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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