1. Photosynthesis
STEP Grade 9

2. Simple Diagram of a Leaf

3. Cross Section of a Leaf

4. The Chloroplast

5. The Chloroplast
Stroma:  The matrix surrounding the grana in the inner membrane of chloroplasts. The area between membranes (thylakoids, grana) inside the chloroplast.
Grana: A series of stacked thylakoid disks containing chlorophyll; found in the inner membrane of chloroplasts.

6. Chlorophyll
Most common chlorophyll – Chlorophyll a, other types b and carotenoids

7. Reactions of Photosynthesis
6CO2 + 6H2O C6H6O6 + 6O2
The process is a lot more complex
Actually takes place in two separate stages:
The Light reactions – occurs in grana
The Dark reactions – occurs in stroma

8. The Light Reactions
The purpose of the light reactions is to change light energy into chemical energy in the form of 2 chemicals ATP and NADPH.
Requires light
Light energy used to make ATP.
The light splits water into hydrogen ions (H+) and oxygen atoms.
The oxygen is released to the air.
The H+ ions are used to make NADPH
ATP carries energy to the dark reactions.
NADPH carries energy and H+ to the dark reactions.

9. The Dark Reactions
The purpose of the dark reactions is to change CO2 into sugar by adding energy & the H+ ions from ATP & NADPH.
Can occur in light or dark.
6 CO2 & lots of ATP & NADPH are needed to make one sugar molecule.
The sugar is then used for plant growth or stored for use in fruits and leaves of plants as food for animals

10. Light & Dark Reactions

11. Limiting Factors Factors affecting the rate of photosynthesis.
As the rate of photosynthesis increases so will the plants growth rate.
Three factors limit photosynthesis from going any faster: Light level, carbon dioxide level, and temperature.
Without enough light a plant cannot photosynthesize very fast, even if there is plenty of water and carbon dioxide. Increasing the light intensity will make photosynthesis faster.

12. Limiting Factors
Sometimes photosynthesis is limited by the level of carbon dioxide. Even if there is plenty of light a plant cannot photosynthesize if it has run out of carbon dioxide.
Temperature can be a limiting factor too. If it gets too cold the rate of photosynthesis will slow right down; equally, plants cease to be able to photosynthesize if it gets

13. Limiting Factors

14. Questions
Which graph best shows the effect of increasing light intensity on the rate of photosynthesis?
Which graph best shows the effect of increasing carbon dioxide concentration on the rate of photosynthesis? A
Which graph best shows the effect of increasing temperature if light and carbon dioxide are not limiting (i.e. the levels of light and carbon dioxide are high). A
1 – c light increases the rate of photosynthesis until some other factor, CO2 or temperature limits it
2 – c carbon dioxide increases the rate of photosynthesis until light or temperature limits it
3 – d increasing temp increases the rate of reactions, after the optimum temp the enzymes denature and the rate slows down