Single and multicellular organisms

Features of single celled organisms

.They are small large surface area to volume ratio

.therefore they have a small diffusion distance

.decreasing the distance over which the nutrients oxygen etc have to diffuse through is smaller

.higher rate of diffusion

.OVERALL low metabolic demand

What does the fact that single celled organism have a low metabolic demand and a large SA:V mean ?

Can rely directly to gas exchange

Because diffusion of oxygen and removal of co2 out of the cell happen at a rate that is sufficient to meet the metabolic demand of the cell.

Features of multicellular

Large →small SA:V

Large diffusion distance over which 02 has to enter and C02 has to be removed

High metabolic demand

Why do multicellular organisms have high metabolic demand

They are more active

They regulate they win temperature

Demand for entry of 02 and removal of C02 is very high

Why is a specialised exchange system required to meet metabolic rate of multicellular organisms

Simple diffusion cannot meet metabolic rate

Specialised exchange surface is required

To provide fast delivery of oxygen and glucose and fast removal of oxygen taste products such as Co2