Plant Growth And Development Revision Notes For NEET

PLANT GROWTH AND DEVELOPMENT

        Growth is an irreversible change, increase in physiological parameters like length, height, weight, etc. of living being. Determinate growth ends after attaining maturity while indeterminate growth is unending.

        Phases of growth are the series of events during growth. In meristematic phase active growth occurs, followed by elongation phase where size increase and maturation phase signifies structural and functional differentiation, i.e. cell develops into specialised tissues, e.g. xylem and phloem.

Types of growth

  Arithmetic growth, i.e. Constant rate, i.e. 2, 4, 6 and 8, etc. expressed as Lt=L₀+rt

  Geometric growth is the repeated division of each cell. It has a lag phase exponential and stationary phase and it is expressed as W₁=W₀eʳᵗ

        Growth rate is the increased growth per unit time.

        Absolute growth rate measures total growth per unit time while relative rate measures growth rate per unit time per unit of initial parameter.

        Measurement of growth is the measure of increase in length, surface area, volume, dry weight, etc. Auxanometer, Crescograph and Horizontal microscope are used for this measurement.

        Conditions for growth are light, temperature, water, salts, food and oxygen are external factors. Internal factors growth hormones, enzymes and genetics.

        Differentiation, Dedifferentiation and Redifferentiation

 A permanent localised qualitative change in size, biochemistry, function, etc. is differentiation. The attainment of dividing ability by differentiated cells is de differentiation.

The process where dedifferentiated cells again loose ability to divide is rediffrentiation.

        Development includes all changes and organism goes through during its life cycle.

        Plasticity is the ability of a plant to modify its development due to extrinsic and intrinsic factors.

        Plant hormones are the organic compounds, which regulate the growth and development in plants. Based on their functions they can be promoters, e.g. auxin, gibberellin and cytokinin and inhibitors, e.g. abscisic acid and ethylene.

        Seed dormancy is the inactive state of the seed, caused by impermeability of seed coat, chemicals and mechanical resistance, etc. Dormancy allow viable seed storage for long, effective dispersion, etc.

        Photoperiodism is the effect or requirement of relative length of day and night on flowering plants. SDP’s require shorter photoperiod, long day plants require long light photo period day, neutral plants are independent of photoperiodism, short long day plants require both short days (flowering) and long days (blossming).

        Phytochrome a blue green-pigment which receives photo-periodic stimulus in leaves; exists in Pᵣ(660 nm) Pfᵣ(730 nm).

        Florigen in the flowering stimulus for plants.

        Vernalisation the process of exposing plants to low temperature (0-4℃), to induce flowering. Occurs in actively dividing cells, at low temperature in aerobic conditions requires water and adequate nourishment. Devernalisation is reverse process of vernalisation.

        Plant movements are changes in the position plants or their parts, due to stimuli present in the external environment. It can be locomotory or curvature.

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