Photosynthesis uses energy to change carbon dioxide and water into glucose and oxygen.
Takes place in chloroplasts
- they contain pigments like chlorophyll that absorb light.
Energy is transferred to the chloroplasts from the environment by light.
Photosynthesis is endothermic - this means energy is transferred from the environment in the process.
The word equation for photosynthesis is:
light
carbon dioxide + water ----> glucose + oxygen
The symbol equation is:
Light Intensity Equation:
light intensity = 1/d^2
measured in a.u.
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Uses for Glucose in Plants
respiration to release energy for chemical reactions
making cellulose for structural growth, making new cell wallsand increasing biomass
making amino acids and proteins for growth
stored as lipids
stored as insoluble starch in leaves and storage organs, e.g. potatoes and seeds
sucrose (for transport) as it's more soluble than glucose
chlorophyll, made using magnesium ions and glucose
DNA, made using nitrates, phosphates and glucose
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Limiting Factors
A limiting factorslows the rate of photosynthesis, such as:
Light Intensity
light provides energy needed for photosynthesis
as light levels increase, the rate of photosynthesis increases steadily up to a point
beyond this point, the limiting factor has changed, even as light levels increase, the rate will no longer increase - it could be carbon dioxide concentration or temperature, but it is not light intensity
* the point where the graph constant is the point where the limiting factor changes
Temperature
temperature provide the energy needed for enzymes to catalyse chemical reactions
if temperature is too low, enzymes don't have enough kinetic energy to catalyse reactions fast enough, so the rate of photosynthesis slows down
if the temperature is too high, enzymes can begin to denature, so the rate of photosythesis will slow down
Carbon Dioxide Concentration
raw material needed for the photosynthesis reaction (see Photosynthesis Overview)
as the carbon dioxide concentration increases, the rate of photosynthesis increases steadily up to a point
beyond this point, the graph falttens out - as the carbon dioxide concentration increases, the rate no longer increases and the limiting factor changes to either temperature or light intensity
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Photosynthesis Required Practical
Canadian pondweed can be used to measure the effect of light intensity on the rate of photosynthesis.
The rate at which the pondweed produces oxygen corresponds with the rate of photosynthesis
- the faster the rate of oxygen production, the faster the rate of photosynthesis
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