Topic 1: Lifestyle, Health and Risk

• How does oxygen move into the cells of a worm?


  Diffusion (high Surface Area to Volume ratio)
• How does oxygen move into the cells of a frog?


  Adult frogs have lungs (baby frogs which are tadpoles get oxygen by diffusion due to their high Surface Area to Volume ratio)
• How does oxygen move into the cells of a fish?


  Diffusion (oxygen in water moves into the bloodstream by running through the gills)
• How does oxygen move into the cells of an insect like a cricket?


  They have a tracheal system.
• What is the tracheal system?


  A series of tubes/airways which allow oxygen to move into the bloodstream
• What factors affect the rate of diffusion?

  • concentration gradient
  • surface area
  • diffusion distance
  • temperature
  • size of molecules
• The rate of diffusion increases when the surface area to volume ratio increases
• The greater the concentration gradient, the higher the rate of diffusion
• The rate of diffusion increases when the diffusion distance decreases.
• The rate of diffusion increases when the temperature is increased because particles move faster as they gain more kinetic energy
• If the size of molecules is larger, the rate of diffusion decreases
• Diffusion can be demonstrated by observing bromine gas diffusion in a clear tube
• Diffusion experiment:

  • Cotton wool soaked with ammonium hydroxide is introduced to the open end of the tube
  • Ammonia gas is given off
  • Ammonia turns litmus paper blue
  • Use a timer to record when each litmus paper turns blue to work out the speed of diffusion

  
• The majority of cells in a multicellular organism are not in contact with the organism's surroundings. Oxygen and glucose must be transported from outside the organism to every cell in the body. For this, a mass flow system is needed.
• A mass flow system transports substances in bulk down a pressure gradient. This enables substances to move long distances at a sufficient rate. The larger the organism, the greater the distance that oxygen and glucose must travel, the greater the pressure required.
• Requirements for a mass flow system:

  • circulatory fluid
  • contracting pump to move fluid
  • tubes through which fluid can circulate
• Examples of mass flow systems:

  • circulatory system
  • digestive system
  • respiratory system
  • lymphatic system
• Mass flow system - circulatory system

  Materials moved - blood

  Pump - Heart and contractor blood vessels
• Mass flow system - digestive system

  Materials moved - food, water

  Pump - peristalsis surrounding intestines
• Mass flow system - respiratory system

  Materials moved - air

  Pump - intercostal muscles, diaphragm
• Mass flow system - lymphatic system

  Materials moved - lymph (salt solution that has to be returned to the heart)

  Pump - contraction of skeletal muscles
• What kind of circulatory system does a penguin have?


  Double closed
• What is a closed circulatory system?


  A circulatory system in which blood stays within blood vessels
• What are the two circuits in a double circulatory system?


  Systemic and Pulmonary
• What is the fluid that bathes the cells in a closed circulatory system?

  Tissue fluid
• What is the major benefit of having a double, closed circulatory system?


  Maintains high pressure
• What sort of circulatory system do fish have?


  Single closed
• What is the definition of a single circulatory system?


  Blood flows through the heart once
• What sort of circulatory system do bees have?


  Open
• What is an open circulatory system?


  A circulatory system in which blood flows into the body cavity and tissues are bathed in blood
• In open circulatory systems, blood is not fully contained in blood vessels. Most insects and molluscs have this.
• In open circulatory systems...

  • The heart pumps blood into the body cavity and tissues are bathed in blood
  • When the heart pumps relaxes, blood is drawn into the heart through valves
  • The blood is called hemolymph because it is mixed with tissue fluid
• In closed circulatory systems...

  • blood is contained within blood vessels
  • blood is kept at high pressure throughout the body
  • the oxygen concentration gradient is high because oxygenated and deoxygenated blood do not mix (in mammals)
• From largest to smallest:

  • heart
  • veins and arteries
  • valves
  • venules and arterioles
  • capillaries
• From smallest to largest:

  • capillaries
  • venules and arterioles
  • valves
  • veins and arteries
  • heart
• How is the direction of blood flow maintained in a circulatory system


  High pressure in a pressure gradient keeps blood flowing towards area with lower pressure
• How is the direction of blood flow maintained in veins?


  Valves open to let blood into a junction of the vein and then close to prevent the backflow of blood, thus controlling the direction of blood flow
• In a single circulatory system...


  Blood passes through the heart once as it circulates the body
• In a double circulatory system...


  blood passes through the heart twice as it circulates the body
• In a single circulatory system blood circulation to organs is organised in series