Exchange surfaces - Insect and fish gas exchange.

Question 1

Define exoskeleton.

Answer 1

An external skeleton of some organism. Made of chitin.. Water proof to reduce water loss.

Question 2

Define spiracle.

Answer 2

A small openings along the thorax and abdomen of an insect that open and close to control the amount of air moving in and out of the gas exchange system.

Question 3

Define the term trachea.

Answer 3

The main airway, supported by incomplete rings of cartilage which carries warm moist air down from the nasal cavity into the chest.

Question 4

Define the term tracheoles.

Answer 4

A small pipe that branches of a trachea in insects and is used for gas exchange.

Question 5

Define the term tracheal fluid.

Answer 5

Fluid found at the end of the tracheoles in insects that helps control the SA available for gas exchange and water loss.

Question 6

Outline the structure of the insect gas exchange system and describe the way oxygen reaches the body
cells.

Answer 6

• Air moves into the tracheae through pores on the surface called spiracles.
• O2 travels down the conc grad towards the cells.
• CO2 from the cells moves down its own conc grad towards the spiracles to be released into the atmosphere.
• The tracheae branch off into smaller tracheoles which have thin permeable walls and go to individual cells.
• They also contain tracheal fluid which oxygen dissolves in so the oxygen then diffuses from this fluid into body cells.
• CO2 diffuses in the opposite direction.

Question 7

Explain why insects will tend to keep spiracles closed when oxygen demands are very low.

Answer 7

Spiracles are a channel for water loss, so unless it is necessary to have a lot of oxygen the insect will keep them closed to reduce water loss.
(Spiracles can be opened and closed by sphincters)

Question 8

Describe the adaptations of the insect gas exchange system that make it an efficient exchange surface.

Answer 8

• The tracheoles provide a large SA for gas exchange.

- The tubes are thin which allows the tracheoles to get very close to cells to minimise diffusion distance.

Question 9

Describe how activity changes the volume of tracheal fluid in the tracheoles, and explain the value of
this occurring.

Answer 9

• When oxygen demands build up lactic acid builds up in the tissues which results in water moving out of the tracheoles (tracheal fluid) by osmosis which exposes more SA for gaseous exchange.

Question 10

Describe two adaptations that insects with very high energy demands have to increase the efficiency of
their gas exchange system.

Answer 10

1) Mechanical ventilation of the tracheal system - air is actively pumped into the system by muscular pumping movements of the thorax and/or abdomen. These movements change the volume of the body which changes the pressure in the tracheae and tracheoles which means that air is drawn into or forced out of them as pressure changes.
2) Collapsible, enlarged tracheae or air sacks which act as reservoirs - these are used to increase the amount of air moved through the gas exchange system. Usually they are inflated or deflated by the ventilating movement of the thorax and abdomen.

Question 11

Describe the advantages of, and challenges faced by, gas exchange systems operating in water rather
than air.

Answer 11

Advantages:
- water loss isn’t an issue
- water provides structural support which air doesn’t.
Disadvantages:
- much lower oxygen concentration, lower concentration gradient so it’s more difficult to obtain sufficient O2.
- water is more viscous and dense than air.

Question 12

Define the term opperculum.

Answer 12

• The bony flap covering the gills of bony fish. Part of the mechanism that maintains a constant flow of water over the gas exchange surfaces.

Question 13

Define the term buccal cavity.

Answer 13

The space inside the mouth of a fish.

Question 14

Define the term opercular valve.

Answer 14

The flap that allows to opperculum to be moved outwards whilst keeping it closed.

Question 15

Define the term gill arch.

Answer 15

A bony structure that supports the gill filaments.

Question 16

Define the term gill filament (primary lamellae).

Answer 16

A thin projection from the gill arch, creating a large SA.

Question 17

Define the term gill plates (secondary lamellae).

Answer 17

Raised plates on the surface of gill filaments which in total create an even larger SA for gaseous exchange. The gill plates have a lot of blood capillaries and a thin surface layer of cells to speed up diffusion between water and blood.

Question 18

Label and annotate a diagram showing the features of the gas exchange system in bony fish.

Answer 18

• Water enters the fish through its mouth and passes out through its gills.
• Each gill is made of lots of thin plates called gill filaments (or primary lamellae).
• The gill filaments are covered in lots of tiny structures called gill filaments (or seconday lamellae).
• Each gill is supported by a gill arch.
• The gills plates have lots of blood capillaries and a thin surface later of cells to speed diffusion between water and blood.

Question 19

. Describe the mechanism of ventilation in bony fish.

Answer 19

1) Fish opens mouth which lowers the floor of the buccal cavity.
2) The volume of the buccal cavity increases, decreasing the pressure inside the cavity. Water is sucked into the cavity.
3) The fish closes its mouth and the floor of the buccal cavity is raised again.
4) The volume inside the cavity decreases and the pressure increases so water is forced out of the cavity across the gill filaments.
5) Each Gill is covered by a bony flap called the operculum (which protects the gill). The increase in pressure forces the operculum on each side of the head to open, allowing water to leave the gills.
6) The process starts again.

Question 20

Describe the adaptations that make the bony fish gas exchange system an efficient exchange surface.

Answer 20

• Gill filaments and gill plates combined make a very large surface area for gas exchange
• The gill plates have a good supply of blood by capillaries so a steep concentration gradient is maintained.
• The gill plates have a very thin cell surface which minimises diffusion distance.
• The countercurrrent flow system maintains an oxygen concentration gradient between the blood and water all along the gill. Maximum oxygen saturation of blood achieved.

Question 21

Define the term “countercurrent exchange system”.

Answer 21

Blood and water flow in opposite directions so an oxygen concentration gradient between the water and the blood is maintained all along the gill. Oxygen continues to diffuse down the concentration gradient so a much higher level of oxygen saturation in the blood is achieved.
- Refer to diagram, OCR p170 -

Question 22

Define the term ‘’ parallel exchange system’’.

Answer 22

• Blood in the gills and water flowing over the gills travel in the same direction.
• Gives an initial steep oxygen concentration gradient between water and blood.
• Diffusion takes places until the oxygen concentration in the blood equalises with the oxygen conc in the water.
• After that there is no net movement
• diagram OCR p170-

Question 23

Draw a diagram to show how a much higher oxygen saturation of the blood can be achieved by a
countercurrent exchange system as compared to a parallel exchange system.

Answer 23

Check with diagrams on p170 OCR

Question 24

Describe the features of a gas exchange system that become apparent under microscopic examination
that aren’t easily seen when observing the whole organ system.

Answer 24

The features that increase the SA on the exchange surface i.e. alveoli, tracheoles and lamellae.
They are very small projections so they cannot be seen with the naked eye.
You cannot see the short distance of diffusion without a microscope.