3.1 Surface area to volume & 3.2 Gas Exchange

Question 1

How does an organism’s size relate to their surface area to volume ratio?

Answer 1

The larger the organism, the lower the surface area to volume ratio

Question 2

How does an organism surface area to volume ratio relate to their metabolic rate?

Answer 2

The smaller the surface area to volume ratio, the higher the metabolic rate

Question 3

How might a large organism adapt to compensate for its small surface area to volume ratio?

Answer 3

Changes that increase surface area e.g. folding; body parts becoming larger

Question 4

Why do multicellular organisms require specialised gas exchange surfaces?

Answer 4

Their small 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-celled organism.

Question 5

Name three features of an efficient gas exchange surface.

Answer 5

. Large surface area e.g. folded membranes in mitochondria
. Thin/short distance e.g. wall of capillaries
. Steep concentration gradient, maintained by blood supply or ventilation e.g alveoli

Question 6

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

Answer 6

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

Question 7

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

Answer 7

Spiracles= Holes of the body’s surface which may be opened or closed by a valve for gas or water exchange.
Tracheae = Large groups extending through all body tissue, supported by rings to prevent collapse.
Tracheoles = smaller branches dividing off the trachea

Question 8

Explain the process of gas exchange in insects

Answer 8

. Gases move in and out of the tracheae through the spiracles
. A diffusion gradient allows oxygen to diffuse into the body tissue whilst waste CO2 diffuses out.
. Contraction of muscles in the trachae allows mass movement of air in and out.

Question 9

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

Answer 9

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

Question 10

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

Answer 10

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.

Question 11

Explain the process of gas exchange in fish

Answer 11

. The fish opens its mouth to enable water to flow in, then closes its mouth to increase. 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 of the gills

Question 12

How does the counter current exchange system maximise oxygen absorbed by the fish?

Answer 12

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

Question 13

Name and describe three adaptations of a leaf that allows efficient gas exchange.

Answer 13

1. Thin and flat to provide short diffusion pathway and large surface area to volume ratio.
2. Many minute pores in the underside of the lead (stomata) allows gases to easily enter.
3. Air spaces in the mesophyll allow gases to move around the leaf, facilitating photosynthesis.

Question 14

How do plant limits their water loss while still allowing gases to be changed?

Answer 14

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 15

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

Answer 15

Nasal Cavity –> trachea –> bronchi –> bronchioles –> alveoli

Question 16

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

Answer 16

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

Question 17

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

Answer 17

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

Question 18

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

Answer 18

. 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 of them, one for each lung.
. Allow passage of air into the bronchioles.

Question 19

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

Answer 19

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

Question 20

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

Answer 20

. 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 21

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

Answer 21

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

Question 22

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

Answer 22

1. External intercostal muscles relax (while internal contract), bringing the ribs down and in.
2. Diaphragm relaxes and comes upwards.
3. Volume of the thorax decreases.
4. Air pressure inside the lungs is therefore higher than the air pressure outside, so air moves out to rebalance.

Question 23

What is tidal volume?

Answer 23

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

Question 24

What is breathing rate?

Answer 24

The number of breaths we take per minute

Question 25

How do you calculate pulmonary ventilation rate?

Answer 25

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.