Photosynthesis is a really efficient way of making nutrients. Instead of wasting time finding, eating and digesting food, plants use solar power to transform carbon dioxide and water into oxygen and sugars. The plant generates fuel for itself, and air for us to breathe. The magic happens inside specialised organelles, called chloroplasts, which contain the green photosynthetic pigment chlorophyll.


Some animals have managed to harness the power of photosynthesis. For example, when sacoglossan sea slugs chow down on photosynthetic green algae, chloroplasts from the algae become incorporated into the animals’ gut cells where they continue to pump out nutrients long after the rest of the algae have been digested and expelled. It’s a feat called ‘kleptoplasty’.

Other animals, including some clams and flatworms, also use the photosynthetic powers of algae, but adopt a symbiotic approach where the algae remain unharmed. Corals are the classic example. Most reef-building corals contain colonies of algae, called zooxanthellae, which live in their tissues and bequeath the coral their hue. During the day, the algae provide the coral with most of their energy needs and, in return, the algae get a safe place to live with a stunning sea view.

The only vertebrate animal known to harness solar power is the spotted salamander. Here, water-dwelling algae colonise salamander eggs shortly after they are laid, then become incorporated into embryonic cells where they help to feed the developing animal from within. Experiments reveal that embryos with more algae survive better and develop more quickly than embryos with fewer algae.

All of which begs the question, could we humans ever photosynthesise? Even if we could crowbar working chloroplasts into our cells (which we can’t) and precisely alter our genomes to control them (which we can’t), we still don’t have a big enough surface area to volume ratio to generate the energy we’d require to live. Put simply, humans just aren’t leaf-shaped!

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Asked by: Abdullah Rizwan, Kidderminster


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Helen Pilcher
Helen PilcherScience writer, presenter and performer.

Helen Pilcher is a tea-drinking, biscuit-nibbling science and comedy writer, with a PhD in cell biology.