2. Mass transport system

• What essential substances do animals require to survive?

  Oxygen and carbon dioxide
• How do small organisms meet their transport needs?

  Through diffusion due to large surface area
• What happens to the surface area to volume ratio as organism size increases?

  It decreases
• Why does diffusion become insufficient in larger organisms?

  Because diffusion distance increases and metabolic rate rises
• What is a mass transport system in larger organisms composed of?

  Heart and circulation
• What are the features of a mass transport system?

  1. A network to move through (e.g., vessels)
  2. A medium for movement (e.g., blood)
  3. Controlled direction for substance movement
  4. Maintenance of speed through pressure gradients
• What type of molecule is water?


  A polar molecule
• What process gives cells energy?

  Respiration
• What substances are needed for respiration?

  Glucose and oxygen
• How do unicellular organisms obtain necessary substances?

  They diffuse directly across the cell membrane
• Why can't diffusion be used in multicellular organisms?

  It would be too slow due to large distances
• What is the solution for substance transport in multicellular organisms?

  Mass transport system
• What is meant by 'mass transport system' and 'mass flow'?

  • Mass transport system: Mechanism for moving substances
  • Mass flow: Movement of fluids in one direction
• Describe the types of circulatory systems.

  • Open circulatory system
  • Closed circulatory system
  • Single circulation
  • Double circulation
• Why do many animals have a heart and circulation?

  To efficiently transport substances throughout the body
• How are substances exchanged in unicellular organisms?

  Through diffusion of nutrients and waste products
• What happens to the volume to surface area ratio as size increases?

  The volume to surface area ratio decreases
• What factors affect the need for a specialized circulatory system?

  Surface area: volume ratio and metabolic rate
• How do substances move around multicellular organisms?

  Through a mass transport system and mass flow
• What is mass flow?

  Movement of fluids in one direction down a pressure gradient
• What are substances that organisms must carry?

  Nutrients, gases, and waste products
• What is the difference in blood circulation speed between open and closed systems?

  Closed systems have faster blood circulation
• What type of blood does the heart pump away in single circulation in fish?

  Deoxygenated blood
• Where is deoxygenated blood pumped to in fish?

  To the gill capillaries
• What happens to the blood after it is oxygenated in fish?


  It travels to the rest of the body via systemic capillaries
• How many times does blood flow through the heart in one complete circuit in mammals?

  Twice
• Why does blood flow through the heart twice in mammals?

  To ensure oxygenated blood reaches the body
• Compare the advantages and disadvantages of single and double circulation.

  Single Circulation:

  • Advantages: Less complex, lower pressure
  • Disadvantages: Slow movement, low activity level

  
  

  Double Circulation:

  • Advantages: High pressure, fast flow
  • Disadvantages: More complex, requires complex organs
• What is the role of Daphnia in heart rate investigations?

  To investigate the effect of chemicals on heart rate
• What are key terms related to the mass transport system?

  • Mass transport system
  • Mass flow
  • Open circulatory system
  • Closed circulatory system
  • Single circulation
  • Double circulation
  • Diffusion
• What are the functions of mass transport systems in multicellular organisms?

  • Carry raw materials from specialised exchange organs to body cells
  • Remove metabolic waste from cells
• Open circulatory system

  • Blood circulates in large Open Spaces
  • Simple heart
  • In insects
  • Substances can diffuse between blood and cells.
  • Hot pumps blood out into cavities around animals organs.
  • Blood travels slower
  • Heart relaxers and blood is drawn back into the heart through small valve openings along heart length  
• Close circulatory system  

  • Capillaries bring the blood into closed contact with cells for exchange
  • Blood enclosed within tubes called blood vessels
  • High blood pressure
  • Blood travels faster
  • More efficient blood system are delivering substances around the body
  • In larger more active animals   
• Single vs double circulatory systems

  Advantages and disadvantages

  
• Explain why many small animals such as daphnia have a heart

  1. Reference to mass flow or having a mass transport system
  2. Name a suitable substance transport to the example oxygen
  3. Comment on blood pressure or fast movement or blood to cells.
  4. Idea of increased concentration gradient of solutes for example oxygen or surface area to volume ratio is too small. 
  5. Idea that diffusion alone would be too slow
  6. It has a high metabolic rate  
• Metabolic rate increases

  as organism increases/gets bigger