Exchange Surfaces and Breathing

Question 1

What are the main factors that warrant whether an organism needs a specialised exchange system?

Answer 1

Size

Surface area to volume ratio

Level of activity

Question 2

How does the ‘size’ of an organism affect the need for an exchange system?

Answer 2

cytoplasm in small organisms is close to the environment so diffusion will supply enough oxygen and nutrients to keep the cells alive and active

Multicellular organisms may have several layers of cells and so anything diffusing in from the outside has a longer diffusion pathway meaning diffusion will be slow and won’t enable sufficient supply

Question 3

How does ‘surface area to volume ratio’ affect an organism’s need for an exchange surface?

Answer 3

Some larger animals have small surface area to volume ratios which means it’s difficult to exchange enough substances to supply a large volume of animal with oxygen and nutrients through a small outer surface

Question 4

How does an organism’s ‘level of activity’ affect its need for an exchange system?

Answer 4

Metabolic activity uses energy from food and requires oxygen to release the energy in aerobic respiration

If an organism is more active, its cells will need good supplies of nutrients and oxygen to supply the energy required for movement

Question 5

What features do all good exchange features have in common?

Answer 5

A large surface area to provide more space for molecules to pass through

A thin barrier to reduce the diffusion distance and that is permeable to the substances being exchanged

A good blood supply which can bring fresh supplies of molecules, to keep the concentration high or that can remove molecules to keep the concentration low

Question 6

How is a large surface area often achieved?

Answer 6

By folding the walls and membranes involved

Question 7

Why is a good blood supply important in a good exchange surface?

Answer 7

It maintains a steep concentration gradient so that fast diffusion can occur

Question 8

What does the gaseous exchange system in mammals consist of?

Answer 8

The lungs - 2 inflatable sacs lying in the chest cavity - and the associated airways that carry air into and out of them

Lungs are protected by the ribcage and the ribs are held together by the intercostal muscles

Question 9

How does air get from the environment into the body?

Answer 9

Air passes through the nose, along the trachea, from the back of the mouth to the lungs, down the bronchi and bronchioles, smaller airways leading into the lungs, it then reaches alveoli, folds of the lung epithelium, which is where gas exchange takes place

Question 10

What happens during inspiration?

Answer 10

Diaphragm contracts and flattens, displacing the digestive organs

External intercostal muscles contract

Rib cage moves upwards and outwards

As volume of thorax increases, the lung pressure drops below atmospheric pressure and air is moved into the lungs

Question 11

What happens during expiration?

Answer 11

Diaphragm relaxes and is pushed up by displaced organs becoming curved

External intercostal muscles relax

Rib cage moves downwards and inwards

As volume of thorax decreases, the lung pressure rises above the atmospheric pressure and air is moved out of the lungs

Question 12

Why must the lungs maintain a steep concentration gradient in each direction?

Answer 12

To ensure that diffusion can continue

The blood system transports CO2 from the tissues to the lungs ensuring the concentration in the blood is higher than that in the air of the alveoli - CO2 diffuses into alveoli

The blood transports O2 away from the lungs ensuring the concentration of O2 in the blood is kept lower than that in the alveoli - O2 diffuses into the blood

Question 13

How are alveoli adapted for gaseous exchange?

Answer 13

Individually are very small but are numerous so have a large surface area to volume ratio

Lined by a thin layer of moisture which evaporates as we breathe out

Internally coated with a surfactant produced by the lungs to reduce the cohesive forces between water molecules preventing collapse

Question 14

What is the barrier to exchange comprised of?

Answer 14

The wall of the alveolus and the wall of the blood capillary

Question 15

How are the lungs adapted to reduce the diffusion distance of gases?

Answer 15

Alveolus is one cell thick

Capillary wall is one cell thick

Both walls consist of squamous (flattened) cells

Capillaries are in close contact with alveolus walls

Capillaries are narrow so that red blood cells are squeezed against the capillary wall, making them closer to the air in alveoli

Question 16

What does ventilation ensure?

