Transportation

INTRODUCTION TO TRANSPORTATION
Transport is the movement of substances within an organism.
All living cells require oxygen and food for various metabolic processes.
These substances must be transported to the cells.
Metabolic processes in the cells produce excretory products which should be eliminated before they accumulate.
The excretory products should be transported to sites of excretion.
Organisms like amoeba are unicellular.
They have a large surface area to volume ratio.
The body is in contact with the environment.
Diffusion is adequate to transport substances across the cell membrane and within the organism.
Large multi-cellular organisms have complex structure where cells are far from each other hence diffusion alone cannot meet the demand for supply and removal of substances.
Therefore an elaborate transport system is necessary.