transport systems

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• Edexcel IGCSE Biology: Double Science
• Contents

  • 2.51 Unicellular Organisms & Diyusion
  • 2.52 The Need for a Transport System in Multicellular Organisms
  • 2.53 Role of the Phloem
  • 2.54 Role of the Xylem
  • 2.59 Compostion of the Blood
  • 2.60 Role of Plasma in Transport
  • 2.61 Adaptations of Red Blood Cells
  • 2.62 Immune Response to Disease
  • 2.65 Structure & Function of the Heart
  • 2.66 Heart Rate & Exercise
  • 2.67 Risk Factors for Coronary Heart Disease
  • 2.68 Blood Vessels: Structure & Function
  • 2.69 Circulatory System: General Structure

  
• Unicellular Organisms

  Single-celled organisms
• Unicellular organisms

  • Have very large surface areas (SA) in comparison to their volumes
  • The distance between the surface of the organism to its centre is very small
• Unicellular organisms do not need to have specialist exchange surfaces or transport systems; as diyusion, osmosis and active transport through the cell membrane occur at a suzcient rate to meet the organisms needs
• Multicellular Organisms

  Organisms with bodies made up of more than one cell
• The bodies of multicellular organisms contain many layers of cells, meaning that the distance between the surface of the organism to its centre is relatively long and the diyusion distance is too great to rely on diyusion alone

  
• Diyusion cannot occur at a suzcient rate to meet the needs of the organism, so larger organisms usually have transport systems
• Circulatory system

  The transport system in animals that carries necessary substances around the body in the blood
• Vascular system

  The transport system in plants: the xylem moves water and mineral ions from roots to shoots, the phloem moves sugars and amino acids to where they are needed in the plant

  
• Humans and some plants have specialised transport systems
• Phloem

  Vessels that transport food materials (mainly sucrose and amino acids) made by the plant from photosynthesising leaves to non-photosynthesising regions in the roots and stem

  
• Movement in the phloem can be in any direction around the plant
• Phloem

  • The cells are living cells and are not hollow
  • Substances move from cell to cell through pores in the end walls of each cell
• Xylem

  Vessels that transport water and minerals from the roots to the stem and leaves

  
• Xylem

  • It is composed of dead cells which form hollow tubes
  • Xylem cells are strengthened by lignin and so are adapted for the transport of water in the transpiration stream

  
• Components of Blood

  • Red blood cells
  • White blood cells
  • Platelets
  • Plasma
• Over half of the volume of the blood is made up of plasma
• The majority of the other half is made up of red blood cells
• The remaining fraction consists of white blood cells and platelets
• Plasma

  A straw coloured liquid which the other components of the blood are suspended within
• Substances transported in plasma

  • Carbon dioxide
  • Digested food and mineral ions
  • Urea
  • Hormones
  • Heat energy

  
• Red blood cells

  • They are full of haemoglobin, a protein that binds to oxygen to form oxyhaemoglobin
  • They have no nucleus which allows more space for haemoglobin to be packed in
  • The shape of a red blood cell is described as being a 'biconcave disc' - this shape gives them a large surface area to volume ratio to maximise diyusion of oxygen in and out
• Phagocytes

  White blood cells that carry out phagocytosis by engul|ng and digesting pathogens
• Lymphocytes

  White blood cells that produce antibodies
• Immune response to infection

  1. The pathogen enters the blood stream and multiplies

  2. A release of toxins (in the case of bacteria) and infection of body cells causes symptoms in the patient

  3. Phagocytes that encounter the pathogen recognise that it is an invading pathogen and engulf and digest (non-speci|c response)

  4. Eventually, the pathogen encounters a lymphocyte which recognises its antigens

  5. The lymphocyte starts to produce speci|c antibodies to combat that particular pathogen

  6. The lymphocyte also clones itself to produce lots of lymphocytes (all producing the speci|c antibody required)

  7. Antibodies cause agglutination of pathogens

  8. Phagocytes engulf and digest the agglutinated pathogens

  9. After the patient has recovered, they retain antibodies speci|c to the disease as well as memory cells (lymphocytes that recognise the pathogen)

  10. If the patient encounters the same pathogen again, it will trigger a secondary immune response

  11. Memory cells can produce much larger quantities of the required antibody in a much shorter time to |ght oy the pathogen before the patient suyers any symptoms
• Antigen

  A molecule found on the surface of a cell
• Antibody

  A protein made by lymphocytes that is complementary to an antigen and, when attached, clumps them together and signals the cells they are on for destruction
• Antitoxin

  A protein that neutralises the toxins produced by bacteria
• Heart

  A double pump organ
• Circulation of blood in the heart

  1. Oxygenated blood from the lungs enters the left side of the heart and is pumped to the rest of the body (the systemic circuit)

  2. Deoxygenated blood from the body enters the right side of the heart and is pumped to the lungs (the pulmonary circuit)

  3. A muscle wall called the septum separates the two sides of the heart

  4. Blood is pumped towards the heart in veins and away from the heart in arteries
• Left ventricle

  • Has a thicker muscle wall than the right ventricle as it has to pump blood at high pressure around the entire body
• Right ventricle

  • Pumps blood at lower pressure to the lungs
• Antigen

  A substance that, when attached, clumps cells together and signals the cells they are on for destruction
• The heart organ is a double pump
• Pathway of blood through the heart

  1. Deoxygenated blood flows through vena cava into right atrium

  2. Atrium contracts, blood forced through tricuspid valve into right ventricle

  3. Ventricle contracts, blood pushed through semilunar valve into pulmonary artery

  4. Blood travels to lungs, gas exchange occurs

  5. Oxygenated blood returns via pulmonary vein to left atrium

  6. Atrium contracts, blood forced through bicuspid valve into left ventricle

  7. Ventricle contracts, blood forced through semilunar valve out through aorta
• Left ventricle

  • Has thicker muscle wall than right ventricle as it has to pump blood at high pressure around the entire body