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:
carbon dioxide + water ----> glucose + oxygen
The symbol equation is:
Light Intensity Equation:
light intensity = 1/d^2
measured in a.u.
Uses for Glucose in Plants
- respiration to release energy for chemical reactions
- making cellulose for structural growth, making new cell walls and 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
A limiting factor slows the rate of photosynthesis, such as:
- 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 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
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
Why Do Plants Need Minerals?
Lack of magnesium ions means...
- yellow leaves
- due to less chlorophyll, so less photosynthesis
Lack of nitrates means...
- stunted growth
- used to make amino acids ----> proteins
> proteins needed for growth