Biology Paper 2 Question and Answers - KCSE 2020 Past Papers

THE KENYA NATIONAL EXAMINATIONS COUNCIL
Kenya Certificate of Secondary Education
231/2 BIOLOGY Paper 2 (THEORY)

Instructions to Candidates

1. This paper consists of two sections; A and B.
2. Answer all the questions in section A in the spaces provided.
3. In section B answer question 6 (compulsory) and either question 7 or 8 in the spaces provided after question 8.
4. This paper consists of 12 printed pages.
5. Candidates should answer the questions in English.
   For Examiner's Use Only

SECTION A (40 marks)
Answer all questions in this section in the spaces provided.

1. Below are photographs E and F, of two organisms, taken from their natural habitats. 
   
   1.  
      1. State the main nitrogenous waste product of the organism in photograph E. ( 1 mark)
      2. Give a reason for your answer in a(i) above. (1 mark)
   2. State why the organism in photograph E is usually found on top of rock surfaces even during hot, sunny days. (b) mark)
   3.  
      1. Which of the two organisms would have a higher biomass if both were left in their natural ecosystem.(1 mark)
      2. Give a reason for your answer in c(i). (1 mark)
   4. With reference to observable features, explain why the organism in photograph F is usually found in a wider range of habitats.(3 marks)
2. The genetic make-up of a man was found to be XXY.
   1. Name the syndrome the individual could be suffering from. (1 mark) (a)
   2. Explain how the syndrome occurs. (4 marks) .
   3.  
      1. State how the chemical, colchicine induces polyploidy in plants.(1 mark)
      2. State one advantage of polyploidy in wheat farming(2 marks)
3. In an experiment to investigate the effect of temperature on seed germination, soaked maize seeds were subjected to varying temperatures as tabulated below. 3.
   

   Temperature (°C)	0	6	12	17	28	33	41.5	51
   Percentage germination (%)	0	0	2.5	5	13	44	26	3

   
   
   
   1. Account for the percentage germination at:
      1. 6°C; (3 marks)
      2. 33°C. (3 marks)
   2. State two internal factors that affect seed germination( 2 marks)
4. A student could clearly read a book placed 10cm away but could not clearly identify a fellow student 12m away.
   1. Name the eye defect the student was suffering from( 1 mark).
   2. Explain why the student could not clearly identify his colleague yet could read the book. (3 marks)
   3. Using a diagram, illustrate how the defect can be corrected.( 3 marks)
   4. Name the vitamin whose deficiency in the diet results in poor vision.( 1 mark)
5. The table below shows the volume of gases contained in 100cm³ of a blood sample tapped at two points in the mammalian circulatory system
   
   

   Gas	Blood entering lungs (cm3)	Blood leaving lungs  (cm3)
   Oxygen	8.65	20.25
   Nitrogen	0.75	0.75
   Carbon (IV) oxide	55.60	31.65

   1. Account for the difference in the gaseous composition of
      1. Blood entering the lungs; (2 marks)
      2. Blood leaving the lungs. (2 marks)
   2. Name the blood vessel through which blood enters the lungs. (1 mark)
   3.  Explain why most athletes prefer training from high altitude areas. (3 marks

SECTION B (40 marks)
Answer question 6 (compulsory) and either question 7or & in the spaces provided after question 8.

6. The data below shows the average number of ticks per animal in a certain farm before and after spraying the animals with a certain chemical. The spraying was done once every month. The data was tabulated as shown below.
   
   

   Time( months)	0	2	4	6	8	10	12	14
   Average number of ticks	200	90	40	20	16	25	45	90

   
   
   1. Plot a graph of ticks against time ( 6 marks)
   2. Account for the shape of the graph between:
      1. 0 and 8 months;(3 marks)
      2. 10 and 14 months. (3 marks)
   3. From the graph, determine the average number of ticks after spraying the animals for five months. (1 mark)
   4. If the animals were allowed to graze in an open field, construct a food chain with five organisms in which ticks are secondary consumers. (4 marks)
   5. State three methods by which the average number of ticks per animal could have been estimated. (3 marks)
7.    
   1. Explain the role of the liver in blood sugar regulation. (3 marks)
   2. Describe how human blood is adapted to its function. (17 marks)
8.    
   1. Explain how the presence of chloroplasts in guard cells affect the opening of stomata. (5 marks)
   2. Describe how various environmental factors affect the rate of photosynthesis. (15 marks)

MARKING SCHEME

SECTION A (40 marks)
Answer all questions in this section in the spaces provided.

