exchange surfaces and breathing

Question 1

Describe what all living cells need to survive, what they need for this and factors which affect this

Answer 1

• all living cells need a supply of oxygen and nutrients to survive
• also need to remove waste products so they don’t build up and become toxic
• in very small organisms, this exchange can take place over the surface of the body- don’t need a specialised exchange system
• in larger organisms with more than 2 layers of cells, the body surface is no longer sufficient- need a specialised surface for exchange of substances with their environment

3 factors that affect need for an exchange system:

• size
• surface area to volume ratio
• level of activity

Question 2

Describe how size affects need for exchange surfaces

Answer 2

• in ver small organisms, such as single-celled organisms, all the cytoplasm is very close to the environment in which they live- diffusion will supply enough oxygen and nutrients to keep the cells alive and active
• however, multicellular organisms may have several layers of cells- here, any oxygen or nutrients diffusing in from the outside have a longer diffusion pathway- diffusion is too slow to enable a sufficient supply to the innermost cells

Question 3

Describe how surface area to volume ratio affects need for exchange surfaces

Answer 3

• small organisms have a small surface area, but also small volume- large SA:V ratio as SA relatively large compared to volume- means SA is large enough to supply all their cells owth sufficient oxygen
• larger organisms have larger SA and V but as size increases, V rises faster than SA- small SA:V ratio
• some organisms increase SA by adopting a different shape- e.g. flatworm has very thin, flat body- larger SA:V ratio but such a body form limits the overall size that the animal can reach
• most large organisms need a range of tissues to give body support and strength- volume increases as their body gets thicker, but SA doest increase as much- SA:V ratio of large organism is relatively small

Question 4

How to find the surface area to volume ratio of cuboids

Answer 4

Volume:
length x width x height

Surface area:
(4 x length x height) + (2 x height x width)

Question 5

How to find the the surface area to volume ratio of cylinders

Answer 5

Volume:
π r^2 x height

Surface area:
(2 π r x height) + 2 π r^2

Question 6

How to find the surface area to volume ratio of spheres

Answer 6

Volume:
4/3 π r^3

Surface area:
4 π r^2

Question 7

Describe how level of activity affects need for exchange surfaces

Answer 7

• some organisms more active than others
• metabolic activity uses energy from food and requires oxygen to release the energy in aerobic respiration
• the cells of an active organism need good supplies of nutrients and oxygen to supply the energy for movement
• this need for energy is increased in those animals, such as mammals, that keep themselves warm

Question 8

Describe features of a good exchange surface

Answer 8

• large surface area to provide more space for molecules to pass through- often achieved by folding the walls and membranes involved- e.g. root hairs in plants
• a thin barrier to decrease diffusion distance- must be permeable to the surfaces being exchanged- e.g. alveoli in lungs
• a good blood supply- can bring fresh supplies of molecules to one side (supply side), keeping the concentration high, or it may remove molecules from the demand side to maintain a steep concentration gradient so that diffusion can occur rapidly- e.g. gills in fish

Question 9

Describe the gas exchange system in mammals

Answer 9

• consist of the lungs and associated airways that carry air into and out of the lungs
• the lungs are a pair of inflatable sacs lying in the chest cavity
• air can pass into the lungs through the nose and along the trachea, bronchi, and bronchioles
• reaches tiny air-filled sacs called alveloi- where gas exchange takes place
• lugs are protected by the ribcage and the ribs are held together by the intercostal muscles
• the action of these muscles and the diaphragm ( a layer of muscular tissue beneath the lungs) helps to produce breathing movements (ventilation)

Question 10

Gaseous exchange system diagram

Answer 10

Question 11

Describe how gaseous exchange happens in the lungs (briefly- exchange surfaces)

Answer 11

• gases pass by diffusion through the thin walls of the alveoli
• oxygen passes from the air in the alveoli to the blood in the cappillaries
• carbon dioxide passes from the blood to the air in the alveloli
• the lungs must maintain a steep concentration gradient in each direction in order to ensure diffusion can continue

