Lesson 4 - Gaseous exchange systems in insects

Question 1

Why can’t insects use diffusion?

Answer 1

Exoskeleton through which no diffusion can occur

Question 2

How is oxygen transported around insects?

Answer 2

Oxygen is delivered directly to cells and carbon dioxide is removed directly, as they have no blood pigments that can carry oxygen.

Question 3

Spiracles

Answer 3

Small openings in the thorax and abdomen of insects. Air enters through them and water is lost.

Question 4

How is water loss through spiracles prevented?

Answer 4

Sphincters open and close spiracles. Spiracles are closed as much as possible to prevent water loss.

Question 5

What is the first tube after the spiracles?

Answer 5

Tracheae

Question 6

Diameter of the tracheae?

Answer 6

1mm

Question 7

Support for the tracheae?

Answer 7

Lined by spirals of chitin to keep them open when bent or pressed.

Question 8

Does gaseous exchange occur in the tracheae?

Answer 8

Chitin makes up the cuticle. This is impermeable to gases, preventing diffusion.

Question 9

What is after the tracheae?

Answer 9

tracheoles

Question 10

Diameter of tracheoles?

Answer 10

0.6 - 0.8 micrometers

Question 11

What are tracheoles?

Answer 11

Single elongated cells. They are very small, so spread throughout tissues of the insect and run between individual cells. Most gaseous exchange occurs here.

Question 12

Where is tracheal fluid?

Answer 12

Near the ends of the tracheoles

Question 13

What is the purpose of tracheal fluid?

Answer 13

Increases the surface area of the tracheoles for osmosis when lactic acid builds up in the tissues.

Question 14

What does tracheal fluid limit?

Answer 14

Penetration of gases by diffusion. This is because O2/CO2 dissolve in moist lining of cells.

Question 15

Two ways of increasing O2 and CO2 exchange in larger insects?

Answer 15

• Mechanical ventilation of tracheal system
• Collapsible or enlarged tracheae or air sacs

Question 16

Large insects examples:

Answer 16

• Wasp
• Bee
• Grasshopper
• Locusts
• Beetles
• Flies

Question 17

Mechanical ventilation of tracheal system:

Answer 17

Air is actively pumped into tracheal system by muscular pumping movements of the thorax and abdomen. These movements change the volume of the body and this changes the pressure in the tracheae and tracheoles. Air is drawn into the tracheae / tracheoles, or forced out, as the pressure changes.

Question 18

Collapsible enlarged tracheae or air sacs

Answer 18

Act as reservoirs. Increase the amount of air moved through the gaseous exchange system. Inflated and deflated by the ventilating movements of the thorax and abdomen.

Question 19

DGC

Answer 19

Discontinuous gas exchange cycle

Question 20

Three states of discontinuous gas exchange cycle:

Answer 20

• Closed
• Open
• Fluttering

Question 21

DGC - closed:

Answer 21

When the spiracles are closed no gases move in or out of the insect. Oxygen moves into the cells by diffusion from the tracheae and carbon dioxide diffuses into the bodily fluids where it is held in a process called buffering.

Question 22

Buffering

Answer 22

When CO2 is stored in the bodily fluids of an insect

Question 23

DGC - Fluttering

Answer 23

When spiracles flutter, they open and close rapidly. This moves fresh air into the tracheae to renew supply of oxygen, while also minimising water loss.

Question 24

DGC - open

Answer 24

When carbon dioxide levels build up really high in the bodily fluids of the insects, spiracles open widely and carbon dioxide diffuses out rapidly. There may also be pumping movements of the thorax and abdomen when spiracles are open to maximise gaseous exchange.

Question 25

Purposes of the DGC?

Answer 25

Original theory:
- Conserve water and prevent water loss
Current theory:
- Helping gaseous exchange in insects that spend lives underground in burrows
- Reducing entry of fungal spores, which can parasite an insect