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BIOLOGY FORM 3 TERM 1

  1. Two herbivorous mammalian species were introduced into an ecosystem at the same time and in equal numbers. The graph below represents their population growth during the first seven years. Study the graph and answer the questions that follow  
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a) Which species is better adapted to the ecosystem?              

          Give a reason.                                             ( 2 mks)

     b) Account for the shape of the curve for species A between

     i)   1 ½ years and 3 ½ years.

    ii) 3 ½ years and 7 years                                     ( 2 mks)

c)  A natural predator for species was introduced into the ecosystem, with a

reason, state how the population of each species would be affected  ( 4 mks)

  • Give a reason why two species in an ecosystem can not occupy the same niche                                                                                          ( 2 mks)
  • The diagram below shows a feeding relationship in a certain ecosystem
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  • Construct two food chains ending with a tertiary consumer in each case.  

                                                                                                       ( 2 mks)

  • ………………………………………………………………………
  • ………………………………………………………………………
  • Which organism has the largest variety of predators in the food web.  ( 1 mk)

…………………………………………………………………………………….

( c) Name secondary consumers in the food web                                          ( 2mks)

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(d) Suggest three ways in which the ecosystem would be affected if there was a prolonged drought.                                                                                    ( 3 mks)

  • ………………………………………………………………………………..
  • ………………………………………………………………………………..
  • ………………………………………………………………………………..

3. State three characteristics that ensure cross-pollination takes place in flowering

plants.                                           ( 3 mks)

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

4. To estimate the population size of crabs in a certain lagoon, traps were laid at   random 400 crabs were caught, marked and released back into the lagoon. Four days later, traps were laid again and 374 crabs were caught. Out of the 374 crabs, 80 were found to have been marked.

(a) Calculate the population size of the crabs in the lagoon using the formula below

                                 n x M

                             N =    m

      Where N = Total population of crabs in the lagoon

                   n = Total number of crabs in the second catch

                  M = Number of marked crabs during the first catch

                  M = Number of marked crabs in the second catch                                                                                                                                ( 2 mks)

……………………………………………………………………………………………………………………………………………………………………………………

  (b) State two assumptions that were made during the investigation       ( 2 mks)

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

  ( c) What is the name given to this method of estimating the population size ( 2 mk)

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5. Explain why sexual reproduction is important in organisms              ( 3 mks)

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

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6. The diagram below represents a mammalian nephron.

  • Name the:

(i) Structure labelled    P                                             ( 2 mks)

………………………………………………………………………………………

   (ii) Portion of the nephron between point  X and  Y.                (2 mks)

……………………………………………………………………………………….

  • Name the process that takes place at point  Q.            ( 2 mks)

……………………………………………………………………………………….

( c) Name one substance present at point R but absent at point S in a healthy mammal.                                                                                                 ( 1 mk)

……………………………………………………………………………………….

( c ) The appearance of the substance you have named in ( c) above is a symptom of a certain disease caused by a hormone deficiency. Name the:

(i) disease                                                                                                 ( 1 mk)

………………………………………………………………………………………….

(ii)hormone                                                                                             ( 1 mk)

………………………………………………………………………………………….

7. Besides the abdomen, name the other body part of members of Arachnida    ( 1 mk)

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8. (a) Name the bacteria found in the root nodules of leguminous plants          ( 1 mk)

…………………………………………………………………………………………

     (b)State the association of the bacteria named in (a) above with the leguminous

plants

………………………………………………………………………………………….

9. In what form is oxygen transported from the lungs to the tissue?        ( 1 mk)

………………………………………………………………………………………….

10. Explain why the carrying capacity for wild animals is higher than for cattle in a given piece of land.                                                                                  ( 2 mks)

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11. The chart below shows the number of chromosomes before and after cell division and fertilization in a mammal.

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 (a)What type of cell division takes place at  Z?                                ( 1 mk)

…………………………………………………………………………………..

  (b) Where in the body of a female does process Z occur?             ( 1 mk)

………………………………………………………………………………………

( c) on the chart, indicate the position of parents and gametes.           ( 1 mk)

…………………………………………………………………………………….

12. A student placed a drop of pond water in a cavity slide and observed it under the microscope. The student observed many fast moving organisms, one of which is represented in the diagram below.

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  (a) (i) Name the phylum to which the organism belongs                ( 1 mk)

………………………………………………………………………………………….

    (ii) Give a reason for your answer in (a) (i) above                        ( 1 mk)

………………………………………………………………………………………….

  (b) Name the structure labelled N, P and Q                                     ( 3 mks)

N ……………………………………………………………………

P …………………………………………………………………….

Q ……………………………………………………………………

(c ) State two observable features that enable the organism to move fast.    ( 2 mks)

13. Ascaris  lumbricoides is an example of an endo-parasite

     (a) the name Ascaris refers to                                                                 ( 1 mk)

…………………………………………………………………………………………

     (b) State the habitat of the organism                                                     ( 1 mk)

………………………………………………………………………………………….

( c) State two ways in which the organism is adapted to living in its habitat. 

                                                                                                                    ( 3 mks)

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14. (a) What is meant by:        

          (i) Autecology                                                                             ( 1 mk)

…………………………………………………………………………………………

  (ii) Synecology                                                                                  ( 1 mk)

………………………………………………………………………………………….

(b) The number and distribution of stomata on three different leaves are shown in the table below.

                 Leaf                  Number of stomata   Upper epidermis            Lower epidermis
            A             B             C           300                                0           150                              200             02                                13

Suggest the possible habitat of the plants from which the leaves were obtained.

                                                                                             ( 3 mks)

Leaf                                                              Habitat

A      ……………………………………………………………………………

B      …………………………………………………………………………….

C      …………………………………………………………………………….

( c) State the modifications found in the stomata of leaf  C.      ( 3 ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

SECTION  B

15. The data below represents the increase in the number of yeast cells over a period of 50 minutes.

Time(mins) 0                  10            20            30            40              50
Number of cells 2                  3               50            124          139             140
  1. Draw a graph of time against number of cells    5 marks

   (a) Name the type of curve drawn                                                         ( 1 mk)

  (b) Determine the number of yeast cells after 26 minutes                       ( 1 mk)

………………………………………………………………………………………….            

 ( c ) Work out the rate of cell division between 24 and 28 minutes           ( 2 mks)

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(d) After how long was the population of yeast cells 128?                         ( 1 mk)

………………………………………………………………………………………….

 (f)  Give reasons for the shape of the graph AT LAG PHASE        ( 3 mks)

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

(h) Describe how the quadrant method can be used to estimate the population of various species of plants in a given habitat.                                          ( 5 ms)

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SECTION B

Answer any one question in this section

  16. A. Describe how insect pollinated flowers are adapted to pollination      ( 12 mks)

         B. Compare and contrast the processes of meiosis and mitosis    8 marks

17. A. Describe the adaptations of the skin to its functions      (14 marks)

      B. describe the photosynthetic theory of opening and closing of the stomata

          (6 marks)