B8: Photosynthesis

Question 1

What is the method for testing starch formed after photosynthesis?

Answer 1

1.Pour 150 cm3 of boiling water into a beaker.
2.Place the leaf to be tested in the water for 2 minutes. This kills the leaf, stopping further photosynthesis
3.Remove the leaf from the water and place it in a boiling tube.
4.Add enough ethanol to the boiling tube to cover the leaf.
5.Place the boiling tube into the beaker with new hot water for 10–15 minutes. The ethanol should boil and remove the chlorophyll from the leaf.
6.Remove the leaf from the ethanol.
7.Dip the leaf into the hot water using forceps. This is to soften it.
8.Spread the leaf out on a white tile.
9.Cover the leaf with iodine solution
10.Areas of the leaf that turn black contain starch, while areas of the leaf that stay brown do not contain starch

Question 2

Why is the leaf boiled in water?

Answer 2

Kill the leaf, photosynthesis stops

Question 3

Why is the leaf boiled in ethanol?

Answer 3

To remove chlorophyll (ethanol breaks down/ disrupts membranes)

Question 4

Explain why you can’t simply add iodine to an untreated leaf to test for starch

Answer 4

• The chlorophyll wouldn’t be removed so would make it difficult to observe the iodine test
  • iodine would not be able to diffuse into the cells

Question 5

What is the word equation for phtoosynthesis?

Answer 5

Water + carbon dioxide > Glucose + Oxygen

Question 6

What is the formula for photosynthesis?

Answer 6

6CO2 + 6H2O > C6H12O6 + 6O2

Question 7

What are the two stages of photosynthesis?

Answer 7

Stage 1 - water is split into oxygen and hydrogen ions (using light energy)
Stage 2 - hydrogen ions and carbon dioxide combined to form glucose (and water which
gets used up)

Question 8

How does carbon dioxide reach the cells which are photosynthesising?

Answer 8

The stomata open during times of high water concentration. This allows for the diffusion of carbon dioxide into the leaf. Carbon dioxide them doffuses through the spongy mesophyll layer to the palisade cells.

Question 9

How does water reach the cells which are photosynthesising?

Answer 9

Water is absorbed through osmosis through root hair cells and transported upwards towards the leaves through the transpiration stream within the xylem vessel.

Question 10

How does the plant use glucose?

Answer 10

• Plants build up glucose into cellulose to strengthen cell walls
• plants convert some of the glucose into starch to be stored- insoluble in water and thus has no effect on water balance of plants
• Starch stored in cells of leaves, providing energy store when it’s dark or light intensity is low
• Starch also kept in special storage areas of a plant
• Plants use some of the glucose to make amino acids by combining with nitrate ions. These amino acids are then built up onto proteins to be used in the plants (eg: enzymes)
• Plants use some of the glucose and energy transferred from respiration to build up fats and oil- may be used as energy stores, sometimes used in cell walls for strength
• Plants often use fats/oils as energy store in seeds, providing food to respire as it germinates