Pupil sheet · Limits on photosynthesis
Limits on photosynthesis — final check
Name ______________________ Date ____________
Work alone, with the lesson closed. Answer every question; there are no hints.
1. describe
Describe how you would investigate the effect of light intensity on the rate of photosynthesis of pondweed. (a) Describe the method. (b) Describe how you would keep (i) the temperature and (ii) the carbon dioxide concentration the same.
(a) Method
(b) Keeping the temperature and the carbon dioxide the same
2. describe / explain
Another plant gives these mean rates: 12 bubbles per minute at 15 °C, 20 at 25 °C, 26 at 35 °C and 9 at 45 °C. (a) Describe the effect of temperature on the rate. (b) Explain the results.
(a) Describe
(b) Explain
3. identify / explain
Supplement. A grower measures the rate of photosynthesis of a sweet pepper plant, in cm³ of oxygen per hour, at four light intensities (in arbitrary units) under four conditions. The table shows the results. Identify the factor limiting the rate in each case. Then explain your choice for condition P at light intensity 8.
| Condition | Light intensity 1 | Light intensity 2 | Light intensity 4 | Light intensity 8 |
|---|---|---|---|---|
| P: 15 °C, ordinary air | 4 | 7.5 | 8 | 8 |
| Q: 15 °C, extra carbon dioxide | 4 | 7.5 | 8 | 8 |
| R: 25 °C, ordinary air | 4 | 8 | 13 | 14 |
| S: 25 °C, extra carbon dioxide | 4 | 8 | 16 | 22 |
Write the number of the matching option.
- light
- temperature
- carbon dioxide
- condition P at light intensity 1: ______
- condition P at light intensity 8: ______
- condition R at light intensity 8: ______
- condition S at light intensity 2: ______
Explain your choice for condition P at light intensity 8.
4. identify / calculate / describe
A pupil dissolves different masses of sodium hydrogencarbonate in 200 cm³ of water around a sprig of pondweed. The lamp stays at one distance, with a heat filter, and the water bath stays at 25 °C. She counts the bubbles in one minute four times at each mass. (a) Identify the anomalous count. (b) Calculate the mean rate at 0.4 g, leaving out the anomalous count. Give your answer to 3 significant figures. (c) Describe the effect of the carbon dioxide concentration on the rate.
| Sodium hydrogencarbonate in 200 cm³ of water (g) | Count 1 | Count 2 | Count 3 | Count 4 |
|---|---|---|---|---|
| 0 | 3 | 4 | 3 | 4 |
| 0.2 | 9 | 8 | 10 | 9 |
| 0.4 | 17 | 19 | 7 | 19 |
| 0.8 | 23 | 24 | 22 | 23 |
| 1.2 | 24 | 23 | 24 | 25 |
(a) Anomalous count: ______________ unit ________
(b) Mean rate at 0.4 g without it: ______________ unit ________
(c) Describe the effect of the carbon dioxide concentration on the rate.
5. predict / explain
A sprig of pondweed is put into a bunged tube of red hydrogencarbonate indicator. The tube stands in bright light for 7 hours, and is then moved into a dark cupboard for the next 12 hours. (a) Predict the colour after the 7 hours in the light, and how the colour changes in the cupboard. (b) Explain each colour change in terms of photosynthesis and respiration.
(a) Colours
(b) Explanation
6. describe
Describe how to investigate the effect of light and dark on gas exchange in pondweed using hydrogencarbonate indicator. Include the control and how you make the comparison fair.
7. explain
A bunged tube of red hydrogencarbonate indicator with a sprig of pondweed is left for a day on a shelf at the back of a dim storeroom. It is still red. A pupil concludes that the pondweed must be dead. Explain why her conclusion may not be valid.
8. identify / explain
A pupil looks at a cross-section of a privet leaf with a microscope. The table describes its four layers of cells, but not in order from top to bottom. Identify each layer, and the three other structures listed. Then explain how layer Z is adapted for photosynthesis.
| Layer | Depth below the upper surface (mm) | Shape of the cells | Chloroplasts in each cell | Gaps between the cells |
|---|---|---|---|---|
| W | 0.16 | rounded, loosely packed | about 15 | large gaps |
| X | 0.01 | flat, in a single row | none | none |
| Y | 0.24 | flat, in a single row | none, except in pairs of bean-shaped cells | small pores, each between a bean-shaped pair |
| Z | 0.07 | tall and narrow, packed side by side | about 50 | almost none |
Write the number of the matching option.
- upper epidermis
- palisade mesophyll
- spongy mesophyll
- lower epidermis
- stoma
- guard cell
- air space
- cuticle
- xylem
- layer W: ______
- layer X: ______
- layer Y: ______
- layer Z: ______
- the small pores in layer Y: ______
- each bean-shaped cell of a pair in layer Y: ______
- the large gaps between the cells of layer W: ______
Explain how layer Z is adapted for photosynthesis.
9. calculate / explain
A pine needle is round in cross-section, about 1.0 mm across, with stomata all round its surface. A broad, thin leaf of a garden plant is about 0.2 mm thick. In each, carbon dioxide diffuses in from the surface to the cells in the very middle. (a) Calculate how many times further carbon dioxide must diffuse to reach the middle of the needle than to reach the middle of the broad leaf. (b) Inside the needle, the mesophyll cells are packed tightly, with very few air spaces. Explain how this would slow photosynthesis in the needle.
(a) How many times further in the needle: ______________ unit ________
(b) Explain how the tightly packed mesophyll, with very few air spaces, would slow photosynthesis in the needle.
10. identify / suggest
A pupil drops a fresh leaf into a beaker of water at about 60 °C. The heat makes the air inside the leaf expand. Many small bubbles of air stream out of the lower surface of the leaf, but only a few come out of the upper surface. (a) Identify the structures that the bubbles come out of. (b) Suggest two reasons why so few bubbles come out of the upper surface. (c) Suggest why having most of these structures in the lower surface helps a leaf in a sunny place.
(a) The structures
(b) Two reasons
(c) Why the lower surface