1. What is photosynthesis?
Plants make their own food by photosynthesis.
This process is a chemical reaction that uses light energy.
light energy
The word photosynthesis comes
from the Greek language:
“photo” means “light”
“synthesis” means “putting together”
Photosynthesis just means “putting together with light”.
What do green plants “put together” to make their food?

2. Photosynthesis: raw materials
The raw materials for photosynthesis come from the air and the soil.
What are these raw materials called?
What else do plants need to turn
carbon dioxide
and water into food?
carbon
dioxide
water

3. Photosynthesis: energy for the reaction
light energy
Photosynthesis is a chemical reaction between carbon dioxide and water.
Energy is needed for this reaction to take place.
Where do plants get this energy from?
carbon
dioxide
water

4. Photosynthesis: where it happens
Plants use light energy from the Sun to power photosynthesis.
Where in the leaf does this reaction take place?
Photosynthesis takes place in what part of plant cells?
light energy
carbon
dioxide
water

5. Photosynthesis: where it happens
Photosynthesis takes place in plant cells
with chloroplasts.
Chloroplasts contain the green chemical called chlorophyll.
Chlorophyll absorbs the energy from sunlight that allows carbon dioxide and water to react.
What are the products of this reaction?
light
energy
chlorophyll
carbon
dioxide
water

6. Photosynthesis: products of the reaction
The products of the reaction between carbon dioxide and water are glucose
and oxygen.
Which of these products is used
by plants?
What happens to the ‘waste’ product?
light
energy
chlorophyll
carbon
dioxide
oxygen
glucose
water

7. Photosynthesis: products of the reaction
Glucose is the useful product for plants.
Some glucose is used straightaway by plant cells, some is converted to starch for storage and later used for food.
Oxygen is the ‘waste’ product. This gas is transported out of the leaf into the air.
Why is this important for humans and other living things?
light
energy
chlorophyll
carbon
dioxide
oxygen
oxygen
glucose
glucose
water

8. Photosynthesis: summary
Summarize the process of photosynthesis in one sentence.
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.
Photosynthesis is a chemical reaction which means it can also be summarized in a word equation.
What is the word equation for this vital chemical reaction?

9. Photosynthesis: word equation
light energy
carbon
dioxide
water
glucose
oxygen
chlorophyll
light
energy
chlorophyll
carbon
dioxide
oxygen
glucose
water

10. Photosynthesis: chemical formulae?
Photosynthesis is a chemical reaction involving molecules.
glucose
light energy
chlorophyll
carbon
dioxide
water
oxygen
CO2
H2O
C6H12O6 O2
The chemical formula of a glucose molecule is C6H12O6.
What are the chemical formulae of the simple molecules that make up carbon dioxide, water and oxygen?

11. !!!YOU MUST LEARN THIS EQUATION!!!!
PHOTOSYNTHESIS
Using Sunlight Energy
Carbon Dioxide
6CO2 +
Water
6H2O
Glucose
C6H12O6 +
Oxygen
6O2
Absorbed by Chlorophyll
Glucose sugar is made and stored as starch. Oxygen is given off as a waste product
These four things must all be present in order to make food by Photosynthesis

12. Leaves: maximizing photosynthesis
Leaves are the most efficient solar panels on Earth!
Why can they be called this?
Light energy is absorbed
by the chlorophyll in leaves and used to carry out photosynthesis.
Leaves come in all shapes and sizes but what features do they have in common
to maximize photosynthesis?

13. Structure of a leaf
How are leaves designed to maximize photosynthesis?
Leaves are wide and flat
to create a large surface
area and absorb as much
light as possible.
Leaves are thin so gases
can reach cells easily.
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.

14. Structure of a leaf activity

15. Take a look inside a leaf

16. What happens to the glucose?

17. 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?

18. 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?

19. The rate of photosynthesis
Photosynthesis is a chemical reaction and so has a rate.
Is the rate of photosynthesis always the same?
glucose
light energy
chlorophyll
carbon
dioxide
water
oxygen
The rate of photosynthesis varies depending on three main factors:
light
carbon dioxide
temperature
How do these factors affect the rate of photosynthesis?

20. Light and the rate of photosynthesis
Light energy has to be absorbed by chlorophyll for photosynthesis to take place.
glucose
light energy
chlorophyll
carbon
dioxide
water
oxygen
The brighter the light, the more light energy there is,
so will photosynthesis be faster or slower?
More light energy means that photosynthesis will be faster.
If light intensity is too high plant cells can be damaged.
How is photosynthesis affected if this happens?

21. Carbon dioxide and the rate of photosynthesis
Carbon dioxide is one of the raw materials used by plants to make their food.
glucose
light energy
chlorophyll
carbon
dioxide
water
oxygen
The concentration of carbon dioxide in the air (0.03%) is actually quite low.
Why is the concentration of carbon dioxide in commercial greenhouses often raised to about 0.1%?
More carbon dioxide means more photosynthesis, so plants make more food and grow quicker.

22. Temperature and the rate of photosynthesis
Photosynthesis is controlled by enzymes.
Enzymes usually work best at warmer temperatures.
glucose
light energy
chlorophyll
carbon
dioxide
water
oxygen
Why is the rate of photosynthesis slower on a sunny day
in winter?
If the temperature gets too hot (above 40 °C), plant enzymes begin to break down and are destroyed or denatured.
Why does photosynthesis stop under such conditions?

23. What is a limiting factor?
What is the ideal combination of factors for the maximum rate of photosynthesis?
enough light
enough carbon dioxide
ideal temperature (not too hot or cold)
How is the rate affected if one of these factors is restricted?
If one of the factors is restricted, the rate of photosynthesis will be below the maximum possible rate.
The restricted factor controls how quickly photosynthesis occurs and so limits the rate. It is called the limiting factor.

24. Photosynthesis and light – limiting factors
How does the amount of light affect the rate of photosynthesis on this labelled graph?
As the amount of light increases, so does the rate. The limiting factor is light. 1 2 2
Here, increasing the amount of light has no affect on the rate. The limiting factor is now carbon dioxide or temperature.
What must be increased for the rate to increase?
rate of photosynthesis 1
light intensity

25. Photosynthesis and carbon dioxide – limiting factors
How does the amount of carbon dioxide affect the rate of photosynthesis on this labelled graph? 1
As the amount of carbon dioxide goes up, so does the rate. The limiting factor is carbon dioxide. 2 2
Here, increasing the amount of carbon dioxide has no affect on the rate. Light or warmth is now the limiting factor.
What must be increased for the rate to increase?
rate of photosynthesis 1
concentration of
carbon dioxide