4: Gas Exchange

Question 1

Why do insects need gas exchange?

Answer 1

Need high oxygen requirements. Have system which delivers oxygen directly to the cells and remove CO2 therefore very efficient

Question 2

What are spiracles in insects?

Answer 2

Found along the thorax and abdomen of most insects. Site of entry and exit for respiratory gases. Sporades can be open or closed to control water loss.

Question 3

What is the trachea in insects?

Answer 3

Largest tubes of insect respiratory system. Carry air directly into body for gas exchange with the cells, running both into the body and along it.

Question 4

What are the trachea tubes in insects made of?

Answer 4

Chitin in spirals. Same material that makes up the insect cuticle. The chitin spirals hold the trachea open if they are squashed or deformed as the insect moves.

Question 5

What does the chitin in insects cause?

Answer 5

Makes the trachea relatively impermeable to gases, so little gas exchange takes place in these vessels.

Question 6

What are the tracheoles in insects?

Answer 6

Minute tubes branching off from the trachea. Each one is a single elongated cell and they have no chitin lining. As a result, are freely permeable to gases.

Question 7

Where are the tracheoles in insects?

Answer 7

So small they run between and even penetrate individual cells. Where most of the gas exchange takes place.

Question 8

How does the insect respiratory system work?

Answer 8

Air enters through spiracles, when they are open.
Air moves along trachea and tracheoles by diffusion Alone.
Large surface area therefore gas exchange takes place.
Tracheoles May contain water at the end of length, therefore limits penetration of gases for diffusion. Osmosis helps this.

Question 9

Why are spiracles a major site for water loss in insects

Answer 9

Due to open spaces which lead o the cells. To minimise this, the spiracle sphincters are kept closed as much as possible.

Question 10

When do the spiracles open in insects?

Answer 10

Were the insect becomes active, the oxygen demand is higher and the spiracles open.

Question 11

What is beneficial in the tracheoles for diffusion and gas movement in insects?

Answer 11

Huge network of tracheoles, give a very large surface area and therefore a lot of gas exchange occurs

Question 12

What happens when there is water build up at the end of the length of the tracheoles in insects?

Answer 12

When the inset is very active and needs more oxygen, lactic acid builds up in the muscle tissues. This affects the osmotic concentration of the cells and so water moves out of the tracheoles into the cells by osmosis.
Therefore, more surface area for gas exchange.

Question 13

How does the nervous system help coordinate gas engage in insects?

Answer 13

The opening and closing of the spiracles are the normal control, this is coordinated by respiratory centres i the nervous system, which are stimulated by increasing CO2 levels and by lactic acid build up in active tissues.
Combination of the 2 factors: lack of oxygen and CO2 build up, works together to provide insect with gas.

Question 14

What are examples of very active insects?

Answer 14

Dragonflies, wasps, bees, large beetles, flies, moths, butterflies

Question 15

How has the system of very active insects evolved?

Answer 15

Mechanical ventilation

Collapsing tracheae or air sacs

Question 16

What does mechanical ventilation help large insects achieve?

Answer 16

Air is actively pumped into the tracheal system. Spiracles open and the insect makes muscular pumping movements of the thorax, abdomen or both. These “ventilating movements” change the volume and the pressure inside the body and draws air in and out of the tracheae and tracheoles.

Question 17

What does collapsing tracheae and air sacs do to active insects?

Answer 17

Increase the volume of air moved through the system. The ventilating movement of the thorax and abdomen inflate and deflate them. In some insects they can be ventilated by general body movement.

Question 18

Why do fish need an gas exchange system?

Answer 18

Have high oxygen demand because they are very active. However, they cannot go about gas exchange through scaly external covering because it isn’t permeable to gases. Therefore have evolved a system to enable gas exchange.

Question 19

What are the gills needed for in fish?

Answer 19

Gills have a large surface area for diffusion, a good blood supply to maintain concentration gradients and thin walls giving short diffusion paths, so they are well adapted for successful gaseous exchange.

Question 20

what d the gills o bony fish covered by?

Answer 20

Contained in a Gil cavity and is covered by a bony protective flap called the operculum.

Question 21

What is the operculum in fish?

Answer 21

Important in maintaining a flow of water over the gills, even when fish is stationary. Is in the gills.

Question 22

What is the structure of the gills in fish?

Answer 22

Occur in large stacks, need water to keep them apart and so to expose the large surface area needed. Gill lamellar is main site for gas exchange. Very rich blood supply

Question 23

What is the main area of gas ehcnage in fish?

Answer 23

Gill lamellae

Question 24

What does the blood do during fish gas exchange?

Answer 24

Blood leaving the gills flows in the OPPOSITE direction to the incoming waters therefore o ensuring the most effective possible exchange of gases.
Counter current system

Question 25

Why do fish require a constant flow of water t the gills?

Answer 25

Diffusion in water is very slow, so to get the oxygen needed for cellular respiration, fish requires constant flow of water over the gills.

Question 26

What happens when a fish is out of water?

Answer 26

It cannot survive long because the gill filaments all stick together. The remaining exposed surface area is not big enough for effective gas exchange to take lace, therefore the fish has no oxygen content and dies.

Question 27

What do cartilaginous fish not have?

Answer 27

They do not have an operculum.

Question 28

What do cartilaginous fish have to do, because they have no operculum?

Answer 28

They have to be on constant move, swimming l the time to keep water flowing in through their mouths and out over gills.

Question 29

What is the inside of a cartilaginous fish mouth called?

Answer 29

Buccal chamber.

Question 30

How do gills maximise efficiency in fish?

Answer 30

Large surface area, rich blood supply, thin walls. 2 adaptations:
Counter current system.
Overlapping gill filaments

Question 31

what is the counter current system in fish?

Answer 31

The blood in the gill filaments and the water moving over the gills flow in opposite directions. Called countercurrent system. Diffusion occurs down a concentration gradient, and the steeper the gradient, the more effective diffusion.
A countercurrent system maintains a steep conc gradient than if the blood and water were going to same way.
80% more oxygen due to this.

Question 32

What do overlapping gill filaments do to fish?

Answer 32

Diffusion in water is slow, so if water passes over gills too quickly, it limits the amount of oxygen and CO2 that can be exchanged.
The tips of he adjacent gill filaments overlap, increasing the resistance to the flow of water. This slows down the flow of water over the gills surfaces, giving more time for the exchange of gases to occur.