Gas Exchange A1

Question 1

Describe the relationship between the size of an organism and its SA to volume ratio.

Answer 1

surface area to volume ratio decreases as the organism gets larger therefore specialised exchange systems and mass transport systems are needed in larger organisms.

Question 2

What do organisms rely on for exchange of oxygen and CO2 down their concentration gratients?

Answer 2

diffusion

Question 3

Explain how gas exchange happens in a single celled organism?
(2)

Answer 3

1. have a larger surface area to volume ratio
2. can meet gas exchange by diffusion across the surface (very small diffusion distance)

Question 4

What is the equation for Fick’s law?

Answer 4

rate of diffusion = (SA X change in concentration)

/(divided by)

diffusion distance

Question 5

What makes a good exchange surface?
(3)

Answer 5

1. large SA
2. large concentration gradient
3. thin exchange surface

Question 6

How does oxygen move through the insect?
(4)

Answer 6

1. oxygen diffuses through spiracles and into trachea
2. spiracle closes
3. oxygen moves through the trachea into the tracheoles
4. oxygen delivered directly to the respiring tissues

Question 7

What may insects have to limit water loss?
(2)

Answer 7

1. waterproof covering on exoskeleton (waterproof cuticle)
2. small surface area to volume ratio ( minimise area over which water is lost)

Question 8

How does CO2 leave the insects body?
(3 marks)

Answer 8

1. carbon dioxide produced by the respiring tissue
2. moves in opposite direction
3. and leaves the insect when spiracles open

Question 9

What is the driving force for gas exchange in insects?
(2)

Answer 9

1. respiration
2. keeps high concentration gradient so oxygen constantly flowing in and out

Question 10

What is the driving force for gas exchange in plants?

Answer 10

photosynthesis - CO2, simple diffusion

Question 11

What diffusion happens in the gas exchange systems (tracheal system) of insects.
(6)

Answer 11

1. tissues respire using oxygen - reduces O2 concentration at tissue
2. O2 moves from high to low so from trachea to tissue
3. this lowers O2 concentration in trachea so oxygen moves into trachea from outside insects via spiracles
4. tissues respire using CO2, increasing concentration in tissue
5. moves from high in tissue to low in trachea
6. then from high concentration in trachea low outside insects via spiracles

Question 12

What is ventilation?
(in insects)
(4)

Answer 12

1. movement of insects muscles creates mass movement of air in and out of the trachea
2. therefore speeding up the gaseous exchange
3. the also have small air sacs in trachea
4. muscles around these air sacs contract and pump air sacs deeper into tracheoles

Question 13

How does an insect get additional oxygen during flight?
(5)

Answer 13

1. when insect at rest, water builds up in tracheoles
2. during flight, insect may partially respire anaerobically and produce some lactic acid
3. this lowers water potential of muscle cells
4. as lactase builds up, water passes via osmosis from tracheoles into muscle cells
5. this draws air into tracheoles closer to the muscle cells and therefore reduces the diffusion distance for oxygen when its most needed.

Question 14

A fish uses its gills to absorb oxygen from water.
Explain how the gills of a fish are adapted for efficient gas exchange.
(6)

Answer 14

1. large surface area provided by many lamellae/many filaments
2. increases diffusion/makes diffusion efficient
3. thin epithelium/distance between water and blood
4. water and blood flow in opposite directions / counter-current
5. this maintains concentration gradient (along gill)/equilibrium not reached
6. as water always next to blood with lower concentration of oxygen
7. circulation replaces blood saturated with oxygen
8. ventilation replaces water (as oxygen removed)

Question 15

Describe the counter current system.
(3)

Answer 15

1. blood and water flow in opposite directions
2. maintains concentration gradient
3. along the entire gill filament

Question 16

Describe counter current flow.
(3)

Answer 16

1. no equilibrium is reached
2. a concentration gradient is maintained all the way across the lamellae/capillary
3. almost all the oxygen in the water diffuses into the blood

Question 17

Describe how CO2 in the air outside a leaf reaches the mesophyll cells inside the leaf.
(4)

Answer 17

1. CO2 enters vis stomata
2. stomata opened by guard cells
3. diffuses through air spaces
4. down diffusion gradient

Question 18

Name three adaptations of a leaf for gaseous exchange.

Answer 18

1. flat - large SA
2. stomata - pores allow air to move in and out leaf
3. air spaces - short distance between mesophyll cells and air

Question 19

Describe how oxygen leaves the plant.

Answer 19

1. oxygen produced during photosynthesis
2. O2 diffuses into air spaces from cells
3. this increases concentration of O2 in air spaces, causing O2 to move from air spaces into outside leaf vie stomata

Question 20

Give 6 adaptations xerophytic plants use (live in dry environments) and how does it relate to Fick’s law?

Answer 20

1. reduced number of stomata - less SA for water loss
2. stomata in pits - reduced concentration gradient
3. hairs to trap water vapour - reduced concentration gradient
4. rolled leaves - reduces concentration gradient
5. leaves reduced to spines - less SA for water loss
6. thick waxy cuticles - increased diffusion distance

Question 21

Why would a logarithmic scale be good for plotting body mass?

Answer 21

1. large/uniform range of values
2. so can fit on a graph

Question 22

How do small animals obtain sufficient oxygen for respiration?

Answer 22

1. large surface area to volume ratio
2. short diffusion distance of gases

Question 23

Suggest why an oceans concentration of oxygen may be higher on the surface than seabed?

Answer 23

1. oxygen from air dissolves on surface
2. via diffusion
3. higher O2 concentration in air than SA of water

Question 24

A fish used its gills to absorb oxygen from water.
Explain how the gills of a fish are adapted for efficient gas exchange.
(6)

Answer 24

1. large surface area provided by many lamellae over many gill filaments
2. increases diffusion efficiency
3. thin epithelium/distance between water and blood
4. water and blood from in opposite directions / counter current
5. this maintains concentration gradient along gill (equilibrium not reached)
6. as water always next to blood with lower concentration of oxygen
7. circulation replaces blood saturated with oxygen
8. ventilation replaces water (as oxygen removed)