Gas Exchnage In Insects Flashcards
Insects have a three-part structure. Head – thorax – abdomen.
• Insects have an air-filled tracheal system which directly supplies air to all respiring tissues. Air enters
via spiracles (external opening/pore that allows air in/out of the tracheae).
• Oxygen travels down the concentration gradient towards cells, CO2 moves down its concentration
gradient towards the spiracles to be released into the atmosphere.
• The air is transported through the body in the tracheae (series of tubes). These divide into smaller
tubes called tracheoles – which give a large surface area, also have thin walls.
• The ends of tracheoles are filled with tracheal fluid which oxygen dissolves in. Gaseous exchange
occurs between the air in the tracheole and tracheal fluid, as well as across the thin, permeable tracheole walls.
When the tissues are active tracheal fluid can be withdrawn into the body fluid to increase SA of tracheole wall exposed to the air, allowing more oxygen to diffuse into cells when insects are active.
Remember: Spiracles -> Trachea -> Tracheoles
Larger insects can ventilate their tracheal system by mechanical ventilation (movement):
•Movements of the wings can alter the volume of the thorax. As thorax vol decreases, air in the
tracheal system is put under pressure and is pushed out of the tracheal system. When thorax vol
increases, the pressure drops, and air is pushed inside.
•Locusts can alter their abdomen volume by specialised breathing movements, coordinated with
opening & closing valves in spiracles. Rhythmic abdominal movements cause spiracles at the front to
open and air to enter, and then the spiracles at the rear of the body open and air can leave.
•Parts of the tracheal system are expanded and have flexible walls. These form air sacs, which can be
squeezed by flight muscles. Repetitive expansion and contraction of these sacs ventilate the tracheal system. Air sacs act as reservoirs and improve air flow.
Practical – Dissection of gaseous exchange system in insects:
Fix the insect to dissecting boards using pins, to examine the tracheae cut and remove part of the exoskeleton from along the abdomen. Use a syringe to fill the abdomen with saline solution, tracheae filled with air to like a network of thin grey tubes. Tracheae can be examined under light microscope using a wet mount slide. Rings of chitin support the tracheae in insects, like cartilage in humans.
