Year 8 Science · Unit 1 · Lesson 8
Foundation Worksheet
Learning Goals
Fill the gap
Choose the correct word from the word bank. Two words will not be used.
Plants have no , but they still exchange gases with the air. This happens mainly in the . Gases pass in and out through tiny pores called . Each pore is opened and closed by a pair of . In bright light, a healthy leaf overall takes in and gives out .
Put the carbon dioxide path in order
Number the steps 1 (first) to 4 (last) for carbon dioxide getting from the air to the cells that use it.
| Step (1–4) | What happens to the carbon dioxide |
|---|---|
| It spreads through the air spaces in the spongy layer. | |
| It is in the air around the leaf. | |
| It is used for photosynthesis inside a palisade cell. | |
| It passes through an open stoma on the lower surface. |
Sort it: day and night
Write each statement about a leaf in the correct box. “Overall” means the gas that wins out once photosynthesis and respiration are added together. For this task, assume a healthy leaf in bright daylight, with open stomata and photosynthesis faster than respiration. Day only gets three statements; the other two boxes get two each.
Day only (light)
Night only (dark)
Day and night
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
1. Plants cannot exchange gases, because they do not have lungs.
Correct it:
2. In most leaves, the stomata are mainly on the lower surface.
Correct it:
3. Plant cells respire only at night, when there is no light for photosynthesis.
Correct it:
4. When the guard cells are full of water (turgid), the stoma between them is open.
Correct it:
5. Closing its stomata cuts down the water vapour a leaf loses.
Correct it:
Read the data
Scenario: four thirsty bean plants
Four bean plants grew in the same sunny spot but were watered different amounts. After two weeks, at 11 am, the class looked at 40 stomata on the lower surface of one leaf from each plant and counted the open ones.
| Plant | Watering over two weeks | Open stomata (out of 40) |
|---|---|---|
| A | every day | 33 |
| B | every third day | 24 |
| C | once a week | 11 |
| D | not watered | 2 |
Source: sample class results.
1. Which plant had the most open stomata? How many of its 40 stomata were closed?
2. Use the words guard cells and water to explain why Plant D had so few open stomata.
3. Plant D is in bright sunlight, but almost all its stomata are closed. Which gas will its leaves be short of, and which leaf process will slow down as a result?
4. Sam says: “Plants can’t swap gases with the air. They don’t have lungs, so they don’t breathe.” Explain why Sam is wrong: where and how does a plant exchange gases, and which gases move in and out overall in bright daylight?
Fill the gap
lungs; leaves; stomata; guard cells; carbon dioxide; oxygen. Not used: roots, xylem.
Put the carbon dioxide path in order
Reading down the table as printed: 3, 1, 4, 2. (Air around the leaf, through an open stoma, through the spongy air spaces, used in photosynthesis in a palisade cell.)
Sort it: day and night
Day only: photosynthesis happens; overall, the leaf takes in carbon dioxide; overall, the leaf gives out oxygen. Night only: overall, the leaf takes in oxygen; overall, the leaf gives out carbon dioxide. Day and night: respiration happens in the leaf cells; cells use glucose to release energy.
True or false
1. False: plants do exchange gases, through the surfaces and stomata of their leaves; lungs are not needed. 2. True. 3. False: plant cells respire all the time, day and night; only photosynthesis stops in the dark. 4. True. 5. True.
Read the data
1. Plant A (33 open), so 40 − 33 = 7 were closed. [2 marks: 1 plant, 1 number]
2. Plant D was short of water, so its guard cells lost water and went floppy (flaccid). Floppy guard cells close the stoma between them. [2 marks: 1 guard cells lose water, 1 stoma closes]
3. Carbon dioxide cannot get in, so photosynthesis slows down (the leaf makes less glucose and gives out less oxygen). [2 marks: 1 carbon dioxide, 1 photosynthesis]
Show What You Know
4. Marking guide: 1 gas exchange defined, no lungs needed; 1 leaf as main site; 1 stomata as pores opened and closed by guard cells; 1 carbon dioxide in, oxygen out overall in bright daylight; 1 evidence (oxygen bubbles from pond weed in sunlight). Model answer: Sam mixes up lungs with gas exchange, which is gases moving between a living thing and its surroundings. In a plant it happens mainly in the leaves, through tiny pores called stomata that guard cells open and close. In bright daylight the leaf overall takes in carbon dioxide and gives out oxygen; pond weed in sunlight gives off bubbles of oxygen. [5 marks]
Common error to watch for: saying plants never use oxygen. Plant cells respire all the time; carbon dioxide in and oxygen out is the overall result when photosynthesis is faster than respiration. Dim light does not guarantee this net direction.