Biology Key Topic 4
4.4 Bioenergetics
4.4.1 Photosynthesis
4.4.1.1 Photosynthetic reaction
Photosynthesis is represented by the equation:
- Carbon dioxide + water (light) glucose + oxygen
It takes place in chloroplasts in green plants’ cells
It is an endothermic reaction – it takes in energy from the environment
Plants are adapted for photosynthesis by:
- having many leaves on a plant to form a mosaic so they have a large surface area to
absorb the maximum amount of sunlight
- leaves are flat and broad with a large surface area to absorb more sunlight for
photosynthesis
- thin leaves have lots of air spaces, so CO2 can diffuse rapidly into lea cells for
photosynthesis. In the spongy layer the CO2 diffuses rapidly into lead cells
- the leaf cells contain a lot of chloroplasts containing chlorophyll to absorb more
sunlight for the process
- palisade cells are long and closely packed together so there are more cells in the top
layer inside the lead – giving a larger surface are to absorb more light for
photosynthesis
4.4.1.2 Rate of photosynthesis
These factors (temperature, light intensity, carbon dioxide concentration and the
amount of chlorophyll) interact and any one of them may be the factor that limits
photosynthesis
- At night, light is the limiting factor, in winter temperature is the limiting factor and
if it is warm enough, the amount of CO2 is the limiting factor
- The amount of chlorophyll in a plant can be affected by disease or environmental
stress, such as lack of nutrients. These cause chloroplasts to become damaged or
to not make enough chlorophyll. This means that the rate of photosynthesis is
reduced because they cant absorb as much light
- As the light level increases, the rate of photosynthesis increases steadily, but only
up to a certain point. Beyond that, it wont make a difference – as light intensity
increases, the rate will no longer increase because temperature or CO2 level will
now be the limiting factor
- CO2 will only increase the rate of photosynthesis up to a certain point, and after
this it is no longer the limiting factor. If light and CO2 are in supply, temperature
must be the limiting factor
4.4 Bioenergetics
4.4.1 Photosynthesis
4.4.1.1 Photosynthetic reaction
Photosynthesis is represented by the equation:
- Carbon dioxide + water (light) glucose + oxygen
It takes place in chloroplasts in green plants’ cells
It is an endothermic reaction – it takes in energy from the environment
Plants are adapted for photosynthesis by:
- having many leaves on a plant to form a mosaic so they have a large surface area to
absorb the maximum amount of sunlight
- leaves are flat and broad with a large surface area to absorb more sunlight for
photosynthesis
- thin leaves have lots of air spaces, so CO2 can diffuse rapidly into lea cells for
photosynthesis. In the spongy layer the CO2 diffuses rapidly into lead cells
- the leaf cells contain a lot of chloroplasts containing chlorophyll to absorb more
sunlight for the process
- palisade cells are long and closely packed together so there are more cells in the top
layer inside the lead – giving a larger surface are to absorb more light for
photosynthesis
4.4.1.2 Rate of photosynthesis
These factors (temperature, light intensity, carbon dioxide concentration and the
amount of chlorophyll) interact and any one of them may be the factor that limits
photosynthesis
- At night, light is the limiting factor, in winter temperature is the limiting factor and
if it is warm enough, the amount of CO2 is the limiting factor
- The amount of chlorophyll in a plant can be affected by disease or environmental
stress, such as lack of nutrients. These cause chloroplasts to become damaged or
to not make enough chlorophyll. This means that the rate of photosynthesis is
reduced because they cant absorb as much light
- As the light level increases, the rate of photosynthesis increases steadily, but only
up to a certain point. Beyond that, it wont make a difference – as light intensity
increases, the rate will no longer increase because temperature or CO2 level will
now be the limiting factor
- CO2 will only increase the rate of photosynthesis up to a certain point, and after
this it is no longer the limiting factor. If light and CO2 are in supply, temperature
must be the limiting factor
