Rate of Photosynthesis

Rate of Photosynthesis

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Are you curious about how plants absorb light energy? Through a technique called chromatography, you can investigate the pigments present in a single plant leaf. But how does light energy turn into chemical energy, and what affects this process? Biologists use different factors to measure the rate of photosynthesis. Chromatography separates a mixture into its parts, and it's the perfect way to isolate the different pigments that give leaves their distinct colours. So, what sort of factors affect how efficiently light energy is turned into ATP? Keep reading to find out! Remember, the rate of photosynthesis is a crucial factor in understanding how plants grow and thrive.

The redox indicator and the rate of photosynthesis

To investigate the rate of photosynthesis, we use a substance called a redox indicator. 'Redox' stands for 'oxidation-reduction', which is a reaction where electrons are both lost and gained. Redox indicators are a type of chemical that you can add to a solution. When the solution is reduced or oxidised, the redox indicator causes a sudden colour change. We use redox indicators in many chemistry and biology experiments, including when we investigate the rate of respiration. In this experiment, we can use redox indicators like DCPIP or methylene blue to measure the rate of photosynthesis. These indicators are crucial to understanding how plants convert light energy into chemical energy.

How to investigate the rate of photosynthesis using redox indicators

Generally, photosynthesis is affected by three main factors: light intensity, carbon dioxide concentration, and temperature.

Reaction mechanism

The light-dependent reactions of photosynthesis take place in the plant cell’s chloroplasts, along the thylakoid membrane.

Diagram of a chloroplast
Diagram of a chloroplast

During photosynthesis, chlorophyll absorbs light energy in the form of photons. This energy causes the electrons in chlorophyll to move to a higher energy level, allowing them to participate in other reactions. An electron acceptor will then pick up these high-energy electrons and move down an electron transport chain. However, if a redox indicator is present, it will take up these high-energy electrons instead and cause a colour change, allowing us to measure the rate of photosynthesis.

The light-independent reaction is known as the Calvin Cycle. This process needs carbon dioxide to form glucose. One molecule of carbon dioxide combines with a molecule named RubP and splits into two molecules of 3-phosphoglycerate. ATP and NADPH, both produced at the start of the light-dependent reaction, donate a Hydrogen atom to 3-phosphoglycerate, transforming it into G3P, a type of sugar. The two molecules of GP the glucose needed plant Calvin Cycle typically uses six carbon dioxide molecules and produces only one molecule of glucose at a time. The leftover G3Ps are recycled back into RubP, allowing the cycle to continue. Understanding the Calvin Cycle is essential to understanding how plants convert carbon dioxide into glucose, which fuels their growth and survival.

Which factors affect the rate of photosynthesis?

Photosynthesis is affected by a number of factors. However, the following factors can limit the rate of photosynthesis when they are in short supply:


As the intensity of light increases, so does the rate of light-dependent reactions in photosynthesis. This means that increasing the intensity of light will increase the overall rate of photosynthesis. This is because the photons will activate more electrons in the chlorophyll, allowing water to be oxidised faster. As a result, the production of ATP and NADPH increases, and more cycles of the light-independent reaction occur.

However, there limit to how much light a certain point, the rate of photosynthesis remains constant even if the light intensity increases. This is because one or more of the other factors, such as carbon dioxide concentration, temperature or water availability, become limiting factors. Once these factors become limiting, the rate of photosynthesis cannot increase further, even if light intensity continues to increase. Understanding the factors that limit photosynthesis is crucial to improving crop yields and plant growth.

Carbon dioxide concentration

Increasing the concentration of carbon dioxide can increase the rate of photosynthesis up to a certain point. This is because more carbon dioxide molecules being available means that more cycles of the light-independent reaction can occur at a higher rate. As a result, more glucose molecules are produced, and more NADPH and ATP are used up. Additionally, more RuBP is produced, which is crucial for the primary acceptance of carbon dioxide during the Calvin Cycle, further increasing the rate of photosynthesis.

However, at a certain level, the rate of photosynthesis will be limited by other factors such as the availability of light energy or heat energy. This means that even if the concentration of carbon dioxide increases, the rate of photosynthesis will not be able to increase beyond a certain.

It is important to carbon concentration cannot be measured a as involved of photosynthesis the factors that limit photosynthesis is essential for improving crop yields and plant growth.


Temperature is a crucial limiting factor for the rate of enzymes control the of temperature to point. However, unlike with carbon dioxide concentration and light intensity, the rate of photosynthesis reaches an optimal point before drastically declining.

The enzymes that control photosynthesis work best at around 35°C-40°C. If the temperature increases past this optimum point, the enzymes start to denature. This can cause the enzyme's active site shape to change, and the substrate no longer fits. This is why there is a sharp decline in photosynthesis rate at higher temperatures. If the temperature is lower than 35°C, photosynthesis occurs at a slower rate because the enzymes do not move as fast. This means fewer reactions can occur since it is harder to find the substrate.

It is important to note that water is not a limiting factor for photosynthesis. There is very little water needed in the entire process of photosynthesis. However, even if there was a shortage of water to the point where photosynthesis would be restricted, the plant's stomata would begin to close and absorb carbon dioxide at a slower rate. Therefore, other processes would stop before water could have a limiting effect on them. Understanding these factors that limit photosynthesis is crucial for improving crop yields and plant growth.

Rate of Photosynthesis - Key takeaways

of that can be added to a solution to determine if it has been oxidized or reduced. These indicators cause a sudden color change in the solution when it is oxidized or reduced. Examples of redox indicators include DCPIP or methylene blue. To investigate the rate of photosynthesis, a redox indicator is typically combined with a leaf extract. The redox indicator is used to take up the high-energy electrons that are usually taken by an electron acceptor. This will cause the color change that can be observed in the experiment.

There are three main factors that generally affect the rate of photosynthesis: light intensity, temperature, and carbon dioxide concentration. By controlling these factors, it is possible to optimize the rate of photosynthesis and improve plant growth. Understanding the impact of these factors on the rate of photosynthesis is crucial for improving crop yields and plant growth.

Rate of Photosynthesis

How does light intensity affect the rate of photosynthesis?

More light means photosynthesis can occur faster. 

What factors affect the rate of photosynthesis? 

Light, carbon dioxide concentration, water, oxygen, pollutants, minerals, and temperature.

What factors increase the rate of photosynthesis? 

Light, carbon dioxide concentration, and temperature.

How does temperature affect the rate of photosynthesis?

Low temps limit the rate of molecular collisions, and high temps denature the enzymes. 

How do you measure the rate of photosynthesis? 

You can measure the rate by studying the production of oxygen, an increase in pH due to increasing carbon dioxide, and an increase in biomass.

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