Exchange Surfaces

Question 1

Why do multicellular organisms require specialised gas exchange surfaces ?

Answer 1

Their smaller surface area to volume ratio means the distance that needs to be crossed is larger and substances cannot easily enter the cells as in a single-called organism

Question 2

How is surface area to volume ratio calculated ?

Answer 2

Ratio = Surface area/Volume

Question 3

Name three features of an efficient gas exchange surface

Answer 3

Large surface area, e.g. root hair cells
Thin/short distance, e.g. alveoli
Steep concentration gradient, maintained by blood supply or ventilation, e.g. gills

Question 4

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

Answer 4

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

Question 5

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

Answer 5

Like the trachea they are supported by rings of cartilage and are lined by ciliated epithelium cells and goblet cells
However they are narrower and there are two of them, one for each lung
Allow passage of air into the bronchioles

Question 6

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

Answer 6

Narrower than the bronchi
Do not need to be kept open by cartilage, therefore mostly have only smooth muscle and elastic fibres so that they can contract and relax easily during ventilation
Allow passage of air into the alveoli

Question 7

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

Answer 7

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 8

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

Answer 8

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 to rebalance

Question 9

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

Answer 9

External intercostal muscles relax (while internal contract), 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 to rebalance

Question 10

How does a spirometer works

Answer 10

Used to measure lung volume. A person breathes into an airtight chamber which leaves a trace on a graph which shows the volume of the breaths

Question 11

Define vital capacity

Answer 11

The maximum volume of air that can be taken in or expelled from the lungs in one breath. can be calculated from the spirometer graph by finding the maximum amplitude

Question 12

Define tidal volume

Answer 12

The volume of air we breath in and out during each breath at rest. Can be calculated from the spirometer graph by finding the amplitude at rest

Question 13

Define breathing rate

Answer 13

The number of breaths we take per minute. Can be calculated from the spirometer graphs by counting the number of peaks in one minute

Question 14

Name and describe the two main features of a fishs gas transport system

Answer 14

Gills = located within the body, supported by arches, along which are multiple projections of gill filaments, which are stacked up in piles 
Lamellae = at right angles to the gill filaments, give an increased surface area. Blood and water flow across them in opposite directions (countercurrent exchange system).

Question 15

Explain the process of gas exchange in fish

Answer 15

Buccal cavity volume increased to enable water to flow in, reduced to increase pressure.
Water is pumped over the lamellae by the operculum, oxygen diffuses into the bloodstream
Waste carbon dioxide diffuses into the water and flows back out of the gills

Question 16

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

Answer 16

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 17

Name and describe the three main features of an insects gas transport system

Answer 17

Spiracles = Holes on the body’s surface which may be opened or closed by a valve for gas or water exchange 
Trachea = Large tubes extending through all body tissues, supported by rings to prevent collapse 
Tracheoles = Smaller branches dividing off the trachea

Question 18

Explain the process of gas exchange in insects

Answer 18

Gases move in and out of the trachea through the spiracles
A diffusion gradients allows oxygen to diffuse into the body while waste CO2 diffuses out
Contraction of muscles in the trachea allows mass movement of air in and out