1. Key Area 2: Photosynthesis and Energy Transfer
Unit 3: Sustainability and Interdependence

2. Photosynthesis
Photosynthesis is the process by which green pants trap light energy and use it to produce carbohydrates.
What carbohydrates are produced in plants?
Glucose, starch, cellulose
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3. Chloroplasts Chloroplasts are found in many green plants and algae.
These organelles contain the many structures and enzymes that are necessary for photosynthesis.
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4. Chloroplasts Lamella Starch grain Stroma Granum Outer membrane Inner
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5. Variation Chloroplasts are surrounded by a double membrane.
Inside this double membrane is a central space called the STROMA.
This space contains many enzymes for photosynthesis.
The stroma also contains structures called GRANA.
The grana contain the photosynthetic pigments and provide a large surface area for the absorption of light.
LAMELLAE are the network of membranes that run between the grana.
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6. Photosynthesis There are two stages of photosynthesis Photolysis
The Calvin Cycle
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7. Photolysis - light dependant stage
Photolysis occurs in the GRANA.
Molecules of chlorophyll absorb the light.
When this occurs the electrons in the chlorophyll become excited and are raised to a higher energy state.
These high energy electrons are then transferred through an electron transport chain driving ATP synthase to form ATP.
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8. Photolysis - light dependant stage
The light energy also splits a molecule of water into:
Hydrogen
Oxygen
The oxygen is released back in to the atmosphere by diffusion.
The hydrogen combines with a hydrogen acceptor called NADP.
Once this occurs the NADP is known as NADPH or the reduced hydrogen acceptor.
The NADPH and ATP formed here are carried over into the second stage.
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10. How Chlorophyll uses the light
Wavelengths in chlorophyll absorption spectrum
Wavelengths not in the absorption spectrum of chlorophyll
Absorbed by.
Chlorophyll
Chlorophyll* or ………………… chlorophyll contains high energy ……………
First stage of photosynthesis
Called
……………………..
Taking place in the
……………………
which is released
These can be used in energy transport chains to drive
………………………..
to make ………
from ………………
Coenzyme NADP
(hydrogen acceptor)
(reduced hydrogen acceptor)
Resources carried over from first stage to second =
ATP and NADPH

11. The Calvin Cycle
This is the second stage of photosynthesis and takes place in the STROMA.
It consists of a series enzyme controlled reactions that occurs in a cycle.
Carbon dioxide enters the cycle and attaches itself to ribulose biphosphate (RuBP).
An enzyme, rubisco or RuBisCO controls this reaction.
An intermediate carbon compound is formed which is then converted into G3P.
Some of the G3P formed is regenerated in to RuBP, while the remainder is converted into glucose.
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12. Second Stage of Photosynthesis – The Calvin Cycle
Ribulose bisphosphate
(…………………)
Enzyme = ………………… +
Intermediate carbon compound
ATP
NADPH
Glyceraldehyde-3- phosphate
(…………..)
Used in ………………………………..
Providing energy source
Sugars
most common ……………………….
Built into …………………………
Providing energy store
Other biosynthetic pathways producing many different metabolites
Built into ………………………….
For structural use in cells

13. Uses of sugar
The sugar that is formed during photosynthesis goes on to be used in many processes.
Glucose
Biosynthesis
Respiration pathways
Cellulose
Starch (structural Fats Nucleic
(storage carbohydrate and Acids
carbohydrate) e.g.cell wall) oils
Proteins
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14. Plant productivity What is meant by the word productivity?
Producing or having the power to produce; fertile.
To plant producers productivity means the rate at which plants generate new biomass.
The productivity of a plant is defined as :
The biomass produced in a given area over a given time.
Biomass is defined as:
The dry mass of organic material
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15. Plant productivity
In any ecosystem the production of a new biomass is measured as:
Units of biomass per unit area per unit of time
e.g. grams per square metre per year (gm-2y-1)
Productivity depends on the shape, arrangement and number of leaves on a plant.
Plants can therefore grow in a particular pattern to ensure that the maximum surface area of leaf is presented to the light.
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16. Plant productivity
The leaf area index (LAI) is the ratio of total leaf area to area of ground covered by the leaves.
The LAI can indicate the efficiency of light interception by the leaves.
Why is dry mass used to measure the biomass?
The water content of plants can vary greatly over short periods of time.
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17. Plant productivity Why is per leaf area used?
Leaves are not a standard size, will be using leaves with different starting masses.
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18. Plant productivity
Productivity can also be affected by the density of the planting.
If plants are planted far apart, light will be wasted as it will fall onto bare ground between the plants.
Weeds will also be able to grow freely in the spaces between the plants and compete for resources with the crop.
This results in a low productivity.
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19. Plant productivity
A more densely planted crop will have increased productivity as the available light will be used to a maximum and the minimum area of land will be wasted.
Increased density of planting, however, will reach an optimum above which productivity does not increase.
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20. Assimilation
Assimilation occurs in plant when the food they have produced is converted into cell walls and cell constituents.
This results in the plant growing and therefore an increase in the biomass of the plant.
However, some of the food that is produced during photosynthesis is used up in respiration.
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21. Assimilation
Net assimilation is the overall increase in biomass made by the plant.
It can be calculated by:
Net assimilation =
mass increase due loss in respiration
to photosynthesis
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22. Assessing productivity
For a crop to be productive, it must grow efficiently and produce a maximum yield.
The growing potential of a field and crop must be able to be assessed by those involved in all aspects of agriculture
e.g. farmers and scientists and policy makers.
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23. Economic Yield
The economic yield of a crop is the mass of the desired product.
It is the quantity that a farmer can use after post harvest losses.
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24. Harvest Index The harvest index of a crop can be calculated .
Harvest Index = Dry mass of economic yield
Dry mass of biological yield
This figure is often expressed as a percentage.
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25. The rate of photosynthesis
Productivity of a plant depends on the rate of photosynthesis.
How can the rate of photosynthesis be measured?
Number of oxygen bubbles released per minute, uptake of CO2, increase of carbohydrate.
What can photosynthesis be affected by?
Temperature, CO2 concentration, light intensity.
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26. The rate of photosynthesis
Whichever of these factors is in short supply is termed the limiting factor.
This means that the rate of photosynthesis is affected by this factor.
These factors can be investigated experimentally.
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