problem 1) List three human activities which could cause the loss of a species.

problem 2) Distinguish between the terms 'pesticide', 'insecticide' and 'herbicide.

problem 3)(a) What is the special property of a 'persistent' insecticide?

(b) In what ways is 'persistence’ (i) a useful property, (ii) a harmful property?

problem 4) Put the following events in the most probable order.

(a) Predatory birds poisoned by insecticide.
(b) Trees sprayed with insecticide.
(c) Earthworms eat leaves which fall from trees.
(d) Predatory birds eat small birds.
(e) Beetles damage trees by spreading a virus.
(f) Insecticide absorbed by tree leaves.
(g) Small birds eat earthworms.

problem 5) Put the following events in the most probable order.

(a) Dead algae decomposed by bacteria.       
(b) Bacteria use up oxygen.   
(c) Excess nitrate and phosphate.                  
(d) Aquatic algae die.
(e) discharged into river.                               
(f) Water depleted of oxygen.
(g) Aquatic algae grow rapidly.
(h) Fish die of suffocation.                             

problem 6) What are the principal sources of excessive nitrate and phosphate in rivers and lakes?

problem 7) List the short-term and long-term effects of forest destruction  (a) on hillsides, (b) in the tropics. 

problem 8) In what ways does over-grazing lead to soil erosion?

problem 9) Which of the following are likely to help conserve soil and prevent erosion?

(a) Ploughing slopes.                           (f) Removing trees from hillsides.
(b) Planting trees on steep slopes.       (g) Growing the same crops each year.
(c) Using chemical fertilisers.                (h) Keeping as many animals as possible on grassland.      
(d) Terracing hillsides.                          (e) Using organic manure.

problem 10)(a) What are the two main pollutants that contribute to acid rain?

(b) Where do these pollutants come from?

(c) What direct or indirect effect is 'acid rain' thought to have on

(i) lakes,

(ii) forests and

(iii) buildings?