3.1.1 - Exchange Surfaces (set B - Insect/fish Ventilation)

Question 1

Outline the gaseous exchange system in insects?

Answer 1

• Insects are very active during parts of their life cycle and they have relatively high oxygen requirements
• tough exoskeleton prevents gas exchange and they lack Haemoglobin
• deliver oxygen directly to cells and remove carbon dioxide similarly

Question 2

Explain what spiracles are?

Answer 2

Small openings along the insects thorax and abdomen

• air enters and leaves through them - water also lost through them
• open and close during periods of high and low oxygen demand

Question 3

Outline the process of spiracles opening and closing?

Answer 3

In many insects the spiracles can be opened or closed by sphincters

• kept closed as much as possible to minimise water loss - and when oxygen demands are low
• when oxygen demands rise or carbon dioxide builds up, more of the spiracles open

Question 4

explain what the tracheae are - mention briefly the structure?

Answer 4

• Largest tubes of the respiratory system - lead away from the spiracles (1mm diameter)
• carry air into body - they run into and along the body of the insect
• lined by spirals of chitin - relatively impermeable so little gas exchange takes place in the tracheae

Question 5

Explain what the tracheole are - briefly explain the structure?

Answer 5

• Tracheae branch forming narrower tubes until they divide into tracheoles
• very small, single, greatly elongated cell - spread throughout the tissue of the insect (between individual cells)
• no chitin lining - permeable to gases
• fluid lined

Question 6

Explain how oxygen enters the insects respiratory system?

Answer 6

• Air moves along tracheae and tracheoles by diffusion
• reaches all the tissues - oxygen dissolves in moisture on the walls of the tracheoles and diffuses into surrounding cells (large SA due to lots of tiny tracheoles)
• tracheal fluid prevents further penetration of oxygen

Question 7

Explain how some insects have alternate methods for increase gas exchange?

Answer 7

• mechanical ventilation of the tracheal system
• collapsible enlarged trachea or air sacs

Question 8

Outline how mechanical ventilation of the tracheal system enhances gas exchange in high metabolic insects?

Answer 8

• air is actively pumped into system by muscular pumping movements of the thorax and abdomen
• changes volume of the body and therefore pressure in the tracheae and tracheoles - creates pressure gradient
• air drawn into trachea and tracheoles or forced out

Question 9

Outline how collapsible enlarged trachea/ air sacs enhances gas exchange in high metabolic insects?

Answer 9

• act as air reservoir’s
• increases the amount of air moved through the gas exchange system
• usually inflated and deflated by the ventilating movements of the thorax and abdomen

Question 10

Explain the significance of chitin in insects?

Answer 10

• chitin spirals line trachea - impermeable to gases which prevents gas exchange taking place
• reinforces the tube to keep the airway open during body movements - ensures the gas exchange system is ventilated
• no chitin in tracheoles - allows for gas exchange

Question 11

Outline how tracheal fluid can be withdrawn during periods of high oxygen demands?

Answer 11

• limits the penetration of oxygen in tracheoles (reducing SA for diffusion)
• during time of high oxygen demand lactic acid builds up which results in water moving out of tracheoles and being withdrawn into surrounding tissues by osmosis
• exposes more surface area

Question 12

Explain the importance of tracheal fluid?

Answer 12

fills the end of the tracheoles - gases can dissolve into the fluid and easily diffuse into the surrounding tissue

• moisture on walls of tracheoles
• controls SA for penetration of gases

Question 13

Explain the role of the tough exoskeleton?

Answer 13

• Protects insect from the environment and prevents the insect from loosing water from their body
• insect evolved so oxygen is delivered directly to cells - carbon dioxide removed directly as well

Question 14

Outline a significant problem aquatic animas face in regard to getting oxygen from water?

Answer 14

• water is 1000 times denser than air - 100 times more viscous
• water has a much lower oxygen content
• would use to much energy to move dense, viscous water in an out of a lung-like respiratory system - easier to move it in 1 direction

Question 15

Explain why bony fish require a specialised gas exchange system?

Answer 15

• relatively big - small SA:V ratio
• diffusion would be too slow
• very active - cells have high oxygen demand
• scaly outer covering - prevents gas exchange

Question 16

Outline the respiratory system in bony fish?

