3.2 Gas exchange

Question 1

Name three features of an efficient gas exchange surface

Answer 1

1. Large surface area, e.g. folded membranes in mitochondria
2. Short distance, e.g. wall of capillaries
3. Steep concentration gradient, maintained by blood supply or ventilation, e.g. alveoli

Question 2

Why can’t insects use their bodies as an exchange surface?

Answer 2

They have a waterproof chitin exoskeleton and a small surface area to volume ratio in order to conserve water

Question 3

Name the three main features of an insect’s gas exchange

Answer 3

• Spiracles
• Tracheae
• Tracheoles

Question 4

Describe spiracles

Answer 4

Holes on the body’s surface which may be opened or closed by a valve for gas or water exchange

Question 5

Describe tracheae

Answer 5

Large tubes extending through all body tissues, supported by rings to prevent collapse

Question 6

Describe tracheoles

Answer 6

Smaller branches dividing off the tracheae

Question 7

Explain the process of gas exchange in insects

Answer 7

• Gases move in and out of tracheae through the spiracles
• A diffusion gradient allows oxygen to diffuse into the body tissue while waste carbon dioxide diffuses out
• Contraction of muscles in the tracheae allows mass movement of air in and out

Question 8

Why can’t fish use their bodies as an exchange surface?

Answer 8

They have a waterproof, impermeable outer membrane and a small surface area to volume ratio

Question 9

Name the two main features of a fish’s gas transport system

Answer 9

• Gills
• Lamellae

Question 10

Describe gills

Answer 10

Located within the body, supported by arches, along which are multiple projections of gill filaments, which are stacked up in piles

Question 11

Describe lamellae

Answer 11

At right angles to the gill filaments, they give an increased surface area. Blood and water flow across them in opposite directions (countercurrent exchange system)

Question 12

Explain the process of gas exchange in fish

Answer 12

• The fish opens its mouth, lowering the buccal cavity, which enables water to flow in
• Then the fish closes its mouth, causing the buccal cavity to raise, increasing the pressure
• The water passes over the lamellae. and the oxygen diffuses into the bloodstream
• Waste carbon dioxide diffuses into the water and flows back out the gills

Question 13

Describe the countercurrent exchange system

Answer 13

Blood and water flow in opposite directions to each other across the lamellae

Question 14

How does the countercurrent exchange system maximise oxygen absorbed by the fish?

Answer 14

Maintains a steep concentration gradient, as water is always next to blood of a lower oxygen concentration. Keeps rate of diffusion constant and enables 80% of available oxygen to be absorbed

Question 15

Name three adaptations of a leaf that allows efficient gas exchange

Answer 15

• Thin and flat
• Stomata
• Air spaces

Question 16

Describe how a thin and flat leaf allows efficient gas exchange

Answer 16

Thin and flat to provide short diffusion pathway and large surface area to volume ratio

Question 17

Describe how stomata allows efficient gas exchange

Answer 17

Many minute pores in the underside of the leaf (stomata) allow gases to easily enter

Question 18

Describe how air spaces allows efficient gas exchange

Answer 18

Air spaces in the mesophyll allow gases to move around the leaf, facilitating photosynthesis

Question 19

How do plants limit their water loss while still allowing gases to be exchanged?

Answer 19

Stomata regulated by guard cells which allows them to open and close as needed. Most stay closed to prevent water loss while some open to let oxygen in

Question 20

Describe the pathway taken by air as it enters the mammalian gaseous exchange system

Answer 20

• Nasal cavity
• Trachea
• Bronchi
• Bronchioles
• Alveoli

Question 21

Describe the function of the nasal cavity in the mammalian gaseous exchange system

Answer 21

A good blood supply warms and moistens the air entering the lungs. Goblet cells in the membrane secrete mucus which traps dust and bacteria

Question 22

Describe the trachea and its function in the mammalian gaseous exchange system

Answer 22

• Wide tube supported by C-shaped cartilage to keep the air passage open during pressure changes
• Lined by ciliated epithelium cells which move mucus towards the throat to be swallowed, preventing lung infections
• Carries air to the bronchi

Question 23

Describe the bronchi and their function in the mammalian gaseous exchange

Answer 23

• Like the trachea they are supported by rings of cartilage and are lined by ciliated epithelium cells
• However, they are narrower and there are two
• Allow passage of air into the bronchioles

Question 24

Describe the bronchioles and their function in the mammalian gaseous exchange system

Answer 24

• Narrower than the bronchi
• Don’t need to be kept open by cartilage, therefore mostly have only muscle and elastic fibred so that they can contract and relax during ventilation
• Allow passage of air into the alveoli

Question 25

Describe the alveoli and their function in the mammalian gaseous exchange system

Answer 25

• Mini air sacs, lined with epithelium cells, site of gas exchange
• Walls only one cell thick, covered with a network of capillaries, 300 million in each lung, all of which facilitates gas diffusion

Question 26

Describe ventilation

Answer 26

Ventilation is the flow of air in and out of the alveoli; it is composed of two stages: inspiration and expiration

Question 27

How does ventilation occur?

Answer 27

Ventilation occurs with the help of two sets of muscles, the intercostal muscles and the diaphragm

Question 28

Explain the process of inspiration and the changes that occur throughout the thorax

Answer 28

• External intercostal muscles contract (while internal relax), pulling the ribs up and out
• Diaphragm contracts and flattens
• Volume of the thorax increases
• Air pressure outside the lungs is therefore higher than the air pressure inside, so air moves in

Question 29

Explain the process of expiration and the changes that occur throughout the thorax

Answer 29

• External intercostal muscles relax (while internal relax), bringing the ribs down and in
• Diaphragm relaxes and domes upwards
• Volume of the thorax decreases
• Air pressure inside the lungs is therefore higher than the air pressure outside, so air moves out

Question 30

What is tidal volume?

Answer 30

The volume of air we breathe in and out during each breath at rest

Question 31

What is breathing rate?

Answer 31

The number of breaths we take per minute

Question 32

How do you calculate pulmonary ventilation rate?

Answer 32

Tidal volume x breathing rate
These can be measured using a spirometer, a device which records volume changes onto a graph as a person breathes

Question 33

What is vital capacity?

Answer 33

The maximum volume of air that can be inhaled or exhaled in a single breath

Question 34

What is residual volume?

Answer 34

The volume of air in which is always present in the lungs