Question

In plants, it is responsible for increase in thickness​

Answer 1

Plant growth is an irreversible and permanent increase in the size of the plant parts, organs, tissue, entire plant or an individual cell. Growth is the most fundamental characteristic of the living plants, similar to any other living organism. Plant growth is also accompanied by metabolic processes such as catabolism and anabolism that requires spending energy.

Growth in plants is an open form of growth i.e. it is indeterminate and some cells are continuously dividing and helping in the increase in size of cell or tissue. Cells that continuously divide are called meristematic cells

Plant growth is measurable since an increase in protoplasmic content takes place. Also, an increase in fresh or dry weight takes place, an increase in length & size and an increase in the number of cells occur which can be all measured.

Three Phases of Growth in Plants

The period of growth in plants are divided into three phases, namely-

Meristematic or Formative Phase- The tip region of the root of a plant consists of meristematic cells which are continuously dividing and are isodiametric (with no spaces between the cells); and that zone is called meristematic zone; here, cells in meristematic zone have rich protoplasm with large and conspicuous nucleus. Cell walls of these cells are primary in nature, thin and consist of cellulose. These cells have white plasmodesmatal connection.

Elongation Phase- The cells present next to meristematic cells are present in the elongation phase. These cells elongate due to enlargement of the vacuole present in the cell and hence that zone is called zone of elongation. The cell enlargement and new cell wall formation takes place in the cells present in the elongation phase. Modifications like larger vacuoles take place in the cells here.

Maturation Phase- The next cells found after the elongation zone are present in maturation phase and they attain the maximum size. They do not divide further after reaching the maturation phase. The zone of maturation is found as a mass differentiation phase where cells differentiate to perform special functions in the plants.