Topic 4- Bioenergetics
Photosynthesis
● Photosynthesis uses light energy to change carbon dioxide and water into glucose and oxygen.
● It takes place in chloroplasts in green plant cells - they contain pigments like chlorophyll that absorb light.
● Energy is transferred to the chloroplasts from the environment by light
● It is endothermic - energy is transferred from the environment in the process. The word equation:
How plants use Glucose:
1. For respiration - This transfers energy from glucose which enables the plants to convert the rest of the glucose into other useful substance
2. Making Cellulose - Glucose is converted into cellulose for making strong plant cell walls
3. Making amino acids - Glucose is combined with nitrate ions (absorbed from the soil) to make amino acids, which are then made into
proteins
4. Stored as oils or fats - Glucose is turned into lipids for storing in seeds
5. Stored as starch - Glucose is turned into starch and stored in roots, stems and leaves, to use when photosynthesis isn’t happening(winter
6. Starch is insoluble, which makes it a better store than glucose - a cell with lots of glucose in would draw in loads of water and swell up
The rate of Photosynthesis
These factors have a combined effect on the rate of photosynthesis, but which factor is limiting at a particular time depends on the environmental
conditions
- At night it’s pretty obvious that light is the limiting factor
- In winter it’s often the temperature
- If it’s warm enough and bright enough, the amount of CO2 is usually limiting
Chlorophyll can also be a limiting factor of photosynthesis:
- The amount of chlorophyll can be affected by disease or environmental stress, such as a lack of nutrients. These factors can cause
chloroplasts to become damaged or to not make enough chlorophyll
- This means the rate of photosynthesis reduced because they can’t absorb as much light
The effect of Light
● Light provides the energy needed for photosynthesis
● As the light level is raised, the rate of photosynthesis increases steadily - but only up to a
certain point
● Beyond that, it won’t make any difference - as light intensity increases the rate will no longer
increase, as either temperature or the CO2 level is now the limiting factor
The effect of Carbon dioxide
● As with light intensity, the amount of Co2 will only increase the rate of photosynthesis up to a
point
● After this the graph flattens out - as CO2 is no longer the limiting factor
● As long as light and Co2 are in plentiful supply then the factor limiting photosynthesis must be
temperature
The effect of Temperature
The temperature has to be just right - temperature affects the rate of photosynthesis because it affects
the enzymes involved
● If the temperature is the limiting factor it’s usually because it’s too low -the enzymes
needed for photosynthesis work more slowly at low temperatures
● But if the plant gets too hot, the enzymes it needs for photosynthesis and its other
reactions will be damaged
● This happens at about 45℃
, Graphs
Measuring the Rate of Photosynthesis
Canadian pondweed can be used to measure the effect of light intensity on the rate of photosynthesis. The rate of oxygen produced is directly
proportional to the rate of photosynthesis. The faster the rate of oxygen production, the faster the rate of photosynthesis.
Method
1. A source of white light is placed a specific distance from the
pondweed.
2. The pondweed is left to photosynthesise for a set amount of
time. Oxygen produced during this time will be put into a
capillary tube.
3. At the end of the experiment, a syringe is used to collect the
oxygen bubble produced. The length of the gas bubble is then
measured. This is proportional to the volume of O2 produced.
4. For this experiment, any variables that could affect the results
should be controlled, e.g the light intensity and time the
pondweed is left to photosynthesise.
5. The experiment is repeated twice with the light source at the
same distance and the mean volume of O2 produced is
calculated.
6. Then the whole experiment is repeated with the light source at different distances from the pondweed.
The apparatus can be altered to measure the effect of temperature or CO2 on photosynthesis.
For example;
- The test tube can be put into a water bath at a set temperature, or a measured amount of sodium hydrogen carbonate can be dissolved in
the water ( which gives off CO2).
- The experiment can then be repeated with different temperatures of water or concentrations of sodium hydrogen carbonate.
Inverse Square Law
When the lamp is moved away, the amount of light on the pondweed decreases.
This is because light intensity and distance are inversely proportional to one another.
However, it is not as simple as that. Light intensity is inversely proportional to the square of the distance. This is called the inverse square law.
1
--- can be used as a measure of
d2 light intensity.
