The most abundant elements in plants are carbon, hydrogen, and oxygen . These are the major elements in all organic molecules. Hydrogen is acquired from water , which is why plants evolve O 2 gas as a by-product, and carbon and oxygen from CO 2 are incorporated in plants by way of photosynthesis . The other elements essential to plant growth can be acquired by the plant from the soil solution. It is also a component of chlorophyll , the pigment that imparts the green color to plants, and that is essential for the transfer of energy from sunlight through photosynthesis.
Proteins are responsible for the selectivity of membrane transport .
The four bases that constitute the code used in DNA are all nitrogenous compounds. It is the nitrogen that gives these compounds their basic nature. N is mobile in the plant, meaning that it can move from older to younger leaves , and the most pronounced early symptom of nitrogen deficiency is yellowing or chlorosis of older leaves . Because N is a fundamental requirement for cell division, the plant breaks down proteins in older leaves and sends N to younger leaves . The yield of crop plants can be determined in part by the amount of N that is applied , because vegetative growth is roughly proportional to N availability if other nutrients are not limiting .