3.2 Gas exchange

Question 1

what gives a leaf a large surface area

Answer 1

mesophyll cells with air spaces between them

Question 2

what gives a leaf a large concentration gradient (4 things)

Answer 2

1. constant use and removal of gases
2. air spaces continuous with air
3. huge number of stomata
4. leaves help of to let breeze renew the air

Question 3

what gives a leaf a short diffusion distance (2 things)

Answer 3

1. thin cell walls
2. mesophyll cells close to stomata

Question 4

xerophytes adaptions to reduce water loss (5 things)

Answer 4

reduced leaf area - through needles
thick waxy cuticle - reduce evaporation
hairy leaves - hairs trap a layer of saturated air
sunken stomata - the pits above the stomata become saturated
rolled leaves - this reduces the area exposed to the air and keep the stomata on the inside so increasing the water vapour inside the roll

Question 5

3 xerophyte adaptions to increase water intake

Answer 5

deep extensive root system - to maximise water uptake
accumulation of solutes in the root system - to reduce the ψ so making the ψ gradient from the soil to the root cells steeper
some very shallow roots to absorb dew which condenses on the soil at night

Question 6

why do plants close their stomata

Answer 6

as at night there is no sun to carry out photosynthesis so they want to close their stomata to reduce water loss as there is no need to absorb CO2. The stomata are also closed around midday as there is more heat so they want to hold water and reduce loss through transpiration as there would be a shallower concentration gradient.

Question 7

3 features of single celled organisms for efficient exchange

Answer 7

1. large surface area to volume ratio
2. small diffusion distance - only pass through one membrane
3. large concentration difference - oxygen is continually being used in respiration and CO2 produced so there is always a concentration gradient

Question 8

5 features of specialised exchange

Answer 8

1. a large surface area to volume ratio - increases the rate of exchange
2. very thin - so that the diffusion distance is short and therefore materials cross exchange surface rapidly
3. selectively permeable - to allow selected materials to cross
4. movement of the environmental medium - air to maintain diffusion gradient
5. a transport system - to ensure the movement of the internal medium such as blood in order to maintain a diffusion gradient

Question 9

why are insects not bigger

Answer 9

as if they were bigger they would have more cells which means more demand for oxygen and the tracheal system could not provide for the respiratory demands

Question 10

order of exchange systems in insect

Answer 10

spiracles > trachea > thracheols > muscle fibres

Question 11

how do muscular contractions help an insect during exercise

Answer 11

muscular contractions help maintain a concentration gradient during exercise by increasing ventilation rate allowing a higher rate of oxygen for the insect

Question 12

why is there moisture at the end of tracheoles in an insect

Answer 12

so oxygen can dissolve and then diffuse easier

Question 13

three steps of inspiration in insects

Answer 13

increase volume from relaxing muscles
decreases pressure
air force in

Question 14

three steps of expiration in insects

Answer 14

decrease volume from contracting muscles
increase pressure
Air forced out

Question 15

three insect adaptations to reduce water loss

Answer 15

small surface area to volume ratio to minimise area over which water is lost
waterproof coverings over the body
spiracles can be closed to reduce water loss with trapping humid air with hairs around spiracles

Question 16

steps of water flow in gills

Answer 16

water enters the mouth > buccal floor closes shutting mouth increasing pressure forcing it over the gills > over the lamellae > oxygen moves into blood in blood vessels

Question 17

why counter currant

Answer 17

water passes over gill plates in opposite direction to the flow of blood so the blood meats water with a higher oxygen concentration than its own. This increases the efficiency of oxygen extraction by ensuring there is a diffusion gradient along the whole gill plate so the blood absorbs more oxygen. this is because if the blood flowed the same way they will both quickly reach equilibrium and the blood would extract less of the available oxygen from the water.

Question 18

6 steps of counter current flow

Answer 18

1. as the blood flows in the opposite direction to the water, to always flows next to the water that has given up less of its oxygen
2. this way the blood is absorbing more and more oxygen as it moves along
3. even as the blood reaches the end of the lamella and is 80% or so saturated with oxygen, it is flowing past water which is at the beginning of the lamella and is 90-100% saturated
4. this means hat even when the blood is highly saturated having flowed past most of the length of the lamellae
5. there is still a concentration gradient and it can continue to absorb oxygen from the water
6. meaning oxygen can diffuse over the whole length of the gill.

Question 19

3 ways the gills have a large surface area

Answer 19

• each gill has 2 rows of lamellae
• each lamellae has a series of gill plates at right angles
• each gill plate has a mass of capillaries

Question 20

3 ways the gill has a short diffusion distance

Answer 20

• lamellae walls are only one cell thick
• capillary walls are only one cell think
• blood close to surface gradient

Question 21

3 ways the gill maintains a diffusion gradient

Answer 21

• ventilation ensures continual flow of water
• circulation of blood
• counter currant flow

Question 22

describe the trachea

Answer 22

a flexible airway that is supported by rings of cartilage. this cartilage prevents the trachea collapsing and the tracheal walls are made of muscles lined with ciliated epithelium and goblet cells producing mucus

Question 23

describe the bronchi

Answer 23

are two divisions of the trachea each leading to one lungs. similar in structure to the trachea

Question 24

describe bronchioles

Answer 24

are a series of branching subdivisions of the bronchi, their walls are made of muscles lined with epithelial cells, this muscle allows them to constrict so that they can control the flow of air in and out of the alveoli

Question 25

describe the alveoli

Answer 25

little air sacs at the end of bronchioles, between the alveoli there are some collagen and elastic fibres, the alveoli are lined with epithelium and the elastic fibres allow the alveoli to stretch as they fill with air when breathing in. these then spring back during breathing out in order to expel the CO2 in the air.

Question 26

define inspiration

Answer 26

the air pressure of the atmosphere is greater than the air pressure of the lungs so air forced in

Question 27

define expiration

Answer 27

the air pressure in the lungs is greater than that of the air pressure so air forced out

Question 28

6 steps of inspiration

Answer 28

1. diaphragm contracts and flattens
2. external intercostal muscles contract
3. ribs move up and out
4. volume of thoracic cavity increases
5. pressure decreases
6. air pushed into lungs as the air moves down the pressure gradient

Question 29

6 steps of expiration

Answer 29

1. diaphragm relaxes and curves up
2. external intercostal muscles relax
3. ribs move down and in
4. volume of thoracic cavity decreases
5. pressure increases
6. air pushed out of lungs as the air moves down the pressure gradient

Question 30

what is the diaphragm

Answer 30

a sheet of muscle that separates the thorax from the abdomen

Question 31

what are the intercostal muscles

Answer 31

they lie between the ribs

there are two types:
- the internal intercostal muscles whose contraction leads to expiration
- the external intercostal muscles whose contraction leads to inspiration