.1 Surface area to volume ratio .2 Gas exchange

Question 1

Why are cells microscopic?

Answer 1

Gives them high SA:V ratio to get nutrients + substances they need

Question 2

Features of an exchange surface: adaptations and features

Answer 2

Large Surface Area
Many microscopic structures

Small distance to diffuse
Thin, flat body shape
Branching network of vessels
Exchange surface is one cell thick.

Maintenance of large concentration gradient
Ventilation of the exchange surface (movement of air or water)
A rich blood supply (e.g. a dense network of capillaries)
(Movement of blood)
Counter current flow in fish

Question 3

Biggest problem for gas exhange on land vs water

Answer 3

Water is more dense than air so things likes gills won’t work as water is not available to hold them up, they will collapse and stick together, giving a lower SA to V ratio aka ventilation system will collapse without presence of dense water

Also water loss

Question 4

Gas exchange in insects- what are the branching net of tubes called, function, what are they made of and why

Answer 4

Spiracles (small openings that can open and close) connected to trachea which are connected to trachioles
Can open and close to minimise water loss

Tracheae and Trachioles- increase SA, lower distance to diffuse
Made of chitin, hard material, to stop collapsing w/o high density water

Question 5

What three ways do respiratory gases move in and out of the tracheal system?

Answer 5

• Along a diffusion gradient. When cells are respiring, oxygen is used up and so its concentration towards the ends of the tracheoles falls. This creates a diffusion gradient that causes gaseous oxygen to diffuse from the atmosphere along the tracheae and tracheoles to the cells. Carbon dioxide is produced by cells during respiration. This creates a diffusion gradient in the opposite direction. This causes gaseous carbon dioxide to diffuse along the tracheoles and tracheae from the cells to the atmosphere. As diffusion in air is much more rapid than in water, respiratory gases are exchanged quickly by this method.
• Mass transport. The contraction of muscles in insects can squeeze the trachea enabling mass movements of air in and out. This further speeds up the exchange of respiratory gases.
• The ends of the tracheoles are filled with water. During periods of major activity, the muscle cells around the tracheoles respire carry out some anaerobic respiration. This produces lactate, which is soluble and lowers the water potential of the muscle cells. Water therefore moves into the cells from the tracheoles by osmosis. The water in the ends of the tracheoles decreases in volume and in doing so draws air further into them. This means the final diffusion pathway is in a gas rather than a liquid phase. and therefore diffusion is more rapid. This increases the rate at which air is moved in the tracheoles but leads to greater water evaporation.

Question 6

Gas exchange in insects- Basics, how is the conc gradient maintained?
Which gases are being exchanged?
Which direction are they moving?
By what process are they moving?
What maintains the concentration gradient?

Answer 6

High conc O2, low conc CO2 Air OUTSIDE spiracles⇔Air INSIDE tracheoles Low conc. of O2, high conc of CO2

Maintained by RESPIRATION inside so O2 always low conc inside as being used by cells, CO2 being released so always high conc inside

MOVEMENT of air outside- air next to spiracles always fresh air

Question 7

SA:V ratio of cubes side lengths 1-6

Answer 7

Textbook page 131

Question 8

What general things need to be exchanged and how can they be exchanged?

Answer 8

respiratory gases (oxygen and carbon dioxide); 
nutrients (glucose, fatty acids. amino acids. vitamins, minerals); 
excretory products (urea and carbon dioxide); and heat. 

Except for heat, these exchanges can take place in two ways:
• passively (no metabolic energy is required), by diffusion and osmosis
• actively (metabolic energy is required), by active transport

Question 9

Organisms have evolved one or more of the following features:

Answer 9

• a flattened shape so that no celJ is ever far from the surface (e.g. a flatwornm or a leaf)
• specialised exchange surfaces with large areas to increase the surface area to volume ratio (e.g., lungs in mammals, gills in fish).

Question 10

Diff vs Osmosis vs Mass flow: What is moving, how is it moving, what type of gradient do they move down, how far are they moved

Answer 10

Diffusion
Osmosis
Mass Flow

What is moving?
molecules
water
vol of liquid or gas

How is it moving?
randomly
randomly
directional

What type of gradient do they move down?
High to low
High water pot. to low water pot.
P grad

How far are they moved?
V small dist
V small dist
Large distances

Question 11

(Graph) How do large insects maintain conc. grad? What patterns can you see in the data? Explain what is happening in terms of pressure changes inside the tracheae. How would O2 levels change?

