Gas exchange and SA:V

Question 1

What are examples of things that need to be exchanged?

Answer 1

• respiratory gases eg. oxygen and carbon dioxide
• nutrients eg. glucose, amino acids, fatty acids and glycerol
• excretory products eg. urea, salt
• heat

Question 2

What are the 2 types of exchange?

Answer 2

active eg. active transport and co-transport

passive eg. diffusion and osmosis

Question 3

What is fick’s law?

Answer 3

surface area x difference in concentration divided by length of diffusion path

Question 4

Describe the relationship between size and surface area to volume ratio of organisms

Answer 4

the larger the size of an organism, the smaller the SA:V ratio

Question 5

How is gas exchange achieved in single-celled organisms eg. amoeba?

Answer 5

• 1 cell therefore very large SA:V ratio
• folds in surface called pseudopods - increase surface area
• thin cell membrane - short diffusion distance
• partially permeable which allows movement of O2 and CO2 by simple diffusion
• engulfs food using pseudopods for nutrients

Question 6

What are xerophytic plants?

Answer 6

Plants adapted to dry conditions with little water

Question 7

What are the adaptations of xerophytic plants?

Answer 7

Thick - larger diffusion distance so little water loss

Rolled up leaves - traps air within the roll which becomes saturated with water vapour, so has a very high water potential - no water potential gradient therefore no water loss

Hairy leaves - traps still, moist air on the leaf surface which reduces water potential gradient so less water loss through evaporation

Stomata in grooves - trap still moist air which reduces water potential gradient

Small SA:V ratio - reduced water loss

Root system - deep to penetrate water table and shallow to absorb rainfall

Question 8

How have insects evolved for gas exchange?

Answer 8

• insects have evolved an internal network of tubes called trachae, which are supported by strengthened rings to prevent them from collapsing
• trachae divide into smaller tubes called tracheoles which extend throughout the body tissues
• oxygen is brought directly into respiring tissues as there is a short diffusion distance from tracheoles to body cells

Question 9

How do gases move into an insect along a diffusion gradient?

Answer 9

• when cells respire, oxygen is used up so concentration of oxygen at the ends of tracheoles falls
• this creates a diffusion gradient that causes oxygen to diffuse from the atmosphere along the trachae and tracheoles to the cells
• CO2 is produced by cells during respiration
• this creates a diffusion gradient in the opposite direction which causes CO2 to move along tracheoles and trachae from cells to the atmosphere

Question 10

How do gases move into an insect through mass transport?

Answer 10

rhythmic contraction of abdominal muscles can squeeze the trachea, ‘pumping’ air in and out

Question 11

How do gases move into an insect due to the ends of tracheoles being filled with water?

Answer 11

• during periods of major activity, muscle cells around the tracheoles respire and carry out anaerobic respiration
• this produces lactate which is soluble and lowers water potential of muscle cells, therefore water moves into the cells from tracheoles by osmosis
• water in the ends of tracheoles decreases which draws air further into them
• this means the final diffusion pathway is in a gas rather than liquid phase, so diffusion is more rapid

Question 12

How do gases enter and leave the trachae?

Answer 12

Through tiny spores called spiracles on the body surface which are opened and closed by valves. Insects close spiracles to prevent water loss.

Spiracles open to air filled pipes called trachae which branch into trachaeoles and capillaries

Question 13

How do insects maintain a steep concentration gradient?

Answer 13

Muscle cells rapidly use up oxygen during respiration leading to a low oxygen concentration in muscles. There is always a high concentration of oxygen in the air

Question 14

How do insects have a large surface area?

Answer 14

• small - large SA:V ratio
• large SA through legs/wings
• lots of trachae and trachaeoles

Question 15

How do insects have a short diffusion pathway?

Answer 15

There is a direct link between tracheoles and muscle cells

Question 16

What is the structure of fish gills?

Answer 16

• made up of gill filaments
• gill lamallae which increases the surface area of the gills

Question 17

How does water move across the gills?

Answer 17

• water enters through the mouth - volume increases and buccal cavity lowers
• this lowers the pressure which allows water to flow in from high to low pressure
• water flows over the gill into the opercular cavity
• mouth closes and buccal cavity raises which increases pressure - operculum opens and water flows out

Question 18

How do fish gills have a large surface area?

Answer 18

presence of gill filaments and lamellae

Question 19

How do fish gills have a steep concentration gradient?

Answer 19

• countercurrent flow
• good blood supply - oxygen absorbed by diffusion from water into blood vessels

Question 20

How do fish gills have a short diffusion path between water and gills?

Answer 20

lamellae and filaments are very thin - 1 cell thick

Question 21

What is the countercurrent exchange principle?

Answer 21

• blood and water flow over gill lamallae in opposite directions
• blood always passing water with a higher oxygen concentration
• maintains a concentration/diffusion gradient of oxygen
• oxygen uptake is maintained across the entire length of the lamellae

Question 22

How are leaves adapted for efficient gas exchange?

