B7 - Exchange and transport

Question 1

Why is diffusion enough for single-celled organisms?

Answer 1

• low metabolic activity (low O2 demands, low CO2 production)
• large SA:V ratio (enough to supply all cells with sufficient oxygen)

Question 2

Why do larger organisms need specialised exchange surfaces?

Answer 2

• size:
  
  • several layers of cells (longer diffusion distance)
  • diffusion is too slow to enable sufficient supply
• SA:V ratio:
  
  • as surface area increases, volume increases much faster
  • so larger organisms have a smaller SA:V ratio
• metabolic activity:
  
  • multicellular organisms are much more active and need good supplies of nutrients/oxygen to supply energy for movement

Question 3

What are the features of an efficient exchange surface?

Answer 3

• increased SA:
  
  • provides area needed for exchange
  • root hair cells/villi
• thin layer:
  
  • short diffusion distance (making the process fast and efficient)
  • alveoli
• good blood supply:
  
  • brings fresh supplies of molecules on one side
  • maintains steep conc. gradient
  • alveoli, gills
• good ventilation:
  
  • (for gases) this helps maintain conc. gradient
  • alveoli, gills

Question 4

What are the four main ways that breathing can be measured?

Answer 4

• vital capacity
• tidal volume
• breathing rate
• oxygen uptake

Question 5

How is the volume of air drawn in/out of lungs measured?

Answer 5

• spirometer
• peak flow meter (often used by people with asthma)
• vitalographs (more sophisticated)

Question 6

What is tidal volume?

Answer 6

• volume of air inhaled/exhaled in one breath at rest

Question 7

What is vital capacity?

Answer 7

• the greatest volume of air that can be expelled from the lungs after taking the deepest possible breath

Question 8

What is breathing rate?

Answer 8

• the number of breaths per minute
• can be calculated from the spirometer by counting the number of peaks/troughs in a minute

Question 9

What is the residual volume?

Answer 9

• the remaining vol. of air left in lungs after exhaling as hard as possible

Question 10

What is the inspiratory reserve volume?

Answer 10

• the maximum amount of air inhaled (above normal inhalation/tidal volume)

Question 11

What is the expiratory reserve volume?

Answer 11

• the maximum amount of air exhaled (above normal exhalation/tidal volume)

Question 12

What is total lung capacity?

Answer 12

• the sum of the vital capacity and the residual volume

Question 13

What is the ventilation rate?

Answer 13

• total vol. of air inhaled in one minute
• ventilation rate = tidal vol. x breathing rate (one min.)

Question 14

Where does mammalian gas exchange take place?

Answer 14

• lungs (alveoli)

Question 15

What are the key structures of the gaseous exchange system?

Answer 15

• nasal cavity
• trachea
• bronchus
• bronchioles
• alveoli

Question 16

What are the features of the nasal cavity?

Answer 16

• large SA with good blood supply (warms air to body temp.)
• hairy lining (secretes mucus to trap dust/bacteria)
• moist surfaces (increases humidity, reduces evaporation)

Question 17

What are the features of the trachea?

Answer 17

• wide tube with incomplete rings of cartilage (flexible) to prevent trachea from collapsing
• lined with ciliated epithelium (moves mucus away from lungs) with goblet cells (secrete mucus)

Question 18

What are the features of the bronchus?

Answer 18

• left bronchus (left lung), right bronchus (right lung)
• similar to trachea with supporting rings of cartilage (smaller)

Question 19

What are the features of the bronchioles?

Answer 19

• smaller ones have no cartilage rings
• walls contain smooth muscle (allows it to contract/constrict and relax/dilate)
• lined with thin layer of flattened epithelium

Question 20

What are the features of the alveoli?

