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KCSE-Biology

Q1. Explain the meaning of each of the following terms.

  • Cell - Basic unit of organization in an organism
  • Tissue these are cells of a particular type grouped together to perform a certain function

Q2. State the importance of nutrition

  • For respiration to get energy
  • For growth
  • For development
  • To repair and replace worn out and damaged tissues

Q3. State the importance of photosynthesis

  • Formation of sugars/glucose which is a source of energy
  • Purification of air
  • storage of energy to be used later in respiration

Q4. Discuss how the human ear is adapted to its functions. (20mks)

  • Pinna a funnel shaped structure / made of skins and cartilage; receive sound waves and direct it to ear tube/ external auditory meatus.
  • External auditory meatus, a canal lined with hair and wax secreting cells to allow passage of sound waves of eardrum/ middle ear (hair and wax) to trap dust particle.
  • Wax maintains the flexibility of the eardrum.
  • The tympanum/eardrum is a thin, sheet-like structure to receive sound waves, vibrate and pass vibration to ossicles.
  • Ear ossicles (malleus tiny bones incus stapes) act as lever system which amplifies and transmit vibration to the oval window.
  • The eustachian tube is a hollow structure that connects the middle ear nasal cavity and equalizes pressure between inside and outside of the eardrum/ balancing.
  • The inner ear has interconnected canals filled with fluids that conduct vibration from middle ear hearing has semi-circular canals filled with fluids that suspend hair cells in the ampullar for balancing.
  • Fluids also absorb mechanical shock to protect the delicate sensory structures.
  • The cochlea is coiled to increase surface area for sound reception.
  • The cochlea has an auditory nerve that transmits sound impulses to the brain for interpretation.

Q5. Explain how comparative embryology is evidence for organic evolution. (2mks)

is comparing formation and development of embryos; this study shows that vertebrate embryos have similar morphological features during their early development and it is impossible to tell them apart; this indicates a common ancestry; some features include a single circulatory system, segmented myotomes gill slits/ visceral clefts, notochord and tail.

Q6. Describe the structure and functions of the various parts of the human ear. (18mks)

  • Pinna- its funnel shaped to collect and direct sound waves into the auditory meatus.
  • External auditory meatus- concentrates or direct sound waves to the tympanic membrane which vibrates; has hair that prevents entry of dust particles or any foreign materials to avoid obstruction of sound waves
  • Ear ossicles- they are joined firmly to one another by ligaments/muscles to transmit vibration across the middle ear
  • The oval window-thin membrane vibrates effectively, and smaller in size than the tympanic membrane; and transmits them to the fluids in the cochlea.
  • Eustachian tube –opens at the pharynx to communicate to the mouth cavity; to equalize the air pressure in the middle ear with the atmospheric air pressure
  • Round window- is a thin membrane that stops disturbance/ displacement /distortion of cochlea fluid; by pushing towards the middle ear for vibration to die/ diffuse off.
  • Cochlea – has fluids perilymph and endolymph; that distort/displace sensory hair thereby generating a nerve impulse.

Q7. Describe the mechanism of gaseous exchange in a mammal.(16mks)

Inhalation(breathing in )

external intercostal muscle contract; while internal intercostal muscles relax; this cause rising of the ribcage upward and outwards; muscle of the diaphragm contract hence diaphragm flattens; the volume of the thoracic increases; and pressure decreases than the atmospheric pressure; the higher air pressure in the atmosphere forces air into the lungs; and inflate

Exhalation(breathing out)

the intercostal muscles relax; while the internal intercostal contract; this causes the ribcage dome-shape; this makes the volume of the thoracic cavity to decrease; while pressure increase compared to the atmospheric pressure; higher pressure in the thoracic cavity forces air out of the lungs and the lungs deflate.

Q8. Explain the mechanism of stomatal opening in plants. (4mks)

 

  • during the day photosynthesis takes place in the guard cell; forming sugar/ glucose; glucose is osmotically active hence guard cells draw water by osmosis from adjacent  epidermal cells; guard cells become turgid and bulge outwards; thin outer walls expand faster hence thick inner wall curve; causing the stomata aperture to open

Q9. Explain the role of human skin in:

Thermo-regulation.(16mks)

when the temperature is low, the erector pili muscles contract; marking the hair follicles to stand erect; the hair follicles trap a layer of hair; between them which reduces heat loss due to poor heat conduction

the skin has a sweat gland which secretes sweat; when the temperature is high water from the sweat evaporates

blood vessels vasoconstrict; less blood flows close to the skin surface; hence less heat is lost to the environment

When the temperature is low no sweat is produced.

