Exchange & Transport in Animals

• All organisms must take in substances that they need from the environment and get rid of any waste products.
• In single-celled organisms, gases and dissolved substances can diffuse directly into the cell across the cell membrane because they have a larger surface area compared to its volume, so enough substances can be exchanged across the membrane to supply the volume of the cell.
• Multi-cellular organisms have a smaller surface area compared to their volume. This makes it difficult to exchange enough substances to supply their entire volume across their outside surface alone.
• What are the 3 factors that affect the rate of diffusion ?

  Distance - substances diffuse more quickly when they haven't got as far to move.

  Concentration Gradient - substances diffuse faster if there is a big difference in concentration between the area they are diffusing from and the area they are diffusing to.

  Surface Area - the more surface there is available for molecules to move across, the faster they can get from one side to the other.
• The job of the lungs is to transfer oxygen to the blood and to remove waste carbon dioxide from it.
• Gas exchange takes place in little air sacs called alveoli.

  Blood arriving at the alveoli has just returned to the lungs from the rest of the body, so it contains lots of carbon dioxide and not much oxygen. This maximises the concentration gradient for the diffusion of both gases.

  Oxygen diffuses out of the air in the alveoli and into the blood. Carbon dioxide diffuses in the opposite direction to be breathed out.
• Alveoli are specialised to maximise the diffusion of oxygen and carbon dioxide. They have:

  • a moist lining for dissolving gases
  • a good blood supply to maintain the concentration gradients of oxygen and carbon dioxide
  • very thin walls - minimising the distance that gases have to move
  • a very large surface area
• rate of diffusion is proportional to

  surface area x concentration difference / thickness of membrane
• Red blood cells carry oxygen from the lungs to all of the cells in the body.

  They have a biconcave disc shape to give a large surface area for absorbing oxygen.

  They don't have a nucleus - this allows more room to carry oxygen.

  They contain a red pigment called haemoglobin, which contains iron.

  In the lungs, haemoglobin binds to oxygen to become oxyhaemoglobin. In body tissues, the reverse happens - oxyhaemoglobin splits up into haemoglobin and oxygen, to release oxygen to the cells.
• Phagocytes are white blood cells that can change shape to engulf unwelcome microorganisms - this is called phagoctyosis.
• Lymphocytes are white blood cells that produce antibodies against microorganisms. Some also produce antitoxins to neutralise any toxins produced by the microorganisms.
• When you have an infection, your white blood cells multiply to fight it off - so a blood test will show a high white blood cell count.
• Platelets are small fragments of cells.

  They have no nucleus.

  They help the blood to clot at a wound - to stop all your blood pouring out and to stop microorganisms getting in.

  Lack of platelets can cause excessive bleeding and bruising.
• Plasma is a pale straw-coloured liquid which carries nearly everything:

  • red and white blood cells and platelets
  • nutrients like glucose and amino acids
  • carbon dioxide from the organs to the lungs
  • urea from the liver to the kidneys
  • hormones
  • proteins
  • antibodies and antitoxins produced by the white blood cells.
• What do Arteries do ?

  they carry the blood away from the heart
• What do Capillaries do ?

  they are involved in the exchange of materials at the tissues
• What do the Veins do ?

  they carry the blood to the heart
• All mammals have a double circulatory system - meaning that the heart pumps the blood around the body in two circuits.

  In the 1st circuit, the heart pumps deoxygenated blood to the lungs to take in oxygen. Oxygenated blood then returns to the heart.

  In the 2nd circuit, the heart pumps oxygenated blood around all the other organs of the body to deliver oxygen to the body cells. Deoxygenated blood then returns to the heart.
• The right atrium of the heart receives deoxygenated blood from the body through the vena cava.
• The deoxygenated blood moves through to the right ventricle, which pumps it to the lungs via the pulmonary artery.
• The left atrium received oxygenated blood from the lungs through the pulmonary vein.
• The oxygenated blood moves through to the left ventricle, which pumps it out round the whole body via the aorta.
• Valves prevent the backflow of blood in the heart.
• cardiac output = heart rate x stroke volume
• What are the 2 types of respiration ?

  Aerobic and Anaerobic
• What is the equation for Aerobic Respiration ?

  glucose + oxygen ---> carbon dioxide + water
• What is the equation for Anaerobic Respiration ?

  glucose ---> lactic acid
• What is the equation for Anaerobic Respiration in Plants ?

  glucose ---> ethanol + carbon dioxide