Question 12

Name 4 features of the lungs that make them a good exchange surface

Answer 12

• surface area
• permeability
• thin barrier
• blood supply

Question 13

Why the lungs make a good exchange surface- surface area

Answer 13

• the individual alveoli are very small- about 100-300 micrometers across
• however, they ate so numerous that the total surface area of the lungs is much larger than that of our skin
• total surface area of the exchange surface in humans is about 70m^2 (roughly half a tennis court)
• alveoli lined by thin layer of moisture- which evaporates and is lost as we breath out
• the lungs must produce a surfactant that coats the internal surface of the alveoli to reduce the cohesive forces between the water molecules, as these forces tend to make the alveoli collapse

Question 14

Why the lungs make a good exchange surface- permeability

Answer 14

• the barrier to exchange is comprised of the wall of the alvelolus and the wall of the blood capillary
• the cells and their plasma membranes readily allow the diffusion of oxygen and carbon dioxide as the molecules are small and non-polar

Question 15

Why the lungs make a good exchange surface- diffusion distance

Answer 15

Many adaptions to reduce the distance the gases have to difuse:

• the alveolus is 1 cell thick
• the capillary wall is 1 cell thick
• both walls consist of squamous cells (flattened or very thin)
• capillaries are in close contact with the alveolus walls
• the capillaries are so narrow that the red blood cells are squuezes against the capillary wall- making them closer to the air in the alveoli and reducing their rate of flo
• so, the total barrier to diffusion is only 2 flattened cells and is less than 1 micrometer thick

Question 16

Why the lungs make a good exchange surface- blood supply

Answer 16

The blood suppl helps to maintain a steep concentration gradient, so that the gases continue to diffuse

• The blood system transports carbon dioxide from the tissues to the lungs. This ensures that the concentration of carbon dioxide in the blood is higher than that in the air of the alveoli. Therefor carbon dioxide diffuses into the alveoli
• the blood also transports oxygen away from the lungs. This ensures that the concentration of oxygen in the blood is kept lower than the alveoli- so oxygen diffuses into the blood

Question 17

describe how mamallian ventillation works

Answer 17

• breathing movements ventilate the lungs
• replaces used air with fresh air- bringing in more oxygen and removing carbon dioxide
• ensures that the concentration oxygen in the air of the alveolus remains higher than that of the blood and the concentration of carbon dioxide in the alveoli remains lower than that in the blood- concentration gradient necessra for diffusion is maintained

Question 18

Describe inspiration

Answer 18

• Diaphragm contracts to move down and become flatter- displaces the digestive organs downwards
• external intercostal muscles contract to raise the ribs
• volume of thoracic cavity increased
• pressure in lungs drops below atmospheric pressure
• air is moved into lungs

Question 19

Describe expiration

Answer 19

• diaphragm relaxes and is pushed up by displaced organs underneath
• external intercostal muscles relax and the ribs fall- internal intercostal muscles can contract to help push air out more forcefully- usually only happens during exercise or coughing/sneezing
• volume of thoracic cavity decreased
• pressure in lungs increases and rises above the pressure in the surrounding atmosphere
• air moved out of lungs

Question 20

What are alveoli comprised of

Answer 20

• squamous epithelium
• surrounded by blood capillaries
• contain elastic fibres which stretch during inspiration and recoil to help push air out during respiration
• alveolus walls thin so may not be possible to distinguish between cells under a microscope
• picture- alveoli wall= squamous epithelium

Question 21

Describe the airways

Answer 21

• must be large enough to allow sufficient air flow without obstruction
• must be supported to prevent collapse when the air pressure is low inside during inspirtation
• must be flexible in order to allow movement
• lined by ciliated epithelium, which contribute to keeping the lungs healthy
• goblet cells in the epithelium release mucus, which traps mucus
• • the cilia then move the mucus up to the top of the airway, where it is swallowed
• the glandular tissue in loose tissue also produces mucus

Question 22

Describe the trachea and bronchi

Answer 22

• have a similar structure, but the bronchi are smaller
• supported by rings of cartilage which prevent collapse during inspiration
• C-shaped rather than a complete ring which allows flexibility and space for food to pass down the oesophagus

