06) Plant nutrition 1.8, 2.2

Question 1

1.1. Describe photosynthesis

Answer 1

The process by which plants synthesise carbohydrates from raw materials using energy from light

Question 2

1.2. State the word equation for photosynthesis

Answer 2

carbon dioxide + water → glucose + oxygen
in the presence of light and chlorophyll

Question 3

1.3. State what chlorophyll is

Answer 3

A green pigment that found in chloroplasts

Question 4

1.4. What does chlorophyll do?

Answer 4

Transfers energy from light into energy in chemicals, for the synthesis of carbohydrates

Question 5

1.5. Outline the subsequent use and storage of the carbohydrates made in photosynthesis

Answer 5

(a) starch as an energy store
(b) cellulose to build cell walls
(c) glucose used in respiration to provide energy
(d) sucrose for transport in the phloem
(e) nectar to attract insects for pollination

Question 6

1.6. Explain the importance of nitrate ions and magnesium ions

Answer 6

Nitrate ions make amino acids

Magnesium ions make chlorophyll

Question 7

1.7.1. Investigate the need for chlorophyll for photosynthesis

Answer 7

1. Drop a leaf in boiling water to kill the cells and break down the cell membranes
2. Leave it for 5-10 minutes in hot ethanol in a boiling tube to remove chlorophyll so colour changes from iodine can be seen more clearly (be careful as ethanol is extremely flammable, so use a electric water bath to heat it instead of Bunsen Burner)
3. Dip it in boiling water to soften it and spread it out on a white tile and cover it with iodine solution

In a green leaf, the entire leaf will turn blue-black as photosynthesis is occurring in all areas of the leaf

This method can also be used to test whether chlorophyll is needed for photosynthesis by using a variegated leaf (one that is partially green and partially white). The white areas of the leaf contain no chlorophyll and when the leaf is tested only the areas that contain chlorophyll stain blue-black

Question 8

1.7.2. Investigate the need for light for photosynthesis

Answer 8

1. Destarch the plant by placing it in a dark cupboard for 24 hours, so any starch already present will be used up
2. Partially cover a leaf with aluminium foil and place the plant in sunlight for a day
3. Drop a leaf in boiling water to kill the cells and break down the cell membranes
4. Leave it for 5-10 minutes in hot ethanol in a boiling tube to remove chlorophyll so colour changes from iodine can be seen more clearly (be careful as ethanol is extremely flammable, so use a electric water bath to heat it instead of Bunsen Burner)
5. Dip it in boiling water to soften it and spread it out on a white tile and cover it with iodine solution

The covered area remains yellow-brown as it did not receive any sunlight, while the area exposed to sunlight will turn blue-black, proving that light is necessary for photosynthesis

Question 9

1.7.3. Investigate the need for carbon dioxide for photosynthesis

Answer 9

1. Destarch the plant by placing it in a dark cupboard for 24 hours, so any starch already present will be used up
2. Place one plant in a bell jar containing a beaker of sodium hydroxide (absorbs carbon dioxide from surrounding air)
3. Place the other plant in a bell jar containing a beaker of water (control, does not absorb carbon dioxide)
4. Place both plants in bright light for several hours
5. Drop a leaf in boiling water to kill the cells and break down the cell membranes
6. Leave it for 5-10 minutes in hot ethanol in a boiling tube to remove chlorophyll so colour changes from iodine can be seen more clearly (be careful as ethanol is extremely flammable, so use a electric water bath to heat it instead of Bunsen Burner)
7. Dip it in boiling water to soften it and spread it out on a white tile and cover it with iodine solution

The sodium hydroxide plant will remain yellow-brown as it could not photosynthesise due to lack of carbon dioxide, whereas the water plant should turn blue-black as it had all necessary requirements for photosynthesis

Question 10

1.8. Investigate and describe the effects of varying light intensity, carbon dioxide concentration and temperature on the rate of photosynthesis

Question 11

1.9. Investigate and describe the effect of light and dark conditions on gas exchange in an aquatic plant using hydrogen carbonate indicator solution

Answer 11

Plant are always respiring so cells take in oxygen and releasing carbon dioxide as a result of aerobic respiration

During daylight hours, they need to take in carbon dioxide and release the oxygen made in photosynthesis

At night, plants do not photosynthesise but continue to respire, so they take in oxygen and give out carbon dioxide

During the day, especially when the sun is bright, plants photosynthesise at a faster rate than they respire, so there is a net intake of carbon dioxide and a net output of oxygen

Carbon dioxide is an acidic gas when dissolved in water, so we can use hydrogencarbonate indicator to see the concentration (highest to lowest: yellow to purple, red is atmospheric level. Yellow means respiration > photosynthesis, and vice versa)

Several leaves from the same plant are placed in stoppered boiling tubes containing some hydrogencarbonate indicator, and the effect of light can be investigated over a few hours

Question 12

1.10. State the balanced chemical equation for photosynthesis

Answer 12

6CO2 + 6H2O → C6H12O6 + 6O2

Question 13

1.11. Identify and explain the limiting factors of photosynthesis in different environmental conditions

Question 14

2.1. State the adaptations of leaves for photosynthesis and their effects

Answer 14

Large surface area:

Thin:

Question 15

2.2. Identify in diagrams and images the following structures in the leaf of a dicotyledonous plant: chloroplasts, cuticle, guard cells and stomata, upper and lower epidermis, palisade mesophyll, spongy mesophyll, air spaces, vascular bundles, xylem and phloem

Question 16

2.3. Explain how the following structures adapt leaves for photosynthesis: chloroplasts, cuticle, guard cells and stomata, upper and lower epidermis, palisade mesophyll, spongy mesophyll, air spaces, vascular bundles, xylem and phloem