3 Plants and food Flashcards
What do all plants contain?
Starch.
What is the main carbohydrate storage made by plants?
Starch.
Why do plants store starch?
It is a good way of storing carbohydrate because it is insoluble, compact and can be be broken down easily.
How do you test leaves for starch?
1) You remove the leaf from a plant which has been in the sunlight.
2) You de-wax the leaf using forceps in boiling water for 30 seconds.
3) Let the leaf cool down.
4) After the leaf has cooled, you immerse the leaf in boiling ethanol.
5) When the leaf has turned colourless, we remove it and put it under cold water to soften it.
6) Then put it on a tile and add iodine.
Why do you remove the leaf from a plant which has been in the sunlight?
Because the leaves contain starch from photosynthesis after glucose has been converted so we can test for it.
Why do you de-wax the leaf?
Because without de-waxing it, the leaf will not be able to absorb the solution, and the leaf needs to be de-colourised because the green colour of the leaf would hide the colour change.
Why do you wait for the leaf to cool down?
Because ethanol is highly flammable.
When do you remove the leaf from the ethanol?
When it has turned colourless or pale yellow.
What will the colour change in the iodine be if starch is present?
Orange-brown to blue black.
Under what circumstances will this work?
If the plant has had plenty of light for some hours before the test.
What is a way of de-starching a plant?
By placing it in the dark for 2 or 3 days. The plant uses up the starch stores in its leaves. De-starched plants are used to find out the conditions needed for the plant to make more starch by photosynthesis.
Where is starch only made?
in the parts of plants that contain chlorophyll.
How can you show that starch is only made in parts of plants that have chlorophyll?
By testing a leaf from a variegated plant, which has green and white areas to its leaves. The white parts of the leaf will give a negative starch test, staining yellow-brown with iodine solution. Only the green areas will stain blue black.
What does an investigation of conducting a starch test on a leaf, where the leaf was taken from a plant that had been under a bright light for 24 hours look like?
Why is the argument about chlorophyll and starch not justified?
- The leaf could have photosynthesised in the white areas and the sugars been transported elsewhere in the plant.
- The green areas may not be photosynthesised at all, but simply laying down starch from glucose made somewhere else.
Why do we assume this about chlorophyll then?
We assume this because chlorophyll is needed for photosynthesis.
What is another way of making sure that a plant can’t make starch in its leaves?
By placing it in a closed container containing a chemical called soda lime.
What does soda lime do?
This substance absorbs carbon dioxide from the air around the plant.
What happens if the plant is kept under a bright light without carbon dioixide?
It still won’t be able to make starch.
What are the factors that are needed for starch production in leaves?
- Uses carbon dioxide from the air.
- Needs light.
- Needs chlorophyll in the leaves.
- Oxygen.
When does a plant make oxygen gas?
When it is in the light.
What is starch composed of?
Long chains of glucose.
How is starch produced?
The plant first produces glucose, which is then joined together in chains to form starch molecules.
What is the formula for glucose?
C6H12O6