3. Insect & Fish Gas Exchange

Question 1

Spiracles

Answer 1

Small holes in an insect’s exoskeleton. Air enters through them.

Question 2

The spiracles open to a network of fine tubes called…

Answer 2

tracheae. These are lined with rings of chitin

Question 3

Why are the tracheae lined with rings of chitin?

Answer 3

Strength - so that it doesn’t collapse.

Ensures airways are always open.

Question 4

Tracheae sub-divide into tubes of smaller diameter called…

Answer 4

tracheoles - these are UNLINED

Question 5

Where do the tracheoles end?

Answer 5

At the insect’s body cells

Question 6

The entire tracheal system of an insect relies on…

Answer 6

a diffusion gradient

Question 7

Ventilation of small insects/insects that aren’t very active

Answer 7

They are able to rely on enough oxygen reaching their tissues through their spiracles

Question 8

Ventilation of active insects

Answer 8

They need to speed up the movement of oxygen to their tissues, so they pump their abdomens in & out using muscles.

Question 9

What does the pumping of the abdomen in active insects do?

Answer 9

This helps fresh air to enter the tracheae.

Question 10

Adaptations of tracheoles

Answer 10

1. Very large number of fine tracheoles: large SA
2. Thin walls: short diffusion pathway
3. Use of oxygen and production of CO2 sets up: steep diffusion gradient
4. Ends of tracheoles are fluid-filled: gases can dissolve so rate of diffusion is faster

Question 11

What happens to the tracheoles at rest vs during flight?

Answer 11

At rest: water fills the ends of the tracheoles

During flight: the water diffuses into the muscle

Question 12

4 other adaptations of insect gas exchange system when they fly

Answer 12

1. Muscle cells anaerobically respire & produce lactic acid
2. Lowers water potential of muscle cells
3. Water moves by osmosis from tracheoles into muscle cells
4. Reduces diffusion distance so diffusion of oxygen is much faster

Question 13

EXAM QUESTION: Describe how an insect is able to obtain oxygen and limit water loss (6)

Answer 13

1. Air enters through spiracles
2. Through tracheae
3. Diffusion gradient in trachea
4. Tracheae associated with all cells/closely associated with cells
5. Oxygen diffuses into cells
6. Ventilation replacing air in tracheae
7. Body covered with waterproof waxy layer/cuticle
8. Spiracles are able to close

Question 14

How do fish gills extract oxygen from the water?

Answer 14

Counter current mechanism

Question 15

Units of partial pressure of oxygen

Answer 15

mm Hg

Question 16

What is partial pressure?

Answer 16

The pressure of a single gas in the mixture as if that gas alone occupied the container. Also the pressure exerted by a single gas in a mixture of gases

Question 17

Bony fish have:

Answer 17

1. waterproof scales

2. small SA:vol ratio

Question 18

Fish gill system in a nutshell

Answer 18

Oxygenated water enters through mouth -> water passes over gills -> deoxygenated water leaves

Question 19

Where are gills?

Answer 19

In a cavity on the side of a fish’s head

Question 20

How many pairs of gill arches are their on each side of a fish’s head?

Answer 20

4

Question 21

On each arch are ____ series of stacked ______ splayed out as a ______

Answer 21

two; gill filaments; V

Question 22

Disc-like projections called ________ are on the upper and lower surfaces of each ________

Answer 22

gill lamellae; gill filament

Question 23

Where exactly is gas exchange carried out in the gills?

Answer 23

Across the surface of the lamellae

Question 24

4 gill adaptations

Answer 24

1. Very large SA
2. Single layer of thin epithelial cells
3. Dense network of capillaries carrying blood running underneath (close to the surface)
4. Fish pushes water over the gills to ensure constant ventilation

Question 25

Explain what the counter-current system is

Answer 25

The flow of blood and water over the gill lamellae occurs in opposite directions.
Water always passes near blood that has less oxygen in it

Question 26

Compare oxygen concentration in blood and water

Answer 26

Water higher than blood always.
Hence a conc. gradient is maintained right along the surface where gas exchange takes place.
Equilibrium is never reached and diffusion of oxygen from water into blood constantly takes place