This document contains answers to objective, structured, and essay questions. For the objective questions, the answers provided are letters A through D. The structured questions address topics like population calculations, causes of water pollution, and reasons for declining fish populations. The essay questions discuss pioneer species adaptations and factors affecting dissolved oxygen levels in lakes.

1. Answers
Objective Questions
1A
2C
3D
4C
5A
6C
Il)
8C
9B
10A
11 D
t2B
13A
74D
15A
16B
t7A
18D
19D
20D
Structurcd Question
(a) Population : Number caught and marked x Number recantured
|{umber marked at the second capture
(b) (i) Yes
(ii) Number of pests s decreases 3 w-eeks after predator T is introduced
(c) (i) Deteriorates
(ii) Because its food, which is pest S has decreased
(d) 1 Predator T is specific for pest S, that is predator T does not damage vegetables 2 The population of predator T can be controlled naturally
(e) I Is not removed easily 2 Does not attract the attention of the predator
(f) Chemical substances such as insecticide
Essay Question (a) The first organism to colonise a barren area is usually plants.
(b) 4 adaptation characteristics ofapioneer is: I Fibrous root system to absorb a lot of water quickly 2 Succulent leaves to store water
3 Produce a lot of small and light seedlings so that they can be dispersed by the
wind
4 Creeping stems so that an a.rea can be colonised quickly

2. Answers
Objective Questions 1D
2C
J2]nJ
4A
5B
IftDD
7B
8B
9A
10c
11 B
t2D
13D
t4c
lsc
Structured Question
(a) 20km
(b) (t) Poiiution of the river water reduces the number of fish, decreases the concentration
of dissolved oxygen in the water and increase the number of bacteria. (ii) Domestic waste disposal / rvaste materials
(c) 1 Lorv rate of fish reproduction
2 Lack offish food because ofdependence on producer
Essay Question (a) The quantity of oxygen that is requrred by the microorganisms to deeompose the
organic substances in the water.
(b) . Wastes/domestrc uaste matenal e DecomposeC b,v decomposing bactena o Increase the usage oforygen
r Flou, of hot u'ater from the factones increase the lvater temperature o Decrease the solubility of orygen in ihe rvater o Florv of organic fertilisers from agricultural areas o Encourages algae growth. which prevents light from reactung the bottom of the lake o Decrease the rate of photos.r,nthesis and decrease the rate of oxygen release o Aquatic animals die as a result of a lack of ox-_vgen o DecomFosition of dead animals (and plants) increases B.O D. o The effect of B.O.D. increase is the death/migration of aquatic animals
(c) 1 Replace cFC with easily biodegradable substances such as HCFC
- reduce the thinning of the ozone la.v-er 2 Process the faciory/domestic rvaste products/filtered cilmneys
- reduces water pollution that is caused by the decomposition of organic substances 3 Prepare a special disposal area for radioactive substances I metal
- reduce environmental poliution that is caused b,-v raciioactive rays 4 Recycle substances such as glass/plastic lp ap er I aluminium
- maintain natural resources
5 Use electric/soiar powered vehicles to reduce air poiiution that is caused by
hydroearbon gases
6 Bum garbage in incinerators to reduce soil and air pollution. 7 change oil paim remains into biogas to maintain naturar resources
B Use biotechnology methods to clean up oil spills in order to control water pollution 9 Design houses that save energy
- reduce the usage of substances tbr air-conditioners
i0 Cloud seeding to reduce haze resulting from forest bumrng