When the temperature is high the blood vessels vasodilate and this encourages loss and more heat; as more flow close to the skin surface

Protection        (4mks)

the skin has a cornified layer made of dead cells which protect the entry of bacteria and inner tissues from mechanical damage; the sebaceous gland, secrete sebum which has antiseptic properties hence protects the body from bacteria. The skin has melanin pigments which protect the body from harmful UV rays

Q10. State the structural adaptation of the insects' tracheal system. (10mks)

  • spiracles are openings through which gases(oxygen and carbon (14) oxide) enter or exit the tracheal system;/ventilate;
  • vales on the spiracles; control opening and closing of spiracles;
  • tracheoles have a moist lining that dissolves respiratory gases before they diffuse
  • tracheoles have a thin epithelium; to shorten distance over which gases diffuse;
  • the trachea is highly branched into tracheoles; to increase surface area for gaseous exchange;
  • hair on the spiracles traps dust/foreign particles and prevent their entry into the tracheal system

Q11. Describe how various hormones influence the menstrual cycle. (10mks)

Follicle stimulating hormone;

Stimulate the development of Graafian follicles in the ovary;

Stimulates the ovarian tissues to secrete oestrogen

Oestrogen;

Initiates/ stimulates the healing and repair of the uterine lining after menstruation

High levels stimulate the pituitary gland to secrete luteinizing hormone;

Luteinizing hormone

Stimulates maturation of Graafian follicle;

Stimulates the rapture of mature Graafian follicle to release the ovum during ovulation.

Stimulates the remains of Graafian follicle to from corpus luteum/yellow body;

Stimulates the corpus luteum to secrete progesterone;

 

Progesterone

Promotes the thickening of the uterine lining in preparation for implantation;

Inhibit secretion of follicle stimulating hormone and luteinizing hormone

Q12. Explain the process of formation and removal of urea in the human body.(20mks)

  • Excess amino acid are deaminated  in the liver; the amino acid group is reduced to form ammonia; the carboxyl group is oxidized to release energy, or converted glycogen and store in the liver; can also be converted to fats; the ammonia produced is converted to urea; urea form in the liver is shed into the bloodstream; it is transported through the blood plasma;; out of the liver through the hepatic vein; into inferior vena cava to right auricle; through the tricuspid valve into right ventricle; through the pulmonary artery into lungs; blood carrying urea flows out of the lungs through the pulmonary vein to the left auricle; through bicuspid valve into left ventricle; out through aorta; to dorsal aorta then into renal artery which branch into afferent arteriole to glomerulus; into bowman’s capsule; proximal convoluted tubules loop of henle; distal convoluted tubule; enter into the collection dust which drains urea in urinary bladder; the through urethra excreted as urine;

Q13. Describe the adaptation of floating water lily leaf its photosynthetic function.(10mks)

  • Broad/flat lamina/ large; to provide a large surface for carbon (IV) oxide; and light absorption
  • Thin leaf to allow light/ carbon (IV) oxide to pass through a short distance
  • Presences of numerous/ many stomata; on the upper epidermis, ensuring efficient diffusion of carbon (IV) oxide
  • Cuticle/epidermis translucent;  to allow penetration of light to palisade cells/photosynthetic cell
  • Numerous aerenchyma cells; for buoyancy; to reach light and carbon (IV) oxide
  • Has an extensive network of veins; conducting water and mineral salts; to the photosynthetic cells

Q14. Describe the following stages of photosynthesis

Light stage

  • Occurs in the grana/ granum containing chlorophyll which traps/ absorbs light energy
  • Energy splits water molecules/ photolysis into hydrogen ion and hydroxyl ion
  • Oxygen gas removed through stomata/ respired
  • Light energy used in ATP formation; dark stage / carbon (IV) oxide fixation
  • Simple sugars formed respired/ oxidized or converted to storable form
  • ATP energy from light stage/ photolysis used to catalyze the reaction

Q15. Discuss how the mammalian heart is adapted to  its function( 20mks)