1. Below are photographs E and F, of two organisms, taken from their natural habitats. 
   
   1.  
      1. State the main nitrogenous waste product of the organism in photograph E. ( 1 mark)
         
         • Uric acid
      2. Give a reason for your answer in a(i) above. (1 mark)
         
         • Uric acid requires little water to eliminate/ removal of uric acid conserves water/ it's less toxic, poisonous
   2. State why the organism in photograph E is usually found on top of rock surfaces even during hot, sunny days. (1 mark)
      
      • It is an octotherm/ poikilotherm/ exotherm
   3.  
      1. Which of the two organisms would have a higher biomass if both were left in their natural ecosystem.(1 mark)
         • F
      2. Give a reason for your answer in c(i). (1 mark)
         • Occupies lower trophic level/ biomass/ energy decreases up the trophic level
         • organism F is eaten by E
   4. With reference to observable features, explain why the organism in photograph F is usually found in a wider range of habitats.(3 marks)
      • Dorsal-ventrally flattened thus able to penetrate crevices for food & safety
      • Has wings to fly
      • Antennae for sensory purposes
      • Exoskeleton for protection/ water conservation
      • Legs for movement
2. The genetic make-up of a man was found to be XXY.
   1. Name the syndrome the individual could be suffering from. (1 mark) 
      • Klinefeller's syndrome( ignore spelling)
   2. Explain how the syndrome occurs. (4 marks) .
      • Chromosomal abnormalities/ mutation resulting in addition of a whole chromosome. It occurs during meiotic division/meiosis where homologous chromosomes fail to segregate and move on to the same gamete cell/ If gamete with XX fuses with gamete with Y, then offspring becomes XXY
        

        	X	Y
        XX	XXX	XXY
        O	XO	YO

        
        
        
   3.  
      1. State how the chemical, colchicine induces polyploidy in plants.(1 mark)
         • Prevents spindle formation during cell division leading to cells with extra chromosome.
      2. State one advantage of polyploidy in wheat farming(2 marks)
         • Drought/ pest/ disease resistant
         • High yields
         • Early maturity
3. In an experiment to investigate the effect of temperature on seed germination, soaked maize seeds were subjected to varying temperatures as tabulated below. 3.
   

   Temperature (°C)	0	6	12	17	28	33	41.5	51
   Percentage germination (%)	0	0	2.5	5	13	44	26	3

   1. Account for the percentage germination at:
      1. 6°C; (3 marks)
         • No germination due to low temperature, inactivating enzymes
      2. 33°C. (3 marks)
         • Percentage germination highest as temp was most favourable/ enzymes worked their best/ optimum
   2. State two internal factors that affect seed germination( 2 marks)
      • Embryo
      • Seed coat
      • Growth hormones
      • Enzymes
      • Inhibitors
      • Viability
4. A student could clearly read a book placed 10cm away but could not clearly identify a fellow student 12m away.
   1. Name the eye defect the student was suffering from( 1 mark).
      • Myopia/Short(near)-sightedness - reject Short(near)-sighted
   2. Explain why the student could not clearly identify his colleague yet could read the book. (3 marks)
      • Long eyeball, resulting in rays from colleague (12m away) being focused at point in front of retina. Light rays on book focused on retina
   3. Using a diagram, illustrate how the defect can be corrected.( 3 marks)
      (thick lens for long eyeball)
      
   4. Name the vitamin whose deficiency in the diet results in poor vision.( 1 mark)
      • Vitamin A
5. The table below shows the volume of gases contained in 100cm³ of a blood sample tapped at two points in the mammalian circulatory system

   Gas	Blood entering lungs (cm3)	Blood leaving lungs  (cm3)
   Oxygen	8.65	20.25
   Nitrogen	0.75	0.75
   Carbon (IV) oxide	55.60	31.65

   1. Account for the difference in the gaseous composition of
      1. Blood entering the lungs; (2 marks)
         • Blood entering lungs has lower concentration of O₂ and higher concentration of CO₂ since most O₂ has been used up in respiration, yielding more CO₂
      2. Blood leaving the lungs. (2 marks)
         • Blood leaving lungs has lower CO₂ levels and higher O₂ levels since it has been purified. volume of nitrogen remains unchanged as it isn't used up during respiration.
   2. Name the blood vessel through which blood enters the lungs. (1 mark)
      • Pulmonary artery
   3.  Explain why most athletes prefer training from high altitude areas. (3 marks)
      • High altitude areas have low oxygen concentration, thus the body produces more red blood cells, increasing amount of oxygen carried around the body for respiration, making athletes more energetic.

