Organisms Exchange Substances

• Describe and explain one feature of the alveolar epithelium that makes the epithelium well adapted as a surface for gas exchange.

  flattened cells reduces diffusion pathway

  permeable and allows diffusion of oxygen and carbon dioxide
• Explain how the counter-current principle allows efficient oxygen uptake in the fish gas exchange system.

  1.Blood and water flow in opposite directions;

  2. Diffusion/concentration gradient (maintained) along (length of) lamella/filament;
• Describe and explain the mechanism that causes lungs to fill with air

  inspiration

  Diaphragm muscle contracts and external intercostal muscles contract Causes volume of the thorax to increase and pressure decrease

  Air moves down a pressure gradient
• Explain how the counter current mechanism in fish gills ensures the maximum amount of the oxygen passes into the blood flowing through the gills.

  Water and blood flow in opposite directions

  Blood always passing water with a higher oxygen concentration

  Diffusion gradient maintained throughout length of gill

  If water and blood flowed in same direction equilibrium would be reached
• Describe how the structure of an individual lamella in fish gills creates a short diffusion pathway for oxygen and carbon dioxide

  the capillaries in each lamella bring the blood very close to the surface.In addition, the surface of each lamella is made up of just a single layer of flattened cells
• By which process do lipoproteins move out of epithelial cells?

  Lipoproteins move out of epithelial cells via exocytosis
• Compare the diameter, length and number of tracheae found in human and insect breathing systems

  1. A human trachea has a much bigger diameter and length than an insect trachea
  2. Humans only have one trachea, whereas insects have many tracheae
• There is a carbon dioxide concentration gradient in an insect gas exchange system.Describe how this gradient is formed

  Aerobic respiration in muscle tissue produces carbon dioxide.As a result, the concentration of carbon dioxide in the muscle tissue is greater than the concentration in the air.So, there is a carbon dioxide gradient from the respiring tissues to the air
• Describe the conditions that create a diffusion gradient for oxygen in the insect gas exchange system

  Aerobic respiration in insect muscle tissue uses oxygen.This makes the oxygen concentration inside the insect lower than the oxygen concentration in the air.As a result, there is an oxygen concentration gradient from the air into the tissues
• When an insect is active, tracheal fluid is replaced in the tracheoles by air.This changes the rate of diffusion between the tracheoles and the muscle tissue because the rate of diffusion through gas is…

  faster than the rate of diffusion through liquid
• How does the structure of an arteriole compare to the structure of an artery?

  Compared to arteries, arterioles have a thicker muscle layer. 

   

  Arterioles also have a thinner elastic layer.

   
• How is the valve system in veins adapted to its function?

  Valves help ensure that, despite low blood pressure, the blood does not flow backwards
• Capillaries are numerous and highly branched. How does this support their function?

   

  They provide a large surface area for exchange.
• How does the structure of an artery compare to the structure of a vein?

  Arteries have a thicker muscle layer than veins

  Arteries don’t have valves, whereas veins do.

  Arteries have a thicker overall wall than veins.
• Describe how tissue fluid is formed

  Blood moving into the capillaries has a high hydrostatic pressure.

   

  This pushes blood plasma, which is made up of water and other dissolved substances, out of the capillaries. The result is tissue fluid
• Describe how tissue fluid returns to the capillaries

  At the venous end of the capillaries the loss of fluid, combined with the remaining plasma proteins, reduces the water potential and hydrostatic pressure.

   

  This allows tissue fluid to return to the blood as a result of osmosis and external hydrostatic pressure.

   
• Most of the tissue fluid that forms returns to the circulatory system by osmosis. How does any remaining fluid get returned to the circulatory system?

  via the lymphatic system