Answer 11

Line is CO2 being released.

Spiracles open: Abdomen contracts, Low volume inside as high pressure inside as space inside decreases, gases pushed out so volume inside decreases

Contraction stops- abdomen expands. Pressure decreases so no gases getting out because spiracle closed, now low pressure inside and high pressure outside

Spiracle opens: Air moves into abdomen- high pressure to low pressure (as abdomen now expanded) so spike in CO2

Cycle starts again

Question 12

Gas Exchange In Larger Insects: what’s the difference? What is this called (begins with V)
Which gases are being exchanged between inside and outside of the insect’s body? (draw diagram) What is moving through the tracheoles and tracheae? By what process are they moving? Why is this necessary for larger insects?

Answer 12

High pressure when abdomen contracts, Low pressure when abdomen expands

Air moving in and out bc of pressure gradient- MASS FLOW

Called VENTILATION- movement so maintains conc. grad

Question 13

The damselfly larva is a carnivore that actively hunts prey. It has gills to obtain oxygen from water. Some other species of insect have larvae that are a similar size and shape to damselfly larvae and also live in water. These larvae do not actively hunt prey and do not have gills. Explain how the presence of gills adapts the damselfly to its way of life.

Answer 13

1. Damselfly larvae has high(er)
   metabolic/respiratory (rate);
2. (So) uses more oxygen (per unit time/per
   unit mass);

Question 14

The ends of tracheoles connect directly with the insect’s muscle tissue and are filled with water. When flying, water is absorbed into the muscle tissue. Removal of water from the tracheoles increases the rate of diffusion of oxygen between the tracheoles and muscle tissue. Suggest one reason why.

Answer 14

1. Greater surface area exposed to air;
2. Gases move / diffuse faster in air than through water;
3. Increases volume / amount of air;

Question 15

Describe the struct of the gills

Answer 15

Four layers of gills on each side of head- made up of gill filaments.

The gill filaments are stacked up in a pile- covered in gill lamellae- at right angles to the filaments

Gill lamellae increase the surface area of the gills.

Water is taken in through the mouth and forced over the gills and our through an opening, operculum, on each side of the body.

From this figure you will notice that the flow of water over the gill lamellae and the flow of blood within them are in opposite directions. This is known as a countercurrent flow

Question 16

Adaptations of gills for effective gas exchange

Answer 16

Large SA:v ratio- many gill filaments covered in many lamellae

Short dist to diff- diffusion happens only on very thin gill lamellae
capillary network inside lamellae

Maintaining conc. grad- counter current flow

Question 17

Explain and describe countercurrent flow (vs concurrent flow)

Answer 17

-When H2O flowing over gills opp dir to blood in capillaries
-Ensures equilibrium not reached
Diff in conc grad maintained across ENTIRE length of lamellae

The essential feature of the countercurrent exchange system is that the blood and the water that flow over the gill lamellae do so in opposite directions.
This arrangement means that:
• Blood that is already well loaded with oxygen meets water, which has its maximum concentration of oxygen. Therefore diffusion of oxygen from the water to the blood takes place.

• Blood with little oxygen in it meets water which has had most, but not all, of its oxygen removed. Again, diffusion or oxygen from the water to blood takes place.

As a result, a diffusion gradient for oxygen uptake is maintained across the entire width of the gill lamellae. In this way, about 80% of the oxygen available in the water is absorbed into the blood of the fish. If the flow of water and blood had been in the same direction (parallel flow), the diffusion gradient would only be maintained across part of the length of the gill lamellae and only 50% of the available oxygen would be absorbed by the blood.

Question 18

How do fish maintain concentration gradient?

