5. Homeostasis and Response (required practical 8 - plant responses)

Question 1

What is the practical investigating?

Answer 1

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

Question 2

What are the steps for investigating the effect of light intensity on the seedlings?

Answer 2

1. Place cotton wool in three petri dishes and then soak them with equal volumes of water
2. Place 10 mustard seeds in each dish
3. Leave the dishes in a warm place and allow the seeds to germinate
4. Water the seeds every day with the same volume of water
5. After a few days the seedlings will germinate so you need to make sure that the three dishes have the same number of seedlings by removing the necessary seedlings
6. Use a ruler to measure the height of each seedling. Hold the stems so that they are straight
7. Place the petri dishes in different conditions. One in full sunlight, one in partial light, and the last in darkness
8. Measure the height of each seedling every day for at least 5 consecutive days and record the results in a table
9. Calculate a mean seedling height for each day and draw diagrams to show the different effects of light intensity on the seedlings

Question 3

What is the IV for the experiment investigating the effect of light intensity?

Answer 3

the light intensity

Question 4

What is the DV for the experiment investigating the effect of light intensity?

Answer 4

the height of the seedlings

Question 5

What are the CVs for the experiment investigating the effect of light intensity?

Answer 5

• the volume of water
• the type of seed
• number of seedlings

Question 6

What set of seedlings would you expect to grow the longest and why? The ones in full sunlight, partial sunlight, or darkness?

Answer 6

the ones in darkness - as the seeds usually germinate underground and they grow rapidly to reach the light

Question 7

Why are the leaves of the seedlings that were in the dark small and yellow?

Answer 7

once the seedlings have used all their energy stores, they cannot carry out photosynthesis in the dark

Question 8

What are the steps for investigating the effect of gravity on the seedlings?

Answer 8

1. Place four seedlings on damp cotton wool on a petri dish
2. Place the dish of seedlings on its side in the dark for a few days
3. The shoots will grow upwards, against the direction of gravity, and the roots grow downwards towards the direction of gravity

Question 9

Why does the root grow in the direction of gravity?

Answer 9

• gravity causes auxin to build up on the lower side of the root
• so the lower side grows more slowly than the upper side and this makes the root grow in the direction of gravity