KNEC KCSE BIOLOGY TOPICAL QUESTIONS AND ANSWERS

Describe how the mammalian eye is structurally adapted to its function.

1/7/2020

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K.C.S.E Biology Q & A - MODEL 2017PP2QN08

Describe how the mammalian eye is structurally adapted to its function.

answers

Has the eyelid; which protects the cornea from mechanical/physical/chemical damage;
Eye lid; protects the eye from bright light by reflex action;
Sclera/Sclerotic layer; which contains (inelastic) collagen fibres which protects/maintains shape of the eyeball;
Cornea; transparent to allow light pass through/has convex shape to refract light towards the retina;
Conjunctiva (thin) epithelium for protection of cornea/has goblet cells for secretion of mucus for lubrication/ transparent to allow light pass through;
Choroid/choroid layer; rich in blood vessels/highly vascularized, supplying the retina with nutrients/oxygen/remove metabolic wastes/covered with (black) pigment cells to prevent reflection of light within the eye;
Ciliary muscles; have (contractile) muscles that contract/relax to alter the shape of the lens during accommodation;
Lens; transparent to allow light pass through/elastic to allow adjustment of the shape of lens/ biconvex to refract light/focus light onto retina;
Iris; — has radial and circular muscles to alter diameter/size of the pupil, hence controlling the amount of light entering the eye/contain pigments that absorb light and stop it getting through to the retina;
Vitreous homour; — clear/transparent to allow light pass through/is a fluid that refracts light rays onto the retinal maintain shape of the eye balls supports the eye;
Retina; contains cones, rods/photoreceptors to perceive light;
Optic nerve;- has sensory neurons/nerve cells that transmit impulses to the brain;
Fovea (centralis); — (most sensitive part of retina) contains numerous/high concentration of cones for visual acuity/accurate vision;
Pupil ; a hole/an aperture/opening in the iris, lets in light;
Suspensory ligaments;-are fibrous/inelastic fibres that hold lens in position;
Aqueous humour is clear/transparent to allow light to pass through/is a fluid/liquid (exerting hydrostatic pressure) to maintain the shape of the eyeball/refract light rays onto the lens/cornea/contain glucose for nourishment;
Blind spot a point where the optic nerve leaves the eye to the brain/passage of blood vessels since has no photoreceptors;

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K.C.S.E Biology Q & A - MODEL 2017PP2QN07

1/7/2020

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K.C.S.E Biology Q & A - MODEL 2017PP2QN07

Explain the importance of protecting the forest ecosystem with reference to the following:
(a) climate change
(b) biodiversity
(c) biotechnology
(d) water conservation
(e) pollution.

answers

a) Climate change

Promote(regular) rainfall/precipitation/prevent desertification;
Act as wind breakers;
Keep earth temperatures cool/reduce global warming;
Keeps biogeochemical cycles going e.g. hydrological, carbon,nitrogen, phosphorous, sulphur cycles;

b) Biodiversity

Conserve diverse flora/ fauna;
Conserve genetic variety;
Prevent extinction of rare species;
Source of research/employment;
Aesthetic/attracting tourism in foreign exchange;
Have impact on culture/religion/politics; ‘
Food and shelter for other organisms and man;
Source of oxygen;

c) Biotechnology

Manufacture of medicines/directly used as medicinal;
Source of food/food products;
Provide fuel (when regulated);
Provide paper and related by-products (when regulated);
Provide timber (when regulated);
Products used in other industries e.g. tannin, wax, rubber, oil, honey;

d) Water conservation

Increased ground water/high water tables;
Adds into rivers/lakes/permanency ¡n existing water bodies/reservoirs;
Water towers/water catchment;

e) Pollution .

Minimize soil pollution/ensuring cover against surface run-off/wind erosion/denudation;
Trees/vegetation clean the soil surface by absorbing nutrients from decomposed matter e.g. sewage;
Large scale clean-up of polluted air/dust;
Muffle noise pollution;

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K.C.S.E Biology Q & A - MODEL 2017PP2QN06

1/7/2020

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K.C.S.E Biology Q & A - MODEL 2017PP2QN06

In an investigation, two potted plants G and H belonging to the same species were exposed to increasing light intensities at different temperatures, 30°C and 20°C respectively. The rate of photosynthesis was measured for each plant and results recorded as shown in the table below:

(a) On the same axis, plot graphs of rate of photosynthesis against light intensity for plants G and H.
(b) State the aim of the investigation.
(c) Account for the difference in the rate of photosynthesis in the two plants.
(d) Account for the difference in the rate of photosynthesis in the two plants between the following light intensities:
(i) 1—4 units
(ii) 4—8 units.
(e) (i) Predict the rate of photosynthesis at light intensity of 16 units.
(ii) Give a reason for your answer in (e) (i) above.
(f) State one internal and one external factor that could be limiting in the investigation.

