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B4 B) The Rate of Photosynthesis
B4 B) The Rate of Photosynthesis
Plants create glucose by undertaking photosynthesis. Photosynthesis is where plants turn carbon dioxide and water into glucose and oxygen. The word and chemical equation for photosynthesis are shown below.
The Rate of Photosynthesis
There are three main factors that affect the rate of photosynthesis. These are:
All three of these factors can be a limiting factor. A limiting factor is where the rate of photosynthesis will not increase unless the limiting factor is increased. For example, if the concentration of carbon dioxide was the limiting factor for photosynthesis, the rate of photosynthesis would not increase unless we increased the concentration of carbon dioxide. Even if we increased the other factors (light intensity and temperature), the rate of photosynthesis would not increase because it is the concentration of carbon dioxide that is the limiting factor. The rate of photosynthesis will only increase when the limiting factor is increased (in this example, the rate of photosynthesis will only increase when the concentration of carbon dioxide increases).
In addition to these 3 factors, the rate of photosynthesis can be affected by the amount of chlorophyll/ chloroplasts that the plant has. Sometimes plants can be affected by a disease (like tobacco mosaic virus) or environmental stress (like a lack of nutrients), which can cause the plant to not make enough chlorophyll/ chloroplasts or cause the plant’s chloroplasts to become damaged. If the plant does not make enough chlorophyll/ chloroplasts or has damaged chloroplasts, the plant will not be able to absorb enough light, and therefore wont photosynthesis as well as a healthy plant. This will likely result in the plant have stunted or reduced growth; it may even result in the plant dying.
We are now going to have a look at the graphs that show how the rate of photosynthesis is affected by light, concentration of carbon dioxide and temperature.
There are three main factors that affect the rate of photosynthesis. These are:
- Light intensity
- Concentration of carbon dioxide
- Temperature
All three of these factors can be a limiting factor. A limiting factor is where the rate of photosynthesis will not increase unless the limiting factor is increased. For example, if the concentration of carbon dioxide was the limiting factor for photosynthesis, the rate of photosynthesis would not increase unless we increased the concentration of carbon dioxide. Even if we increased the other factors (light intensity and temperature), the rate of photosynthesis would not increase because it is the concentration of carbon dioxide that is the limiting factor. The rate of photosynthesis will only increase when the limiting factor is increased (in this example, the rate of photosynthesis will only increase when the concentration of carbon dioxide increases).
In addition to these 3 factors, the rate of photosynthesis can be affected by the amount of chlorophyll/ chloroplasts that the plant has. Sometimes plants can be affected by a disease (like tobacco mosaic virus) or environmental stress (like a lack of nutrients), which can cause the plant to not make enough chlorophyll/ chloroplasts or cause the plant’s chloroplasts to become damaged. If the plant does not make enough chlorophyll/ chloroplasts or has damaged chloroplasts, the plant will not be able to absorb enough light, and therefore wont photosynthesis as well as a healthy plant. This will likely result in the plant have stunted or reduced growth; it may even result in the plant dying.
We are now going to have a look at the graphs that show how the rate of photosynthesis is affected by light, concentration of carbon dioxide and temperature.
Light
Photosynthesis is an endothermic reaction, which means that it takes in energy from its surroundings (the products have more energy than the reactants). The plant gets the energy needed for photosynthesis from light. The graph for light intensity and the rate of photosynthesis is shown below.
Photosynthesis is an endothermic reaction, which means that it takes in energy from its surroundings (the products have more energy than the reactants). The plant gets the energy needed for photosynthesis from light. The graph for light intensity and the rate of photosynthesis is shown below.
If there is no light, the rate of photosynthesis would be zero. As we increase the light intensity, the rate of photosynthesis will increase because light intensity was the limiting factor (providing that there is enough carbon dioxide and a sufficient temperature). However, as we increase light intensity even more, the rate of photosynthesis will only increase up until a certain point, where it will flatten out because one or more of the other factors (concentration of carbon dioxide or temperature) is limiting the rate of photosynthesis. After this point, any increase in light intensity will not increase the rate of photosynthesis.