Question 23

Describe the bronchioles

Answer 23

• much narrower than the bronchi
• larger bronchioles have some cartilage, but smaller ones have none
• the wall is comprised of mostly smooth muscle and elastic fibres
• the smallest bronchioles end in clusters of alveoli

Question 24

drawn trachea/bronchus diagram

Answer 24

Question 25

describe smooth muscle and elastic tissue

Answer 25

• the smooth muscle can contract
• the action of the smooth muscle will constrict the airway
• makes the lumen of the airway narrower
• constriction of the lumen can restrict the flow of air to and from the alveoli- controlling flow of air can be important if there are harmful substances in the air
• the contraction of smooth muscle and control of airflow is not a voluntary act and may occur as a result of allergic reaction
• once the smooth muscle has contracted, it can not reverse this effect on its own
• the smooth muscle is elongated again by the elastic fibres
• when the muscle contracts, it deforms the elastic fibres
• as the muscles relax, the elastic fibres recoil to their original size and shape- acts to dilate the airway
• antagonistic

Question 26

airway cells diagram

Answer 26

Question 27

What equipment is used to measure lung volume, describe

Answer 27

Spirometer:

• device that smashes the movement of air in and out of the lungs as a person breathes
• a float-chamber spirometer consists of a Chamber of air or medical grade oxygen floating on a tank of water
• sharing inspiration, air is drawn from the chamber so that delete moves down comet during expiration the Air turns to the chamber, raising the lid
• these movements may be recorded on a data logger#
• the carbon dioxide rich air exhales is passed through a Chamber of soda line, which absorbs the carbon dioxide- allows the measurement of oxygen consumption

Question 28

What precautions must be taken when using a spirometer

Answer 28

• the subject should be healthy and, in particular, free from asthma
• the soda lime should be fresh and functioning
• fat should be no air leaks in the apparatus, as this would give invalid or inaccurate results
• the mouthpiece should be sterilised
• the water chamber must not be overfilled or water may enter the air tubes
• Modern spirometers maybe small and simple hand held devices- these records the movements of air in an out of the lungs, however many cannot measure rate of oxygen consumption

Question 29

What direction will a spirometer graph trace go when expiring and inspiring

Answer 29

• inspiring- down

- expiring- up

Question 30

What direction does the overall trace of a spirometer go throughout the experiment, why

Answer 30

Down:

• The spirometer contains Soda lime which absorbs carbon dioxide
• When breathing, we are using up the oxygen from the tank, while the carbon dioxide we breathe out is absorbed by the soda lime
• As a result the gas volume of tank decreases over experiment
• Decreases by volume of oxygen used up by the participant

Question 31

Spirometer graph labelled

Answer 31

Question 32

Define tidal volume, average values

Answer 32

• The volume of air that moves into and out of the lungs with each resting breath
• 500cm³ / 0.5dm³ in the average adult
• 15% of the vital capacity

Question 33

Define vital capacity, average values, what this depends on

Answer 33

• The largest volume of air that can be breathed in and then exhaled in one breath.
• 5000cm³ / 5dm³ in the average adult
• the size of a person- height, their age and gender, their level of regular exercise

Question 34

Define inspiratory reserve volume

Answer 34

The maximum volume of air you can breath in over and above normal inhalation

Question 35

Define expiratory reserve volume

Answer 35

Maximum volume of air you can force out of your lungs over and above the normal tidal volume of air you breath out

Question 36

Define residual volume, average value

Answer 36

The volume of air that is left in your lungs when you have exhaled as hard as possible
This cannot be directly measured. Approximately 1.5 dm3

Question 37

Define total lung volume

Answer 37

The sum of the vital capacity and the residual volume

The total potential amount of air in the lungs at any one time

Question 38

Describe how rates of oxygen uptake can be measured from a spirometer graph

Answer 38

• breathing supplies oxygen for respiration and removes carbon dioxide produced in respiration. As a person breathes from the spirometer, oxygen is absorbed by the blood and replaced by carbon dioxide. This carbon dioxide is absorbed by the soda lime in this barometer, so that the volume of air in the chamber decreases. We can assume that the volume of carbon dioxide released and absorbed by the soda line equals the volume of oxygen absorbed by the blood.
• therefore, measuring the gradient of the decrease in volume enables us to calculate the rate of oxygen uptake
• draw a line from the two points on either top or bottom of waves between the correct length of time
• measure the difference in volume between the points, divide this by the time taken for this decrease
• units will be dm3/s-1

