Specialised Exchange Surfaces

All organsism, whatever their size need to exchange substances with their enviro:

1) Need to take in substances for aerobic respiration and more metabolic processes

2) Excrete waste products

So why do multicellular organisms need exchange surfaces?

• Diffusion across outer membranes is slow! Unlike in unicellular orgasnims
• Some cells are deep in body
• Large animals have low SA;V, cant exchange enough substances to supply large volume through smalle SA.
• Higher metabolic rate, so use up oxygen and glucose faster

Smaller animals have a higher SA;V

LARGE SURFACE AREA

Example: Root Hair Cell- they are cells on plant roots that grow into long hairs with stick out into the soil. Each roots branch covered in millions of microscopic hairs. Increases rate of absorption of water.

THIN SURFACES

Example: Alevoli- single layer of thin, flat cells called alveolar epithelium. The thin falt cells decrease the distance over which oxygen and carbon dioxide diffuses. Increases the rate of diffusion.

GOOD BLOOD SUPPLY AND/OR VENTILATION

Example: Alveoli- large capillary network each alevolus its own blood supply. Constantly takes oxygen away from alveoli and brings more carbon dioxide.Lungs ventilated so air constantly replaced. Help maintain concentration gradients oxygen and carbon dioxide.

Example: Fish Gills- large netwrok of capillaries, well-supplied with blood, well-ventilated, fresh water constanly passes over them. Maintain concentration gradient. Invreasing rate of oxygen diffsuion