Gas exchange surface insects

• Explain why single celled organisms do not need specialised gas exchange surfaces

  Single-celled organisms are so small that their surface area to volume ratio is very large; this means they carry out all exchange needed by diffusion across their cell-surface membrane.
• Describe the gas exchange surface of an insect

  Spiracles are openings on the surface of the exoskeleton that can open and close.

  These lead to a network of tubes called tracheae that have chitin rings to prevent them collapsing under pressure changes. Tracheoles are smaller tubes branching off the tracheae that end in the muscles so that no cell is far away from a tracheole
• Describe and explain how the gas exchange surface of an insect is adapted

  Tracheoles have thin walls so short diffusion distance to cells; They are highly branched so short diffusion distance to cells; they are highly branched so large surface area for gas exchange; Tracheae provide tubes full of air so fast diffusion into insect tissues; Fluid in the end of the tracheoles that moves out into tissues during exercise so faster diffusion through the air to the gas exchange surface; Body can be moved by muscles to move air so maintains concentration gradient for oxygen and carbon dioxide;
• Explain the importance of spiracles opening and closing

  They must close to stop the insect from dehydrating as water vapour can evaporate through them. Opening them allows for gas exchange to occur.
• Explain the movement of oxygen into the gas exchange system when the insect when it is at rest

  Oxygen used by the cells in aerobic respiration and diffuses into cells from the ends of the tracheoles; so oxygen a concentration is lower at the ends of the tracheoles, a gradient is established; so oxygen diffuses in from the air; (when the spiracles are open).
• Explain how an insect ventilates- muscle contraction

  Muscle contraction during movement- Contraction of muscles compresses the tracheal system. This decreases the volume of the tracheal system and increases the pressure. This causes movement of air out of the spiracles down a pressure gradient. When the muscles relax, compression stops and air fills the tubes. This expels carbon dioxide and maintains the oxygen concentration gradient.
• Explain how an insect ventilates- abdominal pumping

  Abdominal pumping-Rhythmic contractions of the abdomen compresses the tracheal system. This decreases the volume of the tracheal system and increases the pressure. This causes movement of air out of the spiracles down a pressure gradient. Expels air containing carbon dioxide and brings fresh air into through the spiracles to maintain the oxygen concentration gradient
• during intense exercise, the insect's muscles produce lactate which is soluble. Explain how this results in an increased rate of diffusion of oxygen into muscle cells.

  Lactate lowers the water potential of the muscle cells. Water moves from the ends of the tracheoles into muscle cells by osmosis leaving just air at the end of the tracheole. The oxygen is closer to the cells decreasing the diffusion distance. Diffusion of oxygen to the cells can occur quicker air than through water