transport in plants

• Circulatory systems can be open (in insects) or closed (in fish and mammals)
• Closed circulatory systems come in two forms:

  • Single form: heart with two chambers, blood passes through the heart once for every circuit of the body
  • Double form: heart with four chambers, blood passes through the heart twice for every circuit of the body
• Important structures and functions:

  • Arteries: carry blood away from the heart, thick walled to withstand high blood pressure, contain elastic tissue to stretch and recoil, contain smooth muscle to vary blood flow, lined with smooth endothelium to reduce friction
  • Arterioles: branch off arteries, have thinner and less muscular walls, feed blood into capillaries
  • Capillaries: smallest blood vessels, site of metabolic exchange, one cell thick for fast exchange of substances
  • Venules: larger than capillaries but smaller than veins
• • Veins: carry blood from the body to the heart, contain a wide lumen to maximize blood volume, thin walled under low pressure, contain valves to prevent backflow
• Tissue fluid:

  • Contains dissolved oxygen and nutrients
  • Enables exchange of substances between blood and cells
• Hydrostatic pressure:

  • Created when blood is pumped along arteries, arterioles, and capillaries
  • Forces blood fluid out of the capillaries
  • Only small substances can escape through capillary wall to form tissue fluid
• Lymphatic system:

  • Carries remaining tissue fluid back
  • Contains lymph fluid with less oxygen and nutrients, main purpose is to carry waste products
  • Contains lymph nodes that filter out bacteria and foreign material
• Mammalian heart and cardiac cycle:

  • Heart is myogenic
  • Sinoatrial node in right atrium is pacemaker
  • Atrial systole: atria contract, atrioventricular valves open
  • Ventricular systole: ventricles contract, atrioventricular valves close, semilunar valves open
  • Cardiac diastole: atria and ventricles relax, semilunar valves close
• Haemoglobin:

  • Water soluble globular protein with two alpha and two beta polypeptide chains
  • Carries oxygen in the blood, can carry four oxygen molecules
  • Affinity for oxygen varies with partial pressure
  • Fetal haemoglobin has higher affinity for oxygen than adult haemoglobin
  • Affinity for oxygen is affected by partial pressure of carbon dioxide (Bohr effect)