Answer 20

• consists of thin flattened epithelial cells
• collagen/elastic fibres (allows for alveoli to stretch and return to normal resting size, which is elastic recoil)
• large SA:
  
  • maximises amount of diffusion
• thin layers:
  
  • alveoli and capillaries have walls that are one cell thick
  • so it has a short diffusion distance
• good blood supply:
  
  • constant blood flow brings CO2 and carried off O2
  • maintains a steep conc. gradient
• good ventilation:
  
  • breathing moves air in/out of the lungs (replaces used air with fresh air)
  • maintains conc. gradient for diffusion

Question 21

What is inspiration?

Answer 21

• diaphragm moves down
• intercostal muscles move up and out
• thoracic volume increases
• thoracic pressure decreases
• air flows into lungs to equalise pressure difference

Question 22

What is expiration?

Answer 22

• diaphragm moves up
• intercostal muscles move down and in
• thoracic volume decreases
• thoracic pressure increases
• air flows out lungs to equalise pressure difference

Question 23

Why do insects have a different gaseous exchange system?

Answer 23

• they have an exoskeleton (little to no gas exchange)
• no blood pigments to carry oxygen
• ** so gaseous exchange system delivers oxygen directly to the cells/removes CO2) **

Question 24

What is the thorax?

Answer 24

• chest cavity

Question 25

How does gas exchange take place in insects?

Answer 25

• air enters/leaves through spiracles (water is also lost)
  
  • inactive = O2 demands low, closed spiracles
  • active = O2 demand raised, CO2 build up, more spiracles open
• air then moves into the tracheae (lined with chitin)
  
  • relatively impermeable so little gaseous exchange takes place here
• they branch to form tracheoles (no chitin)
  
  • spread throughout tissues of insect
  • where most gaseous exchange takes place between air/respiring cells
  • O2 dissolves in moisture of walls and diffuses into cells
• tracheal fluid is found towards the end of tracheoles
  
  • when O2 demand builds up (and lactic acid is produced), w.p. of cells lowers
  • causes water from tracheal fluid to move into the cells by osmosis
  • ** exposes more SA for gaseous exchange **

Question 26

What are the alternative methods of gas exchange in insects?

Answer 26

• mechanical ventilation of tracheal system:
  
  • air actively pumped into system by pumping movements of thorax/abdomen
  • this changes the vol. of the thorax (changes pressure) causing air to move in/out
• collapsible tracheae/air sacs:
  
  • flight muscles can cause air sacs to be squeezed
  • the inflation/deflation of the sacs ventilate the tracheal system

Question 27

Why do fish have a different respiratory system?

Answer 27

• they do not need to prevent water loss
• water is much denser than air and has a lower O2 content
• their scaly outer covering does not allow for gaseous exchange

Question 28

What are the features of fish gas exchange system?

Answer 28

• operculum:
  
  • active in maintaining a flow of water over the gills
• water flows over the gills:
  
  • absorbs oxygen dissolved in the water and releases CO2 into the water
  • ** O2 conc. in water is much lower than in air **
• gill filaments:
  
  • occur in large stacks which need a flow of water
  • this exposes the large SA needed
• gill lamellae:
  
  • rich blood supply and large SA
  • main site of gaseous exchange in fish

Question 29

How does ventilation take place in fish?

Answer 29

• mouth opens and floor of buccal cavity is lowered (increases vol.)
  
  • pressure drops
  • water moves into cavity
    ‎
• opercular valve is shut and oper. cavity (gills) expands
• floor of buccal cavity moves up
  
  • increases pressure so water moves over the gills
    ‎
• mouth closes, operculum opens and oper. cavity moves inwards
  
  • increases pressure
  • forces water to move over gills and out of the operculum
• floor of buccal cavity is steadily moved up (maintains water flow)

Question 30

How are gills adapted for effective gas exchange in water?

Answer 30

• large SA for diffusion
• rich blood supply for steep conc. gradient
• thin layers (short diffusion distance)
  ‎
• tips of adjacent gill filaments overlap:
  
  • increases resistance to flow of water
  • allows for more *exchange time
• water and blood flow in a counter-current system:
  
  • maintains a steep oxygen conc. gradient
  • more gaseous exchange can take place
  • O2 continues to diffuse down conc. gradient