Observation

Many candidates attempted this question and performance was average. A few candidates could state some biological activities that would happen to the dead dog; the effects of the biological activities on the dead dog on the environment and name a few products that would be released into the environment. Many could not mention hydrogen sulphide gas and heat as some products released into the environment.

Some candidates named micro decomposers as macro decomposers and vice versa.

The expected answers are:

(a) (i) Biological activities that would happen to the dead dog

- The dead dog would swell up/bloat/there would be accumulation of gases;

- decomposers start to break it down;

- it would give off offensive smell;

- decaying/decomposition starts;

- scavengers/maggot/houseflies will visit the dead dog for food/feed on the dead dog.

(ii) Effects of the biological activities on the environment

- Emission of bad odour from decomposing animal/air pollution;

- Spread of pathogens/germs by houseflies/maggot/wind/air;

- Addition of organic nutrients to the soil/improve soil fertility;

- Increase in the population of houseflies/flies/flea and maggots/pupae;

(iii) Products that would be released into the environment

- Hydrogen sulphide gas;

- Urea; ammonia; nitrate; nitrite;

- Heat;

- Carbon (IV) oxide.

(iv) Best way to save the environment from the effect of the biological activities

Deep burying.

(v) Reason for deep burying

To eliminate bad odour/pathogens/maggot without polluting the environment further.

(b) (i) Micro decomposers

- Fungi/Rhizopus/Mucor/yeast

- Bacteria.

Note: Spellings must be correct to score.

(ii) Macro decomposers

- Mushroom/toadstools

- Earthworm;

- Termite/insects;

- Maggot;

- Millipede;

- Snails/slog.

Note: Spellings must be correct to score.

(c) Characteristics of decomposers

- They secrete digestive enzymes directly onto organic matter/ carryout extracellular digestion;

- They breakdown large organic matter into smaller pieces/ cause decay;

- They are heterotrophic.


(d) Importance of decomposers in the ecosystem

- They release the chemicals stored in the dead organisms back to the ecosystem/nutrient recycling;

- They are a source of vitamins;

- They increase soil fertility;

- They clean up the environment;

- They maintain a link between the consumers to the producers;

- Sources of antibiotics/drugs;

- Sources of food e.g. edible mushroom;

- Used in fermentation processes e.g. Yeast in baking/bread/brewery industries.