Exchange Surfaces & Breathing

Question 1

why do larger multicellular organisms require specialised exchange surfaces but small unicellular organisms don’t?

Answer 1

unicellular cytoplasm is in close proximity to external environment so diffusion & active transport is sufficient to supply the nutrient demands & waste removal

whereas multicellular have high SA/V ratio so diffusion alone would not be sufficient to supply the innermost cells. also they tend to be more metabolically active, eg. endotherms maintain body temp

Question 2

state the 3 features of a good exchange surface

Answer 2

large SA
thin barrier= short diffusion distance
good blood supply to maintain steep concentration gradients

Question 3

explain the gaseous exchange system of bony fish (7 marks)

Answer 3

1. operculum = bony plate that protects gills
2. gill filaments ( primary lamellae) are thin rows of tissues attached to a bony arch; 2 gill arch per gill
3. Gill plates (secondary lamellae) = folded surface of gill filaments well supplied with blood capillaries
4. = COUNTERCURRENT FLOW SYSTEM; the orientation of the gill plates means that blood is flowing in the opposite direction to the water flowing across the gills; maximises O2 exchange between water & blood as concentration gradients remain steep across whole length of the capillary

Question 4

explain the gaseous exchange system of insects (6 marks)

Answer 4

TRACHEAL SYSTEM:
1. air enters trachea via spiracles, and flows into smaller branches called tracheoles
2. tracheoles are bathed in tracheal fluids exchange occurs between the fluid & tracheole air
In some insects:
- air sacs that can be repeatedly squeezed during flight to ventilate
- wing/abdomen movement alters the volume of their thorax/abdomen to control pressure therefore ventilation

Question 5

what is the purpose of ventilation(breathing) in mammals

Answer 5

maintains steep concentration gradient between air in alveoli & blood:

• ensures conc. of o2 in lungs is higher than in blood
• conc. of co2 in lungs is lower than in blood

Question 6

outline inspiration

Answer 6

to draw air in from outside, need to set up pressure gradient for it to move down, so:

1. diaphragm contracts & moves down
2. external intercostal muscles contract, raising the ribs
3. volume increases, therefore pressure of chest cavity decreases
4. pressure of chest is lower than atmospheric air pressure so air is drawn in down pressure gradient

Question 7

outline expiration

Answer 7

to force air out, we must set up a pressure gradient so that the chest cavity air pressure is high than that of atmosphere. so:

1. diaphragm relaxes & moves up
2. external intercostal muscles relax, lowering the ribs
3. volume of chest cavity reduces therefore pressure in chest increases above atmospheric air pressure
4. air drawn out down pressure gradient

Question 8

outline the pathway of air outside into the alveoli

Answer 8

trachea –> bronchus(i) –> bronchioles –> alveoli

Question 9

outline how the alveoli are adapted for exchange

Answer 9

• Numerous, spherical sac structures provide the lungs with a very large surface area
  • Alveolus and capillary walls are both only one cell thick; therefore air is separated from the blood by a barrier only two cells across
  • Capillaries are narrow — squeeze red blood cells against the capillary walls
  • Capillaries are in close contact with alveolus walls • Both capillaries and alveoli consist of squamous cells
  • Alveolus walls contain elastic fibres to help them recoil during ventilation

Question 10

outline how the trachea, bronchi & bronchioles are adapted for exchange

Answer 10

Trachea and bronchi:
• Wide enough to allow for unobstructed air flow
• Supported by C-shaped rings of cartilage to prevent collapse during inspiration whilst maintaining flexibility
• Lined with goblet cells and ciliated epithelial cells to trap and remove pathogens & secreted mucus.
Bronchioles:
• No cartilage
• Wall is made mostly of smooth muscle and elastic fibres
• Contraction of smooth muscle can reduce airflow to alveoli and protect them from harmful substances in the air
• Elastic fibres elongate the smooth muscle once it relaxes, dilating the airways

Question 11

DEFINE VITAL CAPACITY

Answer 11

MAX VOLUME THAT CAN BE EXHALED AFTER A MAXIMUM INHALATION

Question 12

DEFINE RESIDUAL VOLUME

Answer 12

VOLUME OF AIR THAT REMAINS IN LUNGS AFTER EXHALING; ABOUT 1.5dm3

Question 13

DEFINE TIDAL VOLUME

Answer 13

VOLUME OF AIR INHALED/EXHALED DURING A TYPICAL BREATH AT REST

Question 14

OUTLINE HOW A SPIROMETER WORKS

Answer 14

1. inspiration draws air out from chamber so lid moves down
2. expiration: air returned to chamber so lid moves back up
3. lid movements recorded on a cataloguer
4. o2 consumption can be measured as any CO2 exhaled is absorbed by the soda lime

Question 15

how do fish ventilate?

Answer 15

opening & closing of buccal cavity (mouth) pumps water over the gills to ventilate them

Question 16

what does vital capacity depend on?

Answer 16

gender
age
level of regular exercise
height & BMI

Question 17

list precautions to take before using a spirometer

Answer 17

• not asthmatic
• fresh soda lime
• no air leaks in apparatus
• sterile mouth piece
• don’t overfill water chamber- or water could enter air tubes

Question 18

define oxygen uptake and what we assume when using a spirometer to measure it?

Answer 18

o2 volume absorbed by lungs in 1 min

assume that vol. of co2 absorbed = vol of o2 used, as the air decrease in chamber is due to co2 absorption

Question 19

what is total lung capacity

Answer 19

vital capacity + residual volume