SECTION B (40 marks)
Answer question 6 (compulsory) and either question 7or & in the spaces provided after question 8.

6. The data below shows the average number of ticks per animal in a certain farm before and after spraying the animals with a certain chemical. The spraying was done once every month. The data was tabulated as shown below.

   Time( months)	0	2	4	6	8	10	12	14
   Average number of ticks	200	90	40	20	16	25	45	90

   
   
   1. Plot a graph of ticks against time ( 6 marks)
      
   2. Account for the shape of the graph between:
      1. 0 and 8 months;(3 marks)
         • Decrease number of ticks due to the chemical killing them / ticks not yet adapted/ developed resistance
      2. 10 and 14 months. (3 marks)
         • Increased number of ticks due to increased resistance
   3. From the graph, determine the average number of ticks after spraying the animals for five months. (1 mark)
      • 28 ± 2
   4. If the animals were allowed to graze in an open field, construct a food chain with five (d) organisms in which ticks are secondary consumers. (4 marks)
      • Grass → Animal → Tick → bird → Vulture
        ( mark for producer - grass, tick, energy flow, five organisms)
   5. State three methods by which the average number of ticks per animal could have been estimated. (3 marks)
      • Mapping various parts of the animals body
      • Physical counting
      • Sampling the animals
7.    
   1. Explain the role of the liver in blood sugar regulation. (3 marks)
      • When blood glucose is high, insulin hormone is produced by pancreas, stimulating liver cells to  convert excess glucose to glycogen [ some glucose to fat]. When blood glucose is low, pancreas secretes the glucagon hormone, stimulating the liver to convert glycogen/ fats to glucose.
   2. Describe how human blood is adapted to its function. (17 marks)
      • Plasma is the fluid part of blood consisting of dissolved and undissolved substances. The plasma acts as a medium in which various substances are transported in the body. It acts as a medium for various metabolic reactions and plays a role in thermo-regulation/ heat distribution.
      • Platelets contain proteins that help in blood clotting( thromboplastin/ thrombokinase), preventing excessive blood loss/ anaemia and also entry of pathogens into the blood stream.
      • White blood cells have an irregular/ amoebid shape and protect the body against attacks by pathogens by engulfing them and releasing antibodies against the pathogens. They are numerous and act as the body's defense mechanism.
      • Red blood cell are biconcave in shape to increase surface area for difussion of gases/ squeezing through blood capillaries. They lack nuclei to allow for more haemoglobin packing. Haemoglobin has high affinity for oxygen and are numerous to increase surface area for oxygen transport through out the body.They have anyhydrase enzyme for loading and offloading CO₂
8.    
   1. Explain how the presence of chloroplasts in guard cells affect the opening of stomata. (5 marks)
      • Chloroplasts are sites of photosynthesis. During the day, photosynthesis takes place. Glucose is manufactured , and being osmotically active, it increases the internal concentration of guard cells, making them turgid and bulge outward, opening the stomata.
      • ( starch interconversion theory)- Chloroplasts are sites for photosynthesis. When photosynthesis takes place, Co₂ concentration goes up and the pH of the guard cells rise, favouring the conversion of starch to glucose then being osmotically active, it increases the internal concentration of guard cells, making them turgid and bulge outward, opening the stomata.
   2. Describe how various environmental factors affect the rate of photosynthesis. (15 marks)
      • Carbon (IV) oxide concentration - being a raw material for photosynthesis, increase in CO₂ levels leads to an increased rate of photosynthesis up to a given optimum beyond where the rate remains the same due to other limiting factors.
      • Light intensity/ quality of light - it provides the energy required for photosynthesis/ photolysis. Increase in light intensity increases rate of photosynthesis up to an optimum point, beyond which rate remains the same due to other limiting factors
      • Temperature - Low temperatures make enzymes inactive, reducing rate of photosynthesis, as temperature increases, rate of photosynthesis increases up to an optimum. High temperatures beyond optimum denatures enzymes, reducing rate of photosynthesis.
      • Water - is a raw material for photosynthesis. It influences the opening and closing of stomata, affecting diffusion of  CO₂ in the leaves.