Answer 16

The concentration of oxygen in the air of the alveolus remains higher than that in the blood

The concentration of carbon dioxide in the alveoli remains lower than that in the blood

The concentration gradient necessary for diffusion is maintained

Question 17

What do the elastic fibres in the alveoli walls do?

Answer 17

They stretch during inspiration but recoil during expiration to help push air out

Question 18

What requirements must the trachea, bronchi and bronchioles meet to be effective?

Answer 18

Be large enough to allow sufficient air to flow without obstruction

Be supported to prevent collapse when the air pressure inside is low during inspiration

Be flexible in order to allow movement

Question 19

What structure lines the airways?

Answer 19

Ciliated epithelium

Question 20

What is the function of ciliated epithelium?

Answer 20

It contributes to keeping the lungs healthy

Contains goblet cells which release mucus which traps pathogens

The cilia move the mucus to top of the airway where it’s swallowed

Question 21

Which is narrower, trachea or bronchi?

Answer 21

Bronchi

Question 22

What prevents collapse of the airways during inspiration?

Answer 22

Rings of cartilage

C-shaped in the trachea

Question 23

Why is cartilage C-shaped in the trachea rather than a complete ring?

Answer 23

To allow flexibility and space for food to pass down the oesophagus

Question 24

What are the walls of the bronchioles comprised of?

Answer 24

Smooth muscle and elastic fibres

Question 25

What is the function of smooth muscle?

Answer 25

It can contract and so can constrict the airway making the lumen narrower

Question 26

When might controlling the flow of air to the alveoli be important?

Answer 26

If there are harmful substances in the air When an allergic reaction is occurring

Question 27

What is the function of elastic fibres in the trachea?

Answer 27

To elongate the smooth muscle once it has contracted as it cannot reverse this effect on its alone

Question 28

Why must the smooth muscles relax before the elastic fibres can elongate them?

Answer 28

When the muscle is contracted the elastic fibres are deformed and cannot dilate the airways

Question 29

How do the elastic fibres dilate the airways after the contraction of smooth muscle?

Answer 29

As the muscles relax, the elastic fibres can recoil to their original size and shape thus dilating the air way

Question 30

What is a spirometer?

Answer 30

A device that measures the movement of air into and out of the lungs as a person breathes

Question 31

How do spirometers measure the movement of air in and out of the lungs?

Answer 31

A chamber of medical-grade oxygen with a lid floats on a tank of water During inspiration, air is drawn from the chamber so that the lid moves down During expiration, the air returns to the chamber and the lid is raised Movements are recorded on a datalogger that is attached to the chamber lid to produce a trace

Question 32

How does a spirometer measure oxygen consumption?

Answer 32

The air exhaled is passed through a chamber of soda lime, which absorbs the carbon dioxide so that the volume of air in the chamber decreases This decrease can be observed and measured on the spirometer trace and so measuring the gradient of the decrease in volume enables us to calculate the rate of oxygen uptake

Question 33

What precautions must be taken when using a spirometer?

Answer 33

The subject should be healthy and free from asthma The soda lime should be fresh and functioning There should be no air leaks in the apparatus as this would give inaccurate results The mouthpiece should be sterilised The water chamber must not be overfilled or water may enter the air tubes

Question 34

What is one advantage and one disadvantage of modern spirometers?

Answer 34

Advantage - May be small and simple hand-held devices Disadvantage - Many cannot measure the rate of oxygen consumption

Question 35

What does the total lung volume consist of?

Answer 35

The vital capacity and the residual volume

Question 36

What is the vital capacity and how can it be measured?

Answer 36

It is the maximum volume of air that can be moved by the lungs in one breath It is measured by taking a deep breath and expiring all the air possible from the lungs

Question 37

What factors does vital capacity depend upon?

Answer 37

The size of a person The age and gender Their level of regular exercise

Question 38

What region is vital capacity usually in?

