3.3.2 Gas Exchange

Question 1

FISH:

Explain how the gills allow efficient gas exchange

Answer 1

• The lamellae provide a large surface area
• Thin epithelium so a short diffusion pathway
• Counter-current flow maintains the concentration gradient across whole length of lamellae

Question 2

FISH:

Explain how the highly folded structures of the gill (lamellae) increase the efficiency of gas exchange

Answer 2

They increase the surface area over which diffusion can take place

Question 3

FISH:

Describe and explain how the countercurrent system leads to efficient gas exchange across the gills of a fish.

Answer 3

Water and blood flow in opposite directions.
This maintains a concentration gradient across the gill (as there is always a higher concentration of oxygen in the water than blood)

Question 4

Name the process by which carbon dioxide is removed from a single celled organism

Answer 4

Simple diffusion over the body surface

Question 5

INSECTS:

Explain how the tracheal system limits the size of the insect

Answer 5

Because it relies on diffusion to bring oxygen to respiring tissues.
If insects were large it would take too long for oxygen to reach the tissues rapidly enough to supply the insects needs

Question 6

INSECTS:

Give 2 explanations as to why the rate of water loss during gas exchange is very low in most insects.

Answer 6

• Insects have spiracles that can close to reduce water loss

* Insects have sunken spiracles that trap moist air

Question 7

Describe and explain ways in which plants limit water loss.

Answer 7

• Plants have a waxy cuticle which prevents the evaporation of water;
• Plants have hairs on their surface that trap moist air reducing the water potential gradient
• Plants have sunken stomata which again traps moist air reducing the water potential gradient
• The stomata can close which reduces evaporation

Question 8

How can you calculate pulmonary ventilation rate?

Answer 8

= tidal volume (dm3) x breathing rate (min-1)

Question 9

LEAVES:

Explain why less water is lost by a plant when the air is humid.

Answer 9

Humidity reduces the difference in concentration of water between the plant and the air.
Reduced concentration gradient = less water loss

Question 10

During an asthma attack, less oxygen diffuses into the blood from the alveoli.
 Explain why.

Answer 10

Asthma attacks narrow the airways, so not as much oxygen reaches the alveoli.
This means that there is a small concentration gradient (between blood and alveoli) so rate of diffusion is lower

Question 11

What are xerophytes?

Answer 11

Plants that are adapted to living in areas where water is in short supply

Question 12

Give examples of how xerophytes limit water loss

Answer 12

• Thick cuticle
• Waxy cuticle
• Rolled up leaves
• Hairy leaves
• Stomata in pits or grooves
• A reduced surface area to volume ratio
• Deep roots
• Sunken stomata

Question 13

XEROPHYTES:

Explain how having rolled up leaves reduces water loss

Answer 13

• Traps a region of still air within the rolled leaf.
• The trapped region has a high water potential.
• As there is no water potential gradient between the inside and outside of the leaf there is no water loss

Question 14

XEROPHYTES:

Explain how having hairy leaves reduces water loss

Answer 14

• Traps still, moist air next to the leaf surface.

- This reduces the water potential gradient between the inside and outside of the leaf so less water is lost.

Question 15

XEROPHYTES:

Explain how having stomata in pits or grooves reduces water loss

Answer 15

• It traps still, moist air next to the leaf surface.

- This reduces the water potential gradient between the inside and outside of the leaf so less water is lost.

Question 16

Explain why water is always lost from the gas exchange surfaces of terrestrial organisms

Answer 16

• Gas exchange surfaces are permeable.

- As there is a higher concentration of water molecules inside the animal than outside water will diffuse out.

Question 17

Why does every cell inside an insect have a short diffusion distance?

Answer 17

They are only a short distance from the tracheae or the tracheoles

Question 18

INSECTS:

Name the tiny pores on the body surface of insects

Answer 18

Spiracles

Question 19

INSECTS:

For much of the time the spiracles are (open or closed)

Answer 19

Closed, to prevent water loss

Question 20

INSECTS:

Periodically spiracles must open. Why?

Answer 20

To allow gas exchange

Question 21

FISH:

What happens if blood and water flow in parallel?

Answer 21

• Diffusion of oxygen into the blood is less efficient - (only 50%)
• Equilibrium is reached as the conc. gradient cannot be maintained along the whole filament

Question 22

XEROPHYTES:

How can a reduced SA : Vol ratio in leaves be achieved?

Answer 22

eg. Leaves are reduced to pine needles

Question 23

LUNGS:

Starting with nose/mouth, list the structures that air passes through

Answer 23

Trachea - bronchi - bronchioles - alveoli

Question 24

LUNGS:

What prevents the trachea from collapsing?

Answer 24

Rings of cartilage

Question 25

LUNGS:

List the adaptations of the alveoli that make it ideal for gas exchange

Answer 25

Single layer of epithelium cells
Stretch as breathe in
Spring back as breathe out
Huge SA
Moist
Rich blood supply

Question 26

LUNGS:

What happens to the intercostals as we breathe in

Answer 26

External contract

Internal relax

Question 27

LUNGS:

What happens to the rib cage and the diaphragm before we inhale

Answer 27

Ribs - move up and out

Diaphragm - contracts and moves down

Question 28

LUNGS:

What happens to the volume and pressure of the thorax before we inhale air

Answer 28

Volume increases

Pressure decreases

Question 29

LUNGS:

What is the ‘tidal volume’?

Answer 29

The volume of air we breath in and out at rest (typically about 0.5dm3)

Question 30

LUNGS:
List the events of 
a) Intercostal Muscles
b) ribs
c) Diaphragm
                                                            before we inhale

Answer 30

a) Internal contract, external relax
b) Ribs move down and in
c) Diaphragm relaxes, domes up

Question 31

LUNGS:

Typically, what is the normal ventilation rate?

Answer 31

12-20 breaths per min

Question 32

Describe the gross structure of the human gas exchange system

Answer 32

Trachea - Bronchi - Bronchioles - alveoli

Question 33

Describe how we breathe IN

Answer 33

Diaphragm contracts
External intercostal muscles contract
Volume increases and pressure decreases in thorax
Air moves into lungs

Question 34

Describe how we breathe OUT

Answer 34

Diaphragm relaxes
Internal intercostal muscles contract
Volume decreases and pressure increases in thorax
Air moves out of the lungs

Question 35

describe the pathway of an oxygen molecule from alveolus to blood

Answer 35

crosses the single cell alveolar epithelium and then epithelium of the capillary

Question 36

describe ONE feature of the alveolus that allows efficient gas exchange

Answer 36

ONE CELL thick therefore creating a SHORTER diffusion pathway