From rainforest to pasture
311 words over 29 numbered lines, then 6 parts worth 13 marks (Modular Unit 2 (4WBI2) style, 12–13 marks). Read the article, answer each part, then open its mark scheme and set your mark.
Illustrative article written for Scholar Lab, not a Pearson text. The biology is real; the studies, people and figures are invented or rounded for practice unless a source is named.
From rainforest to pasture
In parts of South America, large areas of tropical rainforest have
been cut down and burned to make space for cattle. The land is planted
with grass, and the beef is sold in cities and to other countries.
Soya beans grown to feed farm animals are another reason for clearing
forest. Close to a fifth of the Amazon rainforest has been lost since
1970.
A tropical rainforest stores a large mass of carbon in its trees.
Every day, the leaves take in carbon dioxide from the air for
photosynthesis. When the forest is burned, the carbon in the wood
returns to the air as carbon dioxide. Cattle also release methane,
another greenhouse gas.
The trees play an important part in the water cycle. Their roots take
up water from the soil, and huge amounts of water vapour leave the
leaves by transpiration. This water vapour forms clouds, and much of
it falls again as rain further across the forest. When the trees are
removed, less water vapour enters the air and the region may become
drier.
Soil in a rainforest is often thin and poor in minerals, because most
of the minerals are held in living plants. Once the trees are gone,
heavy rain washes the soil away. Rain also leaches the remaining
mineral ions deep into the ground, beyond the reach of grass roots.
After a few years many pastures produce little grass and are
abandoned, and more forest is cleared to replace them.
Scientists compared a hectare of undisturbed rainforest with a hectare
of nearby cattle pasture. Both sites were on the same type of soil and
received the same rainfall. Their measurements are shown in Figure 1.
Some countries now use satellites to spot new clearings quickly, and
some shops refuse to sell beef from recently cleared land. Others pay
farmers to plant trees again on abandoned pasture.
Figure 1 Measurements from one hectare of rainforest and one hectare of cattle pasture
| Measurement | Rainforest | Cattle pasture |
|---|---|---|
| Carbon stored in plants / tonnes per hectare | 160 | 8 |
| Water released by transpiration / mm per year | 1,200 | 600 |
| Soil lost each year / tonnes per hectare | 0.5 | 15 |
Read the article and study the figure. Use the information in the article and your own knowledge to answer the questions. The lines in brackets show where to look; select them to highlight the text.
Use the information in the article and your own knowledge to answer the questions. The lines in brackets show you where to look; select them to highlight the text.
State what is meant by the term deforestation.
(1)A farmer clears 250 hectares of rainforest to make cattle pasture. Use Figure 1 to calculate the decrease in the mass of carbon stored in plants on this land.
(2)Explain how clearing and burning a rainforest increases the concentration of carbon dioxide in the air.
(3)Explain how deforestation can make a region drier.
(2)Explain why many cattle pastures produce little grass after a few years.
(2)Suggest why scientists are concerned that clearing rainforest for cattle could increase global warming.
(3)Total for this question: 13 marks
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