Biology 3

Starch Test Method

1. Half fill a beaker with water and boil.

2. Cut a section of leaf from a plant.

3. Use forceps to put the leaf into the boiling water.

4. After 1 min, take out the leaf and turn off the Bunsen.

5. Pour ethanol into a boiling tube with a depth of about 4cm.

6. Put the leaf into the boiling tube containig ethanol and place the tube into the beaker with boiling water (Bunsen must be off).

PTO

7. When the leaf has turned white, use the glass rod to remove it from the ethanol and place it in the water in the beaker.

8. Wash the leaf in water for a minute. Then use forceps to remove it on white tile.

9. Add a couple of drops of iodine solution and, after a few minutes, record the colour of the indictor.

Is Carbon Dioxide Necessary for Photosynthesis?

The iodine solution remained an amber colour when the first leaves were tested, meaning the plant didn't contain starch at the start of the experiment.

The iodine solution turned from an amber to a blue-black colour, indicating that the plant contained starch. The plant stayed amber in the areas of the leaf not exposed to carbon dioxide, meaning starch was not present in those areas.

Therefore, as starch was only found in areas exposed to carbon dioxide, carbon dioxide must be present for photosynthesis to take place.

A plant carries out photosynthesis to make food. The food that the plant makes is glucose, which it can store as starch.

Iodine solution is used to test for the presence of starch.

If a leaf had starch present in its cells, this tells us that photosynthesis is occuring in the plant.

If iodine solution turns from an amber to a blue-black colour, starch is present and photosynthesis is taking place.

If iodine solution stays amber coloured, this means that starch is not present and photosynthesis is not taking place.

Is Light Necessary for Photosynthesis?

The iodine solution remained an amber colour when the first leaves were tested, meaning the plant didn't contain starch at the start of the experiment.

The iodine solution turned from an amber to a blue-black colour, indicating that the plant contained starch. The plant stayed amber in the areas of the leaf not exposed to light, meaning starch was not present in those areas.

Therefore, as starch was only found in areas exposed to light, light must be present for photosynthesis to take place.

Is Chlorophyll Necessary for Photosynthesis?

The iodine solution remained an amber colour when the first leaves were tested, meaning the plant didn't contain starch at the start of the experiment.

The iodine solution turned from an amber to a blue-black colour, indicating that the plant contained starch. The plant stayed amber in the areas of the leaf not exposed to chlorolphyll, meaning starch was not present in those areas.

Therefore, as starch was only found in areas exposed to chlorolphyll, chlorolphyll must be present for photosynthesis to take place.

• Oxygen is the gas produced during photosynthesis.
• Water and sunlight in the prensence of chlorophyll are needed for photosynthesis to happen, but are not used up.
• Glucose (sugar) is needed by cells for respiration.
• Glucose is not produced at night when it is too dark for photosynthesis to occur.
• Plants and algae store glucose as insoluable products, like starch, fats and oils.
• Some glucose is used for respiration to release energy.
• Some is used to produce cellulose, which strengthens the cell wall, and proteins, such as enzymes and chlorophyll.

Waxy Cuticle

These cells produce the waxy cuticle and protect the leaf. They containn no chlroplasts so that light can reach the palisade mesophyll cells.

Upper Epidermis

This helps to prevent loss of water and have air spaces between them.

Air sapces allow the movement of gases into and out of the cells of the leaf.

The stomata are tiny holes in the lower p