Answer 18

Ventilation of gills

Mouth opens-Buccal floor lowers

Buccal Volume increases and pressure decreases

Water pressure decreases- pressure gradient formed

Opercula close

Water enters mouth

Mouth closes- Buccal floor rises

Buccal volume decreases- pressure increases

Water Pressure increases

High water pushes opercula open and exits fish

Water passes over gills, gas exchange takes place

Question 19

Ventilating the tracheal system- large insects- air sacs, how they work

Answer 19

Often in larger insects with well-developed powers of flight

Air sacs in the tracheal system- swelling of airways- squeezed by flight muscles to push air in and out

Muscle pulls and pushes on air sac

Air squeezed in and out through spiracle opening

Constantly refreshes air, makes sure fresh air is supplied

Question 20

Gas Exchange in Insects: At Rest vs during Flight

Answer 20

At rest: Air has LOWER ψ than muscle (liquid cytoplasm)

Difference in ψ gradient SO water moves OUT CELL by OSMOSIS
Water fills ends of tracheoles as it moves out of cell, LOWERS GAS EXCHANGE

Flying: Air has HIGHER ψ than muscle cell (produces lactate for an respir so higher conc of solute means lower ψ )

Diff in ψ so water moves back INTO CELL by OSMOSIS
Cell must undergo anaerobic respiration- LACTIC ACID INCREASES
INCREASES SA for GAS EXCHANGE

Question 21

Gas exchange in insects: rest vs flight textbook

Answer 21

• The ends of the tracheoles are filled with water.

During periods of major activity, the muscle cells around the tracheoles respire carry out some anaerobic respiration- produces lactate, which is soluble and lowers the water potential of the muscle cells.

Water moves into the cells from the tracheoles by osmosis.

The water in the ends of the tracheoles decreases in volume and in doing so draws air further into them.

This means the final diffusion pathway is in a gas rather than a liquid phase. and therefore diffusion is more rapid.

This increases the rate at which air is moved in the tracheoles but leads to greater water evaporation.

Question 22

How do plants have the following for GAS EXCHANGE

Large SA:

Small distance to diffuse:

Maintenance of conc. grad

Answer 22

Large SA: no

Small distance to diffuse:
many small pores, called stomata, and so no cell is Car from a stoma
and therefore the diffusion pathway is short (Figure l )
numerous interconnecting air-spaces that occur throughout the mesophyll so that gases can readily come in contact with mesophyll cells

Maintenance of conc. grad
Simple diffusion (don’t have mechanism for ventilation)
Movement of air OUTSIDE
Photosynthesis and respiration

Question 23

Photosynthesis and Respiration: Day vs Night, how they control conc. grad, when are they equal- draw diagrams

Answer 23

Day:PS much higher than rate of Resp- PS maintains conc. grad

Night:PS stops, Resp constant,Resp maintains conc. grad- far lower rate of gas exchange so stomata close

When equal: Dawn and dusk. No gas exchange- All O2 made used up for resp, all CO2 used up by PS

Question 24

Draw and describe structure of a plant leaf and adaptations

Answer 24

waxy cuticle- impermeable to gases, min water loss
upper epidermis- no stomata, min water loss
Layer of palisade mesophyll cells – main photosynthetic layer- lots of chlorophyll
Xylem vessel
Spongy mesophyll layer; layer of irregular shaped
cells with numerous air spaces- gases diffuse quickly in air
Substomatal air space
Lower epidermis
Thin cuticle
Stoma
Guard cell

Adaptations for gas exchange: only few cells thick, air spaces for gases to diffuse

Question 25

What are some adaptations for rapid gas exchange in plant leaves- three

Answer 25

many small pores, called stomata, and so no cell is Car from a stoma and therefore the diffusion pathway is short

• numerous interconnecting a ir-spaces that occur throughout the mesophyll so that gases can readily come in contact with mesophyll cells
• large surface area of mcsophyll cells for rapid diffusion.

Question 26

What are stomata? Surrounded by a pair of… (how adapted to bend)? Why are they important, what do they prevent and how do they do this?

Answer 26

Stomata are minute pores that occur mainly, but not exclusively, on the leaves, especially the underside.

Each stoma (singular) is surrounded by a pair of special cells (guard cells). These cells can open and close the stomata pore (thicker CW inside, thinner outside, how it bends) (Figure 3).

In this way they can control the rate of gaseous exchange. This is imporant because terrestrial organisms lose water by evaporation. Plants have evolved to balance the conflicting needs of gas exchange and control of water loss. They do this by closing stomata at times when water loss would be excessive, open during day, closed during night.

Question 27

State two similarities between gas exchange in a plant leaf and gas exchange in a terrestrial insect.

Answer 27

No living cell is far from the external air, and therefore a source of oxygen and carbon dioxide.

• Diffusion takes place in the gas phase (air), which makes it more
rapid than if it were in water.