Photosynthesis
● Photosynthesis uses light energy to change carbon dioxide and water into glucose and oxygen.
● It takes place in chloroplasts in green plant cells - they contain pigments like chlorophyll that absorb light.
● Energy is transferred to the chloroplasts from the environment by light
● It is endothermic - energy is transferred from the environment in the process. The word equation:
How plants use Glucose:
1. For respiration - This transfers energy from glucose which enables the plants to convert the rest of the glucose into other useful substance
2. Making Cellulose - Glucose is converted into cellulose for making strong plant cell walls
3. Making amino acids - Glucose is combined with nitrate ions (absorbed from the soil) to make amino acids, which are then made into
proteins
4. Stored as oils or fats - Glucose is turned into lipids for storing in seeds
5. Stored as starch - Glucose is turned into starch and stored in roots, stems and leaves, to use when photosynthesis isn’t happening(winter
6. Starch is insoluble, which makes it a better store than glucose - a cell with lots of glucose in would draw in loads of water and swell up
The rate of Photosynthesis
These factors have a combined effect on the rate of photosynthesis, but which factor is limiting at a particular time depends on the environmental
conditions
- At night it’s pretty obvious that light is the limiting factor
- In winter it’s often the temperature
- If it’s warm enough and bright enough, the amount of CO2 is usually limiting
Chlorophyll can also be a limiting factor of photosynthesis:
- The amount of chlorophyll can be affected by disease or environmental stress, such as a lack of nutrients. These factors can cause
chloroplasts to become damaged or to not make enough chlorophyll
- This means the rate of photosynthesis reduced because they can’t absorb as much light
The effect of Light
● Light provides the energy needed for photosynthesis
● As the light level is raised, the rate of photosynthesis increases steadily - but only up to a
certain point
● Beyond that, it won’t make any difference - as light intensity increases the rate will no longer
increase, as either temperature or the CO2 level is now the limiting factor
The effect of Carbon dioxide
● As with light intensity, the amount of Co2 will only increase the rate of photosynthesis up to a
point
● After this the graph flattens out - as CO2 is no longer the limiting factor
● As long as light and Co2 are in plentiful supply then the factor limiting photosynthesis must be
temperature
The effect of Temperature
The temperature has to be just right - temperature affects the rate of photosynthesis because it affects
the enzymes involved
● If the temperature is the limiting factor it’s usually because it’s too low -the enzymes
needed for photosynthesis work more slowly at low temperatures
● But if the plant gets too hot, the enzymes it needs for photosynthesis and its other
reactions will be damaged
● This happens at about 45℃
, Graphs
Measuring the Rate of Photosynthesis
Canadian pondweed can be used to measure the effect of light intensity on the rate of photosynthesis. The rate of oxygen produced is directly
proportional to the rate of photosynthesis. The faster the rate of oxygen production, the faster the rate of photosynthesis.
Method
1. A source of white light is placed a specific distance from the
pondweed.
2. The pondweed is left to photosynthesise for a set amount of
time. Oxygen produced during this time will be put into a
capillary tube.
3. At the end of the experiment, a syringe is used to collect the
oxygen bubble produced. The length of the gas bubble is then
measured. This is proportional to the volume of O2 produced.
4. For this experiment, any variables that could affect the results
should be controlled, e.g the light intensity and time the
pondweed is left to photosynthesise.
5. The experiment is repeated twice with the light source at the
same distance and the mean volume of O2 produced is
calculated.
6. Then the whole experiment is repeated with the light source at different distances from the pondweed.
The apparatus can be altered to measure the effect of temperature or CO2 on photosynthesis.
For example;
- The test tube can be put into a water bath at a set temperature, or a measured amount of sodium hydrogen carbonate can be dissolved in
the water ( which gives off CO2).
- The experiment can then be repeated with different temperatures of water or concentrations of sodium hydrogen carbonate.
Inverse Square Law
When the lamp is moved away, the amount of light on the pondweed decreases.
This is because light intensity and distance are inversely proportional to one another.
However, it is not as simple as that. Light intensity is inversely proportional to the square of the distance. This is called the inverse square law.
1
--- can be used as a measure of
d2 light intensity.
