3.1.1 Exchange surfaces

Question 1

describe the SA to V ratio of a large organism
3.1.1(a)

Answer 1

small

Question 2

describe the SA to v ratio of a small organism
3.1.1(a)

Answer 2

large

Question 3

why do large multicellular organisms need specialised exchange surfaces
3.1.1(a)

Answer 3

they have a small SA to V ratio so there diffusion distance is large so it would take a long time for o2 to diffuse into out bodies

Question 4

What mode of transport is usually used in gaseous exchange surfaces
3.1.1(b)

Answer 4

In gas exchange surfaces, the mode of transport is usually simple diffusion.
Gas exchange surfaces have evolved to be efficient, meaning that they can maximise the rate of diffusion of gases into and out of an organism.

Question 5

what is Ficks Law
3.1.1(b)

Answer 5

Rate of diffusion in particles per second is proportional to surface area and concentration gradient, and inversely proportional to diffusion distance

Question 6

what is the Rate of diffusion
3.1.1(b)

Answer 6

number of particles crossing a surface per second

Question 7

what is the relationship between SA and rate of diffusion
3.1.1(b)

Answer 7

As the surface area doubles, the rate of diffusion also double

Question 8

what is the relationship between concentration gradient and rate of diffusion
3.1.1(b)

Answer 8

as the concentration gradient increases, the rate of diffusion should also increase.
if there is a large difference, the rate of diffusion will be high. If there is a small difference, the rate of diffusion will be low.

Question 9

what are the two adaptations to maintain a high concentration gradient
3.1.1(b)

Answer 9

-a good blood supply
-a good ventilation system

Question 10

how does a good blood supply help maintain a high concentration gradient
3.1.1(b)

Answer 10

as soon as oxygen has diffused into the blood, this blood moves along and is replaced by blood that is low in oxygen

Question 11

how does a good ventilation system help maintain a high concentration gradient
3.1.1(b)

Answer 11

air or water are constantly moving over the exchange surface. As soon as the air in the lungs becomes lower in O2, it is exhaled, and replaced by “fresh” inhaled air

Question 12

what is the relationship between rate of diffusion and diffusion distance
3.1.1(b)

Answer 12

When diffusion distance is multiplied by 2, the rate of diffusion will be multiplied by 1/2. This is known as inverse proportion
It therefore takes longer for particles to travel a further distance, and so the rate of diffusion is lower across greater distances.

Question 13

how are mammalian gas exchange systems adapted to maximise SA
3.1.1(c)

Answer 13

-millions of alveoli give the internal surface of the lung a very high SA
-surfactant coat the inside of the lungs and prevent them from collapsing on exhalation
-elastic fibres made up of elastin protein present in alveolar lining allow stretch when inhaling to increase SA of exchange surface

Question 14

how are mammalian gas exchange systems adapted to maximise concentration gradient for co2 and o2
3.1.1(c)

Answer 14

· Breathing muscles repeatedly contract and relax to move air in and out of the lungs (ventilation)

o So once as much oxygen as possible has been extracted from a breath of air, it is replaced with “fresh” air

· Good blood supply, so once blood has become oxygenated, it moves on and is replaced by deoxygenated blood

· Elastic fibres, made of elastin protein, are present in alveolar lining, and help alveoli to stretch then recoil and force air out

Question 15

how are mammalian gas exchange systems adapted to minimise diffusion distance
3.1.1(c)

Answer 15

· Alveoli lining consists of one layer of squamous epithelial cells, which are short and flat

· Blood capillaries are very close to the lining of the alveoli

Question 16

what are other adaptations of mammalian gas exchange surfaces
3.1.1(c)

Answer 16

· C-shaped rings of cartilage in the trachea and bronchi allow these tubes to be flexible but strong, so they do not collapse

· The gas exchange system is internal and so kept at a warm body temperature, allowing a high rate of diffusion

· Ciliated epithelium lining the trachea and bronchi help to prevent pathogens from entering the lungs

· Elastic fibres are present in the trachea, bronchi and bronchioles which help to maximise the volume of air entering the lungs as these tubes can stretch

· Smooth muscle (not under voluntary control) in the bronchioles and bronchi can relax to allow greater volumes of air to enter the lungs when needed, for example during exercise

Question 17

table for inspiration, passive expiration and forced expiration
3.1.1(d)

Answer 17

in booklet

Question 18

how can lung volume be measured
3.1.1(e)

Answer 18

using a spirometer

Question 19

what does a spirometer do
3.1.1(e)

