You get a snack from the fridge or ask for food whenever you feel hungry. All living beings need food to survive. Animals also get their food in the same manner as us. But what happens to plants? They cannot go elsewhere in search of food. Then how do they survive? Plants are living organisms just like us and need food to survive.

The difference between plants and animals is that plants make their food, while animals depend on others for their food. This is why plants are called autotrophs, and animals are called heterotrophs. The process by which plants make food for themselves is called photosynthesis. We will know about this process as we move further.

What is Photosynthesis?

During the process of respiration, when we give out carbon dioxide, this carbon dioxide is used by the plants to make their food. Carbon dioxide, water, and sunlight are used to make food for plants. Other than plants, even algae and other microorganisms use this process to manufacture their food. Several prokaryotes manufacture food with the process of photosynthesis, for example, cyanobacteria, purple bacteria and green sulfur bacteria.

Plants use light energy from sunlight, water from the roots and carbon dioxide from the air to make glucose and oxygen. Glucose is a form of sugar used by plants to survive. We use oxygen for breathing. This can be observed from the below formula of Photosynthesis as well:

6CO2 + 6H2O + Light Energy → C6H12O6 (Sugar) + 6O2 

The word “Photosynthesis” is derived from two words which mean light and combining together. Thus the word “Photosynthesis” means combining together with the help of light. According to the definition of photosynthesis, the process exclusively occurs in the chloroplasts. The process takes place with the help of photosynthetic pigments such as chlorophyll a, chlorophyll b, carotenoids and xanthophyll.

Which Cell Organelles of Plants are Responsible for Photosynthesis?

Chlorophyll is a pigment in photosynthetic cells, reflecting green light and strongly absorbing red and blue light. Chloroplasts contain chlorophyll. It is in chloroplasts that the process of photosynthesis takes place. Chlorophyll A plays a major role in photosynthesis. We are the types of chlorophyll.

The other types of chlorophyll and various other pigments, including red, brown and blue pigments, respond to light. They may help protect the cell from photo-damage or channel light energy towards chlorophyll A. For example, for eating shellfish, a prompt warning is generated. These warnings are generated by photosynthetic protists called dinoflagellates, which contain numerous light-sensitive pigments, including chlorophyll and direct pigments responsible for the significant colouration.

A double membrane surrounds the chloroplast. Chloroplasts contain a third inner membrane called the thylakoid membrane. This membrane forms long folds within the organelle. When seen under the microscope, thylakoid membranes look like stacks of coins, and the compartments they form are connected like a group of chambers. These thylakoid membranes contain chlorophyll. The space between the thylakoid and the chloroplast membranes is called the stroma.

The Process of Photosynthesis

Now that we know which organelles are responsible for the occurrence of photosynthesis, let us understand how the phenomenon takes place. Photosynthesis takes place in the cell organelle called the chloroplast. Chloroplast contains a green colour pigment called chlorophyll, which gives the leaves a green colour. Leaves consist of a petiole, epidermis and a lamina. The lamina absorbs sunlight and carbon dioxide during the process of photosynthesis.

During photosynthesis, carbon dioxide enters the stomata. The root hairs absorb the water from the soil and carry it to the leaves through the xylem vessels. Chlorophyll absorbs light energy from the sun and splits water molecules into hydrogen and oxygen.

The carbon dioxide from the air and hydrogen from the water molecules are used to produce glucose. The oxygen is liberated into the atmosphere through leaves as a waste product. Glucose act as a source of food for plants. It provides energy for their growth and development. The remaining is stored in roots, leaves and fruits.

The whole process of photosynthesis occurs in two stages:

• Light reaction or light-dependent reaction.
  
• Dark reaction or light-independent reaction.
  
• Light reaction: This process is carried out in the presence of sunlight. The light reaction takes place in the thylakoid membranes. The grana inside the thylakoid collect the light. It is therefore called photosystems. Photosystems have large complexes of pigment and protein molecules present in the cells. This is what plays the major role during light reactions. During light reactions, the light energy is converted into ATP and NADPH, which are generated by two-electron transport chains and are used by the plants in the second phase of photosynthesis. 

Formula of Light Reaction is given by:

2H2O + 2NADP+ + 3ADP + 3Pi → O2 + 2NADPH + 3ATP

• Dark Reaction: Dark reaction can occur during the evening. This reaction occurs in the stroma, where they use NADPH and ATP products. It is also called a carbon fixing reaction. In this reaction, sugar molecules are formed from water and carbon dioxide molecules. The plants capture the carbon dioxide from the atmosphere through stomata, and the process moves towards the Calvin cycle. Calvin cycle involves four major steps: carbon fixation, reduction, carbohydrate formation, and regeneration. In the Calvin cycle, the ATP and NADPH from the light reaction drive the reaction, converting 6 molecules of carbon dioxide into one molecule of glucose.

Formula of Dark Reaction is given by:

3CO2 + 6 NADPH + 5H2O + 9ATP → G3P + 2H+ + 6 NADP+ + 9 ADP + 8 Pi

Importance of Photosynthesis

Let us understand why the process of Photosynthesis is so important.

• Most living organisms depend on cells which contain special pigments to manufacture complex organic molecules and absorb light energy, also called photosynthetic cells. Carbon dioxide from the air and light energy from the Sun to make sugar molecules and oxygen. These sugar molecules form the base for more complex molecules, such as glucose.
  
• By the process of respiration, cells use oxygen and glucose to synthesise carrier molecules that are rich in energy, for example, ATP and produce carbon dioxide as a waste product.  
  
• Photosynthesis is the process by which plants make their own food, thereby making them the primary producers in the food chain. 
  
• Photosynthesis is the process by which plants produce oxygen that living organisms use to breathe. Hence, a vast majority of life on Earth is dependent upon photosynthesis for existence. If photosynthesis ceased to exist, no food would remain on the planet, most organisms would disappear, and there would be no oxygen remaining on the Earth.

The population has increased over time. To ensure that we have adequate space and comfort to accommodate the human being on the planet, we are cutting down trees and constructing buildings. This is impacting our ecosystem. Animals, birds and insects that live in the trees and forests are losing their habitats. This is causing a disbalance in the food chain.

Cutting down trees is also impacting our planet. A rise in temperature and changes in weather patterns have been observed worldwide, a phenomenon widely known as global warming. Reducing this is exceptionally essential. Afforestation is a way in which this can be reduced.

What are the Factors Affecting Photosynthesis?

We can see that for photosynthesis to take place, a number of factors are essential. Let us find out what are those factors.

• Intensity of Light: More the intensity of light, the higher the rate of photosynthesis. Alternatively, the lesser the intensity of light, the lower the rate of photosynthesis.

• Concentration of Carbon Dioxide: A higher concentration of carbon dioxide helps in speeding up the rate of photosynthesis. Usually, carbon dioxide in the range of 300 to 400 PPM, is sufficient for photosynthesis to take place.

• Temperature: A temperature range between 25 degrees to 35 degrees celsius is ideal for photosynthesis.

• Water: The importance of water lies in the fact that this is what supports the plants to take in carbon dioxide. The deficiency of water also prevents stomata from retaining the amount of water they have stored inside them.

• Pollution: When different particulates and pollutants from the industries settle on the surface of the leaf, this can lead to the blocking of the stomatal pores further making it difficult to take carbon dioxide. 

We hope that this information on photosynthesis in plants has helped you. Stay tuned to Embibe for the latest news and updates on photosynthesis in plants.