Lesson: Chapter 15 — The biosphere

Putting the chapter together 2 of 3

The exercise

Worked answers to the chapter's exercise.

Question 1 — multiple choice

	Question	Answer	Why
(i)	The level of organisation that includes the non-living environment	iv — the ecosystem	Individuals, populations and communities count only living things.
(ii)	What a description of a population must include	iv — the species, the time period and the area	A population is one species in a definite area at a definite time.
(iii)	The gas that is not a main cause of acid rain	ii — carbon dioxide	CO2 only makes normal rain slightly acidic (pH 5.6); SO2, SO3 and NO2 cause acid rain.
(iv)	The gas mainly responsible for the greenhouse effect	i — carbon dioxide	It is released in the largest amounts, by burning fossil fuels.
(v)	A bacterium that fixes atmospheric nitrogen as ammonium	i — Rhizobium	Nitrosomonas and Nitrobacter nitrify; Pseudomonas denitrifies.

Question 2

Ecosystems

1. Name two interactions in an ecosystem.
2. Name two communities in a pond ecosystem.
3. Give two things that break the balance of an ecosystem.
4. What is the main way carbon is fixed in an ecosystem?
5. Plants grow lushly and naturally in the Sinharaja forest, but not on a farm. Give reasons.

The answer

1. Feeding (a frog eating an insect); plants taking in carbon dioxide and giving out oxygen; competition for light or food.
2. The fish community and the water-plant community (also insects, frogs, algae).
3. Pollution (agrochemicals, waste); clearing forests; a growing human population.
4. Photosynthesis.
5. In the forest, fallen leaves and dead matter are decomposed and their nutrients return to the soil; the many species form a stable web; nothing is taken away. On a farm, the harvest removes nutrients, a single crop invites pests, and repeated cultivation and agrochemicals degrade the soil.

Question 3

Sustainable development

1. Name two sustainable agricultural practices.
2. Name two fields in which traditional knowledge and technology can be used.
3. What is meant by food miles?
4. Give two steps to shorten food miles.

The answer

1. Mixed cropping, biological pest control, organic fertiliser (any two).
2. Agriculture (local seeds, traditional methods), irrigation (the tank), food and indigenous medicine (any two).
3. The distance a unit mass of a food travels from where it is produced to where it is eaten.
4. Buy locally grown food; grow vegetables and fruit at home; eat food in season rather than imported food.