Question 28

Gas exchange at a stomata- what gases are exchanged where, which ones are in or out and why

Answer 28

Oxygen- out- used for respiration BUT a product of phtotysnthesis so high conc. (in spongy mesohpyll) compared to outside

CO2- in- bc needed for photosynthesis, constantly being used by cells in leaf (particularly palisade mesophyll), maintains conc. grad. Low conc inside (compared to outside) so diffuses in

Question 29

Apply your knowledge of osmosis and water potential to explain why the stoma opens and closes. Remember you have to compare water potentials.
What possible stimuli will trigger the stoma to open?

Answer 29

Stomata open and close as a result of diffusion. Under hot and dry conditions, when water loss due to evaporation is high, stomata must close to prevent dehydration. Guard cells actively pump potassium ions (K +) out of the guard cells and into surrounding cells. This causes water in the enlarged guard cells to move osmotically from an area of low solute concentration (guard cells) to an area of high solute concentration (surrounding cells). The loss of water in the guard cells causes them to shrink. This shrinkage closes the stomatal pore.

When conditions change such that stomata need to open, potassium ions are actively pumped back into the guard cells from the surrounding cells. Water moves osmotically into guard cells causing them to swell and curve. This enlarging of the guard cells open the pores. The plant takes in carbon dioxide to be used in photosynthesis through open stomata. Oxygen and water vapor are also released back into the air through open stomata.

(baso K+ in water in) Open: 1) GC detect light- AT of K+ into GC by AT proteins

2) Conc of K+ inside increases- conc. grad
3) Bc lots of K+(solute) inside, lower ψ inside
4) Higher ψ outside- water moves into GC by osmosis
5) Increase in turgid pressure-GCs move outwards- stoma opens

(baso K+ out water out) Close: 1) K+ diff down conc. grad- diff into neighbouring cells

2) Now more +ve ψ inside (bc less K+, less solute)
3) Lower ψ outside- Water moves OUT of GC by osmosis
4) Turgid pressure descreases, GC flaccid, stoma close

Stimuli that open stomata:

1) Light- Light receptor on plasma membrane of guard cell triggers active transport proteins to pump K+ into guard cell.
2) CO2- Low CO2 concentrations in the leaf as photosynthesis uses it up.

Question 30

Insect adaptations to prevent water loss

Answer 30

1) Small SA to V ratio where water can evaporate from
2) Have a WATERPROOF EXOSKELETON
3) SPIRACLES can open and close to reduce water loss

Question 31

How do gases move into tracheal system- fluid in tracheoles method

Answer 31

During Flight:
1)Muscle cells use up all O2 so must respire anaerobically- produce lactate

2) More solute now inside cell, so has lower water potential
3) Water moves from tracheoles to cells (low water pot. to high water pot.)
4) Tracheoles lose water so lower volume, lower pressure (comp to atm)
5) Lower pressure and volume inside tracheoles, so air from the atmosphere moves into them. (but also leads to greater water evaporation)

Question 32

What are the three basic strategies xerophytes use to conserve water? What are some examples of each?

Answer 32

Much as you budget your money, xerophytes budget water through three basic strategies:

Increase or maximize income: Such adaptations increase water intake.
deep roots, wide spreading shallow roots, and the ability to absorb surface moisture, maintaining a high salt concentration within the roots, they absorb moisture rapidly via osmosis.

Limit and conserve outflow: These adaptations stem the loss of water.
Adaptations which limit water loss affect leaves, stomata, and metabolism-
Small leaves, finely divided leaves, leaves that are deciduous during dry seasons, or leaves which have been lost altogether
Shelter stomata beneath their leaves, rather than exposing them to the heat of sunlight on the upper surface
Some limit the number of stomata (A)
Some, like pines, have “sunken” stomata; their location below the surface of the leaf or needle reduces the drying effects of wind and sun.
A dense covering of hairs or spines reduces evapotranspiration by trapping a layer of moisture over stomata
Leaves that curl up during the day or in wind

Build up reserves: Specialized storage structures take advantage of water when it is available.
succulent leaves, succulent stems, and underground structures such as tubers
This compact, cushion-like growth form minimizes the surface-to-volume ratio and therefore water loss

Summary
Xerophytes grow in arid habitats, where evapotranspiration may exceed precipitation.
Xerophyte adaptations increase water intake, limit water loss, and store water efficiently.
Water intake adaptations include deep or widespread roots, and high salt content to increase osmosis.
Xerophytes have thick cuticles, lost or finely divided leaves, reduced stomata, and CAM photosynthesis.
Water storage adaptations include succulence and protective coverings of color, wax, hair, and/or spines.

