Gas exchange

• What are the features of specialised exchange surfaces?

  1. Large surface area to volume ratio
  2. Thin
  3. Partially permeable
  4. Movement of environmental medium e.g. air
  5. Movement of internal environmental medium e.g. blood
• What are tracheae in insects?

  Internal network of tubes. They are made of rings that are spirals of chitin, for flexibility and support to prevent it from collapsing
• What are tracheoles in insects?

  Small, dead-end tubes that branch off the tracheae
• Insects have no transport system.

  
• How does gas exchange occur via diffusion in insects ?

  Oxygen diffuses along the tracheae, along the tracheoles to the respiring cells. Carbon dioxide is produced by respiring cells, and diffuses along the tracheae to the tracheoles to the atmosphere. This creates a concentration gradient
• How does gas exchange occur via mass transport?

  Contractions of muscles allows fresh air to enter and leave the tracheae. Expanding the abdomen = opens spiracles at the front for oxygen

  Deflating the abdomen = opens spiracles at the back for carbon dioxide to go out
• How does gas exchange occur via osmosis and diffusion?

  1. The ends of the tracheoles are filled with water.
  2. Anaerobic respiration from muscle cells mean lactate is produced, which lowers the water potential of muscle cells.
  3. Water moves into the muscle cells by osmosis
  4. The volume of water in the tracheoles decrease so that more air is drawn in.
  5. Gases diffuse more rapidly across the air-filled tracheole
• What are spiracles in insects?

  Tiny pores on the tracheae, through which gases enter and leave. They are opened and closed by a valve. An open spiracle means water loss via evaporation
• What is a fish like?

  1. Small surface area to volume ratio
  2. Single circulatory system
• What are fish gills?

  Located behind the head, they are made up of gill filaments (very thin) and gill lamellae (which increase the surface area of the gills)
• What is the oral side vs aboral side of the gills?

  Oral side = gills near the mouth

  Aboral side = gills furthest from the mouth
• How is blood pumped around a fish?

  1. Deoxygenated blood is pumped by the heart to 5 pairs of gills covered by a bony plate called the operculum
  2. Blood flows along the gill arch (containing gill filament and gill lamellae).
• How does a fish breathe?

  1. Buccal cavity (mouth) opens. Pressure inside is lower than outside.
  2. Water flows into the buccal cavity.
  3. Buccal cavity closes. Pressure inside is greater than outside
  4. Water moves out through the open operculum, passing through the gills
• Explain counter-current.

  1. Oxygenated water flows from the oral side to the aboral side.
  2. Blood in the capillaries in the lamellae flows in the opposite direction
  3. Oxygen enters the blood from the water
  4. Carbon dioxide enter the water from the blood