Page 21 - 新思维科学学生用书9 样章

1 Photosynthesis and the carbon cycle

Think like a scientist

Planning an investigation into the effect of fertilisers on plant growth

You are going to plan an experiment to find out how fertiliser affects the rate of
growth of duckweed.
You may be able to do your experiment after you have planned it.
Duckweed is a tiny plant. There are lots of different species of duckweed, and they
grow in most countries in the world. Some kinds of duckweed have just a single leaf,

while others may have little groups of leaves. The leaves float on the water surface.
All duckweed plants have roots that dangle down into the water.

5 mm

• You could investigate effects of different kinds of fertiliser, or you could use just
one kind and try different quantities of it.

• You could grow your duckweed in small containers – for example, Petri dishes.
• You could measure how much the duckweed grows by counting the number of
leaves.

Part 1: Planning the investigation
1 Decide on a hypothesis that you will test.
2 How will you change your independent variable?

How many different values will you use?
3 How will you measure your dependent variable?
How many times will you measure it?

4 Which variables will you try to keep the same?
5 What equipment will you need?
6 What risks might there be in your experiment? How will you control the risks?
7 Predict the results you would expect to find and explain why you think this is
what will happen.

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