1. 2.9 Photosynthesis
The background is an microscope image of leaf cells. You can clearly see the cells are packed with chloroplasts. These specialised organelles contain chlorophyll (and other pigments) which trap light energy and use it to build glucose molecules.
Essential idea: Photosynthesis uses the energy in sunlight to produce the chemical energy needed for life.
By Chris Paine

2. Carbon is ‘fixed’ from carbon dioxide and used to produce to glucose.
2.9.U1 Photosynthesis is the production of carbon compounds in cells using light energy.
Photosynthesis is a metabolic pathway. Carbon dioxide and along with water is used to produce carbohydrates. Oxygen is released as a waste gas.
Light energy is transferred to chemical energy stored in the glucose molecule
Water is split: the hydrogen is used to help in the production of glucose, but the oxygen is excreted as a waste gas.
Carbon is ‘fixed’ from carbon dioxide and used to produce to glucose.
n.b. metabolic pathways are controlled by enzymes

3. 2.9.U4 Oxygen is produced in photosynthesis from the photolysis of water. 2.9.U5 Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide.
One use of the energy consumed in photosynthesis is photolysis (splitting of water molecules)
sunlight
Most of the oxygen is excreted as a waste product
Glucose can be used by cell respiration or stored as starch.
n.b. larger molecules tend to contains more bonds than smaller ones. Therefore more ATP is required to build the bonds and generate larger molecules. Consequently large molecules can act as energy stores.
electrons

4. 2.9.U4 Oxygen is produced in photosynthesis from the photolysis of water. 2.9.U5 Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide.
One use of the energy consumed in photosynthesis is photolysis (splitting of water molecules)
sunlight
Reactions and processes than absorb energy from their surroundings are described as being endothermic
Most of the oxygen is excreted as a waste product
Glucose can be used by cell respiration or stored as starch.
n.b. larger molecules tend to contains more bonds than smaller ones. Therefore more ATP is required to build the bonds and generate larger molecules. Consequently large molecules can act as energy stores.
electrons

5. 2.9.U5 Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide.

6. 2.9.U5 Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide.

7. 2.9.U2 Visible light has a range of wavelengths with violet the shortest wavelength and red the longest.

8. 2.9.U3 Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colours.

9. % of the maximum rate of photosynthesis
2.9.S1 Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.
This shows the rate of photosynthesis for all the wavelengths of light as a % of the maximum possible rate.
% of the maximum rate of photosynthesis
(Edited by Chris Paine)

10. % of the maximum rate of photosynthesis
2.9.S1 Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.
This shows the absorbance of light by photosynthetic pigments (here chlorophyll) for all the wavelengths of light.
% of the maximum rate of photosynthesis
(Edited by Chris Paine)

11. 2.9.S1 Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.

12. 2.9.S1 Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.

13. Rate of Photosynthesis
2.9.U6 Temperature, light intensity and carbon dioxide concentration are possible limiting factors on the rate of photosynthesis.
At high levels of light intensity further increases have no effect on the rate of photosynthesis. Therefore light intensity is not the limiting factor, another factor (e.g. temperature, CO2 concentration, enzymes or chloroplasts working at maximum efficiency) is limiting photosynthesis.
Rate of Photosynthesis
When light intensity is increased the rate of photosynthesis increases therefore it is the limiting factor at low levels.
Light intensity
Light intensity refers to the amount of light, of a given wavelength, which is available to the plant.

14. Rate of Photosynthesis
2.9.U6 Temperature, light intensity and carbon dioxide concentration are possible limiting factors on the rate of photosynthesis.
Another factor (e.g. temperature, light, enzymes working at maximum efficiency) is limiting photosynthesis as further increases in carbon dioxide do not increase the rate of photosynthesis.
CO2 is a substrate for the metabolic pathway hence the relationship is similar to how enzyme reactions are limited by substrate concentration.
Rate of Photosynthesis
When carbon dioxide concentration is increased the rate of photosynthesis increases therefore it is the limiting factor at low concentrations.
Carbon dioxide concentration

