growth and mitosis

• Growth is a permanent increase in the number of cells, or in the mass or size of an organism

3 distinct aspects of growth:

• cell division - basis of growth via mitosis increasing number of cells
• assimilation - once the cell has divided it gets larger before dividing again
• cell expansion - resources needed to provide new cells comes from photosynthesis in plants and feeding in animals, when these materials are incorperated into the cell it gets bigger. Cells can also expand via water retention but this could only be tempory therefore not true growth

growth can be effected by many factors including food availability temperature and light aswell as genetic makeup

• Linear division, e.g height or head circumference can be deceptive, a cake can increase in bth height and circumference when heated but it doesn't grow
• measuring mass also is problematic, water content in cells vary greatly especialy in plants and complex mammels
• Dry mass is the most accurate way of measuring growth (body mass of orgnism with all the water removed, however to measure the mass with no water you effectively kill it stopping further growth so you need a large sample of organisms living in very similar conditions, also brings up ethical issues

• growth curves show the growth of an organism throughout its life including where most growth takes place
• in most animals after maturity is reached growth stops
• in plants growth continues throughout life known as continious growth
• insects grow in stages called moults because they have an exoskeleton which they shead while the new exoskeleton is soft they expand by taking in air and water growing the exoskeleton. Once the new skeleton has hardened the water and gas can be let out, allowing the tisue of insect to increase this is called discontinious growth.

continious growth                                                       discontinious growth