Transport in plants- Plant adaptations to water availability

Question 1

What adaptations to most plants have to conserve water?

Answer 1

• waxy cuticle to reduce transpiration

- stomata is mainly found on the underside of the leaf and can close to prevent water loss.

Question 2

what are xerophytes?

Answer 2

plants which have adapted to live in environments with little water availability. This can be cold or hot deserts.

Question 3

give two common examples of xerophytes?

Answer 3

marram grass and cacti

Question 4

how does a thick waxy cuticle in xerophytes conserve water?

Answer 4

minimises water loss by diffusion from stomata

Question 5

how does sunken stomata in xerophytes conserve water?

Answer 5

sunken stomata in pits reduces air movement creating humid air which reduces the water potential gradient, reducing transpiration.

Question 6

how does a reduced number of stomata in xerophytes conserve water?

Answer 6

reduces water loss by transpiration but also reduces gas exchange abilities

Question 7

how does reduced leaves in xerophytes conserve water?

Answer 7

minimises water loss by reducing surface are to volume ratio meaning there is less area for water to diffuse out. Xerophytes can also lose their leaves in times of drought.

Question 8

how do hairy leaves in xerophytes conserve water?

Answer 8

minimises water loss by reducing air flow and creating air which reduces evaporation rate and water potential gradient.

Question 9

how does curled leaves in xerophytes help conserve water?

Answer 9

minimises water loss which confines stomata within a humid microenvironment minimising evaporation and the water potential gradient.

Question 10

how do succulents in xerophytes help conserve water?

Answer 10

minimise water loss by storing water in the parenchyma tissue in the roots and leaves giving a plentiful supply in times of drought.

Question 11

how do modified stem in xerophytes help conserve water?

Answer 11

minimises water loss by expanding to store water which provides plentiful supply in times of drought.

Question 12

how do deep roots in xerophytes help conserve water?

Answer 12

roots can go deep into the ground to access water which is a long way below the surface

Question 13

how do shallow roots in xerophytes help conserve water?

Answer 13

a large network of roots just below the surface of the soil to collect any rainwater that falls.

Question 14

how does dormancy in xerophytes help conserve water?

Answer 14

some plants stop working in times of drought, leaving seeds behind to rapidly germinate when there is enough water

Question 15

how do storage organs in xerophytes help conserve water?

Answer 15

bulbs and tubers can store water below the surface so there is plentiful supply in times of drought.

Question 16

How does dehydration and rehydration in xerophytes help conserve water?

Answer 16

some plants can withstand absolute water loss, appearing dead, then rehydrating when water is available. This is aided by the disaccharide trehalose which enables cells to survive droughts unharmed

Question 17

how do you measure stomatal numbers?

Answer 17

1) wipe clear nail varnish on the underside of a leaf and let it dry
2) place sellotape over nail varnish, and press down firmly
3) peel off gently and place under a light microscope
4) count the number of stomata you can see in the area of the eyepiece and multiply it by the size of the leaf

Question 18

what is a hydrophyte (e.g water lilies)?

Answer 18

plants which are adapted to live in conditions where water is abundant, at the surface, submerged in or at the edge of bodies of water

Question 19

why is there no waxy cuticle in hydrophytes?

Answer 19

maximises water loss so plants don’t become oversaturated, as transpiration is not an issue.

Question 20

why is water logging a major problem for hydrophytes?

Answer 20

excess water fills air spaces of the plant which is needed for gaseous exchange

Question 21

why do hydrophytes have many many stomata on the upper surface?

Answer 21

maximises gaseous exchange and allows water vapour to leave

Question 22

why do hydrophytes have a reduced structure?

Answer 22

it reduces the requirement for mechanical strength as the leaves and water support the plant.

Question 23

why do hydrophytes have wide flat leaves?

Answer 23

maximises the surface area to volume ratio to absorb as much light as possible and to allow water loss

Question 24

why do hydrophytes have small roots?

Answer 24

water can diffuse directly into the stem and leaf tissue so there is no need for uptake by roots

Question 25

why do hydrophytes have air sacs?

Answer 25

they enable the leaves to float at the surface where light intensity is strongest for efficient photosynthesis

Question 26

Why do hydrophytes have aerenchyma?

Answer 26

It is a specialised parenchyma tissue which aids buoyancy and forms an efficient pathway for oxygen into the tissues which are important in anoxic conditions

Question 27

Why do hydrophytes have pneumatophores?

Answer 27

these are special aerial roots which grow directly into air which have many lenticels allowing entry of oxygen.

Question 28

What is the problem about aerenchyma?

Answer 28

provides a low resistant pathway by which methane produced by rice plants can be vented into the atmosphere. Methane contributes to the greenhouse effect.