Unlike animals, plants keep growing throughout their lives, but only in particular regions called meristems. Meristems contain small, unspecialised cells with thin walls and no large vacuole, which divide repeatedly by mitosis.- Apical meristems are at the tips of shoots and roots. They produce growth in length (primary growth).
- Lateral meristems, such as the vascular cambium, produce growth in width (secondary growth) in woody plants.
- Intercalary meristems at the bases of leaves and internodes, for example in grasses, let the plant grow from the base, so grass can regrow after grazing or mowing.
- Meristems in the lateral buds, in the angles between leaves and stem, can grow into side shoots.Growth happens in three stages:1. Cell division by mitosis in the meristem.
2. Cell elongation: the new cells take up water by osmosis into a developing vacuole and expand. This causes most of the increase in length.
3. Cell differentiation: cells become specialised, for example as xylem, phloem or epidermis.Plant growth regulatorsPlant growth is controlled by plant growth regulators (plant hormones). Unlike animal hormones, they are not made in glands. They are produced by cells in many tissues, often the meristems, and move by diffusion, by active transport from cell to cell, or in the xylem and phloem. They often act close to where they are made and at very low concentrations. The main groups are auxins, gibberellins, cytokinins, abscisic acid and ethene. Their effects depend on their concentration, the tissue and the other regulators present.
- Lateral meristems, such as the vascular cambium, produce growth in width (secondary growth) in woody plants.
- Intercalary meristems at the bases of leaves and internodes, for example in grasses, let the plant grow from the base, so grass can regrow after grazing or mowing.
- Meristems in the lateral buds, in the angles between leaves and stem, can grow into side shoots.Growth happens in three stages:1. Cell division by mitosis in the meristem.
2. Cell elongation: the new cells take up water by osmosis into a developing vacuole and expand. This causes most of the increase in length.
3. Cell differentiation: cells become specialised, for example as xylem, phloem or epidermis.Plant growth regulatorsPlant growth is controlled by plant growth regulators (plant hormones). Unlike animal hormones, they are not made in glands. They are produced by cells in many tissues, often the meristems, and move by diffusion, by active transport from cell to cell, or in the xylem and phloem. They often act close to where they are made and at very low concentrations. The main groups are auxins, gibberellins, cytokinins, abscisic acid and ethene. Their effects depend on their concentration, the tissue and the other regulators present.