AQA Biology 4.7.3.4 · Combined and Triple

Deforestation

Why tropical forest is cleared, two separate reasons the carbon dioxide rises, what else is lost, and whether it is worth it.

Combined Science · Higher tier

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Forest to ranch.

A patch of tropical forest is cut down and burned to make a cattle ranch.

If you had to guess, would the air end up with more carbon dioxide, or less?

Why forests are cleared

Three reasons.

Large-scale deforestation in tropical areas has occurred to provide land for cattle and rice fields, and to grow crops for biofuels. Tap each.

The carbon dioxide

Carbon in, carbon out.

Trees take carbon dioxide in by photosynthesis. Burning felled trees releases it. Microorganisms that decay the leftover wood respire, releasing it too. Fell the patch and watch the arrows change.

Standing: the trees take carbon dioxide in by photosynthesis and lock the carbon up as wood.

Give the two separate reasons atmospheric carbon dioxide rises after deforestation. Select both, then check.

Select both reasons, then check.

Why does the decay of felled wood release carbon dioxide?

Pick one.

The forest was also the habitat of many species. When it goes, they go: biodiversity falls. Biodiversity and Maintaining biodiversity take that further.

Evaluate

Worth it?

You should be able to evaluate the environmental implications of deforestation. Put the gains on one side and the costs on the other, then judge. Tap each.

Information · made-up data for practice

A country plans to clear 2000 km² of forest for a biofuel crop. The biofuel would replace 1% of the country’s petrol. The forest holds about 800 species of tree and is home to a monkey found nowhere else.

Which judgement weighs both sides?

Pick one.

Think again · rot or burn?

“Rotting wood doesn’t give off carbon dioxide, only burning does.”

Your call

Choose

Felled trees are left to rot. What happens to the carbon in the wood?

Sort

Reason or consequence?

Place each one.

Tap a card, then tap the box it belongs in. Tap a placed card to take it back.

Command words in this lesson

Describe: Why tropical forest is cleared.
Explain: The two reasons carbon dioxide rises, and the loss of biodiversity.
Evaluate: The implications of deforestation: a benefit, a cost and a judgement.

Key fact

Forest is cleared for cattle, rice fields and biofuel crops. Carbon dioxide rises for two reasons: less is taken in by photosynthesis, and more is released by burning and by microorganisms decaying the wood. Habitats are lost, so biodiversity falls.

Key note · AQA 4.7.3.4

Deforestation

Large-scale deforestation in tropical areas has occurred to provide land for cattle and rice fields, and to grow crops for biofuels.
Carbon dioxide rises for two separate reasons: less is taken in because fewer trees photosynthesise, and more is released by burning and by microorganisms decaying the wood (they respire).
Habitats are destroyed, so biodiversity is reduced.
Evaluate: a gain (food, fuel), the two costs (carbon dioxide, biodiversity), then a judgement using the information given.

Photograph this card. Tomorrow, cover it and say each line first.

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Giving only one reason for the carbon dioxide rise?

The biofuel plan and its figures are made up for practice.