In biology, growth is usually used to describe the increase in size and mass of a living being or one of its parts. In the case of single cells such as bacteria or yeasts , the increase in population , i.e. the number of cells, is viewed as growth instead . More detailed representations can be found for plant growth and for bacterial growth .
The increase in mass is mostly based on the accumulation of species-specific organic substances that are formed either from ingested food or by means of photosynthesis or chemosynthesis from inorganic substances ( heterotrophy or autotrophy ). An exception is elongation growth in plants , which is largely or entirely based on the uptake of water and mineral salts into the vacuoles .
In most living things, growth is linked to cell division, i.e. it results in cell multiplication. In contrast, with coenocytic fungi and algae the formation of cell walls does not occur ; so only the cell nuclei and other organelles are increased. Likewise, no new cell walls are formed when the plants grow elongated.
The great realms of animals (with humans), plants and fungi show fundamental differences in growth. Plants do not grow everywhere at the same time like animals, but only in certain places, based on meristems . On the other hand, their growth is in principle unlimited, while in most animals it comes to a natural end due to their closed body structure. Roundworms and rotifers , which are made up of a fixed number of cells when fully grown ( cell constancy ), represent an extreme . The mycelia of the fungi grow on all hyphae tips at the same time under suitable conditions and can in principle continue this indefinitely.
The growth of an individual must take place in a spatially and temporally structured manner. In multicellular animals, for example, there is hormonal control and also contact inhibition of cell division. In multicellular cells, the cells are often differentiated with the growth and further development of the individual , allowing them to take on various tasks.
The timing of many living things is controlled by environmental factors. A typical growing season for plants in Central Europe will begin in spring and end in autumn. Depending on the special requirements of the locations or living beings, different periods occur. As an example, the undergrowth plants in the European beech forest have to cope with the strong shading from the treetops and therefore show two growing seasons each year. One of these takes place between the end of winter and the beech leaves are spread , the second period lies between the fall of leaves and the following winter.