exchange and transport in animals

• Efficient transport and exchange

  All chemical reactions in your body produce waste which must be excreted. Waste may be toxic. Your body also needs to move substances into it, for chemical reactions. Many of these substances are moved by diffusion, to speed up this the surfaces are: thin + large SA.

  The continual flow of blood, in capillaries, maintains the concentration gradient.

  It would take too long for substances to diffuse through cells on the outside of a tissue to reach the cells on the inside. Multicellular organisms have transport systems to counter this. The larger a cell's SA, the more diffusion in a certain time. However if a cell's volume is too big, the cell cannot fill up with enough nutrients quickly enough. As cells get bigger the SA:V gets smaller, if it gets too small the cell cannot get enough raw material fast enough to stay alive.
• Factors affecting diffusion

  The further the particles have to diffuse, the slower the rate of diffusion.

  AS the thickness of the membrane increases, the rate of diffusion decreases.
• The circulatory system

  Circulatory system: blood flows away from the heart into the arteries. Arteries divide into narrow capillaries. Blood returns to the heart in veins. Each heartbeat causes high pressure blood to be squirted into your arteries. The artery walls are thick to withstand the pressure, but they stretch. This wave are stretching is your pulse. After stretching, elastic and muscle fibres cause the artery contract. Blood flows at low pressure in your veins, so they only need thin walls. Muscles in your skeletal system help to push the blood along. Valves prevent blood flowing the wrong way. Capillaries are narrow tubes that are only one cell thick. The wall being one cell thick allows faster diffusion.
• Blood

  Blood is made up of:

  • Red blood cells; packed haemoglobin which binds to oxygen in the lungs and release it into the tissues. No nucleus so more space for haemoglobin. Biconcave disc shape for large SA:V
  • White blood cells - phagocytes surround foreign cells an digest them. Lymphocytes produce proteins called antibodies that attach to foreign and help to destroy them.
  • Platelets; tiny fragments of cells that are needed to clot blood at injury site.
  • Plasma; straw-coloured liquid that carried dissolved substances such as glucose, carbon dioxide and urea.
• The heart

  structures and functions:

  • pulmonary artery - carries deoxygenated blood from the heart to the lungs
  • aorta - carries oxygenated blood from the heart to the body
  • left atrium
  • left ventricle - muscle wall thicker than the right as it pushes blood all around the body
  • right ventricle
  • right atrium
  • vena cava - brings deoxygenated blood to the heart
  • valves - stops blood flowing the wrong way
• Cellular respiration

  Energy is needed all the time for; keeping warm, moving and producing/ breaking down substances. Cellular respiration is a series of chemical reactions that release energy from glucose. It is exothermic. Aerobic - takes place in the mitochondria and needs oxygen. Anaerobic - takes place in the cytoplasm and doesn't need oxygen. Anaerobic respiration releases less energy. During vey strenuous exercise, oxygen is used up faster than it is replaced. So the energy needed is topped up by anaerobic respiration.

  There are other types of anaerobic respiration e.g. yeast. In animals it also causes muscles to tire quicker. Anaerobic can release a burst of energy, without needing a sudden increase in oxygen. This is important for fast sudden movement. Heart and breathing rates can remain high after exercise because extra oxygen is needed to replace the oxygen lost and to break down lactic acid.