Answer 38

2.5-5.0 dm3

Question 39

What is the residual volume?

Answer 39

The volume of air that remains in the lungs even after forced expiration - usually in the airways and alveoli

Question 40

What is the approximate measurement of residual volume?

Answer 40

1.5 dm3

Question 41

What is the tidal volume and when is it usually measured?

Answer 41

The volume of air moved in and out with each breath which is sufficient to supply all required oxygen usually measured at rest

Question 42

What might a typical tidal volume be at rest?

Answer 42

0.5 dm3

Question 43

How can you calculate oxygen uptake from a spirometer trace?

Answer 43

One trace, draw a line from point A down to the horizontal axis and another line from point B to the horizontal axis Measure the length of time between these points Measure the different in volume between points A and B Divide by the time taken for this decrease The unit will be dm3 s-1

Question 44

How can you measure the breathing rate from a spirometer trace?

Answer 44

Count the number of peaks in each minute

Question 45

What will increase oxygen uptake result from?

Answer 45

Increased breathing rate Deeper breaths

Question 46

What do bony fish use their gills for?

Answer 46

In order to absorb oxygen dissolved in the water and release carbon dioxide into the water

Question 47

What are a bony fish's gills usually like?

Answer 47

Most have five pairs covered by the operculum Each gill consists of two rows of primary lamellae attached to a bony arch These lamellae are very thin and their surface is folded into many secondary lamellae providing a large surface area for where exchange takes place

Question 48

What arrangement in bony fish creates a countercurrent flow and what is its purpose?

Answer 48

Blood flows along the gill arch and along the lamellae to the operculum Blood then flows through capillaries in the opposite direction to the flow of water over the lamellae creating a countercurrent flow This arrangement absorbs the maximum amount of oxygen from the water

Question 49

How does ventilation work in bony fish?

Answer 49

Buccal-opercular pump keeps water flowing over the gills The floor of the mouth moves downwards, drawing water into the buccal cavity The mouth closes and the floor is raised again, pushing water through the gills

Question 50

How are the movements of the buccal cavity coordinated with movements of the operculum?

Answer 50

As water is pushed from the buccal cavity to the gills, the operculum moves outwards This movement reduces the pressure in the opercular cavity, helping water to flow through the gills

Question 51

What kind of circulatory system do insects have?

Answer 51

A slow and open circulatory system in which the body fluid acts as both blood and tissue fluid

Question 52

What mechanism do insects possess that supplies air directly to all respiring tissues?

Answer 52

An air-filled tracheal system

Question 53

Describe an insects tracheal system and how gaseous exchange occurs

Answer 53

Air enters the system via a spiracle in each body segment The air is transported into the body through a series of tubes called tracheae These divide into smaller and smaller tubes called tracheoles which have open ends and the end are filled with tracheal fluid Gaseous exchange occurs between the air in the tracheole and the tracheal fluid

Question 54

How can more oxygen be absorbed when the insect is active?

Answer 54

The tracheal fluid can be withdrawn into the body fluid in order the increase the surface area of the tracheole wall exposed to air

Question 55

How can larger insects ventilate their tracheal system?

Answer 55

By the movements of their body

Question 56

Describe 2 ways insects can ventilate using body movements

Answer 56

Sections of the tracheal system are expanded and have flexible walls, these act as air sacs which can be repetitively expanded and contracted to ventilate the tracheal system Movements of the wings alter the volume of the thorax and as the volume decreases, air in the tracheal system is put under pressure and is pushed out of the tracheal system. When the thorax volume increases, pressure inside drops and air is pushed in from the outside

Question 57

How can locusts alter the volume of their abdomens by specialised breathing movements?

Answer 57

Their breathing movements are coordinated with opening and closing valves in the spiracles As the abdomen expands, spiracles at the front end of the body open and air enters the tracheal system As the abdomen reduces in volume, the spiracles at the rear end of the body open and air leaves the tracheal system