Cellular Metabolism, Respiration and Photosynthesis Explained

Cellular Metabolism: Catabolism and Anabolism

The set of chemical reactions in cells is known as metabolism. It is divided into two main processes: catabolism and anabolism.

Catabolism

Catabolism: A series of reactions in which complex molecules are oxidized and transformed into simpler molecules, releasing energy. Part of this energy is used in the synthesis of new molecules, cell division, mechanical work and the own operation of the cell, while part is lost as heat. Cells cannot use energy directly from food, so they use ATP (adenosine triphosphate), a very stable molecule that accumulates energy and releases it when needed.

Cellular Respiration

In respiration, energy-rich molecules lose electrons, which are transferred to acceptor molecules. The last electron acceptor is usually oxygen in aerobic respiration, although in some bacteria it is another inorganic molecule, in anaerobic respiration. Aerobic respiration produces the total amount of energy available in organic molecules.

Respiration takes place in the mitochondria. Fermentation occurs in the cytoplasm of some cells, while respiration occurs in aerobic organisms.

Anabolism

Anabolism: The set of reactions of reduction that require energy to build complex molecules from simpler ones. Many organic molecules are synthesized from other organic molecules or from inorganic substances. In autotrophs, the organic matter is obtained from inorganic substances.

Anabolic reactions are the reverse of catabolic ones, and they require energy to be carried out.

Photosynthesis

Plants obtain energy from sunlight. It is an oxidation-reduction process in which an electron donor and an inorganic electron acceptor participate. The donor molecule is oxidized and the acceptor is reduced. In photosynthesis, water is the donor and free oxygen is released. Photosynthesis takes place in the chloroplasts of plant cells; in photosynthetic bacteria it occurs in the cell membrane.

Chemosynthesis

Only some bacteria use the energy released by the oxidation of inorganic substances, not sunlight. Examples are nitrifying and sulfur-oxidizing bacteria.

Biological Cycles

In some organisms, meiosis and fertilization alternate, forming the zygote and the gametes, which are haploid.

Diplontic Cycle

Typical of animals and most protozoa. Meiosis takes place in the gonads and produces gametes. The diploid zygote develops into an adult organism.

Haplontic Cycle

Found in primitive algae and fungi. The diploid zygote is the only diploid stage and undergoes meiosis immediately after its formation.

Diplohaplontic Cycle

Present in all plants. It consists of an alternation between a diploid adult organism (sporophyte), which originates spores by meiosis, and haploid cells that are not gametes. These spores develop by mitosis into a new haploid individual, the gametophyte, which produces gametes and represents the sexual reproduction phase.

Plant Meristems

Meristems: Regions of growth in plants, responsible for growth in both length and thickness. Meristematic cells are totipotent, retaining the capacity to differentiate. They are small, with thin walls and small vacuoles, and they divide actively.

Apical Meristems

Located at the tips of roots and stems, they are formed by primary embryonic cells. They are responsible for the growth in length of the plant.

Secondary Meristems

Formed by adult cells that can still divide and differentiate. They are responsible for growth in thickness.

Cambium

Produces new vascular tissue: xylem, which conducts water and minerals, and phloem, which conducts organic nutrients. The outer layer is the protective epidermis, and the inner layer is the cortical tissue called phelloderm.

Adult Plant Tissues

Parenchyma tissues are responsible for nutrition, photosynthesis, storage and reserve.

Chlorophyll Parenchyma

Its cells contain many chloroplasts and are found in the green parts of the plant.

Reserve Parenchyma

Substances such as fat and starch accumulate in these cells. They do not have chloroplasts.

Aquifer Parenchyma

Found in xerophytic plants and in the leaves of some plants. Their cells store large amounts of water.

Aerifer Parenchyma

Its cells are loosely arranged, leaving large air spaces that favor air circulation, acting as a flotation system.