Name ………………………………….candidate’s signature…………………

Date ………………………



Time: 2hrs.


Paper 231/2

Time: 2hrs

Instructions to candidates

.Write your name, index number in the spaces provided above.

.Sign and write the date of examination in the spaces provided above.

.This paper consists of two sections. A and B.

.Anwer all the questions in section a in the spaces provided.

.In section B answer question 7(compulsory) and either question 8 or 9 in the spaces provided after question 9.

.Check to ascertain that all pages are printed and that no questions are missing.


  1 7  
2 6  
3 7  
4 7  
5 6  
6 7  
  7 20  
8 20  
9 20  
Total score 80  



Answer all questions in this section in the spaces provided.

Q1. In an ecosystem energy flows from the sun and is transferred in a series of organisms.  The diagram represents different levels of energy levels of energy transfer.

                                Level D


                        Level C


              Level B


      Level A


(a) Insert the sun in the diagram and using arrows show the direction of energy transfer. (1mk)

(b) Name the trophic levels represented by D and B (2mks)


(c) Identify the general trend in the amount of energy along the path illustrated in (a) give reasons for the trend. (2mks)



(d)Explain short term effect of decreasing the number of individuals in the level C. (2mks)



Q2. In maize, yellow colour W is dominant over white colour.  Describe how one would establish whether a given sample of yellow maize is pure or hybrid.  Show your working. (4mks)



Q3. The sketch graph shows how the metabolic rate in man and lizard is affected by environmental temperature.



  1. Suggest why the metabolic rate was high in man between 5oc and 20o (2mks)



  1. Account for increase in metabolic rate in lizard as environmental temperature was increasing. (2mks)


  1. (i) state two physiological processes that occur in man when environmental temperature rises above 35o (2mks)





(ii) How would the lizard respond to similar temperature changes in (c) (1mk)


Q4. The apparatus shown was set up by a group of students.



  1. What was the aim of the experiment? (1mk)



  1. Explain the results obtained in the set up at the end of the experiment. (2mks)



  1. State the expected results if the cellophane was replaced with a thin section of

(i) Raw arrowroot (1mk)


(ii) Boiled arrowroot (1mk)



(d) (i) Account for the results obtained in ( c) (ii). (1mk)


(ii)  What is the equivalent of sucrose solution in plant tissue? (3mks)





Q5. The diagram represents a plant cell



  1. Name a carbohydrate which forms the structure label S. (1mk)


  1. (i) state the function of the part labeled R (2mks)


(ii) Suggest what would happen in the plant if the number of organelle labeled    T is




(c) Name two cell organelles present in the diagram but absent in animal cells                             (2mks)


Q6. The set of apparatus was assembled by a group of students to investigate some physiological process.


  1. (i) give two aims of the experiment. (2mks)


(ii) Explain the observation expected after 24 hours. (2mks)


  1. Before experiment, the glucose solution was boiled then cooled.

(i) Why was it necessary to boil the solution? (1mk)


(ii) What was the importance of oil layer in the experiment?(1mk)


  1. Describe a control experiment for the set up. (1mk)


  1. Suggest two industrial application of the process being investigated. (1mk)



SECTION B (40mks)

Answer question 7 (compulsory) and EITHER question 8 or 9 in the spaces provided after question 9

Q7 The table below represents body weight, metabolic rate and eaten per day by different mammals. (Compulsory)

Animal Body weight Metabolic rate (cm3) Oxygen/ghr Food eaten per day (kg)
Rat 0.10 800 0.098
Hare 2.00 480 1.2
Dog 8.00 300 3.0
Man 60.00 150 4.0
Horse 200.0 100 15.0
Elephant 800.0 86 40.0



  1. (i) Draw a graph of metabolic rate against body weight of the animals (6mks)


(ii) From the graph estimate the metabolic rate of an animal whose body weight is 35 kg (2mks)



  1. Express the food eaten per day of the following mammals as a percentage of their body weight.

(i) Rat (2mks)


(ii) Elephant (2mks)


  1. Account for the difference in percentage obtained in (b) (4mks)






  1. Which of the six mammals would least suffer dehydration during a sunny day? Give reasons for your answers. (2mks)



  1. A reptile would require less food than a mammal of the same weight. Explain. (2mks)






Q8. (a)Define the terms

(i)Transpiration (2mks)


(ii)Translocation (2mks)


(b)Explain five factors that affect the rate of transpiration in plants.(16mks)


Q9.           (a) Define

(i) Chemical evolution (2mks)


(ii) Organic evolution (2mks)



(b) Describe the evidence of organic evolution (16mks)



level D             Level C            Level B         Level

A (1mk)



(All must be correct)

(b) B-secondary consumers; D-producers (2mks)

(c) Amount of energy decrease along the path (from D to A); some energy is lost through respiration unconverted materials and uneaten individuals. (2mks)

(d) Number of individuals in level B decrease leading to decrease at level A due to starvation/less energy available; number of individuals in level D would increase due to decrease of herbivores/grazers. (2mks)

Q2. (a)Back cross with white maize (ww)

Parent                                             Pure breed                    X                           White

Genotype                                           WW                                                          ww


Gametes                W                                             W                  w                                 w



F1 genotype            Ww           Ww               Ww                                 Ww

NB all yellow NB:Gametes should be circled individually. (2mks)






Hybrid                                                     White

genotype                                           Ww                                                           ww


Gametes                W                                             w                   w                                 w



F1 genotype            Ww           Ww               ww                                  ww

2 yellow                           2 white

Mixture of yellow and white  (2mks)


(b) Male sex chromosome XY female XX.














