(1) Introduction to the importance of photosynthesis to life on Earth

Photosynthesis is the process by which green plants, algae, and some bacteria use sunlight to convert carbon dioxide and water into glucose and oxygen

See section 2. for more chemical details

Plants and algae make food like sugars and starch via sunlight energy and photosynthesis and this increases their biomass - which is an important source of food and energy for animals.

 

Almost all life on Earth depends on photosynthesis in plants and algae at the base of most food chains.

This also means that most chemical potential energy for life is indirectly derived from the Sun, which is used to make a range of organic molecules from complex carbohydrates, sugars, proteins and lipids (fats and oils).

The carbohydrates store chemical potential energy from photosynthesis, which is passed down a food chain from plants/algae to animals when animas eat these photosynthesising organisms.

Only plants, algae like seaweed or phytoplankton and some bacteria can carry out photosynthesis.

Carbon dioxide is slightly soluble in water (as is oxygen) so aquatic organisms in water can carry out photosynthesis near the surface.

Fortunately for animals, photosynthesis in plants keep the oxygen level at around 20% in the Earth's atmosphere and respiration by animals keeps the carbon dioxide level at around 0.04%, which is sufficient for plants to thrive.

For more details see the Carbon cycle

 

 

The importance of photosynthesis

You should appreciate the dependence of almost all life on Earth on the ability of photosynthetic organisms, such as plants and algae, to use sunlight in photosynthesis to build organic molecules that are an essential energy store and provide chemical energy for all cellular chemistry from respiration to protein synthesis, and to maintain levels of oxygen and carbon dioxide in the atmosphere

 

Green plants and algae are producers based on the chemistry of photosynthesis and the start of most food chains and the base of subsequent food webs.

Generally speaking, plants and algae do NOT eat food, but produce it.

(There are plants that trap insects for food, BUT, they are still use photosynthesis too.)

We are highly dependant on crops whether to eat directly, processed food or animal feed - so, we might not be 'green', but we ultimately depend for a lot of our food on photosynthesis!

AND, its not just life on land, all aquatic life e.g. fish, also depend, initially, on photosynthesis in plankton or algae.

 

A food chain is a means of transferring the energy from photosynthesis in the biomass to support many forms of life, including us!

Even the meat we eat, high in protein and fat, did depend at some point on photosynthesis, so there is no getting away from photosynthesis!

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Key points and extra notes on the importance of photosynthesis to life on Earth

Source of information is based on textbooks and syllabus-specifications for students taking the AQA GCSE, Edexcel GCSE and OCR GCSE level biology examinations (~US grades 9-10)

The Importance of Photosynthesis

1. What is Photosynthesis?

Photosynthesis is the process by which green plants, algae, and some bacteria use sunlight to convert carbon dioxide and water into glucose and oxygen.

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2. Why Is Photosynthesis So Important?

a) Provides Food and Energy

• Plants make glucose, which is used for respiration to provide energy for growth and other functions.

• Glucose can be converted into starch, cellulose (for plant cell walls), fats, or proteins.

• All animals and humans depend on plants directly or indirectly for food and energy.

b) Releases Oxygen

• Oxygen is a waste product of photosynthesis.

• Supports aerobic respiration in animals, plants, and other organisms.

• Maintains the oxygen content of the atmosphere, which is vital for life.

c) Removes Carbon Dioxide

• Plants absorb CO₂, helping to reduce the greenhouse effect and combat climate change.

• Balances gas levels in the atmosphere through the carbon cycle.

d) Foundation of Food Chains

• Green plants (producers) are at the base of every food chain.

• Herbivores eat plants, and carnivores eat herbivores—photosynthesis powers it all.

e) Produces Useful Products

• Photosynthesis leads to the formation of wood, cotton, and other plant materials we use.

• Fuels like coal and oil come from ancient photosynthetic organisms.

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3. Link to Exam Concepts

Photosynthesis connects to:

• Respiration: Plants do both—make food and use it for energy.

• Ecosystems: Flow of energy and cycling of matter.

• Adaptations: How leaves are adapted for efficient photosynthesis.

• Human impacts: How deforestation and pollution affect global oxygen and CO₂ levels.

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4. Top Exam Tips

Be ready to:

• Describe why photosynthesis is essential for life.

• Explain how it supports both plants and animals.

• Link it to the carbon cycle, oxygen cycle, and global climate balance.

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Keywords, phrases and learning objectives for this part on photosynthesis

Be able to explain what photosynthesis and the importance of photosynthesis to life on Earth and explain why it is the base of most food chains.

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