Plant Metabolism: Anabolism, Catabolism, and Energy

The Fate of Organic Matter in Plants

Metabolism is the result of the interaction between two types of processes: anabolism and catabolism.

Anabolism and Photosynthesis

Anabolism in plants groups all chemical reactions in which complex substances are produced from other simpler ones. The primary anabolic process carried out by plants is photosynthesis. However, plants also perform other anabolic processes, so that the substances produced during photosynthesis build their own structures or are used as reserve substances synthesized through these processes, such as starch, cellulose, and proteins.

Starch is the primary reserve substance in plants. It is formed from simple sugars in a reversible reaction that is reversed when the plant needs glucose. Starch is stored in specific locations of the plant, which consequently undergo thickening.

Plant Storage Organs and Nutrients

Stems, roots, seeds, and fruits serve as storage sites for reserve substances and can be used as food. Examples include:

• Potato: An underground stem that contains many reserve substances, including starch, stored in a particular type of plastid called amyloplasts.
• Sugarcane: A grass that stores a large amount of sugar in the apex of its stems.
• Beetroot: A root that contains large amounts of sucrose.
• Wheat and rice: Seeds that store large amounts of starch, protein, and other nutrients. Wheat and rice have a higher concentration of nutrients than potatoes.

In addition to starch and glucose, plants need other substances, such as cellulose (for cell wall formation), lipids (for the construction of cell membranes), and proteins (which form part of cell membranes and act as enzymes).

Catabolism and Cellular Respiration

Catabolism in plants is a set of chemical reactions that break down complex organic compounds into other chemically simpler ones, releasing the chemical energy contained within them. The main catabolic process is cellular respiration. The energy obtained in this process is used for vital functions.

One of the peculiarities of catabolism in plants is that plant cells are able to transform fats into carbohydrates, a process of special importance in oilseed plants.