[Biology Class Notes] on Photosynthesis Process Pdf for Exam

Photosynthesis is the process of capturing light energy and transforming it into chemical energy. Green plants and several other organisms use light energy and convert carbon dioxide and water into glucose. In this process, oxygen is produced as a by-product. This process can be seen in green plants and photosynthetic bacteria. They use electromagnetic radiation and convert it into chemical energy. With the help of water and sunlight, they absorb carbon dioxide from the atmosphere and turn it into oxygen and carbohydrates.

The process provides not only energy needed but also helps in forming biomolecules. This reaction is an oxidation-reduction reaction that uses sunlight and nitrogen available in the atmosphere. It is the basic element in the food cycle. All the other organisms derive their energy from green plants and other photosynthetic bacteria. Hence, these plants are called autotrophs as they prepare their own food with the help of naturally available elements. One of the essential requirements for this process is a pigment called “chlorophyll”. This pigment is present in green plants and some bacteria. It helps in tapping sunlight and starting the entire process. 

This process of converting light energy to other forms differs in plants and other bacteria. In the case of plants, water is used to form energy in the form of glucose and oxygen. On the other hand, in the case of bacteria, hydrogen sulphide replaces the water along with carbon dioxide to release carbohydrates, sulfur, and water molecules. Some of the photosynthetic pigments are chlorophyll, phycobilins, bacteriorhodopsin, carotenoids.  Chlorophyll is present in most green plants and helps in receiving sunlight and converting it into energy and glucose. They have single and double bonds alternatively, this makes them effective photoreceptors. Bacteriorhodopsin is another photosynthetic pigment that is generally present in Halobacteria. Phycobilins are present in cyanobacteria and red algae. 

The photosynthesis process step by step conducts these reactions and maintains the balance of oxygen and carbon dioxide in the atmosphere. However, photosynthesis in plant leaves usually occurs in two ways. These are light-dependent reactions and light-independent reactions or dark reactions. 

This process happens in the thylakoid membrane and needs a constant supply of photons or light energy. Chlorophylls use this energy and produce ATP and NADPH. Water molecules are transformed into oxygen through this process. 

This reaction happens in the stroma and can take place in the absence of light. It takes up ATP and NADPH produced from the light reaction to break down carbon dioxide. This process helps in forming three types of carbon sugars that create glucose. 

Let’s understand the photosynthesis process step by step!

Step by Step Procedure of Photosynthesis

Fig: Process of photosynthesis

Plant leaves absorb the photons from sunlight that excite chlorophyll and activate electrons. In the first step, the water absorbed by plant roots is split into oxygen and hydrogen ions. 

Then the excited electrons from ATP and NADPH. This process happens through the electron chain. Likewise, in this process, oxygen is released into the atmosphere through leaves. 

In the next step, the energy from the light reaction transforms carbon dioxide into glucose. This whole process takes place in several stages. The series of reactions start with 3-Ribulose biphosphate (RuBP) and ends with the same molecule forming glucose. 

The Rubisco enzyme is an essential component of this Calvin Cycle that initiates all the reactions. 

All the significant reactions of the photosynthesis process generally take place during the daytime in the chloroplasts of leaves. 

Following is the fundamental equation of photosynthesis

 6CO2 + 6H2O (+ light energy) → C6H12O6 + 6O2

This is the overall overview of how the photosynthesis process step by step takes place. 

Factors that Affect Photosynthesis

Following is the list of factors that influence the rate of photosynthesis.

Generally, with higher light and temperature intensity, the rate of photosynthesis increases. However, after a specific intensity of light, this rate saturates. It solely depends on the growing condition and species of the plants. 

The rate of photosynthesis depends on a steady water supply. A minimal amount of water is required to conduct the reactions. The maximum amount of water transpires through the stomata of leaves. 

In arid areas, therefore, the opening and closing of stomata are limited. This allows reserving the water supply and overall temperature of leaves. 

The concentration of carbon dioxide influences mainly the dark reactions of photosynthesis. Hence, this rate increases with the increased supply of carbon dioxide. 

A few minerals like potassium, iron, magnesium, phosphate, etc. are essential for plant growth. They also hasten the rate of photosynthesis of plants. 

Apart from that, a few other factors like environment, species, etc. affect the rate of photosynthesis. 

Importance of Photosynthesis

• It helps to maintain a healthy relationship between animals, plants, and humans making them mutually dependent.

Pop Quiz 

1. Photosynthesis is a/an _______________ process.

2. _______________ colour of light is responsible for photosynthesis in bacteria. 

3. Which metal is present in both chlorophyll “a” and “b”?

1. Magnesium

2. Iron

3. Manganese 

4. Copper

4. Chlorophyll is the structural unit of photosynthesis. True/False.

Answers: 1- Anabolic, 2-Red, 3-a), 4- False.

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