1. Living Cells
Photosynthesis
Mr G Davidson

2. Photosynthesis Photosynthesis
Green plants are capable of making their own food using energy from sunlight.
This process is called photosynthesis.
Photosynthesis
Light
To make
Tuesday, December 04, 2018
Mr G Davidson

3. Photosynthesis Light is trapped by a green pigment called chlorophyll.
Chlorophyll is found inside the chloroplasts, which are disc shaped organelles found in the leaf cells.
Light is used to combine water and carbon dioxide to make a carbohydrate called glucose, with oxygen being released as a waste product.
Tuesday, December 04, 2018
Mr G Davidson

4. Leaf Cross Section Xylem O2 H2O CO2 CO2 O2 Light
Tuesday, December 04, 2018
Mr G Davidson

5. Chemistry of Photosynthesis
Photosynthesis is a series of enzyme-controlled reactions.
Photosynthesis occurs in 2 stages:
Photolysis which is a light dependent stage.
Carbon fixation which is a temperature dependent stage.
Tuesday, December 04, 2018
Mr G Davidson

6. Photolysis
It is in photolysis that light energy is trapped by the chlorophyll and converted into chemical energy.
Light energy is used to split water molecules into hydrogen and oxygen.
The oxygen is released as a waste product.
Tuesday, December 04, 2018
Mr G Davidson

7. Photolysis
The hydrogen joins with a hydrogen acceptor and this “reduces” it.
The reduced hydrogen acceptor carries the hydrogen to the carbon fixation stage.
ATP is also made during photolysis and this is called PHOTOPHOSPHORYLATION.
This ATP will also be used in the next stage.
Tuesday, December 04, 2018
Mr G Davidson

8. Photolysis WATER (H2O) Oxygen Hydrogen Light energy Next stage
acceptor
Oxygen
Hydrogen
Released
as a waste
product
Reduced
hydrogen
acceptor
Next
stage
ADP + Pi
ATP
Tuesday, December 04, 2018
Mr G Davidson

9. Carbon Fixation
Carbon fixation is the 2nd stage of photosynthesis and also occurs in the chloroplasts.
It is a series of enzyme controlled reactions using the hydrogen and ATP from photolysis, and carbon dioxide from the air.
The carbon dioxide and the hydrogen are combined to produce glucose.
Tuesday, December 04, 2018
Mr G Davidson

10. Carbon Fixation From From photolysis photolysis Glucose Carbon dioxide
Reduced
hydrogen
acceptor
ATP
ADP + Pi
Glucose
Carbon dioxide
From
the air
Tuesday, December 04, 2018
Mr G Davidson

11. Photosynthesis
The glucose made in photosynthesis can be used by the plant in a number of ways.
It can be used by the plant as an immediate energy source for such things as reproduction, growth, etc..
It can be stored in plants as a complex carbohydrate called starch and then converted back to glucose as and when it is required.
It can be used by the plant as a structural carbohydrate called cellulose which is used to make cell walls.
Tuesday, December 04, 2018
Mr G Davidson

12. Factors affecting photosynthesis
There are a number of factors which can affect the rate at which a plant can carry out photosynthesis, and these are called limiting factors.
They include:
Light intensity
Temperature
Carbon dioxide concentration
Tuesday, December 04, 2018
Mr G Davidson

13. Light intensity
In dim conditions, plants will photosynthesise more slowly than in bright conditions.
This is because the more light there is, the more energy is available for photosynthesis to happen.
We can see this using a pondweed called Elodea in the following investigation.
Tuesday, December 04, 2018
Mr G Davidson

14. Light Intensity Oxygen bubbles Dilute sodium bicarbonate (to provide
carbon dioxide)
Filter
funnel
Lamp
Heat shield
Elodea
Tuesday, December 04, 2018
Mr G Davidson

15. Light Intensity
The lamp is moved a certain distance away from the elodea, and the number of bubbles released per minute is counted.
The lamp can then be moved farther away and the bubbles counted again.
The results would look something like the following.
Tuesday, December 04, 2018
Mr G Davidson

16. Light Intensity And from these results we can then plot a line graph.
Tuesday, December 04, 2018
Mr G Davidson

17. Light Intensity
Tuesday, December 04, 2018
Mr G Davidson

18. Light Intensity
As we can see from the graph, the line levels off indicating that further increases in light intensity will not increase the rate of photosynthesis.
Some other limiting factor must be taking effect at this stage.
Tuesday, December 04, 2018
Mr G Davidson

19. Carbon Dioxide Concentration
This investigation also uses the Elodea bubbler apparatus.
This time the lamp is kept in the same place and the mass of sodium bicarbonate in the water is gradually increased.
The results would produce a similar line graph, i.e. it would increase then level off.
Tuesday, December 04, 2018
Mr G Davidson

20. Temperature Temperature is also a limiting factor for photosynthesis.
However, the line graph is not the same if we keep increasing the temperature because the enzymes are eventually denatured by excessive heat.
This means the graph would look like the following.
Tuesday, December 04, 2018
Mr G Davidson

21. Temperature
Tuesday, December 04, 2018
Mr G Davidson

22. Temperature
We can see from the graph that as the temperature increases, so does the rate of photosynthesis.
This happens until it reaches the optimum temperature, when photosynthesis cannot happen any quicker.
After this, the rate of photosynthesis slows down as the enzymes which control it are denatured.
Tuesday, December 04, 2018
Mr G Davidson

23. Horticulture
If we can reduce the limiting factors in photosynthesis, then we may be able to increase the yield of plants.
Obviously this can’t be done by a farmer in his fields, but it can be done in controlled environments such as greenhouses.
Tuesday, December 04, 2018
Mr G Davidson

24. Horticulture
Extra lighting can be supplied to greenhouses to extend the number of daylight hours.
The temperature in winter and spring is often increased using paraffin heaters, and these have the added bonus of releasing extra carbon dioxide which may also be limiting photosynthesis.
This also allows, not only an increased yield, but earlier crops.
Tuesday, December 04, 2018
Mr G Davidson