Gas exchange in insects

• What is the gas exchange surface in insects?

  The tracheal system
• How does the gas exchange surface in insects work?

  -openings called spiracles on the exoskeleton allow air in

  -air passes into the trachea, which has rings of chitin to prevent collapse

  -air passes into the fine trachioles
• What adaptations does the tracheal system have?

  -large surface area due to many small trachioles

  -short diffusion pathway: 1 cell thick squamous epithelium (flattened cells)

  -moist: trachiole ends are filled with fluid
• How is gas exchange carried out when the insect is metabolically active?

  1. A lactic acid type substance builds up in the cell
  2. The addition of the solute decreases the water potential of the cell
  3. Water leaves the fluid filled trachiole by osmosis down a water potential gradient
  4. The level of fluid in the trachiole drops, pulling air into the tracheal system
• Larger and more active insects can ventilate their tracheal system through abdominal movements/pumping
• How is water loss reduced in insects?

  -the gas exchange surface is internal

  -spiracles close

  -there are tiny hairs around the spiracles that trap moisture

  -the exoskeleton is made of chitin, which is waterproof
• Why can't insects exchange gases through their skin?

  Because they have a high surface area to volume ratio, they are susceptible to water loss. An adaptation for this is that they are covered in a chitin exoskeleton which has a layer of waterproof wax on it. The wax is not permeable to gases, so they cannot conduct gas exchange over the surface.
• Spiracles lead to trachae: a system of chitin-lined tubes. The chitin supports the trachae and prevents them from collapsing. The trachae terminate in tracheoles, which are close to the cells. The tracheoles are the gas exchange surface
• How is oxygen delivered to cells in insects?

  Oxygen is delivered directly to cells through the tracheal system.
• How are concentration gradients maintained in insects?

  -oxygen is used in the cells, making the oxygen concentration low, so it diffuses towards the cells

  -carbon dioxide is produced by respiration in the cells, which makes the carbon dioxide concentration high, so it diffuses away from the cells towards the spiracles
• What happens during inspiration in an insect (ventilation)?

  -abdomen expands, decreasing the pressure inside

  -abdominal spiracles close and thoracic spiracles open

  -the lower pressure in the abdomen pulls the air in through the thoracic spiracles
• What happens during expiration in an insect (ventilation)?

  -abdomen contracts, decreasing the volume and increasing the pressure

  -thoracic spiracles close and abdominal spiracles open

  -stale air is forced out of the open abdominal spiracles
• What happens during anaerobic respiration in an insect?

  -lactic acid is produced

  -the lactic acid lowers the water potential of the muscle cells

  -so water leaves the fluid-filled trachioles by osmosis

  -air is pulled into the trachial system, increasing the rate of diffusion of oxygen into cells