answers

b) To investigate/compare the effect of (varying) light intensity/temperature on the rate of photosynthesis;
c) Rate of photosynthesis is higher in plant G (than H); (Photosynthesis being an enzymatic process), enzymes were subjected to favourable/optimal temperatures (of 30°C): hence more activated, unlike in plant H where temperatures were lower (20C);
d) (i) 1-4 units
Rapid increase in rate of photosynthesis increases with the increase in light intensity; due to increase in light energy for photosynthesis/formation of more ATP molecules;
(ii) 4 — 8 units
Slower/gradual increase in the rate of photosynthesis as the light intensity increases: because other factors become limiting/some chlorophyll molecules start bleaching;
e) i) Slight increase/no significant increase/remains constant;
ii) The optimum light intensity has been exceeded/some chlorophyll could be destroyed;
f) Internal factor — Chlorophyll/enzyme concentration;
External factor — Carbon (IV) oxide concentration/amount of water;

Comments

State how in-breeding leads to reduced hybrid vigour

1/7/2020

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K.C.S.E Biology Q & A - MODEL 2017PP2QN05

State how in-breeding leads to reduced hybrid vigour

answer

Chances of recessive/defective genes being combined increase,hence weaker offspring;

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State two advantages of using genetically modified varieties in bean farming.

1/7/2020

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K.C.S.E Biology Q & A - MODEL 2017PP2QN05

State two advantages of using genetically modified varieties in bean farming.

answers

Higher yields;
Enhanced resistance to diseases/pests;
Early/faster maturity;
Enhanced resistance to harsh climatic conditions (drought/extremes in temperature);

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K.C.S.E Biology Q & A - MODEL 2017PP2QN05

1/7/2020

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K.C.S.E Biology Q & A - MODEL 2017PP2QN05

In beans, the gene for purple colour is dominant over the gene for white colour. A pure breeding bean plant with purple colour was crossed with a heterozygous bean plant.
Using the letter P to represent the gene for purple colour, work out the genotypic ratio of the offspring.

answer

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Name the hormone responsible for the development of secondary sexual characteristics in human males.

1/7/2020

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K.C.S.E Biology Q & A - MODEL 2017PP2QN04

Name the hormone responsible for the development of secondary sexual characteristics in human males.

answer

Testosterone;

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State the significance of diploidy.

1/7/2020

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K.C.S.E Biology Q & A - MODEL 2017PP2QN04

State the significance of diploidy.

answers

Ensures that the chromosomes/genetic constitution of the offspring is the same as that of parents;
Ensures perpetuation of a given species’ desired/favourable traits/qualities/continuity of the species;

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K.C.S.E Biology Q & A - MODEL 2017PP2QN04

1/7/2020

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K.C.S.E Biology Q & A - MODEL 2017PP2QN04

(i) Define the term diploidy.
(ii) Name the type of cell division that gives rise to diploid cells.
(iii) Name the type of cells in which the process named in (b) (ii) above Occurs.

answers

i. State of being/having two sets of chromosomes and therefore two copies of genes (especially in somatic/body cells);
ii. Mitosis;
iii. Body cells/somatic cells;

Comments

Explain how the sex of a male child is determined in human beings.

1/7/2020

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K.C.S.E Biology Q & A - MODEL 2017PP2QN04

Explain how the sex of a male child is determined in human beings.

answers

Male produces sperm cells with X or Y chromosomes; if (by chance), Y chromosome containing sperm from male fuses with X chromosome containing egg from female ovum, an XY zygote results, giving rise to a male child;

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K.C.S.E Biology Q & A - MODEL 2017PP2QN03

1/7/2020

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K.C.S.E Biology Q & A - MODEL 2017PP2QN03

The diagram below illustrates the appearance of a plant cell after it had been put in a certain solution.

(a) Explain the appearance of the cell at the end of the treatment.
(b) Explain the results obtained if a red blood cell is subjected to the same treatment.
(c) Explain why transfusion with distilled water is not recommended for a dehydrated patient.

answers

(a) The cell is turgid; its cell sap was hypertonic (compared to the solution in which it was placed); by osmosis, water moved into the cell across its cell semi-permeable membrane, (swelling and becoming turgid);
(b)The red blood cell lacks the cell wall; water molecules move across its semi-permeable membrane by osmosis; into its hypertonic medium (inside the cell),cell contents/cytoplasm swelling and bursting haemolyses;
(c)Would haemolyse; due, to lowering of the osmotic pressure of the blood below normal;

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K.C.S.E Biology Q & A - MODEL 2017PP2QN02

30/6/2020

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K.C.S.E Biology Q & A - MODEL 2017PP2QN02

The table below shows variations in the form carbon (IV) oxide is transported in the blood at rest and during physical exercise.

(a) Explain why more carbon (IV) oxide ¡s transported in the form of bicarbonate ion.
(b)Account for the high total plasma content of carbon (IV) oxide during exercises.
(c) State how one’s involvement in the exercises affects blood pH.
(d) Name the protein responsible for the transport of carbon (IV) oxide in the blood.

