Photosynthesis

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Key points

  • is a process that occurs in the leaves of a plant and needs both and light energy.

  • During photosynthesis, the chlorophyll in leaves help convert carbon dioxide and water into the products oxygen and glucose.

  • The glucose acts as a vital source of food for the plant.

  • Carbon dioxide, water and light are all needed for photosynthesis to take place.

What is photosynthesis?

Photosynthesis takes place inside plant cells in small objects called chloroplasts. Chloroplasts contain a green substance called chlorophyll. This absorbs the light energy needed to make photosynthesis happen. Plants and algae can only carry out photosynthesis in the light.

A diagram of a plant cell
A diagram of a plant cell to show its main components

Plants get carbon dioxide from the air through their leaves, and water from the ground 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 turned into other substances, such as starch and plant oils, which are used as an energy store. This energy can be released by

Video - Creating photosynthesis

The head groundsman at Derby County FC discusses how he uses knowledge of photosynthesis to maintain the pitch.

Can you answer these questions based on the video?

1. Derby County FC has a very big shade issue with regards to the growth of their grass pitch. What do they use to overcome this problem?

2. Name three qualities of the pitch that is measured to ensure healthy, durable grass to play football on?

  1. Artificial lighting.

  2. Moisture, length of the grass and hardness of the surface.

These are the things that plants need for photosynthesis:

  • Carbon dioxide
  • Water
  • Light (a source of energy)

These are the things that plants make by photosynthesis:

  • Glucose
  • Oxygen

The word 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 needed for respiration. All organisms respire to release energy and to stay alive.

Without photosynthesis, life as we know it would come to an end, as almost every depends on it either directly or indirectly. such as algae, seaweed, grasses and phytoplankton all require photosynthesis to make their own food.

Photosynthesis brings about a balance in the ecosystem as it decreases the concentration of carbon dioxide in the atmosphere. Together with other processes such as respiration and , it can help to maintain levels of oxygen and carbon dioxide in the atmosphere.

Without photosynthesis we wouldn’t have fossil fuels such as coal and petroleum, as these were formed from photosynthetic processes. These non-renewable sources were made by the breakdown of older plants.

Plant products such as timber, rubber and oil also require photosynthesis to be made.

If a plant cannot photosynthesise, it will die

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 contributed to maintaining the levels of oxygen and carbon dioxide in the atmosphere, required for survival.

Plants release oxygen into the atmosphere as a by-product of photosynthesis and processes such as respiration and release carbon dioxide into the atmosphere. These processes work , where plants and animals depend on each other to benefit from this. Plants need the carbon dioxide released by respiration and decomposition, whereas animals need the oxygen released by plants from photosynthesis. This cycle helps maintain the balance of carbon dioxide and oxygen in the atmosphere.

Video - Golden jellyfish

Professor Brian Cox sees photosynthesis in action, investigating a unique type of jellyfish

The golden jellyfish has evolved to carry algae within their bodies and feed off the glucose the plants create.

The jellyfish move towards the light of the Sun throughout the day to increase photosynthesis. The symbiotic relationship between the two species allows the jellyfish to live off the glucose the algae produce.

Uses of glucose

Glucose is a useful molecule that is made during the process of photosynthesis. The initial use for glucose, when broken down during respiration, is to release energy.

Glucose is a molecule that can be bonded together to make many types of including cellulose and starch (in plants) and glycogen (in animals). Think of it like each glucose molecule being an individual bead on a necklace and the entire necklace represents the carbohydrate molecule.

Plants only photosynthesise and glucose during the day when there is sunlight, but they use glucose for respiration all the time, including during the night.

An infographic showing starch, which is a chain of glucose molecules bonded together

Cellulose

Glucose is used to make cellulose. Cellulose is an example of a natural . Cellulose is the main component found in plant cell walls and this gives the plant cell strength and support.

Humans cannot digest cellulose, but it is important in your diet as fibre. Fibre assists your digestive system, keeping food moving through the gut and pushing waste out of the body.

Find out more about cellulose

Starch

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

Fats and oils

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

Amino acids

Glucose produced in photosynthesis can be used to help make amino acids. These amino acids are used by the plant to synthesise . Minerals such as nitrate ions are also absorbed by the roots of the plants to help make these amino acids. Foods such as peas are good protein sources.

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