Topic Three

• Why does countercurrent flow increase the rate of gas exchange?

  Diffusion gradient maintained across entire length of gill, so most of the oxygen diffuses into blood.
• Why does parallel flow limit the rate of gas exchange to 50%?

  Diffusion gradient only maintained until both water and blood have 50% oxygen saturation.
• Why does the tracheal system limit the size of insects?

  Relies on having short diffusion pathways.
• What are the functions of gill filaments and gill lamellae?

  Gill filaments take oxygen into blood, having many lamellae on top to increase surface area.
• In what three ways do gases move in and out of the insect tracheal system?

  Along a diffusion gradient, abdominal pumping and lactate-driven osmosis.
• How do insects use abdominal pumping for gas exchange?

  Contract muscles around trachea to squeeze them and force air in or out.
• How do insects set up an oxygen concentration gradient?

  Respiring cells use oxygen, so concentration is lowest at the ends of tracheoles.
• How do insects set up an carbon dioxide concentration gradient?

  Respiring cells produce carbon dioxide, so concentration is highest at the ends of tracheoles.
• How do insects use lactate-driven osmosis for gas exchange?

  Production of lactate lowers cell water potential. Water moves into cells by osmosis, emptying tracheoles of liquid and increasing rate of diffusion.
• What two factors affect the amount of material an organism must exchange?

  Size and metabolic rate.
• How could you find the water potential of a cell?

  Place it in series of solutions of different water potentials. No net gain or loss of water means cell has the same water potential as that solution.
• Describe a turgid plant cell

  Protoplast swells and pushes against cell wall
• Describe a plasmolysed plant cell

  Protoplast shrinks and pulls away from cell wall
• What are the four parts of the protoplast in plant cells?

  Cell membrane, nucleus, cytoplasm and tonoplast.
• What are the five adaptations of xerophytes to limit water loss?

  Thick cuticle, rolled leaved, hairy leaves, sunken stomata, leaves with low SA:V ratio.
• What are the functions of gill filaments and gill lamellae?

  Gill filaments take oxygen into blood. They have many lamellae on top to increase surface area.