Plant Cell Biology, Lund University, Sweden. All living things are made of cells, and the molecular building blocks of cells are much the same for plants, animals and bacteria. Here light energy is absorbed by chlorophyll and stored in the photochemical reactions of photosynthesis. Plants stand still, and when the environment changes, a plant cannot run away to find a new one.
Plants therefore show great versatility in the way their cells adapt to changing environments.
The light-harvesting chlorophyll molecules of photosynthesis itself are bound to proteins that are modified by phosphorylation. This phosphorylation reaction allows the plant cell to balance the rate of energy conversion in photosynthesis with the capacity of the cell to use it. Phosphorylation of proteins also occurs when genes are switched on or off in response to an altered environment. The chloroplast, like the mitochondrion, evolved from a free-living bacterium, and has retained a small outpost of genes, perhaps to encode those of its protein components which are especially dangerous if made in the wrong environment. The plant cell is nature's most complex genetic system, with three sets of genes.