3. A biologist carried out a study to investigate the growth of a certain speciesof herbivorous bony fish and the factors influencing plantand animal lifein four lakes A, B, C and D. The lakes were located in the same geographical area.

Two of the lakes A and B were found to contain hard water due to presence of high content of calcium slats. The mean body length of 2 year old fish, amount of plant life and invertebrates biomass in each lake were determines. The data was as shown in

Lakes Mean body length (cm) Type of water Amount of plant life Invertebrate biomass (g/cm3)

Insects Snails Crabs Worms

A

B

C

D 31.2

28.6

18.4

16.3 Hard

Hard

Soft

Soft 1050

950

1.2

0.5 11

72

97

99 300

100

0

0 10

9

2

1 180

90

20

10

(a) Describe the procedure that may have been used to determine the mean body length of the fish ( 6 marks)

(b) What are the likely reasons for the difference in the mean body length of the fish living in lakes A and D? ( 4 marks)

(c) Suggest one reason for the absence of snails in lakes C and D?

( 1 mark)

(d) (i) Name any six abiotic (physical) factors that are likely to influence

the plant and animal life in lake A. ( 3 marks)

(ii) Explain how each of the factors named in (i) may influence the plant and animals life in Lake A. ( 6 marks)

4. During an ecological study of a lake a group of students recorded the following observations.

(i) Planktonic crustaceans feed onplanktonic algae

(ii) Small fish feedonplanktonic crustaceans worms and insectlarvae

(iii) Worms feed on insect larvae

(iv) Bird species feeds on small fish planktonic crustaceans and worms

(v) Insect larvae feed on small fish

(a) From this record of observations construct a feed web (5 marks)

(b) From the food web you have constructed in (a) above isolate and write down a food chain that ends with

(i) Bird species as a secondary consumer (1 mark)

(ii) Large fish as tertiary consumer (1 mark)

(c) The biomass of the producers in the lake was found to be greater than that of primary consumers. Give an explanation for this observation? (1 mark)

(d) Using either the observations recorded by the students or the food web you have constructed name (1 mark)

(i) Two organisms that compete for food in the lake. (2 marks)

(ii) The source of food the organisms in d (i) above compete for ( 1 mark)

(e) (i) State three ways by which many may interfere with this lake

ecosystem ( 3 marks)

(ii) Explain how each of the ways you have states may affect life in the

lake? ( 6 marks)

5. In an investigation, a student collected two plants A and B. Plant A had hairy leaves and epidermis. Leaves of plant B

(i) Plant A ( 1 mark)

(ii) Plant B ( 1 mark)

6. An investigation was carried out between 1964 and 1973 to study the changes of fish population in a certain small lake. Four species of fish A, B, C and D were found to live in this lake. In 1965 a factory was built near the lake and was found to discharge hot water into the lake raising the average temperature from 250C to 300C. In 1967 sewage and industrial waste from a nearby town was diverted into the lake was stopped. The fish population during the period of investigation is shown in the table below.

Fish species Fish populations during the period

1964 1966 1969 1970 1971 1972 1973

A

B

C

D 6102

208

36

4521 223

30

100

272 26

11

0

23 106

22

0

27 660

63

0

79 4071

311

0

400 7512

405

0

617

(a) (i) In which year were the fish populations lowest?

(ii) State the factors that might have caused the lowest fish populations during the year you have stated in (a) (i) above ( 3 marks)

(iii) Explain how each factor you have stated in (a) (ii) above could have brought about the changes in fish populations (11 marks)

(b) (i) What is the difference in the rate of population recovery of species A and

D? (1 mark)

(ii) Suggest two biological factors that could have led to this difference

(2 marks)

(c) (i) State a method that might have been used to estimate the fishpopulation

in thelake ( 1 mark)

(ii) State one disadvantage of the method you have stated in (c) (i) above

( 1 mark)