Question 33

Xerophytic adaptations: Textbook

Answer 33

• a thick cuticle. Although the waxy cuticle on leaves forms a waterproof barrier, up to I0% of water loss can still occur by this route. The thicker the cuticle, the less water can escape by this means. for example holly.
• rolling up of leaves. Most leaves have their stomara largely, or encirely, confined to the lower epidermis. The rolling of leaves in a way rhat protects the lower epidermis from the oucside helps to trap a region of still air within the rolled leaf. This region becomes sarurated with water vapour and so has a very high water potential. There is no water potential gradient between the inside and outside of the leaf and there l’ore no water loss. Marram grass rolls its leaves.
• hairy leaves. A thick layer of hairs on leaves, especially on the lower epidermis, traps still, moist air next to the leaf surface. The water potential gradient between the inside and the outside of the leaves is reduced and therefore less water is lost by evaporation. One type of heather plant has this modification.
• stomata in pits or grooves. These again trap srill, moisc air next co rhe leaf and reduce the water pocential gradient. Examples of planrs using chis mechanism include pine trees.
• a reduced surface area to volume ratio of the leaves. We saw in Topic 6.1 that the smaller the surface area to volume ratio, the slower the rate of diffusion. By having leaves that are small and roughly circular in cross-section, as in pine needles. rather than leaves that are broad and flat, the rate of water loss can be considerably reduced. This reduction in surface area is balanced against the need for a sufficient area for photosynthesis to meet the requirements of the plant.

Question 34

Adaptations in Cacti

Answer 34

No leaves, only succulent stems reduces SA:Vol ratio

Spines and hairs trap moist air next to stomata.

Stomata open at night!
(All minimise water loss)

Water storage in stems.

Deep roots access water deeper below the surface

Shallow roots absorb rainwater before it evaporates.

Question 35

Explain the benefits of sunken stomata, how they work

Answer 35

The sunken stomata trap moist air which reduces diffusion and reduces water loss and reduce the water potential gradient

Xerophytes contain sunken stomata. because sunken stomata is a stoma in a small pit, which protects the escaping water vapour from air currents and also decreases the water loss from the leaf

Question 36

Adaptations of Marram Grass

Answer 36

Thick waxy cuticle: Minimises water loss

Hairs: trap moisture

Sunken stomata: trap moist air, protect water vapour from wind sun etc

Rolls leaves into cylinder (using hind cells, curve when flaccid): minimises water loss
Water vapour trapped inside curved cylinder, decreases water conc grad

Question 37

Draw and label the lungs, explain structure if possible

Answer 37

Trachea: tracheal rings made of cartilage to prevent airway collapsing under pressure

Right and left Bronchi

Bronchioles: lots of cillia, c shaped cartilage allows for felixibility

Alveoli

Question 38

Where is the site of gas exchange in mammals? How are the alveoli adapted for gas exchange?

Answer 38

The site of gas exchange in mammals is the epithelium of the alveoli.

Around each alveolus is a network of pulmonary capillaries, so narrow (7-1 0 µm ) that red blood cells are flattened against the thin capillary walls in order to squeeze through. These capillaries have walls that are only a single layer of cells thick (0.04-0.2µm). Diffusion of gases between the alveoli and the blood will be very rapid because:

Large SA: V ratio: Lots of microscopic structures (alveoli)
alveoli and pulmonary capillaries have a very large total surface area

Distance to diffuse: Thin walls- one cell thick epithelial cells- RBCs always close
Distance between the alveolar air and red blood cells is reduced as the red blood cells are flattened against the capillary walls
The walls of both alveoli and capillaries are very thin and therefore the distance over which diffusion takes place is very short

Maintaing conc. grad: Rich blood supply- blood flow through the pulmonary capillaries maintains a concentration gradient.
Breathing movements constantly ventilate the lungs and the action of the heart constantly circulates blood around the alveoli. Together. these ensure that a steep concentration gradient of the gases to be exchanged is maintained

• red blood cells are slowed as they pass through pulmonary capillaries, allowing more time for diffusion

