Topic 2: Lungs and gas exchange

Question 1

Define gas exchange

2 points

Answer 1

1. The exchange of OXYGEN (which enters an organism) and CARBON DIOXIDE (which leaves an organism)
   2 (this point is important). by diffusion {from high to low concentration/down diffusion gradients}

Question 2

Where does gas exchange take place:

(a) in a mammal
(b) in a fish
(c) in a plant
(d) in Amoeba (single celled animal)

(1 point for each)

Answer 2

(a) alveoli of lungs
(b) gills
(c) stomata in leaves
(d) across the cell membrane

Question 3

Why is gas exchange important?

2 points

Answer 3

1. Organisms need oxygen for respiration to release energy to keep the organism alive
2. Carbon dioxide is a waste product which needs to be removed

Question 4

Large organisms have a ______ surface area to volume ratio, so need a specialised gas exchange surface e.g. lung alveoli

Answer 4

small

Question 5

Key Summary: Why do {some/large} organisms need a specialised surface for gas exchange (eg. lung alveoli, gills)?
(4 points)

Answer 5

1 (this point is important). To overcome the limitations of diffusion

2. Larger organisms have a SMALL SURFACE AREA TO VOLUME RATIO

3 (this point is important). {Large size/more active/higher metabolic rate} (read the question to make sure all are relevant) means increased demand for oxygen to release energy

4. Outer surface is not large enough to allow oxygen to enter body fast enough by DIFFUSION to supply cells far from the surface with oxygen, to keep organism alive

Question 6

Key Summary: What are the 3 properties of gas exchange surfaces
(3 properties)

Answer 6

1. large surface area to volume ratio
2. thin
3. large difference in concentration (steep concentration gradient)

Question 7

Key Summary: What are the 3 properties that affect {the rate of diffusion/gas exchange}?

Answer 7

1. Surface area to volume ratio
2. Thickness of surface
3. Difference in concentration (concentration gradient)

(these are all related by Fick’s law of diffusion)

Question 8

Give the formula for Fick’s law of diffusion

Answer 8

.
Rate of diffusion ɑ (surface area * difference in concentration) / thickness of surface

(ɑ = proportional)

Question 9

Key Summary: What is the interpretation of the Fick’s law equation?
(3 point)

Answer 9

1. RATE OF DIFFUSION IS PROPORTIONAL TO SURFACE AREA – as surface area increases the rate of diffusion increases
2. RATE OF DIFFUSION IS PROPORTIONAL TO THE DIFFERENCE IN CONCENTRATION – as difference in concentration increases, the rate of diffusion increases
3. RATE OF DIFFUSION IS INVERSELY PROPORTIONAL TO THE {THICKNESS OF THE SURFACE/DIFFUSION DISTANCE} – as thickness of surface increases, the rate of diffusion decreases

Question 10

What is the formula for calculating rate of diffusion?

Answer 10

.
Rate of diffusion = (P * A * (C1 – C2)) / T

P = permeability/diffusion constant

A = surface area

(C1- C2) = difference in concentration

T = thickness of exchange surface

Question 11

The gas exchange surface in mammals is made up of the ______ ______ and the _______ ______, sandwiched together.

It is important for gas exchange that the walls of the alveoli and capillaries are relatively ________ to the small _____-_____ molecules of oxygen and carbon dioxide.

Answer 11

alveoli wall

capillary wall

permeable

non-polar

Question 12

Key Summary: Describe gas exchange in the mammalian lung

6 steps

Answer 12

1. oxygen moves from alveoli to blood
2. carbon dioxide moves from blood to alveoli
3. DOWN A CONCENTRATION GRADIENT from high concentration to low concentration
4. by DIFFUSION
5. gases pass through epithelium of alveoli walls
6. and endothelium of capillary walls

Question 13

Key Summary: Explain how the {lungs/alveoli} are specialised for efficient gas exchange
(4 points)

Answer 13

1. MANY ALVEOLI – create a large/increased alveoli surface area over which O2 and CO2 can diffuse
2. Each alveolus is covered with blood capillaries for LARGE SURFACE AREA OF CAPILLARIES – capillaries deliver CO2 to alveoli and pick up O2 + shorter diffusion distance for O2 to reach blood
3. THIN alveoli walls and THIN capillary walls with FLATTENED CELLS – create a SHORTER DIFFUSION DISTANCE
4. {Circulation of blood/blood flow} and {breathing/ ventilation of lungs} - to MAINTAIN STEEP CONCENTRATION {GRADIENT/difference} between blood and alveoli

Question 14

The gas exchange surface in mammals is _____ giving a _______ diffusion distance for gases (+ faster rate of diffusion)

The wall of the alveolus is next to the wall of the capillary and both are ____ cell thick (extremely thin), as they are made of __________ (squamous) cells – two cells together = 1 micrometre

Answer 14

thin

shorter

one

flattened

Question 15

Many alveoli (in the mammalian lungs) creates a ______ surface area for gas exchange.

Answer 15

large

Question 16

A steep {diffusion/concentration} gradient is maintained in the lungs of mammals due to __________ and ________ _____.

Answer 16

breathing

blood flow

Question 17

For diffusion of oxygen:
– {__________/___________} brings O2 into the ______ (so HIGHER concentration in alveoli than in blood capillaries)
AND
– the {______ ______/____________ _________} carries O2 that has diffused into the blood away to the heart then to ______ (LOWER concentration in lung capillaries than alveoli)

The reverse is true for CO2 – ventilation removes CO2 from ______ and blood CO2 is _____ in lung capillaries, as CO2 returns from tissues to ______.

Answer 17

BREATHING/VENTILATION

alveoli

BLOOD FLOW/TRANSPORT SYSTEM

tissues

lungs

higher

alveoli

Question 18

Key Summary: Describe the features of the mammalian gas exchange surface
(6 points)

Answer 18

1. Large alveolar surface area
2. Large surface area of capillaries
3. Thin alveoli walls
4. Thin capillary walls
5. Shorter diffusion pathway
6. Large concentration gradients