1. Photosynthesis and Plant Responses

2. Nutrition is the way in which living things get their food.
Animals get their food by eating other animals and plants.
Plants make their own food by a process called photosynthesis.

3. Photosynthesis Photosynthesis:
is the way in which green plants make food
converts solar (sun) energy into chemical energy in food
takes place in the green parts of plants, mostly in the leaves
is one of the main differences between plants and animals.

4. Equation for photosynthesis
Photosynthesis can be summarised as:
Sunlight
Carbon dioxide
Glucose + +
Chlorophyll
Water
Oxygen

5. Factors needed for photosynthesis
Carbon dioxide (a gas)
passes into the leaves from the air
enters the under-surface of leaves through tiny openings called stomata.
Water
enters the roots from the soil
passes up through the stem
enters the leaves in the veins.
Water
Carbon dioxide

6. Factors needed for photosynthesis
Light
in the form of sunlight, provides the energy for photosynthesis.
Chlorophyll
is a green pigment or dye made by plants
acts as a catalyst for photosynthesis.
Sun
Water
Carbon dioxide
Light
Chlorophyll

7. Products of photosynthesis
Glucose
is a sugar or carbohydrate
may be used in the plant for:
respiration (i.e. it is broken down to release energy)
storage in the form of starch
making cell walls (i.e. it is converted to cellulose).

8. Products of photosynthesis
Oxygen
is a gas
may be used in the plant for respiration
mostly passes out of the stomata into the air.

9. To show that starch is made by a plant in photosynthesis
Experiment
To show that starch is made by a plant in photosynthesis

10. Method To show that starch is made by a plant in photosynthesis
Leave a pot plant in the dark for two days.
To destarch the leaves, i.e. the starch moves out of the leaves.
Place tinfoil over some of the leaves of the plant.
To prevent light reaching the leaves and, therefore, to prevent photosynthesis. These leaves act as a control or comparison in the experiment.
Leave the plant in strong light for a few hours.
To allow photosynthesis to take place.
Test some of the covered and uncovered leaves for starch.
To show whether or not photosynthesis took place.
Aluminium foil
Light

11. To test leaves for starch
Experiment
To test leaves for starch

12. Method To test leaves for starch
Boil the leaves in water for a few minutes.
Leaves
Water
This kills and softens the leaves.
Tripod
Bunsen burner

13. Method cont. To test leaves for starch
Soak the leaves in hot alcohol for ten minutes.
This removes the chlorophyll from the leaves. Removing the green colour allows any later colour changes to be seen.
Boiling water
Alcohol
Leaves

14. Method cont. To test leaves for starch
Rinse the leaves briefly in boiling water.
Leaves
Water
Alcohol makes the leaves stiff and brittle. Rinsing off the alcohol will soften the leaves.

15. Method cont. To test leaves for starch
Add iodine solution to the leaves.
Iodine solution
Iodine turns from a red-yellow colour to blue-black if starch is present.
Leaf
Tile

16. Results To test leaves for starch
The leaves that were uncovered turn blue-black.
This shows that starch is present.
The leaves that were covered remain red-yellow.
This shows that starch is not present.

17. Conclusion To test leaves for starch
Starch is made by leaves in the presence of light.

18. Plant responses
The ability to respond is one of the characteristics of life.
Plants usually respond slowly (so that often we do not see their responses).
Plants respond to light and gravity by growing towards or away from light or gravity.
A tropism is the change in growth of a plant in response to an outside stimulus.

19. Phototropism is the change in growth of a plant in response to light.
The shoots (aerial parts) of a plant grow towards light due to phototropism.
Phototropism allows shoots to get more light and make more food.

20. To investigate phototropism
Experiment
To investigate phototropism

21. Method To investigate phototropism
Set up the apparatus as shown in the diagram.
Light
Light
Petri dish containing wet cotton wool sprinkled with seedlings

22. Results To investigate phototropism
Section A: the seedlings grow towards the light and bend.
Section B: the seedlings grow straight up towards the light.
Section C: the seedlings turn yellow and do not grow.

23. Conclusion To investigate phototropism
Seedlings grow towards the light.

24. Geotropism is the change in growth of a plant in response to gravity.
The shoots of a plant grow away from gravity.
This means they grow upwards towards the light.
The roots grow towards gravity.
This means they grow into the soil to get a better grip and to absorb more water.

25. To investigate geotropism
Experiment
To investigate geotropism

26. Method To investigate geotropism
Soak some large seeds in water for a day or two.
Set up the apparatus as shown in the diagram.
Leave the apparatus in a warm dark place for a few days.
Damp compost
Blotting paper
Beaker
Soaked seeds

27. Result To investigate geotropism
As the diagram shows:
The shoots grow up away from gravity
The roots grow down towards gravity

28. Conclusion To investigate geotropism
Shoots grow away from gravity and roots grow towards gravity.