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20.0 GROWTH

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20.1 Growth Phases &

Measurement of Growth

Learning Outcome:

At the end of this lesson, student should beable to:

1. Define growth

2. State the phases of growth3. State the parameters of growth

4. Explain sigmoid growth curve

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20.1 Growth Phases & Measurement ofGrowth

Key Concepts/ Terms:

Cell Division

Cell Enlargement

Cell Differentiation

Lag PhaseLog Phase

Linear Growth Phase

Stationary Phase

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20.1 Growth Phases &

Measurement of Growth

What is Growth?

Permanent & irreversible increase in themass orsize

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Growth Phases

3 phases of growth

Cell division

Cell enlargement

Cell differentiation

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a) Cell Division

Cell division produces

new cells by mitosis Important for growth.

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b) Cell enlargement cell increases in size and volume after cell

division.

How the cells expand?

Plant cells :

by osmotic uptake of water leading toenlargement of vacuoles stretching the

primary cell wall.

Animal cells :

growth of cell

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c) Cell Differentation:

Specialisation of cells.

Give rise to variety of cells forming different

types of tissues.

E.g : meristem tissues differentiate to form

parenchyma, collenchyma, schlerenchyma &

vascular bundles.

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Parameters of Growthi. Fresh mass : the mass without internal water

removed

Need large sample to get better result.Advantages: i. Organisms NOT killed

ii. Growth of same specimen can bemeasure continuously

Disadvantages: i. Measurement not accurate(fluctuation in water content)

ii. Animals may have varyingquantities of feacal material &

urine held in the body

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Example Measurement of freshmass

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ii. Dry mass: i. random samples are taken for

drying

ii. Useful for plants

Advantages: Give accurate measurement; noeffect of water content.

Disadvantages: - Organism are KILLED

- Growth of the same specimen

cannot be measured

continuously

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Example measurement of dry mass

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iii. Length : common parameter used to measure

growth

Advantages: i. Easy & quick to measure

ii. Growth can be measured

continually

Disadvantages: i. Measure the length in one

dimension (does not take into account growth inother direction)

ii. In plant, while not increasing in

height, may continue to grow in girth

(or grow sideways)

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Example measurement of length/height

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20.2 Growth Patterns

Sigmoid growth curves

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GROWTHCURVE - SIGMOID

Measurements of growth throughout the lifeof an organism or measurement of increasing

population

Similar for most organisms

After initial slow start, there is a rapid growthuntil maturity (growth slowing down andstops).

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This pattern known as continuous growth,

usually gives an S shapedorsigmoid curve. Parameters against time: height, weight, area

Consists of:

(a) Lag phase

no growth or slow growth

Organism try to adapt to new environment

(b) Log phase

exponential growth

no constrain on growth, with adequate

nutrients and no accumulation of waste

products

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(c) Linear growth phase decelerating phase

period when growth rate becomes limited by

internal or external factors or both.

(e) Stationary phase

growth is stopped

cell division rate same as cell death rate sothe net growth rate is zero.

Followed by senescence and death

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Example of sigmoid curve for organism

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Time (t)

No. of

individual(N)

Example of sigmoid curve for

population