RP8: Plant Responses

Question 1

What is the aim of this experiment?

Answer 1

• Investigate the effect of light or gravity on the growth of newly germinated seedlings

Question 2

Describe how you can investigate the effect of light on the growth of seedlings

Answer 2

1. Pour a fixed volume of water into 3 petri dishes and add cotton wool.
2. Place 10 seeds in each petri dish.
3. Place the petri dishes in a warm location eg. incubator, not to be disturbed.
4. Allow time for the seeds to germinate. If necessary, add more water to the petri dishes
   (same volume for each dish).
5. If not all the seeds have germinated into seedlings, remove any excess ones so that the petri dishes have the same number of seedlings.
6. Place one petri dish in full sunlight by a window. Place a second petri dish in partial
   sunlight. Place a third petri dish in darkness in a cupboard.
7. Use a ruler to measure the height of each seedling every day for at least a week. Record in a table
8. Find the mean height of the seedlings each day.
9. Plot a graph of ‘mean height of seedling’ against ‘day’. 1

Question 3

Which group of seedlings would you expect to grow the most and why?

Answer 3

• The group in the full sunlight - light is required for photosynthesis and these plants will not have light intensity as a limiting factor

Question 4

Why is it necessary to find the mean height of the seedlings?

Answer 4

• Some seedlings may be much shorter/longer than others in the same dish
• Calculating a mean makes the values more representative and allows comparison between groups

Question 5

Name possible sources of error

Answer 5

• Seedlings in the same petri dish may not receive the same exposure to sunlight.
• Sample size for each environmental condition may be too small.
• Temperature may be another factor that affects the growth of the seedlings in addition to light exposure.

Question 6

Give a risk assessment for this experiment

Answer 6

• Seeds may be a biohazard.
• Wash your hands after handling seeds.