7.4 Ventilation And Gas Exchange In Other Organisms

Question 1

Why is the insect gas exchange system the way that it is?

Answer 1

• insects are very active mainly land-dwelling animals with relatively high oxygen requirements.
• however they have a tough, impermeable exoskeleton through which little or no gaseous exchange can take place.
• they also don’t have blood pigments that can carry oxygen.
  Their gaseous exchange system has developed to deliver oxygen directly to the cells and remove carbon dioxide in the same way.

Question 2

When air is breathed in by mammals, what is the order of structures it passes through?

Answer 2

Nasal cavity - pharynx- larynx- trachea - bronchus - bronchioles- alveoli.

Question 3

What are spiracles and their role (insects)?

Answer 3

Small openings found along the thorax and abdomen of most insects.
- air enters and leaves the system through the spiracles, but water is also lost.

Question 4

What are spiracles and their role (insects)?

Answer 4

Small openings found along the thorax and abdomen of most insects.
- air enters and leaves the system through the spiracles, but water is also lost.

Question 5

How is water loss in insects from the spiracles minimised?

Answer 5

The spiracles can be open or closed by sphincters.
-when an insect is inactive and oxygen demands are low, the spiracles will all be closed most of the time.
- when oxygen demand is raised or carbon dioxide levels build up, more spiracles are opened.
This maximises the efficiency of exchange and minimises water loss.

Question 6

What are the tracheae and their role in insects?

Answer 6

The largest tubes of the insect respiratory system and lead away from the spiracles

• they run into and along the body of the insect, carrying air.
• the tubes are lined with spirals of chitin (a fibrous polysaccharide), which keeps them open if they are bent/pressed.
• chitin is relatively impermeable to gases so little gas exchange takes place in the trachea.

Question 7

What are the tracheoles and their role in insects?

Answer 7

The tracheae branch to form narrower tubes called the tracheoles.

• each tracheole is a single, greatly elongated cell (squamous epithelium) with no chitin lining so are permeable to gases.
• they spread throughout the tissues of the insect and this is where most gaseous exchange takes place.
• vast numbers of tracheoles provides large SA.
• oxygen dissolves in moisture on the walls and diffuses into surrounding cells.

Question 8

What is tracheal fluid and its role in insects?

Answer 8

A fluid towards the end of the tracheoles which limits the penetration of air for diffusion.

• however when oxygen demands rise (eg. During flight) a lactic acid build up in the tissues results in water moving out of the tracheoles by osmosis due to a water potential gradient.
• this exposes more SA for gaseous exchange.

Question 9

What alternative methods do insects with very high energy demands have to increase gaseous exchange?

Answer 9

1. Mechanical ventilation- air is actively pumped into the system by muscular pumping movements of the thorax and abdomen. These movements change the volume or the body which changes the pressure in the tracheae and tracheoles. (As volume decreases, pressure increases, vice versa).
2. Collapsible air sacs- act as air reservoirs. Usually inflated/deflated by the ventilating movements of the thorax and are used to increase the amount of air moved through the system.

Question 10

When air is breathed in by insects, what is the order of structures it passes through?

Answer 10

Spiracles- tracheae- tracheoles

Question 11

What are the difficulties bony fish need to overcome?

Answer 11

• water is alot more dense and viscous (thick) than air.
• water has a much lower oxygen content.
• it would use up far too much energy to move the dense, viscous water in and out of lung-like respiratory organs.
  Moving water in one direction is much better in energy and simplicity terms.

Question 12

Why do fish need an exchange system?

Answer 12

Bony fish such as trout and cod are relatively big, active animals.

• this means their cells have a high oxygen demand.
• their high SA:V ratio means diffusion alone is not enough to supply their cells with the oxygen needed.
• their scaly outer covering does not allow gaseous exchange.

Question 13

What are the gills and their function?

Answer 13

• the organs of gaseous exchange.
• fish maintain a flow of water in one direction over the gills.
• gills have a large SA, good blood supply and thin layers for effective gas exchange.
• in bony fish they are contained in a gill cavity.
• bony gill arch supports the structure of the gills.

Question 14

Operculum and its role?

Answer 14

• a protective bony flap that covers the gills.

- it is active in maintaining a flow of water over the gills and so opens and closes accordingly.

Question 15

Gill filaments.

Answer 15

• occur in large stacks called gill plates.
• need a flow of water to keep them apart, exposing the large SA needed for gaseous exchange.
• when in air they remain clumped together, with reduced SA but fan out once in water.

Question 16

Gill lamellae?

Answer 16

• folds that cover the gills.
• are the exact place gas exchange occurs.
• they have a rich blood supply with a maintained steep concentration gradient.
• large SA.
• thin layers.

Question 17

What is the role of the efferent and afferent blood vessel in fish?

Answer 17

• Efferent blood vessel carries the blood leaving the gills in the opposite direction to incoming water which maintains a steep concentration gradient.
• Afferent blood vessel brings blood into the system. Haemoglobin is used to carry oxygen.

Question 18

What is the difference between ventilation in cartilaginous and bony fish?

Answer 18

• cartilaginous fish (sharks/rays) rely on continual movement to ventilate the gills hence why they don’t stay still. This is ram ventilation: they just ram water past the gills.
• bony fish don’t rely on movement generated water flow over the gills. Their exchange system allows them to move water over the gills even when still due to the operculum. They constantly open and close their mouth.

Question 19

Explain how ventilation of the gills takes place.

Answer 19

1. mouth opened. Floor of buccal cavity lowered.
2. This increases volume of buccal cavity= decreased pressure so water moves into mouth to create equilibrium.
3. Opercular valve is shut, opercular cavity containing gills expands.
4. This lowers pressure in opercular cavity, floor of buccal cavity moves up increasing pressure so water moves from buccal c over the gills.
5. Mouth closes. Operculum opens. Sides of opercular cavity moves inwards.
6. This increases pressure in opercular cavity, forcing water over gills and out through operculum.
7. Floor of buccal cavity moves up, maintaining flow of water over gills.
   This is a continuous process.

Question 20

What are the 2 extra adaptions gills have for effective exchange?

Answer 20

1. Tips of adjacent gill filaments overlap. This increases resistance to flow of water over the gill surfaces and slows down water movement, allowing more time for gaseous exchange.
2. Countercurrent system: water and blood flow in different directions. This ensures that steep concentration gradients are maintained allowing more efficient gas exchange.

Question 21

Compare the countercurrent and parallel system.

Answer 21

1. Parallel:
   - blood and water flow in same direction, providing an initial steep conc gradient. Diffusion takes place until there is conc equilibrium. Then no net movement of oxygen into blood occurs.
   This allows cartilaginous fish to only extract 50% of oxygen from the water.
2. Countercurrent:
   - flow in opposite directions so steep gradient between water and blood is maintained along the gill. Oxygen continues to diffuse down the conc gradient so much higher levels of oxygen saturation in blood achieved.
   This allows bony fish to remove 80% of oxygen from the water flowing over them.