7. Industrial wastes may contain metallic pollutants. State how such pollutants may indirectly reach and accumulate in the human body if the wastes were dumped into rivers.

8. State three measures that can betaken to control infectionof man by protozoanparasites ( 3 marks)

9. The chart belowshows a feeding relationship in a certain ecosystem

Green plants Hawks

(a) Construct two food chains endingwith a tertiary consumer in each case (2 marks)

(b) Which organisms has the largest variety of predatorsin the food web?(1 mark)

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

(d) Suggest three ways in which the ecosystem would be affectedif there was prolonged drought ( 3 marks)

10. 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 thepopulationsizeof the crabsin the lagoon using the formula below

N = n x M

M

Where

N= Total population of crabs in the lagoon

n= Total number of crabs in the second catch

M= Number marked crabs during the first catch

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

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

(b) What is the name given to this method of estimating the population size?

( 1 mark)

11. The figure below represents a feeding relationship in an ecosystem

Termites

Gazelles Leopards

(a) Write down the food chains in which the guinea fowlsare secondary consumers

( 1 mark)

(b) What would be the short term effects on the eco- system of lions invaded the area? ( 3 marks)

(c) Name the organisms through which energy from the sun enters the food web.

( 1 mark)