The process of photosynthesis

Plants, unlike animals, can make their own food. They do this using a process called photosynthesis. The food that plants produce is important, not only for the plants themselves, but for the other organisms that feed on the plants. Getting optimum rates of photosynthesis produces maximum plant yields.

Greg Foot explains the effect of temperature, light intensity and carbon dioxide concentration on the rate of photosynthesis

During photosynthesis, plants produce glucose from simple inorganic molecules – carbon dioxide and water – using light energy.

The word and symbol equations for photosynthesis are:

Diagram illustrating the word and symbol equations for photosynthesis
curriculum-key-fact
Be careful not to confuse this photosynthesis equation with respiration which is the reverse of this. The balanced symbol equation shown above is Higher tier only.

Photosynthesis requires energy in the form of light to drive the chemical reaction. Photosynthesis is an endothermic reaction.

The light energy required is absorbed by a green pigment called chlorophyll in the leaves. Chlorophyll is located in chloroplasts in plant cells, particularly the palisade and spongy mesophyll cells. Revise plant cells and their part in photosythesis here.

Plant leaves are the main photosynthetic organ, but any part of the plant exposed to the light will develop chlorophyll and photosynthesise.

The carbon dioxide required for photosynthesis comes from the air. It enters leaves through the stomata. Water enters the plant through the roots, and is transported to the leaves in the xylem.

Oxygen is formed as the waste product. Some is used for the plant's respiration, and also released, which makes it available for respiration to animals and many microorganisms. During the day, provided the rate of photosynthesis is sufficiently high, plant leaves and water plants give out oxygen.

Biosynthesis

Some of the glucose produced by photosynthesis is used for respiration.

Glucose is also the starting point for the biosynthesis of materials that plants need to live.

The glucose not used for respiration is used in the following ways:

An image showing the cycle of gluecose.

There are four major uses of glucose produced in photosynthesis:

  1. Many glucose molecules are joined together to form insoluble starch. This is a storage product of glucose in plants.
  2. Many glucose molecules are joined together to form insoluble cellulose. This is used to build cell walls for new growth.
  3. Glucose is joined with nitrates absorbed from the soil to make amino acids. These are joined together to make proteins during protein synthesis.
  4. Glucose is also converted to lipids, which is often stored in seeds.