-
characteristic
of all
living organisms.
- permanent
irreversible increase in size of an
organism
- due to
increase in its dry mass.
- continue
throughout
the life of an organism (eg: woody perennial plants)
- may cease when
organism reach maturity (eg: man
or other mammals)
- increase in volume of cytoplasm
- Increase in number of cells
- increase
in differentiation of cells
- reaches certain size – divide to form two
separate cells
- size limited - due to distance of cell over which
a nucleus can exert its controlling influence.
- division - results in growth of populations.
- originate from a single cell (the zygote)
- cell division – increase in number of new
cells produced by mitosis
- cell
expansion (cell enlargement) – increase in size,
volume + mass
(due to assimilation of food materials + metabolism)
- cell differentiation:
i. cells undergo
progressive changes in metabolic activities:
– lead to changes in cell
structures – produce diff specialized cells/tissues for dif functions
ii. in higher animals:
– produce tissues (epithelial tissue, nervous tissue, muscle tissue + connective tissue)
iii. in higher plants:
– produces tissues (meristematic tissue, ground tissue + vascular tissue).
5. Morphogenesis
a. result
from:- development
(growth+ differentiation) of overall form of organs
-
formation of multicellular
organism
-
differential expression of genes.
-
certain metabolites
activate/repress gene in dif. cells.
-
some hormones
are able to switch genes on/off (help to determine overall pattern of
development)
FACTORS AFFECTING THE
PATTERN + RATE
OF GROWTH (PLANTS + ANIMALS)
A.
External factors affecting the rate of growth in
plants are:
- light (intensity, wavelength and photoperiod) – affects photosynthesis, photomorphogenesis, meristemic activities and flowering.
- Temperature which affects enzyme activities.
-
Oxygen – require for aerobic respiration and seed
germination.
-
Carbon dioxide – for photosynthesis,
synthesis of organic molecules.
- Water – essential for many metabolic processes (photosynthesis, seed germination, transportation of mineral salts/soluble organic material, vacuolation, maintenance of plant cell turgidity
- Relative humidity of atm – affects rate of transpiration.
- Minerals (K+, Na+, Ca2+, NO3+) for plant
metabolism/growth/development.
- Gravity
– affects distribution of growth regulators for geotropism
- Seasonal influences
– affect dormancy, abscission, reproduction and photoperiodism
- Biotic factors -pathogen-caused plant diseases, intraspecific and interspecific competition for space, sunlight, water and mineral salt).
- Genotype of the plant – determines the synthesis of specific proteins and enzymes, the type of metabolism and size.
-
presence
and absence of growth regulators/plant hormones (auxins, gibberellins, cytokinins,
absciccis acid, ethene)
- Genotype of the animal
-
Animal
hormones
(thyroxine and somathrophin).
-
Environmental conditions (lights
intensity and photoperiod, temperature, oxygen, availability of water and
seasonal influences.
- Biotic factors.
Parameter
|
Advantages + disadvantages
|
|
A
|
 |
Advantages
·
easy + quick to measure.
·
growth can be measured continually
Disadvantages
·
only measures the length in one dimension + does
not take into account growth in other directions.
·
An organism not increasing in height - may
continue to grow in girth or grow sideways (as in plant)
|
B
|
 |
Advantages
·
more accurate
measurement.
·
eg: surface area
of a leaf attached to a plant can be measure at regular intervals over a
period of time.
Disadvantages
·
Dif. + impractical to carry out if the
organism is irregular in shape.
·
It’s assumed that plant growth is directly
proportional to the increase in the surface area of its leaves.
|
C
|
 |
Advantages
·
Suitable for measuring organisms that are spherical
or cylindrical in shape.
Disadvantages
·
Living organisms are rarely exactly spherical
and cylindrical in shape
·
Not accurate measurement.
·
Dif. to carry out – complicated calculation
for organism with irregular shape.
|
D
|
 |
Advantages
·
More accurate
measurement of the organic materials (protein present in the body.
Disadvantages
·
Water has to be removed by drying the
organism.
·
This kills the organism, so continuous growth
of the same organism cannot be measured
·
Have to use a large number of individuals from
the same population which have similar age and size.
·
Dif. plants used may have dif, growth rates.
|
E
|
 |
Advantages
·
Easy to measure
·
No need to kill the
organism.
·
Growth can be measured
continuously as repetitive measurements can be carried out.
Disadvantages
·
Measurement may be inaccurate due to
fluctuations in water content in the body.
·
May be more suitable for measuring growth in
animals but not for a living tree.
|
