7.4 Ventilation and gas exchange in other organisms

Question 1

explain the structure of the gas exchange system in insects

Answer 1

• have a tough exoskeleton
• don’t transport O2 in blood
• have air-filled tracheal system that supplies air directly to all respiring tissues

Question 2

explain how gas exchange takes place in insects

Answer 2

1. air enters via pores called spiracles
2. air passes through the body in a series of tubes called tracheae
3. tracheae divide into tracheoles which open into the tracheal fluid
4. gaseous exchange occurs in the tracheole and tracheal fluid

Question 3

what methods do insects use to increase level of gaseous exchange

Answer 3

1. mechanical ventilation of the tracheal system
   - air actively pumped in by muscular pumping movements of throat/abdomen
   - change body volume and pressure in tracheae/tracheoles
   - as pressure changes, air is drawn in/out
2. collapsible enlarged trachea/ air sacs (act as air reservoirs)
   - increase amount of air moving through the systems
   - inflated/deflated by ventilating movements of the thorax/abdomen

Question 4

explain the structure of the gas exchange system in fish

Answer 4

• use gills to absorb O2 and release CO2
• each gill consists of 2 rows of gill filaments attached to a bony arch
• gills contained in a gill cavity and covered by a protective operculum
• blood capillaries carry deoxygenated blood close to surface of gill plates where exchange happens

Question 5

how are fish adapted to make gas exchange more effective

Answer 5

• filaments are very thin and folded into many gill lamellae which provides large SA
• countercurrent flow of blood and water to maintain steep concentration gradients
• tips of adjacent gill filaments overlap which increases resistance to flow of water over gill surfaces and slows down the movement so more time for gas exchange

Question 6

explain how gas exchange takes place in fish

Answer 6

1. mouth opens (operculum=closed)
2. buccal cavity floor is lowered
3. increase in volume and decrease in pressure of the buccal cavity compared t outside
4. water rushes into mouth down a pressure gradient
5. opercular cavity expands
6. buccal cavity floor is raised
7. pressure in buccal cavity is higher than in the opercular cavity
8. water goes from buccal cavity over gills to opercular cavity
9. mouth closes (operculum=opened)
10. sides of opercular cavity move inwards and increase pressure
11. water rushes out through the operculum