CHAPTER 4 : REPRODUCTION & GROWTH

4.6 – Growth In Multicellular Organisms

LEARNING OUTCOMES• To explain briefly the necessity

for growth in organisms;

• To explain what growth is.

The Necessity For Growth in Organisms

• To increase in size & change in shape.

• To become more specific in form & structure to play vital roles of life (respiration, photosynthesis)

• To interact with external environmental factors

WHAT IS GROWTH?• GROWTH = an irreversible process which involves an increase in the number of cells size, complexity & organ functions in the organism’s body.

• Quantitative changes body size, mass & number of cells.

• Qualitative changes shape, function & complexity/specializations.

GROWTH STAGESa) The stage of cell division

• The number of cells must first increase by mitosis.

• Cells increase in geometric progression : 1248163264128……….

• All daughter cells formed are small & identical to the parent cell (zygote)

b) The stage of cell elongation / enlargement

• Must grow in size• Occurs by assimilation of food into the cells.• Synthesizing protoplasm• Vacuolation absorption of water.

c) The stage of cell specialisation / differentiation

• Maximum size differentiate.• Refers to gradual changes in the structure of

a general cell to turn it into a specialised cell for carrying out a specific function.

• Specific morphological & physiological changes.

• Cells tissue organ organ system complex organism

• May occur throughout the life cycle of at certain times only.

• All parts or certain parts only.

• In plants, limited to the apical meristems & cambium (lateral meristems).

• Growth & development of the shoot also includes growth of leaves leaf promordia (small outgrowth)