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

Plants and algae make food 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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Keywords, phrases and learning objectives for this part on photosynthesis

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

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