KCSE 2017 Biology Paper 3 with Marking Scheme

1. You are provided with the following materials and reagents.
   • A straight portion of raw banana, labelled D
   • Two petri dishes
   • A scalpel sharp razor blade
   • Two beakers containing liquids. E and F
   • A measuring cylinder
   • A stopwatch access to a wall clock
   • Means of labelling
     
     1. Label the two petri dishes, E and F
     2. Place 30 cm³ of liquid E into petri dish E and 30 cm³ of liquid F into petri dish F
     3. Using the scalpel, prepare four thin, straight, flat strips from the raw banana peel
     4. Each strip should measure about 4 cm by 2 mm as illustrated below.
        
        Note: To get a straight, flat, thin strip, remove all the banana flesh, leaving only the peel.
     5. Immerse two strips in petri dish E and the other two in petri dish F and leave the set ups undisturbed for 10 minutes.
        1.  
           1. State your observations in petri dishes E and F after 10 minutes.
              Petri dish E       (1 mark)
              Petri dish F      (1 mark)
           2. Account for the observations made in (a) (i) on page 2
              Petri dish E         (3 marks)
              Petri dish F          (2 marks)
        2. Describe the nature of liquids E and F in relation to the sap in the banana peel used in the experiment.   (2 marks)
        3. With reference to the observations made, compare tlic nature of the outer and inner surfaces of the banana peel.     (1 mark)
        4.  
           1. Name the cell structure responsible for the observations made in this experiment.   (1 mark)
           2. Explain how the cell structure named in (d) (i) above works to bring about the observations made   (2 marks)
2. You are provided with the following materials and reagents.
   
   • Three lest tubes on a rack
   • Dilute egg albumen
   • (Access to) dilute hydrochloric acid with a dropper
   • (Access to) Sodium hydroxide solution with a dropper
   • Solution P
   • Two droppers
   • Three 10 ml measuring cylinders
   • A stop watch access to a wall clock
   • Access to a water bath maintained at 50°C to 60°C
     
     1. Label the test tubes A, B. and C
     2. Put.cm³ of egg albumen into each of the test tubes A. B and C
     3. Add 1cm³ of soluton Pin cach of the test tubes
     4. Into test tube A. add two drops of sodium hydroxide
     5. Into test tube B, add two drops of hydrochloric acid
     6. Into test tube C. add 2 drops of water
     7. Place all the three test tubes in the water bath for 10 minutes.
        
        1.  
           1. State the observations made in test tubes A and B.
              Test tube A    (1 mark)
              Test tube B      (1 mark)
           2. Account for the observations made in a (i) above.
              Test tube A     (3 marks)
              Test tube B      (3 marks)
        2. Explain why the investigation was carried out at the specified temperature range,   (1 mark)
        3. State the purpose of test tube C.   (1 mark)
        4.  
           1. With a reason, identify solution P.    (2 marks)
           2. Name the likely part of the human alimentary canal where the process in this experiment occurs.  (1 mark)
           3. Give a reason for your answer in e (ii) above.    (1 mark)
3. You are provided with specimens labelled Il and K.
   Specimen H is a complete plant while J is a portion of a different plant. Observe the specimens and answer the questions that follow.
   
   1. State three observable differences between the leaves of specimens H and K. (3 marks)
   2.  
      1. Explain three ways in which the stem of specimen H adapts the plant for maximum photosynthesis.
         (3 marks)
      2. Explain three ways in which the plant from which specimen K was obtained is adapted for survival in its habitat.
         (3 marks)
   3. Explain the consequence of adding liquid Fused in question 1 to the soil in which specimen H is growing.
      (2 marks)
   4. State two ecological importance of specimen K in an ecosystem.   (2 marks)

MARKING SCHEME

1.  
   1.  
      1. E-strips curved outwards;  (1 mark) 
         F-strips curved inwards;   (1 mark)
      2. E-Liquid E/water 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)
   2. Liquid E has more solvent molecules/fewer solute molecules/ hypotonic(compared to the sap in the banana peel); while liquid Fis hypertonic/ has more solute molecules/fewer solvent molecules/more concentrated/highly concentrated.  (2 marks)
   3. 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)
   4.  
      1. Cell membrane/plasma membrane/plasmalemma;  (1 mark)
      2. 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)
         13 marks
2.  
   1.  
      1. 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;
         (1 mark)
      2. 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)
   2. To provide suitable/optimum/favourable/best temperature for the working/action of enzyme P: (1 mark)
   3. Control experiment; (1 mark)
   4.  
      1. Solution P is an enzyme/trypsin; protein-digesting enzyme/in the egg albumen in the alkaline medium;
         (2 marks) 
      2. In the duodenum;  (1 mark) 
      3. It has alkaline medium/condition;   (1 mark)
         14 marks
3.  
   1. 
      

      Plant H leaves	Plant K leaves
      Broad/broad lamina  Short leaves  Net-veined/network veins/reticulate;  Leaflets ovate;  Compound and simple;  Petiole present/compact petiole	Narrow lamina;  Long leaves;  Parallel-veined;  Leaves linear,  Simple leaves only: Leaf sheath  petiole absent/petiole modified into sheath;

       Any (3 marks)
   2.  
      1.  
         • 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;
           Any 3
      2.   
         • (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)
   3. 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) 
   4.  
      • 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)