1. Photosynthesis Objective:
Write the word and balanced symbol equation for photosynthesis.
Explain that glucose can be converted to other substances in plants to be used for different functions.
Explain why insoluble substances are used for storage.
Explain the effects of limiting factors on the rate of photosynthesis

2. Key Words Producers – organisms that make their own food.
Respiration – chemical reaction by which all organism make energy.
Mitochondria – organelle where respiration takes place.
Photosynthesis – chemical process by which plants make their food.
Chloroplasts – organelle where photosynthesis takes place.
Chlorophyll – green pigment in plants used in photosynthesis.
Sunlight – light energy needed for photosynthesis.
Cellulose – material used to make cell walls.
Starch – an insoluble carbohydrate.
Glucose – a soluble carbohydrate.

3. “photo” means “light” Photosynthesis
“synthesis” means “putting together
Photosynthesis is a chemical reaction that takes place in the chloroplasts in green plant cells, where light energy is used to convert carbon dioxide and water into glucose and oxygen.

4. What is Photosynthesis?
carbon
dioxide
water
glucose
oxygen
light
energy
chlorophyll

5. Plants make their food from carbon dioxide and water in a chemical reaction called photosynthesis.
Plants need energy for photosynthesis to take place. The energy for photosynthesis comes from the Sun.
Plant cells in the upper surface of the leaves have chloroplasts which contain the green pigment called chlorophyll.
It is chlorophyll that absorbs light energy from the Sun.
The food made by photosynthesis is the sugar glucose.
Oxygen gas is also made as a by-product of photosynthesis.

6. Photosynthesis: word equation
glucose
light energy
chlorophyll
carbon
dioxide
water
oxygen
glucose
light energy
chlorophyll
carbon
dioxide
water
oxygen
CO2
H2O
C6H12O6 O2

7. Structure of a leaf
How are leaves designed to maximize photosynthesis?
Leaves are thin so gases
can reach cells easily.
Leaves are wide and flat
to create a large surface
area and to absorb
as much light as possible.
Leaves have holes, called stomata, on their underside through which gases move in and out.
Leaves have lots of veins to carry water to the cells and carry glucose away.

8. Take a look inside a leaf

9. The Structure of a Leaf
The epidermis protects the leaf and is transparent to let light through.
The palisade mesophyll layer is where photosynthesis mostly takes place. The cells are tall and closely packed to absorb maximum light. They contain many chloroplasts.

10. The Structure of a Leaf
The spongy mesophyll layer contains numerous air spaces where gas exchange takes place. It also captures light and makes food.
The veins contain xylem (top part of vein) for water transport and phloem (lower part of vein) to take away dissolved food.
The stomata has tiny holes in the epidermis of the leaf. They are usually on the underside of the leaves. They control the water loss and gas exchange by opening and closing. Since a lot of water vapour can be lost through the stomata they only open for photosynthesis in daylight; at night they close to reduce loss of water vapour.

11. There are veins in the leaves to transport water and sugar around.

12. Many of the cells are packed with chloroplasts which contain a light trapping pigment- chlorophyll.

13. There is a waxy layer on top to stop water being lost from the leaf.

14. They have ‘holes’ in the leaves to allow carbon dioxide in and oxygen out. These are STOMATA.
Guard
cells

15. Thin leaves provide a short diffusion distance for carbon dioxide to reach the palisade and mesophyll cells

16. HT: How structure of the leaf is adapted for efficient photosynthesis
• Epidermis is transparent;
• Palisade layer at the top containing most of the chloroplasts;
• Air spaces in the spongy mesophyll allow diffusion between stomata and photosynthesising cells;
• Internal surface area / volume ratio very large.

17. Leaf cross section
In pairs examine a slide of

18. Use microscopes to observe internal structure of leaves

19. What happens to the glucose?

20. Photosynthesis and respiration
Only green plants photosynthesize,
but respiration occurs in the cells of all living things to release energy.
Photosynthesis
(energy needed)
glucose
light energy
chlorophyll
carbon
dioxide
water
oxygen
Respiration
(energy released)
carbon
dioxide
glucose
oxygen
water
Compare the reactants, products and energy results of these two chemical reactions. How are they connected?

21. Photosynthesis and respiration
How will the amounts of oxygen and carbon dioxide in the air vary over 24 hours?
amount of
oxygen
amount
of gas
in the air
amount of
carbon dioxide
12 a.m p.m a.m.
What overall effect do photosynthesis and respiration have on the levels of oxygen and carbon dioxide in the air?

22. Clip

23. Testing leaves for starch – procedure

24. Testing leaves for starch – experiment