Chapter 15

• Diffusion is the net movement of atoms or molecules from a region where there is a higher concentration of the atoms or molecules to a region where there is a lower concentration
• Partially Permeable Membrane

  Examples: visking tubing, dialysis tubing, plasma membrane

  Allows some molecules but not all to pass through

  Molecules that can pass through: water molecules, glucose molecules, oxygen molecules, carbon dioxide molecules.

  Molecules that cannot pass through: starch molecules, sucrose molecules and complex sugar molecules.
• Fully Permeable Membrane

  Examples: cell wall of plant cell.

  Allows all dissolved molecules to pass through
• The Visking tubing is partially permeable. The iodine molecules are small enough to diffuse through the Visking tubing and the starch molecules are too large to pass through the Visking tubing. Therefore, the iodine molecules will enter the Visking tubing and react with the starch molecules to form blue black colour.

  
• Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane.
• Water potential is the measurement of the tendency for water molecules to move from one place to another.

  A dilute solution would have more water molecules per unit volume than a concentrated solution, and hence, would have a higher water potential.

  Water molecules always move from a region of higher water potential to a region of lower water potential.
• Turgor

  The cell swells up as water molecules enter the vacuole by osmosis.

  Vacuole increases in size, pushing against the cellulose cell wall.

  This state is also knows as Turgid.
• Pressure exerted by the water molecules on the cell wall is called turgor pressure.
• Plasmolysis

  Water molecules leave the vacuole through a process knows as osmosis.

  Vacuole loses water and decreases in size

  The shrinkage of the cytoplasm and the cell surface membrane from the cell wall is known as plasmolysis.

  The cell is said to be plasmolised.
• The heart has four chambers. The two atria and two ventricles
• The left ventricle has a thicker muscular wall than the right ventricle as oxygenated blood is pumped out of the left ventricle to other parts of the body. Therefore, a lot of force is needed to pump blood through the great distance.
• Valves are found between one atrium and one ventricle on each side of the heart, also at the openings to the aorta and the pulmonary artery.
• Valves prevent backflow of blood so as to keep blood flowing in one direction.
• Arteries transport oxygenated blood away from the heart

  Veins transport deoxygenated blood into the heart
• Capillaries link arteries to veins.

  Capillary walls are one cell thick

  Function : allow higher rate of diffusion of nutrients and oxygen from the blood to the tissue fluid. Waste substances such as carbon dioxide can also be removed when they diffuse from the cells, into the tissue fluid then into the blood.
• Plasma

  Pale yellow liquid, consisting mainly of water

  Function: Transport medium

  - Transports useful substances such as digested food and hormones

  - Transports waste materials such as carbon dioxide and urea
• Red blood cells

  Function: To transport oxygen

  Contain haemoglobin - so as to transport oxygen

  haemoglobin causes the cell to have its red colour

  No nucleus - so as to contain more haemoglobin to transport oxygen

  Biconcave shape - increases surface area to volume ratio of the cells for higher rate of diffusion of oxygen

  Elastic membrane - to squeeze through narrow lumen of blood capillary.

  Life span of around 4 months.
• White blood cells

  Function: Form part of the immune system in fighting infections

  Larger than red blood cell

  Colour: Colourless

  Nucleus is present
• Platelets

  Fragments of cells

  Function : Helps in the clotting of the blood to close open wounds
• The difference in the arteries and veins is the presence and absence of valves.
• The artery has a smaller lumen compared to the vein.
• The arteries transport oxygenated blood to rest of body.
• Capillary walls are one-cell thick to allow for higher rate of diffusion of digested nutrients.
• Blood flows through the heart twice, which is known as the double circulation. Blood flows to and from the lungs. Blood flows to and from other parts of the body.
• • Deoxygenated blood returns to the heart, into the right atrium
  • Right atrium contracts to pump the blood into the right ventricle
  • Cycle repeats itself
• Blood flow through the heart:

  • Right ventricle contracts to pump deoxygenated blood to the lungs
  • Oxygen in the lungs diffuses into the red blood cell in the blood and carbon dioxide diffuses out of the blood into the lungs
  • Oxygenated blood returns to the heart, into the left atrium
  • Left atrium contracts to pump the blood into the left ventricle
  • Left ventricle contracts to pump the oxygenated blood out of the heart to the rest of the body
  • Blood flows through the body, oxygen is lost to the tissues and carbon dioxide is gained
• Artery

  Transport oxygenated blood away from the heart.

  Pressure of blood is higher.

  Blood flow is more rapid and occurs in spurts.

  Thicker muscle wall that contains many elastic fibres.

  Valves are absent ( present in aorta and pulmonary artery )

  Most arteries transport oxygenated blood.

  Smaller lumen


  Vein

  Transports deoxygenated blood into the heart.

  Pressure of blood is lower.

  Blood flow is slower.

  Relatively thinner muscle wall, slightly muscular, with few elastic fibres.

  Valves are present.

  Most veins transport deoxygenated blood.

  Larger lumen.