Circulation

The need for a transport system -

  • Multi-cellular organisms have a high metabolic demand

    • Need for a lot of food & oxygen and produce a lot of waste

    • Diffusion would take too long

  • Move food and oxygen from where it is absorbed to where it is needed

  • Move waste

  • Hormones and enzymes can be moved to target cells or organs.

  • Single celled organisms = large SA : V ratio

Components of circulatory systems -

  • A heart

  • A fluid in which substances are transported

  • Vessels through which the fluid can flow

There are two types of circulatory system:

  • Open = heart pumps fluid into an open cavity

  • Closed = blood remains in vessels at all times

Open circulatory systems -

  • Insects & molluses

  • The heart pumps haemolymph (fluid) through short vessels into the haemocoel (large cavity).

  • The haemolymph directly bathes organs and tissues, enabling diffusion.

  • The haemolymph doesn’t carry oxygen or carbon.

  • Haemolymph is sucked back into heart by pores.

  • The haemolymph moces around the haemocol when the organism moves.

  • Blood is not contained in vessels

Closed circulatory systems -

  • Blood is enclosed within the vessels at all times.

  • Heart pumps blood through a series of progressively smaller vessels

  • In capillaries (smallest vessel) substances diffuse in and out of the blood and cells.

  • They can either be a single or double circulatory system.

Double -

  • Two separate circulations: one to lungs, one to heart.

  • 4 chambers in the heart.

  • Blood passes through the heart twice.

  • Found in birds and mammals

Single -

  • One circulation

  • 2 chambers in the heart

  • Blood passes through the heart once

  • Found in fish

Advantages of double circulatory system -

  • High pressure to the body and low body to the lungs.

  • Mare blood can be pumped faster.

  • The can have a higher body temperature

  • If you don’t have a double circulatory system, alternate methods of oxygenating the blood, or lower metabolic demand/body temperature is needed.

  • Gills are very effective at extracting oxygen from water.

  • Water supports them.

  • Water has a stable temperature, so don’t have to maintain their own.