3.1 Surface Area to Volume Ratio + 3.2 Gas Exchange

Question 1

How does an organisms 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 organisms 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 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 feature 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 7

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

Answer 7

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

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

Tracheolus = smaller branches dividing off the tracheae

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 while waste CO2 diffuses out

Contraction of muscles in the tracheae 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 memebrane 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 direction (countercurrent exchange system)

Question 11

Explain the process of gas exchange in fish

Answer 11

The fish opens its mouth to enable water to flow in, them 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 countercurrent exchange system maximise oxygen absorbed by the fish?

Answer 12

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 13

Name and describe three adaptations of a leaf that allow 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 leaf (stomata) allow gases to easily to enter
3. Air spaces in the mesophyll allow gases to move around the leaf, facilitating photosynthesis

Question 14

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

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 taken 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 moistests the air entering the lungs. Goblet cells in the membrane secrete mucus which traps dust and bacteria

Question 17

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

Answer 17

Wide tubes supported by C-shapes cartilage to keep the air passage open during pressure changes

Lined by ciliates epithelium cells which move mucus towards the throat to be swallowed, preventing lung infections

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 occur throughout the thorax

Answer 21

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 22

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

Answer 22

External intercostal muscles relax (while internal contract) bring 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 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 breathes we take per minute

Question 25

How do you calculate pulmonary ventilation rate?

Answer 25

Tidal volume X breathing rate. These can be measure using a spirometer, a device which records volume changes onto a graph as a person bresthes