O Level Revision : Integrated Science - Transport in Animals

Many substances need to be transported around the body. Nutrients are transported from organs to the individual cells where they are used. Wastes are transported from the body cells to the organs where they are expelled out of the body. Mammals have circulatory systems for the movement of substances in the body. Metabolic processes are facilitated through the circulating system.

These processes include:

  • respiration
  • muscle contraction
  • reproduction
  • maintaining constant body temperature

The circulatory system of animals

  • The mammalian transport system is made up of a heart, blood and blood vessels.
  • The blood vessels are the tubes through which  blood travels.
  • Blood vessels form a network that is able to supply  blood to all the cells in the body.
  • The heart is the pump that provides the force that pushes blood through the blood vessels.
  • Blood carries nutrients, wastes, hormones, heat and other substances around the body.
  • Blood vessels are modified for circulation.
  • The heart pumps oxygen-rich blood from the lungs to all parts of the body through a network of tubes called arteries, and smaller branches called arterioles.
  • The circulatory system maintains a continuous flow of blood around the body.

  The heart

  •  The heart is the pump for the circulatory system.

cardiac muscle

  • It is made up of four chambers: right atrium, left atrium, right ventricle and left ventricle.
  • The right side of the heart contains deoxygenated blood, while the left side contains oxygenated blood.

 The characteristics of the four chambers of the heart

Right atrium

Left atrium


•  Relatively thin walled.

•  Receives oxygenated blood from the

lungs through the pulmonary vein.

• Relatively thin walled.

• Receives deoxygenated blood from the

body through the vena cava.

Right ventricle

Left ventricle


•  Blood flows into it from the left atrium.

•  Pumps oxygenated blood to the whole body

via the aorta.

• When blood is pumped to the body,  it is prevented from flowing back to the left atrium by the closure of a bicuspid valve between the two chambers.

•  Has thicker muscular walls to enable the pumping of blood to the whole body (all parts of the body). Blood is pumped to the body at high pressure.

• Blood flows into it from the right atrium.

• Pumps blood to the lungs via the pulmonary


• When blood is pumped, it is prevented from flowing back to the right atrium by the closure of a tricuspid valve between the two chambers.

• Has thick muscular walls to enable the

pumping action.

Small intestine

  • Generally, arteries carry oxygenated blood and veins carry de-oxygenated blood except for the pulmonary artery which carries de-oxygenated blood while the pulmonary vein carries oxygenated blood.
  • Veins have valves to prevent backflow of blood.
  • The aorta branches into arteries which   branch into arterioles, which branch into capillaries.
  • Capillaries join into venules, which join to form veins. Veins transport  blood  to  the  vena  cava  which  conveys blood back into the heart.



Features of blood vessels


Blood vessels




Fairly wide.                          Carry oxygenated blood from Small lumen.                        the heart to all parts of the body. Thick walled, elastic and

muscular to withstand high pressure due to heart beat.


Tiny vessels.                         Oxygen,  carbon  dioxide, Walls one cell thick and       dissolved nutrients and excretory permeable to allow water     products are exchanged between and other dissolved               vessel and tissues.

substances to pass in and out.


Wider.                                   Return blood which is now de- Large lumen.                        oxygenated from body tissues Thinner walls than arteries   to heart.

since pressure is less. Have valves to prevent backflow of blood.



  • The blood is made up of two parts: the plasma and the blood cells.
  • Plasma is a solution of water, nutrients, wastes, gases.
  • There are three types of blood cells which are: red blood cells, white blood cells and platelets.
  • The cells are suspended in the aqueous solution (the plasma).
  • Blood has homeostatic functions. It helps to maintain a constant internal environment in the body.
  • Homeostasis is a natural process of regulating and maintaining constant temperature, water, sugar and salts in the body.

Components of blood and their functions




Red blood cells

Transport oxygen from lungs to tissues.

White blood cells

They are a part of the body’s defense mechanism against disease.


Helps in the clotting of blood to seal wound thus stopping continuous loss of blood and entry of bacteria.


Carries soluble nutrients. Carries wastes.

Carries hormones.

Carries blood (plasma) proteins. Carries heat.