Answer 19

measures the movement of air into and out of the lungs as the person breathes

Question 20

what is the purpose of the soda lime in the spirometer
3.1.1(e)

Answer 20

absorbs the co2

Question 21

why does the spirometer have a downwards gradient
3.1.1(e)

Answer 21

as oxygen is being consumed

Question 22

what is the total lung capacity
3.1.1(e)

Answer 22

the total volume of air that can fit in the lungs

Question 23

what is the vital capacity
3.1.1(e)

Answer 23

the maximum volume of air that can be moved into or out of the lungs in one breath

Question 24

what is the residual volume
3.1.1(e)

Answer 24

the small amount of air that remains in the airways and alveoli even after a full forced expiration

Question 25

how can vital capacity be measure
3.1.1(e)

Answer 25

taking the deepest possible breath in then expiring as much as possible

Question 26

what is the tidal volume
3.1.1(e)

Answer 26

volume of air moved moved in or out with each normal breath recorded at rest or during exercise

Question 27

how can you measure breathing rate from a spirometer trace
3.1.1(e)

Answer 27

count the number of peaks and divide by the time taken

Question 28

how would you measure rate of oxygen consumption from a spirometer trace
3.1.1(e)

Answer 28

find the volume at the start and at the end
calculate the difference
then divide by the time taken

Question 29

what does each gill consist of
3.1.1(f)

Answer 29

two rows of microscopic gill filaments attached to a gill arch

Question 30

what features maximise the SA of the fish
3.1.1(f)

Answer 30

many gill filaments with many microscopic lamellae

Question 31

how do fish exchange systems maximise concentration gradient between blood and water
3.1.1(f)

Answer 31

-ventilation of the gills
-counter current flow. The blood in the capillaries in the lamella flows in the opposite direction to the water

Question 32

describe how a fish makes water move into its mouth
3.1.1(f)

Answer 32

opens its mouth and lowers the floor of the buccal cavity so volume increases and pressure decreases. Water flows in down a pressure gradient.

Question 33

describe how a fish forces water to flow over its gills and out through the operculum
3.1.1(f)

Answer 33

closes mouth, opens its operculum raises floor of buccal cavity so volume decreases and pressure increases. Water forced out over gills.

Question 34

what decreases the diffusion distance in fish
3.1.1(f)

Answer 34

capillaries are close to the surface of the lamella.
lamella are very thin

Question 35

How does air move through the tracheal system
3.1.1(f)

Answer 35

Air diffuses into the tracheal system through pores called spiracles. The air diffuses along a series of tubes called tracheae, which divide into smaller and smaller tubes called tracheoles.

Question 36

what do the tracheae contain rings of
3.1.1(f)

Answer 36

The tracheae have rings of chitin to provide support and keep them open

Question 37

what happens to the ends of the tracheoles
3.1.1(f)

Answer 37

The ends of the tracheoles are open and filled with fluid called tracheal fluid

Question 38

where can gas exchange occur in insects
3.1.1(f)

Answer 38

Gas exchange occurs between the air in the tracheole and the tracheal fluid.
Some exchange can also occur across the thin walls of the tracheoles

Question 39

how is the diffusion distance decreased in insects
3.1.1(f)

Answer 39

Many insects are very active and need a rapid supply of oxygen. When tissues are respiring anaerobically they produce lactic acid. This makes the water potential inside the cells more negative, so water from the tracheal fluid moves by osmosis into the cells. This reduces the thickness of the tracheal fluid and so the diffusion distance is decreased.

Question 40

why do small insects not need to ventilate there gas exchange surface
3.1.1(f)

Answer 40

Small insects have a high surface area to volume ratio and low metabolic rate so diffusion so diffusion along the trachea will be sufficient to meet their needs

Question 41

how do large insects with a low SA to V ratio, high metabolic rate ventilate there exchange surface
3.1.1(f)

Answer 41

Abdominal muscles can contract to force air in and out of the tracheal system through the spiracles

· Wing movements can achieve the same thing

· Many insects have air sacs attached to the tracheal system which can be forcibly contracted to move air over the exchange surfaces

Question 42

how to dissect a fish
3.1.1(g)

Answer 42

-remove the operculum to access the gills
-cut out a gill arch and place in water to allow the filaments to fan out

Question 43

how to dissect an insect
3.1.1(g)

Answer 43

-cut open the exoskeleton of the insect on the ventral(belly) side
-place the insect underwater so that the trachea and air sacs will inflate (with water)
-for microscopy, stain the tracheoles with methylene blue to make them visible