Photosynthesis

What is photosynthesis?

Plants use photosynthesis to convert carbon dioxide and water, in the presence of chlorophyll and light energy, to make glucose andoxygen. Photosynthesis is important in converting light energy to chemical energy.

Write a sentence or two to describe what photosynthesis is. Use the keywords: light energy, carbon dioxide, water, oxygen, chlorophyll, chemical energy, photosynthesis.

carbon dioxide + water glucose + oxygen 6CO2 6H20 C6H12O6 602

Photosynthesis is an important process because it converts light energy to chemical energy, which is stored in glucose. The chemical energy is released when glucose is broken down during respiration.

light

chlorophyll

Cross-section of a leaf

upper epidermis

spongy mesophyll layer

stomaguard cells

air space

vascular bundle

Palisade cell

Exam question

(c) The leaves produce glucose by photosynthesis. (i) Write the word equation for photosynthesis. ............................................................................................... (2) (ii) Describe how the structure of the leaf is adapted to help obtain the gas required for photosynthesis. ......................................................................................................... ......................................................................................................... ......................................................................................................... ......................................................................................................... ......................................................................................................... .................................................................................................. (2)

Exam question

(c) The leaves produce glucose by photosynthesis. (i) Write the word equation for photosynthesis. carbon dioxide + water glucose + oxygen (2) (ii) Describe how the structure of the leaf is adapted to help obtain the gas required for photosynthesis.

thin; large surface area; stomata; air spaces / spongy (mesophyll);

(2)

• How can we test that photosynthesis has occurred in plants?

• What is the evidence for photosynthesis?• How can we test for starch?

How can we test that

photosynthesis is occurring in

plants?

oxygen given off

starch producedPresence / absence of chlorophyll

Presence/ absence of light

Presence/ absence of CO2

Pondweed experiments

Investigating the requirements for starch production

Why destarch the plants before setting up each investigation?1. Light

• Set up and leave in sunlight for 24 hours

2. Carbon dioxide

soda lime

Spot the difference!What’s the purpose of adding soda lime?

light

2. Carbon dioxide

3. Chlorophyll

• Predict the results of the starch test.

• Take a variegated plant which has been under bright light for 24hours and remove one of the leaves.

• Make a sketch of the leaf showing approximately where the green and non green areas are.

Testing Leaves for Starch

1. Dunk the leaf in a 90oC water bath using forceps until it is soft (2 minutes).

2. Transfer leaf to a boiling tube of ethanol and place in 90oC water bath until the leaf turns white (5 minutes).

3. Wash the leaf in water.

4. Place the leaf on a Petri dish and flood with iodine solution.

ResultsWrite up results and include diagrams.

Condition Treatment Starch Test (diagrams)

Before After

Light

Carbon dioxide

Chlorophyll

Conclusions

• What do your results tell you about photosynthesis and …a. light?b. carbon dioxide?c. chlorophyll?

• What was the control for each experiment?

• It is difficult to set up an experiment to prove that water is needed for photosynthesis. Explain why it is difficult.

Light and starch production

1. Take a finely sliced piece of potato and place on a glass slide

2. add two drops of iodine solution and place a coverslip on top

3. view under the microscope.

What can you see?

• summary