KCSE Past Papers 2017 Biology Paper 3 (231/3)

2017 Biology paper 3

i) E – strips curved outwards; (1 mark) F — strips curved inwards; (1 mark)

ii) E — Liquid Elwater entered inner cells/mesocarp of banana peels by osmosis; the inner cells expanded faster/enlarged more/became longer/ became turgid than the outer cells; (leading to the curvature outwards/outer cells did not expand); (3 marks)

F — (More) water left inner cells/moved out (of banana peels) into liquid F (by osmosis); inner cells shrunk/became flaccid/shorter (causing inward curvature); (2 marks)

Liquid E has more solvent molecules/fewer solute molecules/ hypotonic(compared to the sap in the banana peel); while liquid F is hypertonic/ has more solute molecules/fewer solvent molecules/more concentrated/highly concentrated. (2 marks)

Outer surface(of the banana peel) is impermeable/less permeable/water-proof hence water enters or leaves only from the inner surface/while inner surface is permeable/more permeable; (1 mark)

i) Cell membrane/plasma membrane/plasmalemma; (1 mark)

ii) It is semi-permeable/selectively permeable; thus allowing (selective) movement of materials in and out of the cell/has pores which allow small molecules to pass through; (2 marks)

i) Contents of test tube A are clearer/colourless/form a solution; (1 mark)

Contents of test tube B are cloudy/turbid/form a white precipitate/ suspension/milk/colloidal suspension; (I mark)

ii) NaOH provided an alkaline medium/condition/optimum/best/suitable (in test tube A); suitable for action/working of enzyme P (on egg albumen); effectively digesting the egg albumen/protein; (3 marks)

Contents of test tube B remained cloudy) Hydrochloric acid provided unsuitable/ acidic/unfavourable medium; for the working of enzyme P, hence no break down/ digestion of albumen occurred; (2 marks)

b) To provide suitable/optimum/favourable/best temperature for the working/action of enzyme P; (1 mark)

d) Control experiment; (1 mark)

T) 1 i i) Solution P is an enzyme/trypsin; protein-digesting enzyme/in the egg albumen in the alkaline medium; (2 marks)

ii) In the duodenum; (1 mark)

iii) It has alkaline medium/condition; (1 mark)

i) -Upright/firm stem that exposes leaves to light/ needed for photosynthesis; -Green stem that contains chlorophyll to trap sunlight/light (for photosynthesis); -Stem has phloem to transport the products of photosynthesis; -Stem has xylem vessels for transport of water/mineral salts needed for photosynthesis;

– (Many/numerous) nodes to allow for growing/propagation of the plant; – Extensive/shallow/many fibrous adventitious roots (on each node) to exploit surface water/anchorage/support; – Swollen stem/internode that store food; – Green leaves for photosynthesis; – Scaly leaves that protect the lateral buds from mechanical damage; (3 marks)

c) Liquid F being hypertonic (compared to the plant’s cell sap) would lose water to the soil by osmosis; eventually being dehydrated, wilt/dry up and die; (2 marks)

d) -Food for herbivores/producers/food for primary consumers; -Ground cover/roots bind soil; -Offers camouflage/home for small animals/habiat; -Recycling of nutrients (upon decomposition); -Reduce carbon (IV) oxide in the atmosphere/ carbon (IV) oxide sink; Reduces green house effect; Any 2 (2 marks)

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