So, at the start of the graph, carbon dioxide was the limiting factor for photosynthesis (on the upwards sloping part), and at the end of the graph, one of the other factors (concentration of carbon dioxide or temperature) is the limiting factor for photosynthesis (this is the horizontal part).
So, at the start of the graph, carbon dioxide was the limiting factor for photosynthesis (on the upwards sloping part), and at the end of the graph, one of the other factors (concentration of carbon dioxide or temperature) is the limiting factor for photosynthesis (this is the horizontal part).
Carbon Dioxide
Carbon dioxide is one of the reactants in photosynthesis. The graph below shows how the rate of photosynthesis changes as we increase the concentration of carbon dioxide.
Carbon dioxide is one of the reactants in photosynthesis. The graph below shows how the rate of photosynthesis changes as we increase the concentration of carbon dioxide.
If there is no carbon dioxide, the rate of photosynthesis would be zero. If we then increase the concentration of carbon dioxide, the rate of photosynthesis would increase because carbon dioxide is the limiting factor (providing that there is enough light and a sufficient temperature). However, as we increase the concentration of carbon dioxide even more, the rate of photosynthesis will only increase up until a certain point, where it will flatten out because one or more of the other factors (light intensity or temperature) is limiting the rate of photosynthesis. After this point, any increase in the concentration of carbon dioxide will not increase the rate of photosynthesis.
So, at the start of the graph, the concentration of carbon dioxide was the limiting factor for photosynthesis (on the upwards sloping part), and at the end of the graph, one of the other factors (light intensity or temperature) is the limiting factor for photosynthesis (this is the horizontal part).
The graphs showing how light intensity and the concentration of carbon dioxide affect photosynthesis are very similar to each other.
So, at the start of the graph, the concentration of carbon dioxide was the limiting factor for photosynthesis (on the upwards sloping part), and at the end of the graph, one of the other factors (light intensity or temperature) is the limiting factor for photosynthesis (this is the horizontal part).
The graphs showing how light intensity and the concentration of carbon dioxide affect photosynthesis are very similar to each other.
Temperature
The final factor that affects the rate of photosynthesis is temperature. The graph showing how temperature affects the rate of photosynthesis looks different to the other two graphs.
The final factor that affects the rate of photosynthesis is temperature. The graph showing how temperature affects the rate of photosynthesis looks different to the other two graphs.
Enzymes carry out the photosynthesis reactions. Temperature is the limiting factor for photosynthesis when the temperature is too low. As the temperature rises, the rate of photosynthesis increases. This is because a greater temperature results in the reactants for photosynthesis (carbon dioxide and water) and the enzymes having more kinetic energy. This means that the reactants and enzymes move around faster, which results in more frequent collisions, thus meaning that there is a greater rate of photosynthesis.
However, if the temperature gets too high, the enzymes start to denature. Denaturing is where the excessive temperature causes the bonds that make up the enzyme to break. This changes the shape of the active site for the enzymes, which means that the reactants can no longer fit into the enzyme’s active site, thus resulting in the rate of photosynthesis decreasing. The denaturing temperature depends on the type of plant but is usually around 35-45°C.
So, there are 3 parts on the graph for how the rate of photosynthesis varies with temperature. The first part is where the temperature is too low, and this is where temperature is a limiting factor. The second part is when we reach the optimal temperature where photosynthesis is at its highest. The third part is where the temperature becomes so high that it denatures the enzymes, which causes the rate of photosynthesis to decrease.
However, if the temperature gets too high, the enzymes start to denature. Denaturing is where the excessive temperature causes the bonds that make up the enzyme to break. This changes the shape of the active site for the enzymes, which means that the reactants can no longer fit into the enzyme’s active site, thus resulting in the rate of photosynthesis decreasing. The denaturing temperature depends on the type of plant but is usually around 35-45°C.
So, there are 3 parts on the graph for how the rate of photosynthesis varies with temperature. The first part is where the temperature is too low, and this is where temperature is a limiting factor. The second part is when we reach the optimal temperature where photosynthesis is at its highest. The third part is where the temperature becomes so high that it denatures the enzymes, which causes the rate of photosynthesis to decrease.