gas exchange in plants and animals 3.3.2

Question 1

5 features of a specialised gas exchange surface

Answer 1

• high surface area to volume ratio to increase rate of exchange
• very thin, small diffusion pathway so faster rate of diffusion
• selectively permeable to allow selected materials to cross
• movement of the environment medium (eg air) to maintain a diffusion gradient
• a transport system to ensure the movement of the internal medium (eg blood) to maintain diffusion gradient

Question 2

ficks law

Answer 2

surface area x concentration difference
——————————————————-
length of diffusion path

Question 3

is diffusion more rapid in air or water

Answer 3

air

Question 4

how is a leaf adapted for efficient gas exchange

Answer 4

large SA to volume ratio
very short diffusion pathway
air spaces in the spongy mesophyll layer

Question 5

how do guard cells open and close stomata

Answer 5

when water enters guard cells swell and become turgid
thin elastic wall stretches with turgor pressure
thicker inelastic cell wall (against opening) does not

Question 6

what is a xerophyte

Answer 6

plants that are adapted to living in areas where their water losses due to transpiration may exceed their water uptake.

Question 7

cuticle

Answer 7

forms a waterproof barrier
the thicker the cuticle the less water can escape

Question 8

hairy leaves

Answer 8

traps still moist air next to leaf surface
reduces water potential gradient
less water lost by evaporation

Question 9

rolling leaves

Answer 9

protects lower epidermis from outside helps trap air within the leaf
region becomes saturated with water
water potential gradient disappears

Question 10

stomata in pits/grooves

Answer 10

traps moist air next to the leaf,reducing water potential gradient

Question 11

reduced SA:vol ratio

Answer 11

thin needles
reduce SA
reduce water loss
(but need to have enough SA for sufficient photosynthesis)

Question 12

what is the internal system of tubes where gas exchange takes place in insects called

Answer 12

trachea

Question 13

what are the smaller dead wand tubes of the trachea called

Answer 13

tracheoles

Question 14

what are the open ends of the trachea called

Answer 14

spiracles

Question 15

how is the diffusion gradient in the insect tracheal system maintained

Answer 15

O2 used up so concentration towards tracheole falls
creates a diffusion gradient

Question 16

how does CO2 produce a gradient

Answer 16

creates a diffusion gradient in the opposite direction to oxygen

Question 17

why is diffusion in insects efficient

Answer 17

diffusion in air is more rapid than in water

Question 18

how are the trachea supported and kept open

Answer 18

rings of chitin

Question 19

how can the spiracles be opened and closed

Answer 19

valves

Question 20

what are present at the spiracles to help reduce evaporation

Answer 20

tiny hairs

Question 21

how do tiny hairs at spiracles help reduce evaporation

Answer 21

keep humidity around opening to ensure there is a lower concentration gradient of water vapour - less is lost from insect by evaporation.

Question 22

what are the ends of the tracheoles filled with

Answer 22

water

Question 23

how does the volume of water in the tracheoles change when the insect is at rest

Answer 23

more water when at rest
less when active

Question 24

during periods of intense activity lactate is produced from anaerobic respiration.
lactate is soluble, how does this affect the water in the tracheoles?

Answer 24

decreases water potential of muscle cells.
water therefore moves into the cells from the tracheoles by osmosis.
this decreases the volume of water in the tracheoles.

Question 25

what affect does water moving out of the tracheoles have on diffusion pathway

Answer 25

oxygen is drawn into the tubes
creates a faster diffusion pathway
increases rate of gas exchange
(however results in loss of water which is a downside)

Question 26

what is the main disadvantage of the tracheal system

Answer 26

their size is limited

Question 27

how does the insect reduce water loss (other than spiracle hairs)

Answer 27

1 small surface area to volume ratio
2 rigid outer skeleton of chitin covered by a waterproof cuticle