From photosynthesis to navigation, life may exploit quantum effects

There is tantalising evidence to suggest that photosynthesis in some bacteria depends on quantum coherence and birds’ amazing feats of navigation rely on entanglement

Physics 25 August 2021

Coloured transmission electron micrograph (TEM) of chloroplasts from the yellow portion of a yellow/green variegated Coleus blumei plant. Chloroplasts are the sites of photosynthesis, the process that synthesises carbohydrates from carbon dioxide and water using sunlight. The structure of a variegated chloroplast is slightly different from that of a normal green chloroplast. The granal stacks, formed from parallel thylakoids (membranes, bright lines), that contain the chlorophyll pigments are less ordered in the variegated chloroplast. The pigments themselves are also slightly different. Magnification: x14,300 when printed at 10cm wide.

Chloroplasts in plant cells are centres of photosynthesis – and quantum weirdness, too?

Science Photo Library

ONE response to the question “does life use quantum effects?” comes in the form of another question: “why wouldn’t it?”. All life has evolved to make use of the world we happen to find ourselves in, so why should the magic of quantum effects remain off limits? After all, phenomena such as the telepathic connections implied by entanglement or “quantum tunnelling”, in which quantum objects pass effortlessly through energy barriers that on the face of it they shouldn’t be able to surmount, look like useful survival tools.

The counterargument is that, as any biologist will tell you, living organisms are wet, warm and very, very noisy: their molecules jiggle and their fluids flow, creating an environment where the phenomenon of decoherence would overpower any quantum effects. In recent years, though, we have been able to map out the delicate connections between atoms and molecules inside cells – and found some tantalising hints that life might indeed exploit quantum weirdness.

Take one of the most important innovations in the history of life: photosynthesis, the process by which plants and some bacteria convert sunlight to chemical energy. The reaction starts with photons of light exciting electrons in chlorophyll molecules to generate quasiparticles – packets of energy that move around as if they are particles – called excitons. These are shuttled around until they find “reaction centres” where their energy can be captured and stored. But excitons lose energy as they go, so researchers wondered if they might be able …