How do plants feed themselves... and us?

We may believe that plants rely on us to feed them, but in reality it’s the other way round. Plants are « autotroph » which means that they produce their own food simply using sunlight, carbon dioxide and water. Humans, on the other hand, are « heterotroph » as we cannot produce our own food and are unable to sustain ourselves without eating plants or products derived from plants. If we are meat-eaters, we’ll also consume animals which have themselves been fed plants.

So how do plants convert natural resources into food ? Well, it all happens in the chloroplasts, a tiny cell structure in the green parts of the plant. As soon as the sun rises, chlorophyll (green) molecules contained in the chloroplasts absorb light. In addition to light provided by photons, photosynthesis requires carbon dioxide absorbed by the stomates (microsopic pores on the leaves), and water and minerals provided by the roots. Photosynthesis takes place in two complementary and simultaneous phases. If this sounds highly complex, that’s because it is. However, in brief, during the photochemical phase, which lasts less than a second, light energy is converted into chemical energy. The metabolical phase, which lasts over a minute and potentially more than an hour, uses this chemical energy to reduce CO2 and then form glucose. Oxygen is then rejected. Once the sun goes down, the process stops. This miraculous process is the basis of life on earth. It provides the oxygen we breathe and the food we eat.

Glucose is the primary product of photosynthesis. Through a series of highly elaborate chemical reactions, this glucose is transformed into of all other constituents of the plant. These include carbohydrates, fats, proteins and minerals, which are necessary for the survival of the plant. Molecules such as terpenes, alkaloids and phenols, known as secondary metabolites, are then produced and are often specific to a plant family and its adaptation to its environment. One example of secondary metabolites is flavonoids which are known for their anti-inflammatory, anti-carcinogenic and antioxidative properties [1].

From seeds to leaves and from fruit to roots, plants sustain us and the animals around us. So the next time you bite into a carrot, an apple or a steak, think of the incredible role that plants play in providing us with our food.

To find out more about plant properties, see "The serene smell of Lavender", "How does rosemary improve memory?"and "How Hawthorn helps the heart".

[1] Panche AN, Diwan AD, Chandra SR. Flavonoids: an overview. Journal of Nutritional Science. 2016;5:e47. doi:10.1017/jns.2016.41