Test

• Small organisms like Chlamydomonas


  • Able to exchange substances directly with the environment due to their large surface area: volume ratio
  • Diyusion or transport distance is very small so essential nutrients or molecules can reach necessary parts of the cell ezciently
  • Tend to have lower levels of activity and smaller metabolic demands
• Larger organisms


  • Require specialised mass transport systems due to increasing transport distances
  • Decreasing surface area: volume ratio
  • Increasing levels of activity
• Surface area


  Total area of the organism exposed to the external environment
• Volume


  Total internal volume of the organism
• As the surface area and volume of an organism increase


  The surface area: volume ratio decreases
• Single-celled organisms have a high SA: V ratio which allows for the exchange of substances to occur via simple diyusion</b>
• As organisms increase in size their SA: V ratio decreases
• There is less surface area for the absorption of nutrients and gases and secretion of waste products in larger organisms
• The greater volume in larger organisms results in a longer diyusion distance to the cells and tissues
• Mass transport systems


  Specialised systems that enable the ezcient transport of nutrients and waste in larger organisms
• Mass transport systems


  • Involve bulk movement of materials (mass }ow)
  • Still involve some diyusion but only at speci|c exchange sites
  • Help bring substances quickly from one exchange site to another
  • Maintain diyusion gradients at exchange sites and between cells and their }uid surroundings
  • Ensure eyective cell activity by keeping the immediate }uid environment of cells within a suitable metabolic range
• Circulatory system in mammals


  A well-studied example of a mass transport system
• Single circulatory system


  Blood passes through the heart once during one complete circuit of the body
• Double circulatory system


  Blood passes through the heart twice during one complete circuit of the body
• Single circulatory system in fish


  • Deoxygenated blood is pumped to the gills from the heart
  • Gills are the exchange site for oxygen and carbon dioxide
  • Oxygenated blood flows from the gills to the rest of the body
  • Heart only has one atrium and one ventricle
• Double circulatory system in mammals


  • Blood passes through the heart twice during a single circuit of the body
  • Heart has a left side and right side with a wall (septum) dividing the two
  • Left side contains oxygenated blood, right side contains deoxygenated blood
  • Blood in the right side travels to the lungs, returns to the left side before being pumped around the rest of the body
  • Blood that has just passed through an organ goes straight back to the heart, not to another organ (except hepatic portal vein)
• Advantages of double circulation


  • Maintains higher blood pressure and average speed of flow
  • Allows for more efficient exchange of nutrients and waste with surrounding tissues
• Closed circulatory system


  Blood is pumped around the body and is always contained within a network of blood vessels
• Open circulatory system


  Blood is not contained within blood vessels but is pumped directly into body cavities
• Circulatory system in insects

  • Has one main blood vessel - the dorsal vessel
  • Tubular heart in the abdomen pumps haemolymph into the dorsal vessel
  • Haemolymph surrounds the organs and eventually reenters the heart via one-way valves called ostia
  • Haemolymph is not specifically directed towards any organs
• Insects are able to survive with a less efficient circulatory system because oxygen is delivered directly to their tissues via tracheae
• Arteries


  Transport blood away from the heart (usually at high pressure) to tissues
• Arterioles


  Arteries branch into narrower blood vessels that transport blood into capillaries
• Veins


  Transport blood to the heart (usually at low pressure)
• Venules


  Narrower blood vessels that transport blood from the capillaries to the veins
• Structure of arteries


  • Consist of three layers: tunica adventitia/externa, tunica media and tunica intima
  • Tunica intima has an endothelial layer, a layer of connective tissue and a layer of elastic fibres
  • Tunica media has smooth muscle cells and a thick layer of elastic tissue
  • Tunica adventitia is mostly made up of collagen
• Tunica adventitia/externa


  Outer layer of blood vessel
• Tunica media


  Middle layer of blood vessel
• Tunica intima


  Inner layer of blood vessel
• Tunica intima


  • Made up of an endothelial layer, a layer of connective tissue and a layer of elastic fibres
• Endothelium


  One cell thick layer that lines the lumen of all blood vessels, very smooth to reduce friction for free blood flow
• Tunica media


  • Made up of smooth muscle cells and a thick layer of elastic tissue
• Arteries


  Have a thick tunica media
• Tunica media of arteries


  • Muscle cells strengthen the arteries so they can withstand high pressure, enables contraction and narrowing of lumen for reduced blood flow
  • Elastic tissue helps maintain blood pressure by stretching and recoiling to even out fluctuations
• Tunica adventitia


  Covers the exterior of the artery and is mostly made up of collagen
• Collagen in tunica adventitia


  • Protects blood vessels from damage by over-stretching
• Arteries


  • Have a narrow lumen which helps maintain high blood pressure
  • Have a pulse present
• Arterioles


  • Possess a muscular layer that allows them to contract and partially cut off blood flow to specific organs
  • Have a lower proportion of elastic fibres and a large number of muscle cells
• Veins


  • Tunica media is much thinner as they don't need to withstand high pressure
  • Have a larger lumen to ensure adequate speed of blood return to the heart
  • Contain valves to prevent backflow of blood
• Venules


  • Have few or no elastic fibres and a large lumen as blood is at low pressure after passing through capillaries
  • Do not have a muscular layer