Question 39

How would you measure breathing rates from a spirometer trace

Answer 39

• count the number of peaks in each minute, at rest it is usually about 12 to 14 breaths per minute

Question 40

What factors will oxygen uptake depends on

Answer 40

• a higher oxygen uptake will result from increased demands, such as during exercise when the muscles are respiring more
• increased oxygen uptake will of results from an increased breathing rates and deeper breaths

Question 41

Briefly describe gas exchange in bony fish

Answer 41

• must exchange gases with the water in which they live
• Use gills to absorb oxygen dissolved in the water and release carbon dioxide into the water
• The oxygen concentration will typically be much lower than that found in air
• most fish typically have 5 pairs of gills which are covered by a bony plate- operculum

Question 42

Describe the gills of fish

Answer 42

• each gill consists of 2 rows of filaments (primary lamellae) attached to a bony arch
• the filaments are very thin, and their surface is folded into many secondary lamellae (or gill plates)- provides very large surface area
• Blood capillaries carry deoxygenated blood close to the surface of the secondary lamellae where exchange takes place

Question 43

Describe how ventilation occurs in bony fish

Answer 43

1. Mouth opens (operculum is closed)
2. The buccal cavity floor is lowered
3. This increases the volume and decreases the pressure of the buccal cavity compared to outside
4. Water rushes into the mouth down a pressure gradient
5. Opercular cavity expands
6. The buccal cavity floor is raised
7. The pressure inside the buccal cavity is now higher than in the opercular cavity
8. Water moves from buccal cavity over the gills into the opercular cavity
9. The mouth is now closed and the operculum opens
10. The sides of the opercular cavity move inwards, increasing the pressure
11. Water rushes out of the fish through the opercuum

Question 44

Describe countercurrent flow in gas exchange in bony fish

Answer 44

• blood flows along the gill arch and out along the filaments on the secondary lamellae
• the blood then flows through the capillaries in the opposite direction to the flow of water over the lamellae
• this arrangement creates a countercurrent flow that absorbs the maximum amount of oxygen from the water- favourable concentration gradient is maintained

Question 45

Describe gas exchange in insects

Answer 45

• don’t transport oxygen in blood
• have an open circulatory system in which the body fluid acts as both blood and tissue fluid
• circulation is slow and can be affected by body movements
• insects posses an air-filled tracheal system which supplies air directly to all the respiring tissues
• air enters the system via a pore in each segment, called a spiracle
• the air is transported into the body through a series of pores called tracheae (trachea singular)
• these divide into smaller and smaller tubes, called tracheoles
• the ends of the tracheoles are open and filled with tracheal fluid
• gas exchange occurs between the ai in the tracheole and the tracheal fluid
• some exchange can also occur across the thin walls of the tracheoles
• many insects are very active and need a good supply of oxygen- when tissues are active, the tracheal fluid can be withdrawn into the body fluid in order to increase the surface area of the tracheole wall exposed to air- means more oxygen can be absorbed when the insect is active

Question 46

Insect gas exchange diagram

Answer 46

Question 47

How can larger insects ventilate their tracheal systems

Answer 47

Movements of the body- number of ways:
- in many insects, sections of the tracheal system are expanded and have flexible walls. These act as air sacs which can be squeezed by the action of the flight muscles. Repetitive expansion and contraction of these sacs ventilate the tracheal system.

• In some insects, movements of the wings alter the volume of the thorax. As the thorax volume decreases, air in the tracheal system is put under pressure and us pushed out of the tracheal system. When the thorax increases in volume, the pressure inside drops and air is pushed into the tracheal system from outside.
• some insects have developed this ventilation even further. Locusts can later the volume of air in their abdomen by specialised breathing movements. These are coordinated with opening and closing valves in the spiracles at the front end of the body and air enters the tracheal system. As the abdomen reduces in volume, the spiracles at the rear end of the body open and air can leave the tracheal system.