Plant Growth and Development Class 11 Notes - Chapter 15

Like animals, even plants undergo growth and development. But unlike animals which have a definite lifespan, most plants can grow indefinitely. But how exactly is growth defined?

Plant Growth and Development

Growth is defined as an irreversible change in physical form. In plants, a combination of cell growth and cell division results in an almost indefinite growth. This ability is due to the presence of tissues called meristems at certain parts of the plant body.

See Also: Important Questions for Class 11 Biology- Plant Growth and Development

Growth – Plant Growth Generally is Indeterminate

  • Plants are known to retain the capacity to grow indefinitely throughout their life, hence their growth is unique. This capability can be contributed to the presence of meristems(possessing the capacity to self-perpetuate and divide) at different locations in their body
  • The root and shoot apical meristems are responsible for the primary growth of the plants contributing to the plant elongation through the axis
  • The lateral meristems, vascular cambium, cork-cambium in gymnosperms and dicotyledonous plants appear lateron. These meristems increase the girth of active structures resulting in the secondary growth of plants

Growth – Growth Is Measurable

  • At the cellular level, it is the increase in the amount of protoplasm. Growth is measured by a variety of metrics such as increase in dry weight, fresh weight, area, volume, length, cell number.
  • In some plants, growth is expressed as an increase in the cell number, increase in the cell size, while in some others, growth is measured in terms of growth of pollen tube, lengthwise, increase in surface area and so on.

Growth – Phases Of Growth

Growth period can be classified into three phases – meristematic(root and shoot apex cells that are constantly dividing), elongation (proximal cells to the meristematic region)and maturation(proximal cells to the elongation phase cells)

Growth Rate

Growth rate is referred to as the increased growth per unit time. Entities can produce cells in many ways – arithmetic, geometric. Quantitative similarities or differences between growth of living entities can be done in two ways – absolute growth(measurement and comparison of total growth per unit time) and relative growth rate(growth of given system per unit time)

Differentiation, Dedifferentiation And Redifferentiation

Differentiation –  cells from the root , shoot apical meristems and cambium differentiate and mature to carry out different functions. Here the cells undergo some major structural changes both in cell walls and protoplasm

Dedifferentiation- differentiated cells, after losing the capability to divide, regain the capacity of division in some circumstances. Example – cork cambium forming fully differentiated parenchyma cells.

Redifferentiation – During dedifferentiation, meristems and tissues divide and produce cells again losing the capacity to divide, however mature to carry out specific functions. Example -woody tissues in dicotyledonous plants undergo redifferentiation

Plant Growth Regulators

Plant growth regulators are essentially hormones that control various functions related to the growth and development of the plant. They can be of two types, namely:

  1. Growth Inhibitors
    1. abscisic acid
    2. Benzoic acid
    3. Salicylic acid
    4. Coumarin
  2. Growth Promotors
    1. Auxins
    2. Gibberellins
    3. Cytokinins

In-depth reading:  Plant Growth Regulators

Growth Inhibitors, as the name suggests, inhibit the growth of plants and induce dormancy. Growth Promoters promote flowering, the formation of seeds, cell division etc.

Photoperiodism

The response of plants to durations of day/night is known as photoperiodism as flowering in some plants is based on combination of light and dark exposures and relative durations. Here, the site of perception of light and dark durations are leaves.

Vernalisation

Dependance on exposure to lower temperatures of flowering plants either qualitatively or quantitatively is known as vernalisation. This process checks precocious reproductive development sometime later in the growing seas0n. Especially, it can be referred to the promotion of flowering by a duration of low temperature.

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