Question 39

Describe ventilation of the lungs

Answer 39

External Intercostal muscles contract

Diaphragm contracts and flattens

Volume increases, pressure decreases

Air moves in from high to low pressure

External Intercostal muscles relax

Ribs fall down and in

Diaphragm relaxes and becomes dome shaped

Volume decreases, pressure increases

Air moves out from high to low pressure

Question 40

Ventilation of the lungs (textbook) inspiration and expiration

Answer 40

Inspiration Breathing in is an active process (it uses energy) and occurs as follows:

• The external intercostal muscles contract, while the internal intercostal muscles relax.
• The ribs are pulled upwards and outwards, increasing the volume of the thorax.
• The diaphragm muscles contract, causing it to flatten, which also increases the volume of the thorax.
• The increased volume of the thorax results in reduction of pressure in the lungs.
• Atmospheric pressure is now greater than pulmonary pressure, and so air is forced into the lungs .

Breathing out is a largely passive process (it does not require much energy) and occurs as follows:
• The internal intercostal musdes contract, while the external intercostal muscles relax.
• The ribs move downwards and inwards, decreasing the volume of the thorax.
• The diaphragm muscles relax and so it is pushed up again by the contents of the abdomen that were compressed during inspiration. The volume of the thorax is therefore further decreased.
• The decreased volwne of th e thorax increases the pressure in the lungs.
• The pulmonary pressure is now greater than that of the atmosphere, and so air is forced out of the lungs.

During normal quiet breathing, the recoil of the elastic tissue in the lungs is the main cause of air being forced out (like air being expelled from a partly inflated balloon). Only under more strenuous conditions such as exercise do the various muscles play a major part.

Question 41

How does a spirometer work? What do peaks and troughs of graph tell you?

Answer 41

Hollow lid on tank of water, holes in tank

Person breathes into tube, air travels along tube into take, through holes in tank and out to lift the lid

Lid DOWN: breathing IN
Lid UP: breathing OUT

Pen attached to lid, draws on paper

Deeper breathes= bigger waves
Quick, shallow breaths= small waves, high frequency (skinny)

Question 42

What is epidemiology? What are some difference between epidemiology and scientif research study in terms of number of people, the variables, the type of samples, what they identify, types of graphs etc. Draw a relevant graph for each

Answer 42

E-Large numbers of people, national
data

(Whole populations, 100, 000s)

SRS-Small number of selected volunteers

(10s – 1000s)

E-Random sample of people

Wide variety of different variables

SRS-Variables controlled as much as
possible

Stratified sampling

E-Identifies risk factors (associations
between factors and disease)

SRS-Identifies causes (causative factor)

E-No Independent variable:

= Scatter Graphs

SRS-Researches a specific Independent
variable:

= Line Graphs

Question 43

How to evaluate conclusion, what is IV/DV and where to find, what is CV

Answer 43

1) Describe data that supports the conclusion
2) Then data that disproves conclusion

IV- Investigated effect of
on x axis (excpet if time on x axis)
Tanle: usually first column on LHS

DV- measured
on y axis

CV- constant and unchanged

Repeats/sample size- tells reliability. Can criticise if no repeats (avg on DV means repeats)
sample size e.g 10-15, too small

Time scale- over suitable period of time? e.g lung cancer over two days not suitable

Range- measured suitable range of Ivs?

Question 44

How do TB, fibrosis, asthma and emphysema effect gas exchange
TB- destroys alveoli
Fibrosis- alveoli scarred and stiff
Asthma- swelling of airways
Emphysema- destroys alveoli so instead of lots of little few big, build up scar tissue, difficulty breathing

Answer 44

TB- destroys alveoli so SA decreases, gas exchange more difficult

Fibrosis- alveoli scarred and stiff- Increase distance to diffusem distance between air and blood vessels and alveoli increase bceause of layers of scar tissue

Asthma- swelling of airways- maintain conc. grad- less new air entering lungs so conc. grad in alveoli not maintained

Emphysema- All- decrease sa:v ratio- destroys alveoli so instead of lots of little, few big
Distance to diffuse- build up of scar tissue
Conc. grad- diff to breath, move air in and out

Question 45

Apart from reduced elasticity, explain how changes to the lung tissue reduce the efficiency of gas exchange. (4 marks)

Answer 45

1) Alveolar walls thicken;
2) Longer diffusion pathway;
3) Scarred / fibrous tissue;
4) Reduces surface area (for gaseous exchange);