter than the efferent arteriole; which takes away blood from the glomerulus; the differences in the diameter of the afferent and the afferent vessels causes high pressure; leading to ultrafiltration of blood; the walls of the blood capillaries are one-cell thick; hence glucose, amino acids, vitamins, hormones, salts, creatine, urea and water filter into the Bowman’s capsule; to form glomerular filtrate; white blood cells, red blood cells, plasma proteins such as globulin and platelets are too large to pass through the capillary wall; hence remain in the blood capillaries; useful substances in the human body are selectively reabsorbed; back into the blood stream at the proximal convoluted tubule; the tubule is highly coiled; to increase the surface area for reabsorption of the substances; the useful substances include amino acids, glucose, vitamins, hormones, sodium chloride and water; many mitochondria found at the proximal convoluted tubule; provide energy for reabsorption of these substances against a concentration gradient; the glomerular filtrate flows into the descending and the ascending limb of the loop of Henle; blood in the capillaries and the glomerular filtrate in the loop of Henle move in opposite directions/counter-current flow; this provides a steep concentration gradient that leads to maximum absorption of water through osmosis; sodium chloride is actively absorbed from the ascending limb into the blood capillaries; under the influence of aldosterone hormone; the glomerular filtrate flows into the collecting tubule from where, more water is reabsorbed into the blood stream; antidiuretic hormone influences the amount of water to be reabsorbed depending on the osmotic pressure of the blood; the glomerular filtrate from several collecting tubules now referred to as urine; is emptied into the collecting duct; the urine passes through pyramid, pelvis and ureter into the bladder; where it is stored for some time. The sphincter on the urethra relaxes to allow urine to be released from the body; Max. 20 mks

43. Explain the role of the following hormones during homeostasis

Antidiuretic Hormone (ADH)

Secreted by the (posterior lobe/end) pituitary gland; in response to an increase in the osmotic pressure of blood; the hormone stimulates the distal convoluted tubules and the collecting ducts; to increase their permeability to water; this increases the reabsorption of water into the bloodstream; concentrated and less urine is excreted; when the osmotic pressure decreases, less or no hormone is produced; hence the tubules become impermeable to water; less water is reabsorbed into the bloodstream; hence more dilute urine is excreted; fluctuations in the osmotic pressure is detected by the hypothalamus;

Insulin

Secreted by the pancreas; in response to a rise in blood sugar level; it stimulates liver cells to convert the excess glucose into glycogen and fats for storage in the liver and muscle cells; increases the oxidation of glucose in respiration to yield water energy and carbon (IV) oxide/increases metabolism in the body; this leads to a fall in blood glucose to normal level;

Glucagon

Secreted by the pancreas; in response to a decline in blood glucose level; it stimulates liver cells to convert the stored glycogen and fats back to glucose; stimulates the conversion of amino acids to glucose; and stops the oxidation of glucose in the body cells; the glucose formed is released to the bloodstream causing a rise of blood glucose level to normal; Max. 20 mks

Explain how endotherms respond to heat and cold conditions in their environment

Heat/hot conditions: Increased sweating; to lose heat through latent heat of vaporization; dilation of arterioles under the skin; to bring more blood to the skin surface to lose heat to the atmosphere; decreased body metabolism; to reduce heat generation; erector pili muscles relax; making hair follicles to relax hence hair lies flat on skin, no air is trapped; to lose heat; slow/reduced muscular activity due to slow metabolism; to reduce heat production; panting to expose tongue and mouth; to release heat; moving to shades to avoid direct heat; aestivation; to escape the extreme heat; flapping of ears to create currents to carry away heat; Cold conditions: stamping of feet; to generate heat; basking in the sun to gain heat directly; less production of sweat; to reduce water loss through latent heat of vaporization; vasoconstriction of arterioles; hence less blood flow to the skin surface to reduce heat loss; increased metabolism through release of more thyroxine hormone; to generate heat; erector pili muscles contract; pulling hair follicles hence hair is raised; to trap a layer of moist air; to prevent heat loss; shivering/rapid contraction of muscles; to yield heat to warm body; Max. 15 mks