Photosynthesis in Everyday Life: 8 Places You Meet It

Every time you eat, you are using energy that a plant or alga captured from sunlight. Rice, wheat, maize, fruit and vegetables come straight from plants. Meat, milk and eggs come from animals that ate plants, or ate animals that did. Photosynthetic organisms are the producers at the start of almost every food chain, so almost all the chemical energy in food began as light.

The oxygen in each breath has the same origin. Photosynthesis is the main source of the oxygen in the air, and the ocean matters as much as forests: according to NOAA, about half of Earth's oxygen comes from the ocean, made by tiny drifting phytoplankton, seaweeds and cyanobacteria. One ocean bacterium, Prochlorococcus, produces up to 20% of the oxygen in the biosphere.

Plants turn some of the glucose they make into cellulose, the tough fibre in their cell walls. That is why so many materials around you are, in a sense, stored photosynthesis: wooden furniture, paper and cardboard, and cotton clothes (cotton fibres are almost pure cellulose). Natural rubber and plant oils used in cooking and cosmetics are also built from the products of photosynthesis.

Fossil fuels are photosynthesis from the deep past. Coal formed from the remains of ancient plants, and oil and natural gas mostly from tiny marine organisms, buried before they could decay. When they burn, they release energy that was captured from sunlight millions of years ago, along with the carbon dioxide those organisms once took from the air.

Farmers and growers use what they know about photosynthesis every day. In greenhouses they can raise the temperature, add lighting and pump in extra carbon dioxide so crops photosynthesise faster. In Iceland, where winter days are very short, growers use electricity and heat from geothermal energy to grow tomatoes under glass all year round.

The same idea appears in sports stadiums. Tall stands shade parts of the pitch, so some clubs wheel in rigs of grow lights at night. The extra light (and a little warmth) lets the grass keep photosynthesising and recover between matches.

Autumn colours are a lesson in leaf pigments. Through spring and summer, green chlorophyll hides yellow and orange pigments called carotenoids. As days shorten and temperatures fall, many trees stop making chlorophyll and it breaks down, so the yellow and orange show through. Some trees also make new red pigments, called anthocyanins, in autumn.

On a planetary scale, you can even see photosynthesis in the air. NASA measurements show that the amount of carbon dioxide in the atmosphere falls each northern spring and summer as plants grow, and rises again each winter when growth stops and dead leaves decay. It is as if the whole planet takes a slow breath each year.