[Biology Class Notes] on Photosynthesis Pdf for Exam

Photosynthesis is the process by which a plant produces its food by converting light energy into chemical energy. Plants use water, carbon dioxide and sunlight in the presence of chlorophyll to produce their food or energy in the form of sugar and release oxygen as the byproduct. Understanding the process of photosynthesis means a clear concept about the different cellular and chemical activities going on in the plant body. The word photosynthesis is coined from the Greek word for meaning light along with synthesis. This implies a synthesis i.e a chemical reaction using light energy. This is not always for green plants only but certain bacteria and prokaryotes also use this process to prepare their food. In green plants or algae, the synthesis takes place within an important organelle called chloroplast where the pigment chlorophyll is present. Chlorophyll occurs in their leaves, stems, flowers, sepals and even in plastids.

 

Factors Affecting Photosynthesis

Various factors influence/affect the photosynthesis process. These are:

• Light Intensity: More the light, the more will be the rate of photosynthesis. Similarly, low light will lead to a low rate of photosynthesis.

• The Concentration of CO₂: A higher CO₂ concentration rate in a plant also accelerates the photosynthesis process. The required amount of CO₂ is 300-400 PPM.

• Temperature: If the temperature is between the range of 25 to 35 degrees Celsius, photosynthesis takes place effectively.

• Water: An essential amount of water is required for stomatal opening, and it’s a key factor in the process of photosynthesis.

• Pollution: The increasing rate of polluting particles in the atmosphere block the pores of somatic cells, and the intake of carbon dioxide becomes difficult.

Photosynthesis Equation

Carbon dioxide and water are the two major factors involved in the photosynthesis reaction. It’s an endothermic reaction, and the products resulting from it are oxygen and glucose. The formula is:

[6CO_{2} + 6H_{2}O = C_{6}H_{1}2O_{6} + 6O_{2}]

However, some bacteria don’t produce oxygen as a by-product of photosynthesis. They are called anoxygenic photosynthetic bacteria, and those who do it are called oxygenic photosynthetic bacteria.

 

Photosynthetic Pigments

Four types of photosynthetic pigments are present in the leaves of the plants. They are:

1. Chlorophyll a

2. Chlorophyll b

3. Xanthophylls

4. Carotenoids

 

Structure of Chlorophyll

Chlorophyll is a green colour pigment found in plants that play a vital role in photosynthesis. It allows the plants to absorb the energy coming from the sunlight, which is essential for photosynthesis.

 

Process of Photosynthesis

The photosynthesis process occurs in plants. It takes place in chloroplasts at the cellular level that contains chlorophyll. Leaves have parts called the petiole, epidermis, and lamina that absorb sunlight.

 

Photosynthesis Steps:

The photosynthesis process takes place at two levels or steps. These are:

The process begins in the daylight, by gathering the light. The two types of photosystems convert light energy into ATP and NADPH. During their conversion, oxygen is produced, and water is used. The equation of this step is:

[2H_{2}O + 2NADP + 3ADP + 3P_{i} = O_{2} + 2 NADPH + 3ATP]

This is also called carbon-fixing. It is not dependent on light and takes place in chloroplast where the products from the earlier step are used. Plants intake CO₂ and the Calvin Photosynthesis Cycle begins, where the six molecules of CO₂ are converted into sugar or glucose.

[3CO_{2} + 6NADPH + 5H_{2}O + 9ATP = G3P + 2H + 6NADP + 9ADP + 8P_{i}]

The photosynthesis process is very important for the survival of living beings, and to continue the food chain. It also produces oxygen, which is required for breathing.