ANSWERS

(a) Presence of carbonic anhydrase enzyme; which speeds up the conversion of carbon (IV) oxide to weak carbonic acid; which dissociates into hydrogen carbonate ion/(HCO3) (that diffuses out of the red blood cells into the blood plasma);
(b)The body needs high amount of energy; (for the exercise/muscle activity) hence high respiration rate (more oxygen intake); releasing more carbon (IV) oxide (in the blood plasma);
(c)The high rate of respiration (during physical exercises coupled with normal cellular metabolism) results in the production of more carbon(IV) oxide/faster accumulation of lactic acid; lowering the blood plasma pH/making it more acidic (compared to when one is at rest);
(d)Haemoglobin

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K.C.S.E Biology Q & A - MODEL 2017PP2QN01

30/6/2020

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K.C.S.E Biology Q & A - MODEL 2017PP2QN01

The diagram below represents a nucleus.

(a) Name the structures labelled E and F.
(i) E
F
(ii) State the function of F.
(iii) With reference to the nucleus, state one difference between an animal and a bacterial cell.
(b) Name the plant cell organelle:
(i) that stores chlorophyll
(ii) responsible for intracellular digestion.
(c) State two main functions of the vacuole in the amoeba.

ANSWERS

(a) E—Nucleolus;
F — Nuclear pore/nucleopore;
ii. Facilitates movement of materials in and out of the nucleus;
iii. Nuclear material in the bacterial cell is not enclosed within a membrane /prokaryotic, while in animal cell it is enclosed eukaryotic;
(b) i. Chloroplast;
ii. Lysosome;
(c) i. Feeding (food vacuole);
ii. Osmoregulation (contractile vacuole);
iii. Excretion/removal of wastes;

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K.C.S.E Biology Q & A - MODEL 2017PP1QN23

30/6/2020

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K.C.S.E Biology Q & A - MODEL 2017PP1QN23

The diagram below represents a set up during an experiment.

(a) (i) What was, the experiment investigating?
(ii) State the likely identity for substance K
(iii) Explain your answer in (a) (ii) above
(b) Account for the observations made in flask 2.

answers

a.) i) To investigate how ants respond to moisture/water hydrotaxis (varied environments with/without moisture water);
ii) Silica gel/anhydrous calcium chloride pellets/pyrogallic acid/dehydrating drying agent;
iii) The colour of cobalt (II) chloride paper remained blue/all the moisture water vapour was absorbed/There was no water/moisture in the flask to change the colour of cobalt(II) chloride paper;
b.) (More) ants were attracted) moved into the flask; due to the presence of moisture/water vapour; (evidenced by the change of cobalt (II) chloride paper to pink)

Comments

State two ways by which plants manage their solid wastes.

30/6/2020

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K.C.S.E Biology Q & A - MODEL 2017PP1QN22

State two ways by which plants manage their solid wastes.

answers

Storage in tissues in non-toxic forms;
Deposited in plant tissues/organs- which age and fall off; (e.g leaves, bark, fruits, flowers)

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<<Previous

Describe how the mammalian eye is structurally adapted to its function.

Describe how the mammalian eye is structurally adapted to its function.

K.C.S.E Biology Q & A - MODEL 2017PP2QN07

K.C.S.E Biology Q & A - MODEL 2017PP2QN07

K.C.S.E Biology Q & A - MODEL 2017PP2QN06

K.C.S.E Biology Q & A - MODEL 2017PP2QN06

State how in-breeding leads to reduced hybrid vigour

State how in-breeding leads to reduced hybrid vigour

State two advantages of using genetically modified varieties in bean farming.

State two advantages of using genetically modified varieties in bean farming.

K.C.S.E Biology Q & A - MODEL 2017PP2QN05

K.C.S.E Biology Q & A - MODEL 2017PP2QN05

Name the hormone responsible for the development of secondary sexual characteristics in human males.

Name the hormone responsible for the development of secondary sexual characteristics in human males.

State the significance of diploidy.

State the significance of diploidy.

K.C.S.E Biology Q & A - MODEL 2017PP2QN04

K.C.S.E Biology Q & A - MODEL 2017PP2QN04

Explain how the sex of a male child is determined in human beings.

Explain how the sex of a male child is determined in human beings.

K.C.S.E Biology Q & A - MODEL 2017PP2QN03

K.C.S.E Biology Q & A - MODEL 2017PP2QN03

K.C.S.E Biology Q & A - MODEL 2017PP2QN02

K.C.S.E Biology Q & A - MODEL 2017PP2QN02

K.C.S.E Biology Q & A - MODEL 2017PP2QN01

K.C.S.E Biology Q & A - MODEL 2017PP2QN01

K.C.S.E Biology Q & A - MODEL 2017PP1QN23

K.C.S.E Biology Q & A - MODEL 2017PP1QN23

State two ways by which plants manage their solid wastes.

State two ways by which plants manage their solid wastes.

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