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A Handbook of Biology

GËØMËTRÏÇÅL GRØWTH

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Here, both daughter cells

continue mitotic cell division.

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In most systems, the initial

growth is slow (lag phase),

then it increases rapidly (log

or exponential phase).

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If nutrient supply is limited,

the growth slows down leading to a stationary phase.

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On plotting the parameter of growth against time, we get a typical

sigmoid (S) curve.

(NEET 2015)

Size/weight of the organ

Exponential phase

Stationary phase

Time

Lag phase

An idealised sigmoid growth curve typical of cells in culture,

and many higher plants and plant organs.

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A sigmoid curve is a characteristic of living organism growing in a natural

environment. It is typical for all cells, tissues and organs of a plant

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Exponential growth is expressed as

W1 = W0 e^rt

W1 = final size (weight, height, number etc.)

W0 = initial size at the beginning of period

r = growth rate

t = time of growth

e = base of natural logarithms

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Here, r is relative growth rate. It is also the measure of ability of plant

to produce new plant material (efficiency index). Hence, final size W1

depends on initial size, W0.

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Quantitative comparisons between the growth can also be made in 2

ways:

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Absolute growth rate: Measurement & comparison of total growth per

unit time.

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Relative growth rate: Measurement of growth of the given system per

unit time expressed on a common basis, e.g., per unit initial parameter.