7.4 Ventilation and gas exchange in other organisms

Question 1

Why do insects need gaseous exchange systems?

Answer 1

They have a tough exoskeleton through which little to no gaseous exchange can take place

Relatively high oxygen requirements

No blood pigments that carry oxygen

Question 2

How has the gaseous exchange system of insects evolved?

Answer 2

To deliver oxygen directly to cells and remove CO2 the same way

Question 3

What and where are spiracles?

Answer 3

Small openings along thorax + abdomen

Question 4

What enters and leaves the spiracles?

Answer 4

Air

Question 5

What only leaves the spiracles?

Answer 5

Water

Question 6

In gas exchange, what do both mammals and insects need to be effective?

Answer 6

Maximised efficiency of gaseous exchange

Minimal loss of water

Question 7

What structure controls the opening and closing of spiracles?

Answer 7

Sphincter

Question 8

How do insects minimise water loss?

Answer 8

Keep spiracle sphincters closed as much as possible

Question 9

When the insect is at rest, what state are the spiracles in? Why?

Answer 9

Closed - low O2 demand

Question 10

When the insect is active, what state are the spiracles in? Why?

Answer 10

Open - High O2 demand and CO2 levels build up

Question 11

What’s the first structure following the spiracles?

Answer 11

Trachea

Question 12

Describe the structure of insect trachea.

Answer 12

• Largest tubes of insect respiratory system, 1mm in diameter
• Trachea run into and along the insect’s body

Question 13

What is the function of insect trachea?

Answer 13

• Carry air into the body

Question 14

What are the tubes of the insect trachea lined with?

Answer 14

Spirals of chitin

Question 15

What is the function of spirals of chitin which line the tubes of the insect trachea?

Answer 15

Keep the tubes open when they’re bent or pressed

Question 16

What are the characteristics of chitin?

Answer 16

Relatively impermeable to gases and so little gaseous exchange can occur in the trachea

Question 17

What do the trachea branch into?

Answer 17

Tracheoles

Question 18

Describe the structure of tracheoles.

Answer 18

• Tubes with a diameter of 0.6-0.8 μm

* Each tracheole is a single, elongated cell with no chitin lining

Question 19

What does the lack of chitin lining in tracheoles mean?

Answer 19

Tracheoles are freely permeable to gases

Question 20

What is the benefit of the small size of tracheoles?

Answer 20

Spread throughout the insect’s tissues and cells - this is where most gas exchange occurs between air and respiring cells.

Question 21

Through what process does air usually move along the trachea and tracheoles?

Answer 21

Diffusion

Question 22

How are tracheoles in insects an adaptation for gas exchange?

Answer 22

The tracheal have a large SA - this maximised gas exchange

Question 23

How does oxygen enter the insect?

Answer 23

Oxygen dissolves in moisture on the tracheole walls and diffuses into surrounding cells

Question 24

What is towards the end of the tracheoles? What’s the function of this

Answer 24

Tracheal fluid - limits penetration of air for diffusion

Question 25

What happens when an insect is highly active, such as during flight, and the insect’s oxygen demands build up?

Answer 25

Lactic acid builds up in the insect’s tissues.

Due to this, water moves out of the tracheoles by osmosis.

Question 26

What system supplies all of the insect’s oxygen demands?

Answer 26

Tracheal system

Question 27

What controls the extent of gas exchange in insects?

Answer 27

Opening and closing of spiracles

Question 28

What are the 2 alternative methods which large insects with high energy demands use, such as beetles, to increase the level of gas exchange?

Answer 28

1. Mechanical ventilation

2. Collapsible trachea / air sacs

Question 29

Describe the method of mechanical ventilation in large insects with high energy demands.

Answer 29

Air is actively pumped into the tracheal system by muscular pumping movements of the thorax
• These movements change the vol. of the body, whichc changes the pressure in the trachea + tracheoles
• Air is drawn into the trachea + tracheoles OR forced out as pressure changes

Question 30

Describe the function of collapsible, enlarge trachea or air sacs.

Answer 30

Act as reservoirs - used to increase amount of air moved through gas exch. system
• The trachea / air sacs are inflated + deflated by ventilating movement of thorax + abdomen