  • The heart has atrioventricular valves and semi lunar valves; allowing blood flow in one direction only and prevent backflow
  • Valves have non-elastic chordae tendoneae preventing atrioventricular valves from turning inside out into auricles during ventricular systole
  • Has thick muscular walls which contract to pump and push blood
  • Made of cardiac muscles which are myogenic
  • The heart served by  vagus sympathetic nerves which regulate the rate of heartbeats depending on the body’s physiological/ requirements
  • Cardiac muscle served by coronary artery and coronary vein for the supply of nutrients O2 and removal of waste respectively
  • Has specialized interconnected cardiac Purkinje fibres which spread the wave of excitation throughout the heart muscles
  • Has four chambers that hold the blood briefly before it is pumped to the lungs and the rest of the body
  • Has a septum wall preventing oxygenated blood on the left side of the heart from mixing with deoxygenated blood on the right side
  • Has vena cava and pulmonary vein that transport blood to the heart auricles from the rest of the body and lungs respectively
  • The pulmonary artery and aorta transport blood away from the heart ventricles to the lungs and rest of the body respectively
  • Entire heart is enclosed by a tough double layered protective sac, the pericardium, preventing it from overstretching as it pumps

Q16. Discuss the various evidences which show that evolution has taken place (20mks)

Comparative anatomy/ taxonomy

Members of a phylum/ group show similarities; organisms have similar structures / similar organs performing the same functions

Analogous structure / different structure with different organs performing same functions/ showing convergent evolution

Fossil records/ paleontology

These are remains of organisms preserved in naturally occurring materials for many years; show morphological changes of organisms over a long period of time

Comparative embryology

Vertebrates  embryos are similar; suggesting that  the organisms have a common origin/ ancestry

Geographical distribution

Present continents are thought to have been a large landmass joined together as a result of continental drift; isolation occurred bringing about a different pattern of evolution

Cell biology/ cytological

Occurrence of cell organelles; point to a common ancestry

Q17. Describe the structure and functions of various organelles in a mature animal cell(20mks)

Mitochondria

Has a double membrane the outer and the inner surrounding it; the inner folded to form cristae which increase surface area for attachment of respiratory enzymes

Golgi apparatus

These are stacks of membrane-bound sac-like structures that transport glycoproteins, they also pack glycoproteins

Lysosome

Are spherical shaped organelles bounded by a single membrane they contain lytic enzymes which destroy old worn-out organelles

Endoplasmic reticulum

Are membranes bond cavities in the cytoplasm

Smooth endoplasmic reticulum that transport lipids and steroids

Rough endoplasmic reticulum has ribosomes on its surface and transport proteins

Centrioles

Rod shape located outside the nuclear membrane; for the formation of cilia and flagella

Cytoplasm

It is a fluid medium where chemical reactions occur; contains organelles and inclusion

Granules; cell membranes

The cell membrane encloses all cell organelles; has a phospholipid layer between two protein layers, with pores that selectively allows substances to pass in and out/semi-permeable

Nucleus;

Has double membrane around it; with pores allow substances in and out

Ribosome

Are spherical in shape and suspended in the cytoplasm and attached to the endoplasmic reticulum; synthesis proteins

Q18. Describe how the male reproductive system in suited to its functions

  • Penis; high vascularized / spongy; sensitive glans penis become erect to allow entry/ penetration during copulation; scrotum; contains testis outside the body
  • Testis; contains numerous/ many seminiferous tubules ; on whose walls spermatogenesis take place; the process is favoured by lower temperature; contains Sertoli cells which nourish sperms until they are mature
  • Epididymis; which is the long and coiled tube for storage of sperms
  • Vas deferens; a muscular tube that upon contraction pushes sperms out and allow ejaculation; gametes are produced in large numbers to increase chances of fertilization; has a tail for swimming/ has a large number of mitochondria to provide energy for swimming (to reach the egg)

Q19. Describe the process of fertilization in flowering plants. (10mks)

  • Pollen grains land onto the stigma; and adhere to it as a result of cells secreting a sticky substance pollen absorbs nutrients; and germinates forming a pollen tube; the tube grows down to the ovary ; deriving nourishment from surrounding tissues; the pollen tube nucleus at the tip; the generative nucleus divides mitotically; to give rise to two nuclei; which represents the male gametes; the pollen tube penetrates the ovule/embryo sac, the tube nucleus breaks down; leaving two male nucleus; then enter into the embryo sac, where one fuses with egg nucleus; to form a diploid zygote; which develops into embryo the other male nucleus fuses with the polar nuclei; to from a tripod endosperm nucleus; which becomes the endosperm; this is called double fertilization

Q20. Describe the changes in the eye when moving from bright sunlight into a dimly lit room.(10mks)

  • In bright light the amount of light entering the eye should be reduced to ensure the eye is not damaged by the bright light; light enters the eye through the pupil; the radial muscles of the iris relax; while circular muscle contract; the diameter of the pupil decrease; less light gets into the eye; in dim light; the amount of light entering the eye should be more and hence the pupil should widen; radial muscles contracts; while circular  muscles relax;  causing the diameter of the pupil to increase and hence more light enters the eye