Plants are living organisms. They have different parts called organs, and each organ has a specific function. Plants are part of the Plantae kingdom, and they exist all around Earth.

Plants are important as they release oxygen that we breathe, and they eliminate harmful toxins. Moreover, plants are producers; therefore, they are a source of food for many animals. Plants make their food via the process of photosynthesis. Most of life on Earth depends on photosynthesis.

Photosynthesis is the process that takes place inside a plant. It is when plants use light to make food. An easy way to remember this is to remember that ‘photo’ means light, and ‘synthesis’ means to put something together. This chemical reaction is vital for a plant to survive and grow. Plants need food to respire, grow, and reproduce.

Photosynthesis takes place in the leaves of a plant – specifically in the chloroplasts of leaves containing chlorophyll. We can use an equation to explain the process of photosynthesis.

Photosynthesis word equation:

Carbon dioxide + Water ➜ Glucose + Oxygen 

Photosynthesis balanced equation: 

6CO2 + 6H2O ➜ O2 + C6H12O6 

What is the process of photosynthesis?

There are several stages to the process of photosynthesis.
First, carbon dioxide (CO2) and water (H20) enter the plant through the air and soil. Carbon dioxide enters through the stomata of the leaf via diffusion. Water is absorbed by the roots from the soil. This water is then transported to the leaves via the xylem vessels. Within the plant cell, water is oxidised, and carbon dioxide is reduced – this transforms the water into oxygen and the carbon dioxide into glucose. Remember that oxidised means it loses electrons, and reduced means it gains electrons.

Sunlight provides the energy for the process to take place. The light-absorbing pigment called chlorophyll within the chloroplasts absorbs the light’s energy. Chlorophyll is responsible for giving leaves their green colour; it does this as it absorbs red-light and blue-light waves; and reflects green-light waves. This makes the leaves appear green.

Chlorophyll absorbs energy from light waves and converts it to chemical energy in the form of the molecule ATP and NADPH (Calvin cycle). The energy from ATP and NADPH is used to produce glucose from carbon dioxide.

The products are oxygen and glucose. Oxygen is released back into the air through the stomata of the leaf. Glucose is a source of energy for the plant. Glucose is transported around the plant via the phloem vessels.

How are leaves adapted for photosynthesis? 

• Large surface area
• Contain chlorophyll
• Thin
• Network of veins

Leaves are adapted for photosynthesis in a few different ways.

Firstly leaves are big and they have a large surface area. This allows more sunlight to be absorbed. Secondly, leaves are green due to the chlorophyll in the chloroplasts. This helps them to absorb sunlight. Thirdly, leaves are thin which allows the diffusion of gases in and out of the leaves. Fourthly the leaves have vascular tissues. Tubes that carry food from the leaves to the rest of the plant are known as phloem. Tubes that carry water and nutrients from the roots to the other parts of the plant are called xylem. 

What are the factors that affect photosynthesis?

• ↓ carbon dioxide 
• ↓ water
• ↓ light energy
• ↑ temperature 
• ↓ chlorophyll

Once we understand the process of photosynthesis and the elements involved, then we can understand that if any of these elements are limited, then it will affect the rate of photosynthesis. So if there is not enough carbon dioxide, water, or light energy, then the rate of photosynthesis will be affected.

If there is not enough light, then a plant can’t photosynthesise quickly despite there being plenty of water and carbon dioxide; therefore, increasing light intensity will increase the rate of photosynthesis. Likewise, if there is not enough carbon dioxide, regardless of whether there is enough light or water, the plant won’t be able to photosynthesise. Therefore increasing carbon dioxide concentration will increase the rate of photosynthesis. Furthermore, without water, a plant will eventually dry up and die. This is because water also keeps the plant strong and sturdy; therefore, if there is not enough water, then the pressure inside the plant reduces, and the plant will wilt.

Other factors that affect photosynthesis are the temperature and the amount of chlorophyll. So if the temperature is too high, then enzymes will denature, and they won’t be able to carry out the process of photosynthesis. On the other hand, if there is less chlorophyll in the leaves, then this means that less light energy can be absorbed. Ultimately both will result in a lower rate of photosynthesis.