What is photosynthesis?

Photosynthesis takes place inside plant cells in tiny objects called chloroplasts. Chloroplasts contain a green substance called chlorophyll. This absorbs the light energy needed for photosynthesis to occur. Plants and algae can only photosynthesize in light. Plants obtain carbon dioxide from the air through their leaves and water from the soil through their roots. Light energy comes from the Sun. The oxygen produced is released into the air from the leaves. The glucose produced can be converted into other substances, such as starch and vegetable oils, which are used as an energy reserve. This energy can be released by breathing.

These are the things plants need for photosynthesis:

  • Carbon dioxide
  • Water
  • Light (an energy source)

These are the things that plants do through photosynthesis:

  • Glucose
  • Oxygen

The verbal equation for photosynthesis in the presence of light and chlorophyll is:

Carbon dioxide + water → glucose + oxygen

Why is photosynthesis important?

Photosynthesis provides organisms with oxygen, a gas that many living things need. Oxygen is a product of photosynthesis and is necessary for respiration. All organisms breathe to release energy and stay alive. Without photosynthesis, life as we know it would come to an end since almost all food chains depend on it directly or indirectly. Producers such as algae, kelp, grasses, and phytoplankton require photosynthesis to make their own food.

Photosynthesis causes a balance in the ecosystem as it decreases the concentration of carbon dioxide in the atmosphere. Along with other processes like respiration and combustion, it can help maintain oxygen and carbon dioxide levels in the atmosphere. Without photosynthesis, we would not have fossil fuels like coal and oil, since these were formed from photosynthetic processes. These non-renewable sources were formed by the decomposition of older plants. Plant products such as wood, rubber, and oil also require photosynthesis to take place.

Plants and animals working together

The composition of the atmosphere has changed since the Earth was formed 4.5 billion years ago. Natural processes, such as photosynthesis, have helped maintain the levels of oxygen and carbon dioxide in the atmosphere that are necessary for survival. Plants release oxygen into the atmosphere as a byproduct of photosynthesis, and processes such as respiration and decomposition release carbon dioxide into the atmosphere. These processes work in a symbiotic way, where plants and animals depend on each other to benefit from this. Plants need the carbon dioxide released by respiration and decomposition, while animals need the oxygen released by plants from photosynthesis. This cycle helps maintain the balance of carbon dioxide and oxygen in the atmosphere.

Uses of glucose

Glucose is a useful molecule that is produced during the process of photosynthesis. The initial use of glucose, when it is broken down during respiration, is to release energy. Glucose is a molecule that can be joined together to make many types of carbohydrates, including cellulose and starch (in plants) and glycogen (in animals).

Think of it as if each glucose molecule is an individual bead on a necklace and the entire necklace represents the carbohydrate molecule. Plants only photosynthesize and synthesize glucose during the day when there is sunlight, but they use glucose to breathe all the time, even at night.


Glucose is used to make cellulose. Cellulose is an example of a natural polymer. Cellulose is the main component found in plant cell walls and gives plant cells strength and support. Cellulose cannot be digested by humans, but it is important in their diet as fibre. Fibre helps your digestive system by keeping food moving through the intestine and moving waste out of the body.


Another use of the glucose produced from photosynthesis is to make the insoluble storage molecule starch. Most plants, including rice, potatoes, and wheat, store their energy in the form of starch. Starch is also a polymer and can be converted back to glucose by the plant when needed, for example at night for respiration.

Fats and oils

Glucose can also be converted into fats and oils like olive oil. Fats and oils are also used by the plant as a form of energy storage.

Amino acids

The glucose produced in photosynthesis can be used to help make amino acids. These amino acids are used by the plant to synthesize proteins. Minerals like nitrate ions are also taken up by plant roots to help make these amino acids. Foods like peas are good sources of protein.