50% boys, 50% girls/equal chances (2mks)


Q3. (a) Environmental temperature lower than body temperature more heat was being generated to maintain body temperature. (2mks)

(b) The lizard is poikilothermic, enzymes were inactive at low temperature, their activity increased as temperature increased because enzymes were activated.(2mks)

(c) ) (i) vasodilation, sweating, hair lie flat on skin (first two) (2mks)

(ii)Aestivation, migration to shade, burrowing, sand bathing, (any one correct)(1mk)

Q4. (a) To demonstrate osmosis in non -living tissue (1mk)

(b) Level of sucrose rose in thistle funnel, water drawn into funnel by osmosis,since     sucrose solution was hypertonic to/more concentrated than distilled water. (2mks)

(c)  (i) Sucrose solution level would rise in funnel.(1mk)

(ii) No observable change/sucrose level remained the same.(1mk)

(d) (i) Cell membrane in arrow root destroyed hence no osmosis (1mk)

(ii) Cell sap/dissolve sugars and salts in vacuole.(1mk)


Q5 (a) Cellulose (1mk)

(b) (i) Store sugar/salts/food; create osmotic gradient for osmosis; cause cell turgidity(2mks)

(ii) Rate of photosynthesis would reduce/inadequate food produced.(1mk)

( c ) Cell wall; chloroplast(2mks)

Q6.(a) (i) to show energy is released in anaerobic respiration; to show carbon( IV)  ; oxide is produced in anaerobic respiration. (2mks)

(ii) Increase in temperature since energy is released colour of indicator; changed to yellow due to acidity/carbon. (IV)oxide released changed indicator to yellow. (1mk)

(b) (i) Expel dissolved oxygen; (1mk)

(ii) Prevent entry of air/oxygen into glucose solution.(1mk)

( c) use glucose solution without yeast/used killed yeast cells.(1mk)

(d) Ethanol production in breweries, breads production in bakeries.(1mk)








(i) Labeling axis (2mks)

Scale (2mks)

Curve (1mk)

Plotting (1mk)

(ii) 205cm3 oxygen /ghr  -1            – +   5 evidence from gragh (2mkS)

(b) (i)     RAT                   food eaten                         X           100%    0.098                          X100 =98% (2mks)

Body weight                                           0.1





(ii)Elephant     40  X 100     =5% (2mks)



(C)Rat  eat more food per  unit body  weight  than  elephant; Rat has  larger  surface  area to volume ratio; therefore tend t0 lose more heat per unit body weight; oxidize more food/faster to maintain body temperature(4mks)

(d) Elephant: least  surface  area to  volume  ratio; lose  water very  slowly  since  some  tissues  are  far  from  body  surface; metabolic  rate  very  slow; hence little water lost through sweating per unit body weight(2mks)

(e)Reptile poikilothermic/depend on environmental temperature; mammal homiothermic/oxidize food to maintain body temperature (2mks)

8(a) (i)   Transpiration is the process by which plants lose water to the atmosphere in form of water vapour

(ii)Translocation is the process by which soluble products of photosynthesis/simple sugars are transported from leaves ;to other parts of the plants through phloem

(b)Temperature: high temperature increases water evaporation from mesophyll cell; increase capacity of atmosphere to hold more water due to faster movement of molecules/ low temperatures reduces the rate of water evaporation; air capacity to hold more water hence low transpiration rate

Humidity:high humidity lower the saturation deficit /reduce ability of atmosphere to hold more water;hence low transpiration rate/low humidity offering great saturat

ion deficit;hence high rate of transpiration

Light intensity:at low light intensity stomata close; reduce surface area over which water is lost/low transpiration rate/stomata open at high light intensity;surface area hence increases transpiration rate

Wind/air current:fast air movement /strong air current  sweep away saturated air around plant;increasing transpiration rate ;still air/weak  air currents make water accumulate around the plant lowering transpiration rate

Size of  stomata/number of  stomata/leaf  area:large/many  stomata/leaves/large area; increase  transpiration  rate/few  leaves/small/few  stomata  reduce  surface  area; hence  low  transpiration  rate

Atmospheric  pressure: low  atmospheric pressure  increase  water evaporation; hence  high  rate  of  transpiration/high  atmospheric pressure  reduce  water  evaporation; hence  low  rate  of  transpiration [3marks] award only  once in each condition/low or high. {max 16marks}


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