Answer 16

maintain flow of water in one direction over the gills (their organ for gas exchange) which are well adapted for taking oxygen in and getting rid of carbon dioxide

• gills covered and protected by operculum (bony flap)

Question 17

Explain and describe how the gills of bony fish are adapted for efficient gas exchange?

Answer 17

• large surface area - lamellae provide large SA
• good blood supply - vessels are in close proximity to lamellae + vast network of capillaries
• thin layers - lamellae surface consists of single layer of flattened cells - short diffusion distance

Question 18

Outline the structure of gills in bony fish?

Answer 18

• series of gills on each side of the head
• each gill arch is attached to 2 stacks of filaments
• rows of lamellae on the surface of each filament
• lamellae surface consists of single layer of flattened cells that cover network of capillaries

Question 19

Explain what the gill lamellae are in bony fish?

Answer 19

• main site of gas exchange
• rich blood supply - vast network of capillaries and thin walls
• surface consists of single layer of flattened cells that cover network of capillaries + large SA

Question 20

Explain what gill filaments are?

Answer 20

• occur in large stacks - gill plates
• need flow of water to keep them apart and expose the large SA for gas exchange

Question 21

Explain how ram ventilation works in aquatic animals - how does it differ to bony fish?

Answer 21

• cartilaginous fish rely on continual movements to ventilate gills
• ram water past gills
• bony fish use sophisticated system involving operculum - moves more water over the gills all the time

Question 22

Outline the process of ventilation of the gills - include the first 3 steps (lowering of buccal cavity and expanding of opercular cavity)?

Answer 22

1) mouth opened - floor of buccal cavity lowered (increases volume of buccal cavity)

2) so pressure in cavity drops - water moves into buccal cavity

3) opercular valve is shut - opercular cavity (contains gills) expands - decreasing pressure in opercular cavity

Question 23

Outline the process of ventilation of the gills - include steps 4 and 5 (what happens to buccal cavity and in the opercular cavity)?

Answer 23

4) floor of buccal cavity moves up - increasing pressure - water moves from buccal cavity over the gills

5) mouth closes - operculum open - sides of opercular cavity move inward - increases pressure in opercular cavity

Question 24

Outline the process of ventilation of the gills - include the final step (flow of water over the gills )?

Answer 24

Pressure in opercular cavity increases - forces water over the gills and out the operculum

• floor of buccal cavity is steadily moved up - maintaining flow of water over gills

Question 25

Outline the significance of adjacent gill filaments overlapping in regard to gas exchange?

Answer 25

• increases the resistance to flow of water over the gill surface
• slows movment of water - more time for gas exchange to take place

Question 26

Outline the significance of water flowing over the gills and blood in the gill filaments flowing in different directions?

Answer 26

• establishes countercurrent exchange system - ensures that steeper concentration gradients are maintained
• removes about 80% of oxygen from water flowing over them - parallel systems can only extract about 50%

Question 27

Give 2 more adaptions of the gills?

Answer 27

• tips of adjacent gill filaments overlap
• countercurrent exchange system

Question 28

Outline how a parallel system works?

Answer 28

• blood in gills and water flowing over the gills - travel in the same direction
• provides an initial steep oxygen concentration gradient between blood and water
• diffusion only takes place until oxygen concentration of the blood and water are in equilibrium

Question 29

Outline and describe a problem with parallel systems in fish?

Answer 29

• provides an initial steep oxygen concentration gradient between blood and water - however once the oxygen concentration of the blood and water are in equilibrium, then no net movment of oxygen into blood occurs
• extracts only 50% of oxygen from water

Question 30

Outline how a countercurrent system works?

Answer 30

• blood and water flow in opposite directions - oxygen concentration gradient between water and blood is maintained all along the gill
• oxygen continues to diffuse down concentration gradient - much higher level of oxygen saturation of the blood is achieved

Question 31

Explain a positive feature of the counter current system?

Answer 31

Oxygen concentration gradient between water and blood maintained all along the gill - oxygen constantly diffuses down gradient

• much higher level of oxygen saturation achieved