15. Rate of Photosynthesis
2.9.U6 Temperature, light intensity and carbon dioxide concentration are possible limiting factors on the rate of photosynthesis.
Photosynthesis is a metabolic pathway hence the relationship is similar to how enzyme reactions are affected by temperature.
After the optimum temperature enzymes denature rapidly causing a fast decrease in the rate of photosynthesis as temperature increases further.
Rate of Photosynthesis
As the temperature approaches the optimum the enzymes begin to denature (active site changes to become non-functional) causing the rate of photosynthesis to increase more slowly and eventually peak.
Increases in temperature give molecules more kinetic energy causing substrates to collide with active sites more frequently, this increases the rate of photosynthesis
Temperature

16. Placing the plant in a closed space with water.
2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Placing the plant in a closed space with water.
CO2 reacts with the water producing bicarbonate and hydrogen ions, which increases the acidity of the solution. Increased CO2 uptake -> increased pH -> increased rate of photosynthesis.

17. 2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Aquatic plants can submerged in water in a closed space with a gas syringe attached. Alternatively gas volume can be measured by displacing water in an inverted measuring cylinder or by simply counting bubbles.
Oxygen probes can be used with terrestrial plants kept in closed environments to measure increases in oxygen concentration.

18. starch levels in a plant (glucose is stored as starch)
2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Glucose production can be (indirectly) measured by a change in a plant's dry biomass.
starch levels in a plant (glucose is stored as starch)
can be identified by staining with iodine solution, this can be quantitated using a colorimeter.

19. 2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Before designing an carrying out your own investigation what questions need to be asked and considerations need to be made?

20. The independent variable
2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Before designing an carrying out your own investigation what questions need to be asked and considerations need to be made?
The independent variable
Only one limiting factor should be investigated at a time
The range of values should reflect conditions experienced by the organism
The range of values should allow the limiting factor to range from values that restrict photosynthesis to values that allow photosynthesis to happen at it’s optimum rate.
The increments should be sufficiently in size that a trend can be clearly detected

21. 2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Before designing an carrying out your own investigation what questions need to be asked and considerations need to be made?
Dependent variable
An accurate method for measuring the rate of photosynthesis needs to be used.
Oxygen production per time unit is recommended.
Leaf discs are a successful and easy way to measure oxygen generation by leaves

22. 2.9.S2 Design of experiments to investigate the effect of limiting factors on photosynthesis.
Before designing an carrying out your own investigation what questions need to be asked and considerations need to be made?
The control variables
These should include the limiting factors not being investigated.
Other key control variables should include any factor that affects a metabolic pathway controlled by enzymes, e.g. pH.
Ambient light should be considered as it affects the wavelength and intensity of light absorbed by the organism.
The values chosen for the control variables should be close to their optimum values so that the control variables do not limit photosynthesis. (If the control variables limit photosynthesis it may not be possible to see the impact of the limiting factor being investigated)

23. The control variables - Nature of Science
Nature of Science: Experimental design - controlling relevant variables in photosynthesis experiments is essential. (3.1)
Before designing an carrying out your own investigation what questions need to be asked and considerations need to be made?
The control variables - Nature of Science
Explain why it is essential to control the limiting factors not being investigated.
Evaluate which of the identified reasons are the most important.

24. Iron compounds in the oceans were oxidized:
2.9.A1 Changes to the Earth’s atmosphere, oceans and rock deposition due to photosynthesis.
Primordial Earth had a reducing atmosphere that contained very low levels of oxygen gas (approx. 2%).
 Cyanobacteria (prokaryotes) containing chlorophyll first performed photosynthesis about 2.5 billion years ago.
Photosynthesis creates oxygen gas as a by-product (by the photolysis of water).
Oxygen levels remained at 2% until about 750 million years ago (mya). From 750 mya until the now there has been a significant rise to 20%.
Oxygen generation also allowed the formation of an ozone layer (O3). Ozone shielded the Earth from damaging levels of UV radiation. This, in turn, lead to the evolution of a wider range of organisms.
Iron compounds in the oceans were oxidized:
The insoluble iron oxides precipitated onto the seabed.
Time and further sedmentation has produced rocks with layers rich in iron ore called the banded iron formations.
Oxygen in the atmosphere lead to the production of oxidised compounds (e.g. CO2) in the oceans.