Year 8 Science · Unit 1 · Lesson 21
Foundation Worksheet
Learning Goals
Fill the gap
Choose the correct word from the word bank. Two words will not be used.
Plants take in from the air and use it to build sugars during . Animals release carbon dioxide back into the air when they breathe out, a process called . When plants and animals die, such as fungi and bacteria break them down and release into the soil, where plants can take them up again.
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
1. Fungi and bacteria are both decomposers.
Correct it:
2. When a gum tree dies and rots, the matter it was made of disappears.
Correct it:
3. Plants lose water vapour through their leaves by transpiration.
Correct it:
4. The ash left after a bushfire contains nutrients such as potassium and calcium.
Correct it:
Put the carbon atom’s journey in order
Follow one carbon atom through a patch of bush. Number the stages from 1 (first) to 4 (last).
| Stage (1–4) | Where the carbon atom is and what moves it |
|---|---|
| The koala dies, and decomposers in the soil break down its body. | |
| A koala eats the leaf, and the carbon becomes part of the koala. | |
| The carbon is back in the soil and the air, ready to be used again. | |
| A eucalypt takes in carbon dioxide and builds it into a leaf by photosynthesis. |
1. The koala also breathes out some of the carbon while it is alive. Name this process, and say what form the carbon is in when it leaves the koala.
2. The eucalypt got its energy from sunlight, but the koala cannot pass that energy back to the Sun. Use this example to explain how energy moves through an ecosystem differently from matter.
Read the data
Scenario: the school compost heap
A Year 8 class built a compost heap from lawn clippings, leaves and fruit scraps. Every second day they pushed a thermometer into the centre of the heap and also measured the air temperature beside it.
| Day | Centre of heap (°C) | Air beside heap (°C) | Difference (°C) |
|---|---|---|---|
| 0 | 21 | 20 | 1 |
| 2 | 36 | 22 | 14 |
| 4 | 49 | 19 | 30 |
| 6 | 57 | 21 | |
| 8 | 52 | 20 | 32 |
| 10 | 44 | 22 | 22 |
Source: sample class results.
3. Fill in the empty cell in Table 1. Then state the day when the heap was hottest.
Hottest on day
4. The air stayed at about 20 °C, but the heap got much hotter. Explain where the extra heat came from.
5. After day 6 the heap started to cool, even though the air did not change. Suggest a reason, using the word decomposers.
6. A big eucalypt log falls in the bush and slowly rots over many years. Explain what happens to the matter in the log. Name the decomposers, say what they release, and say where that matter ends up next.
Fill the gap
carbon dioxide; photosynthesis; respiration; decomposers; nutrients. Not used: condensation, predators.
True or false
1. True. 2. False: decomposers break the tree down and its matter goes back into the soil and air, where it is used again. 3. True. 4. True.
Put the carbon atom’s journey in order
Reading down the table as printed: 3, 2, 4, 1. (Photosynthesis in the eucalypt, feeding by the koala, decomposition, back in the soil and air.)
1. Respiration; the carbon leaves as carbon dioxide gas (CO₂). [2 marks: 1 process, 1 form]
2. Energy flows one way: from the Sun into the eucalypt, then the koala, and it is lost as heat, so it cannot go back to the Sun. Matter (the carbon) goes around and around: it returns to the air and soil and is used again by plants. [2 marks: 1 energy one way, 1 matter recycled]
Read the data
3. 57 − 21 = 36 °C. Hottest on day 6. [2 marks]
4. Decomposers (bacteria and fungi) in the heap are breaking down the clippings and scraps, and they release heat as they do it. The heat did not come from the air or the Sun. [2 marks: 1 decomposers, 1 release heat as they break down matter]
5. The decomposers had used up much of the easy-to-break-down material (fruit scraps, fresh clippings), so they were working less and giving off less heat. Accept: the heap is drying out or running short of air, so decomposers slow down. [2 marks: 1 less decomposer activity, 1 sensible reason]
Show What You Know
6. Marking guide: 1 for matter is not lost; 1 for naming fungi and bacteria; 1 for releasing nutrients to the soil and carbon dioxide to the air; 1 for new plants taking up the nutrients (or carbon dioxide) again. Model answer: The matter in the log does not disappear. Fungi and bacteria slowly break the wood down. They release nutrients into the soil and carbon dioxide into the air. New plants take up the nutrients through their roots and the carbon dioxide in photosynthesis, so the log’s matter becomes part of new living things. [4 marks]
Common error to watch for: saying the log “turns into energy” or “is used up”. Matter changes form and place; it is never destroyed.