Surface area to volume ratio & Gas Exchange - 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’s 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 become larger e.g. elephant’s ears; elongating shape; developing a specialised gas exchange surface.

Question 4

Why do multicellular organisms require specialised gas exchange surfaces?

Answer 4

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-celled organism.

Question 5

Name three features of an efficient gas exchange surface.

Answer 5

1. Large surface area, e.g. folded membranes in mitochondria.
2. Thin/short distance, e.g. wall of capillaries.
3. 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 6

Name and describe the three main features of an insect’s gas transport system.

Answer 6

Spiracles = holes on the body’s surface which maybe opened or closed by a valve for gas or water exchange.

Tracheae = large tubes extending through all body tissues, supported by rings to prevent collapse.

Tracheoles = smaller branches dividing off the tracheae.

Question 7

Explain the process of gas exchange in insects.

Answer 7

Gases move in and out of the tracheae through the spiracles.

A diffusion gradient allows oxygen to diffuse into the body tissue while waste CO2 diffuses out.

Contraction of muscles in the tracheae allows mass movement of air in and out.

The trachea ends are filled with water, when cells respire anaerobically a lactate is produced which lowers the water potential of the cells drawing the air in with them

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

Answer 9

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 10

Explain the process of gas exchange in fish.

Answer 10

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 11

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

Answer 11

Maintains a steep concentration gradient, as water is always next to blood of a lower oxygen concentration. Keeps rate of diffusion constant along whole length of gill enabling 80% of available oxygen to be absorbed.

Question 12

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

Answer 12

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 leaf (stomata) allow gases to easily enter.
3. Air spaces in the mesophyll allow gases to move around the leaf, facilitating photosynthesis.

Question 13

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

Answer 13

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 14

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

Answer 14

Nasal cavity → trachea → bronchi → bronchioles → alveoli

Question 15

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

Answer 15

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 16

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

Answer 16

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 17

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

Answer 17

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 18

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

Answer 18

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 19

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

Answer 19

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 20

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

Answer 20

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 21

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

Answer 21

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 22

What is tidal volume?

Answer 22

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

Question 23

What is breathing rate?

Answer 23

The number of breaths we take per minute.

Question 24

How do you calculate pulmonary ventilation rate?

Answer 24

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 25

The increase in potassium ion concentration will affect the water potential of the guard cells, explain how this causes the stomata to open:

Answer 25

It lowers the water potential so water moves in by osmosis making the guard cells turgid so they open.

Question 26

Give one way that the difference in oxygen concentration is maintained:

Answer 26

A good blood supply

Question 27

what is a xerophyte?

Answer 27

Plants that are adapted to dry and arid conditions.

Question 28

What is countercurrent flow in fish?

Answer 28

It makes sure max. diffusion takes place across the gill lamellae, blood with oxygen meets water with more oxygen and diffusion can take place, the blood with little oxygen passes the water that has a higher conc. of oxygen so diffusion can still take place -
The capillary system within the lamellae ensures that the blood flow is in the opposite direction to the flow of water

It is better than parallel flow as the diffusion rate will reach equilibrium