Testing a Leaf for Starch

Year 9 Science

Testing A Leaf For Starch

Prediction

1.  Write down whether you think light or chlorophyll or both are needed for photosynthesis.

Apparatus
·  leaves for testing: one that has been in the light and one that has been in the dark.
·  iodine solution
·  scissors
·  ethanol / ·  large beaker
·  test tube
·  test tube holder
·  forceps
·  pipette
·  Bunsen burner / ·  tripod
·  gauze
·  heat-proof mat
·  eye protection
·  petri dish

Method

1.  Take the two leaves and cut the end off the one that has been in the dark, so you can remember which is which. / 2.  Turn off the Bunsen burner. Half fill a test tube with ethanol. Place two leaves in it using forceps. Place the test tube into the beaker of hot water and leave it for 5 minutes.
3.  Place both leaves in a beaker of boiling water for one minute. / 4.  Take the leaves out of the test tube and wash them with tap water.
5.  Place the leaves on a petri dish and put a few drops of iodine solution on them. If a blue-black colour appears, there is starch in the leaf.

2.  What substance makes iodine solution turn blue-black?

3.  What process produces this substance?

4.  Write down what happened. What colours did each leaf go when iodine solution was added? Did all of the parts of the leaves change colour?

5.  Which parts of the leaf do you think had been photosynthesising? Why do you think this is?

6.  Write down whether you think light is needed for photosynthesis and why you think this is.

7.  Write down whether you think chlorophyll is needed for photosynthesis and why you think this is.

Products Of Photosynthesis

The diagram below shows what happens in photosynthesis:

1.  What are the reactants in photosynthesis?

2.  Complete the word equation for photosynthesis.

...... + ...... (+...... ) ® ...... + ......

3.  Which substance is a by-product of photosynthesis?

4.  A green substance called chlorophyll is needed to allow this process to happen. Where in a plant cell would you find chlorophyll?

5.  Small holes in the leaf allow the air containing carbon dioxide in. What are these called?

6.  Name two other substances that leave the leaf through these holes.

7.  The glucose made by photosynthesis is turned into starch. If iodine solution is added to a leaf, the parts that contain starch go a blue-black colour. In the diagrams below shade in the parts that you think will turn blue-black when iodine solution is added.

This leaf is all green and was grown in the light. / This leaf is all green and was grown in the dark for 48 hours. / This is a variegated leaf. The white border around the outside contains no chloroplasts. It was grown in the light.
This leaf is all green but had a strip of aluminium foil covering part of it. It was grown in the light. / This leaf is dead. It is brown. The plant it was on was growing in the light. / This is a variegated leaf. It was it was grown in the light but had a strip of aluminium foil covering one part.