- 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. Morphogenesisa. 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)
C. Animal growth + development are controlled mainly by:
- 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.
Advantages + disadvantages
· easy + quick to measure.
· growth can be measured continually
· 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)
· more accurate measurement.
· eg: surface area of a leaf attached to a plant can be measure at regular intervals over a period of time.
· 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.
· Suitable for measuring organisms that are spherical or cylindrical in shape.
· Living organisms are rarely exactly spherical and cylindrical in shape
· Not accurate measurement.
· Dif. to carry out – complicated calculation for organism with irregular shape.
· More accurate measurement of the organic materials (protein present in the body.
· 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.
· Easy to measure
· No need to kill the organism.
· Growth can be measured continuously as repetitive measurements can be carried out.
· 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.