Answer 22

• many small pores called stomata which reduce diffusion pathway
• large surface area of mesophyll cells for rapid diffusion

Question 23

How do insects reduce water loss?

Answer 23

• small SA:V ratio - minimises area over which water is lost
• waterproof covering
• spiracles which close to reduce water loss

Question 24

What is the structure of the respiratory system?

Answer 24

• nasal cavity
• trachea
• bronchus
• bronchiole
• alveoli

Question 25

What is the location and function of cartilage in the gas exchange system?

Answer 25

• lines trachea and bronchioles
• keeps vessels open to maintain ventilation

Question 26

What is the location and function of goblet cells in the gas exchange system?

Answer 26

• throughout lungs/bronchioles/alveoli
• secrete mucus which is useful for moisture and diffusion of gases. Also excretes pathogens

Question 27

What is the location and function of cilia in the gas exchange system?

Answer 27

• trachea, bronchus, bronchioles
• ‘woft’ mucus and pathogens along vessels to be excreted

Question 28

What is the location and function of muscle tissue in the gas exchange system?

Answer 28

• intercostal muscles, diaphragm and trachea
• contract and relax to control movement - allows for changes in volume

Question 29

What is the location and function of elastic tissue in the gas exchange system?

Answer 29

• lung tissue in walls of alveoli
• expansion and recoil - allows for increase in size of alveoli when they fill with air

Question 30

How does air move into and out of the lungs?

Answer 30

when pressure of the atmosphere is greater than air pressure inside the lungs, air is forced into the lungs (inhalation)

when air pressure in the lungs is greater than that of the atmosphere, air is forced out of the lungs (exhalation)

Question 31

How are pressure changes of the lungs brought about?

Answer 31

• diaphragm - muscle separating thorax from the abdomen
• internal intercostal muscles, whose contraction leads to expiration
• external intercostal muscles, whose contraction leads to inspiration

Question 32

What happens during inspiration?

Answer 32

• external intercostal muscles contract, while internal intercostal muscles relax
• ribs are pulled upwards and outwards, increasing the volume of the thorax
• diaphragm muscles contract, causing it to flatten which increases the volume of the thorax
• increased volume of thorax results in reduction of pressure in the lungs
• atmospheric pressure is now greater than pulmonary pressure, and so air is forced into the lungs down a pressure gradient

Question 33

What happens during expiration?

Answer 33

• internal intercostal muscles contract, while external intercostal muscles relax
• ribs move downwards and inwards, decreasing the volume of the thorax
• diaphragm muscles relax, and so it is pushed up by the contents of the abdomen that were compressed during inspiration, and the volume of the thorax is further decreased
• decreased volume of the thorax increases the pressure in the lungs
• pulmonary pressure is now greater than that of the atmosphere, so air is forced out of the lungs

Question 34

What is the equation for pulmonary ventilation?

Answer 34

pulmonary ventilation (total volume of air moved into the lungs) =

tidal volume (volume of air taken in during one breath) x ventilation rate (number of breaths per minute)

Question 35

What are the key features of the human gas exchange surfaces?

Answer 35

• short diffusion distance - capillaries and alveoli made of 1 cell thick epithelial cells
• large SA:V ratio - lungs are big and filled with alveoli - internal surface area
• movement of internal medium - constant movement of blood so constantly oxygenated
• movement of external medium - movement of air into the lungs to allow diffusion of oxygen to capillaries for aerobic respiration

Question 36

Why is diffusion of gases between the alveoli and blood rapid?

Answer 36

• red blood cells are slowed as they pass through capillaries, allowing more time for diffusion
• alveoli and capillary walls are thin - short diffusion distance
• alveoli and capillaries have a large surface area
• blood flow through capillaries maintains a concentration gradient

Question 37

What is the structure of an alveolus?

Answer 37

• single cell wall made of epithelial cells
• thin layer of moisture - allows gases to dissolve so they can diffuse quickly
• single cell wall of capillary made of epithelial cells
• low O2 concentration diffuses from blood into and out of the alveolus
• high O2 concentration diffuses from alveolus into the capillaries in blood

Question 38

What is a disadvantage of an alveolus for gas exchange?

Answer 38

• perfect breeding ground for bacteria because:
• constantly open due to cartilage
• warm - internal + good blood supply
• lots of O2 for growth
• layer of moisture - H2O

Question 39

What is pulmonary tuberculosis/fibrosis and what effect does it have on gas exchange?

Answer 39

• breathed in bacteria destroy tissue of the lungs. This results in cavities, where the lungs repair themselves leading to scar tissue
• reduces elastic tissue in alveoli, which reduces ventilation

Question 40

What is asthma and what effect does it have on gas exchange?

Answer 40

• lung condition caused by genetics
• muscles tighten - smaller surface area so less O2 diffusion
• walls of muscle inflame and thicken - larger diffusion distance so slower rate