Chapter 8 - Adaptations for Gas Exchange

Question 1

What is gas exchange?

Answer 1

The diffusion of gases down a concentration gradient across a respiratory surface, between and organism and its environment.

Question 2

What are the essential features of exchange surfaces?

Answer 2

• Have a large surface area, relative to the volume of the organism.
• Be thin for a short diffusion pathway.
• Be permeable.
• Have a mechanism for maintaining a concentration gradient.

Question 3

How is a earthworm adapted for gas exchange?

Answer 3

• Large S.A. to volume ratio.
• Skin is its respiratory surface, which it keeps moist.
• Low O2 requirement as it is slow moving.
• Haemoglobin carries O2 away and maintains a gradient.

Question 4

What is the difference between Cartilaginous fish and Bony fish?

Answer 4

Cartilaginous - Parallel flow.

Bony - Counter-current flow.

Question 5

How do Amphibians and Reptiles exchange gas?

Answer 5

Amphibians, moist permeable skin, so it takes place through the skin and when they’re active, the have lungs.
Reptiles, more complex internal structure, increasing S.A.

Question 6

How are the lungs of birds adapted for function?

Answer 6

They can process large volumes of Oxygen so their ribs and flight muscles ventilate their lungs.

Question 7

Why is a cartilaginous fish’s ventilation system less efficient than that of bony fish?

Answer 7

• They don’t have a special mechanism to force water over the gills so many must keep swimming to enable ventilation.
• Blood travels through the gill capillaries in the same direction as water travels, parallel flow.

Question 8

What is the Operculum on a bony fish?

Answer 8

The covering over the gills of a bony fish.

Question 9

How does the ventilation mechanism operate in bony fish?

Answer 9

• The mouth opens and the operculum closes.
• The floor of the mouth is lowered and the volume inside the mouth cavity increases.
• The pressure inside the mouth cavity decreases.
• Water flows in due to the external pressure being higher than the pressure inside the mouth.

Question 10

What are the thin projections on the gill arch called and what are the gas exchange surfaces on these called?

Answer 10

The thin projections are called gill filaments and the gill lamellae are the gas exchange surfaces.

Question 11

Why do fish die if out of water for more than a very short time?

Answer 11

Because the gill filaments stick together and the gills collapse. Much less area is exposed and so not enough gas exchange can take place.

Question 12

What is counter-current flow?

Answer 12

Blood and water flow in opposite directions at the gill lamellae, maintaining the concentration gradient and, therefore, oxygen diffusion into the blood, along their entire length.

Question 13

How to the lungs in a human inhale?

Answer 13

• External intercostal muscles contract and the diaphragm muscle contract, so it flattens.
• The ribs are pulled upwards and outwards.
• Both actions increase the thorax volume which reduces the pressure in the lungs.
• Atmospheric air pressure is now greater than the pressure in the lungs, so air is forced into the lungs.

Question 14

What feature of lung tissue is important in pushing air out of the lungs?

Answer 14

It is elastic and they recoil and regain their original shape when not being actively expanded.

Question 15

What is coated with surfactant and why is it important?

Answer 15

The inside surfaces of the alveoli are coated with this surfactant and this is an anti-sticking mixture. It has a low surface tension preventing the alveoli collapsing.

Question 16

What features make the alveoli efficient gas exchange surfaces?

Answer 16

• They provide a large surface area:volume ratio relative to the volume of the body.
• Gases dissolve in the surfactant moisture lining them.
• Walls of squamous epithelium which are only one cell thick, so diffusion pathway is short.
• Extensive capillary network surrounds them and maintains the concentration gradients.
• Capillary walls also one cell thick.

Question 17

In insects, what are the paired holes that gas exchange occurs through and what are the air-tubes that they lead into?

Answer 17

The spiracles lead into a system of branched, chitin-lined air-tubes called tracheae which branch into smaller tubes called tracheoles.

Question 18

What features of spiracles make them efficient in preventing water loss?

Answer 18

• They can open/close.

- They have hairs covering them.

Question 19

How to insects ventilate the trachea?

Answer 19

During rest, diffusion alone is sufficient. During periods of activity, movements of the abdomen ventilate the trachea.

Question 20

Why is no respiratory pigment needed in insects?

Answer 20

Because the end of the tracheoles are fluid filled and directly next to the muscle fibres so O2 dissolves in the fluid and then diffuses directly into the muscle cells.

Question 21

Where does most gas exchange in plants take place?

Answer 21

Takes place at the leaves.

Question 22

How do gases diffuse into the leaf of a plant?

Answer 22

Gases diffuse through the stomata down a concentration gradient. The gases diffuse through the intercellular spaces between the spongy mesophyll cells and into cells.

Question 23

What is the stomata?

Answer 23

Pores on the lower leaf surface, and other aerial parts of a plant, bounded by two guard cells, through which gases and water vapour diffuse.

Question 24

What are the cells called that bound the stomata?

Answer 24

Guard cells.

Question 25

How do the guard cells open?

Answer 25

Water enters the cells and they become turgid and swell, causing the pore to open.

Question 26

How do the changes in water content in a guard cell come about?

Answer 26

• ATP from photosynthesis provides energy to actively transport K+ ions into the guard cells from the surrounding epidermal cells.
• Stored starch is then converted to malate and this joins with the K+, consequently lowering the water potential of the cell.
• Water enters by osmosis.
• The cell walls of guard cells are thicker in the areas opposite each other on the two guard cells.

Question 27

What conditions will cause the stomata to close?

Answer 27

• At night, to prevent water loss when there is insufficient light for photosynthesis.
• In very bright light, often accompanied by intense heat, which would increase evaporation.
• If there is excessive water loss.