KCSE 2017 Biology Paper 2 with Marking Scheme

SECTION A (40 marks)

Answer all the questions in this section in the spaces provided.

1. The diagram below represents a nucleus.
             
   
   1. Name the structures labelled E and F.  (2 marks)
      
      1. E..................
         F ...............
      2. State the function of F.    (1 mark)
      3. With reference to the nucleus, state one difference between an animal and a bacterial cell.   (1 mark)
   2. Name the plant cell organelle:
      1. that stores chlorophyll  (1 mark)
      2. responsible for intracellular digestion.   (1 mark)
   3. State two main functions of the vacuole in the amoeba.   (2 marks)
2. The table below shows variations in the form carbon (IV) oxide is transported in the blood at rest and during physical exercise.
   

   Carbon (IV) oxide transport in blood plasma at rest and during exercise
   Form of transport   Dissolved carbon (IV) oxide   Bicarbonate ion   Carbon (IV) oxide bound to protein	Rest (Mol/l)       0.52     12.34      0.26	Exercise (M01/1)          0.97       13.68         0.16
   Total carbon (IV) oxide in plasma	13.12	14.81
   pH of blood	7.42	7.09

   
   
   1. Explain why more carbon (IV) oxide is transported in the form of bicarbonate ion.   (2 marks)
   2. Account for the high total plasma content of carbon (IV) oxide during exercises.   (3 marks)
   3. State how one's involvement in the exercises affects blood pH.    (2 marks)
   4. Name the protein responsible for the transport of carbon (IV) oxide in the blood.    (1 mark)
3. The diagram below illustrates the appearance of a plant cell after it had been put in a certain solution.
   
   
   1. Explain the appearance of the cell at the end of the treatment.     (3 marks)
   2. Explain the results obtained if a red blood cell is subjected to the same treatment.   (3 marks)
   3. Explain why transfusion with distilled water is not recommended for a dehydrated patient.  (2 marks)
4.  
   1. Explain how the sex of a male child is determined in human beings.   (2 marks)
   2.  
      1. Define the term diploidy.    (1 mark)
      2. Name the type of cell division that gives rise to diploid cells.  (1 mark)
      3. Name the type of cells in which the process named in (b)(ii) above occurs.   (1 mark)
      4. State the significance of diploidy.
   3. Name the hormone responsible for the development of secondary sexual characteristics in human males.
      (1 mark)
5. 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.
   1. Using the letter P to represent the gene for purple colour, work out the genotypic ratio of the offspring
      (5 marks)
   2. State two advantages of using genetically modified varieties in bean farming. (2 marks)
   3. State how in-breeding leads to reduced hybrid vigour.   (1 mark)

SECTION B 40 marks)

Answer question 6 (compulsory) and either question 7 or 8 in the spaces provided after question

6. 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:
   

   Light intensity (in arbitrary units)	1	2	3	4	5	6	7	8
   Rate of photosynthesis for plant G at 30°C	0	84	148	196	232	260	284	296
   Rate of photosynthesis for plant H at 20°C	0	72	115	148	170	186	204	216

   1. On the same axis, plot graphs of rate of photosynthesis against light intensity for plants Gand H.
      (8 marks)
   2. State the aim of the investigation.  (1 mark)
   3. Account for the difference in the rate of photosynthesis in the two plants.  (3 marks)
   4. Account for the difference in the rate of photosynthesis in the two plants between the following light intensities:
      
      1. 1-4 units   (2 marks)
      2. 4–8 units.   (2 marks)
   5.  
      1. Predict the rate of photosynthesis at light intensity of 16 units.   (1 mark)
      2. Give a reason for your answer in (e) (i) above.   (1 mark)
   6. State one internal and one external factor that could be limiting in the investigation.   (2 marks)
7. Explain the importance of protecting the forest ecosystem with reference to the following:  (20 marks)
   1. climate change
   2. biodiversity
   3. biotechnology
   4. water conservation
   5. pollution
8. Describe how the mammalian eye is structurally adapted to its function.   (20 marks)

MARKING SCHEME

1.  
   1.  
      1. E-Nucleolus;  (1 mark)
         F-Nuclear pore/nucleopore;   (1 mark)
      2. Facilitates movement of materials in and out of the nucleus;   (1 mark)
      3. Nuclear material in the bacterial cell is not enclosed within a membrane/prokaryotic, while in animal cell it is enclosed/ eukaryotic;  (1 mark)
   2.  
      1. Chloroplast; (1 mark)
      2. Lysosome; (1 mark)
   3.  
      1. Feeding (food vacuole); 
      2. Osmoregulation (contractile vacuole);
      3. Excretion/removal of wastes;
         (2 marks)
2.  
   1. Presence of carbonic anhydrase enzyme; which speeds up the conversion of carbon (IV) oxide to weak carbonic acid, which dissociates into hydrogen carbonate ion/(HCO ) that diffuses out of the red blood cells into the blood plasma); (2 marks)
   2. 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); (2 marks)
   3. 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); (2 marks)
   4. Haemoglobin;  (1 mark)
3.  
   1. 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):  (3 marks)
   2. 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; 
       (3 marks)
   3. Would haemolyse; due to lowering of the osmotic pressure of the blood below normal; (3 marks)
4.  
   1. 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;
      (2 marks)
   2.  
      1. State of being having two sets of chromosomes and therefore two copies of genes (especially in somatic/body cells);   (1 mark)
      2. Mitosis;  (1 mark)
      3. Body cells/somatic cells;   (1 mark)
      4. 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; 
         (2 marks)
   3. Testosterone; (1 mark)
5.  
   1.  
      (5 marks)
   2.  
      • Higher yields;
      • Enhanced resistance to diseases/pests; 
      • Early/faster maturity;
      • Enhanced resistance to harsh climatic conditions (drought/ extremes in temperature);  (2 marks)
        Any two
   3. Chances of recessive/defective genes being combined increase, hence weaker offspring;  (1 mark)
6.  
   1.  
         (8 marks)
      Plotting, all points-(2 marks)
      Labeling axis, X and Y. - (2marks)
      Scale, X and Y, - (2 marks)
      Smooth curves - (2 marks)
   2. To investigate/compare the effect of (varying) light intensity/ temperature on the rate of photosynthesis;
      (1 mark)
   3. 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 (20°C); (3 marks)
   4.  
      1. 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; (2 marks)
      2. 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;  (2 marks)
   5.  
      1. Slight increase/no significant increase/remains constant;   (1 mark)
      2. The optimum light intensity has been exceeded/some chlorophyll could be destroyed;  (1 mark)
   6. Internal factor - Chlorophyll/enzyme concentration;  (1 mark)
      External factor - Carbon (IV) oxide concentration amount of water;  (1 mark)
7.  
   1. Climate change     (3 marks)
      • 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)
   2. Biodiversity   (6 marks)
      • 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;
   3. Biotechnology   (4 marks) 
      • 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;
   4. Water conservation    (3 marks)
      • Increased ground water/high water tables; 
      • Adds into rivers/lakes/permanency in existing water bodies/ reservoirs;
      • Water towers/water catchment: 
   5. Pollution  (4 marks)
      • 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;
8.  
   • 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 comea/has goblet cells for secretion of mucus for lubrication, transparent to allow light pass through; 
   • Choroid/choroid layer; - rich in blood vessels/highly vascularised, 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 retina/ 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/comea/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;