8.2 The rate of photosynthesis + RP

Question 1

Limiting factors def

Answer 1

a factor which is not at optimum level to enable the maximum level of photosynthesis

Question 2

What are the four limiting factors in photosynthesis

Answer 2

• light
• temperature
• carbon dioxide concentration
• chlorophyll levels in leaf

Question 3

How does light intensity affect the rate of photosynthesis

Answer 3

• the higher the light intensity, the higher the rate of photosynthesis
• light intensity decreases as the distance between the plant and the light source increases

Question 4

How does temperature affect the rate of photosynthesis

Answer 4

• The temperature rises as the rate of photosynthesis increases, speeds up
• Enzymes become denatured as the temperature becomes too high and the rate of photosynthesis falls

Question 5

How does the amount of chlorophyll affect photosynthesis

Answer 5

• Less chlorophyll means less photosynthesis
• Some ornamental plants have white, chlorophyll areas which means they grow less vigrously than plants with all green leaves
• If a plant does not have enough minerals it cannot make chlorophyll, rate of photosynthesis drops and plants may die

Question 6

RP: Light intensity and rate of photosynthesis with pondweed

Answer 6

1. Fill a boiling tube 3/4 of the way with 0.2% sodium hydrogen carbonate solution
2. Freshly cut an 8-10cm piece of pondweed and place it in the boiling tube with the cut end at the top
3. Fill a 400cm cubed beaker with 300 cm cubed of water, ensure it is 20-23 degrees using a thermometer
4. Set up a lamp at a distance of 10cm to the boiling tube and leave to settle for 5 minutes
5. Start the stopwatch and count the number of bubbles released in one minute
6. Repeat twice and calculate the mean number of bubbles
7. Repeat steps 1-5 altering distance of the lamp so its 20, 30 and 40cm away from the boiling tube
8. Repeat whole experiment three times and calculate mean

Question 7

What can you say about the effect of the independent variable (distance between the lamp and pondweed) on the dependent variable (number of bubbles)?

Answer 7

as the distance between the lamp and pondweed increases, the number of bubbles decreases

Question 8

how does the rate of photosynthesis change as the light intensity increases?

Answer 8

it increases because the number of bubbles increases

Question 9

state control variables (other than temperature) in this experiment

Answer 9

• amount of pondweed
• type of pondweed
• brightness of lightbulb

Question 10

explain why variables have to be controlled

Answer 10

to ensure it’s a fair test

Question 11

explain why each experiment was carried out three times

Answer 11

to ensure the results were reliable/repeatable

Question 12

why were any anomalous results discarded

Answer 12

to make the mean time more accurate

Question 13

describe two sources of error in this experiment

Answer 13

error in counting bubbles, bubbles may vary in size

Question 14

suggest two ways in which the pondweed experiment could be improved

Answer 14

• measure the exact volume of oxygen produced using a syringe
• always measure between the same places when finding the distance between the boiling tube and the lamp

Question 15

what is the role of chlorophyll

Answer 15

to transfer energy from the environment and use it to synthesise glucose from carbon dioxide and water