Transport in plants

Question 1

State three features of a xerophyte which indicate that it live in a dry environment and explain (6)

Answer 1

• has a reduced surface area - less area which water can be lost
• thick cuticle - waterproofing
• rolled leaves - trapping water
• hairs - trapping water vapoue
• stomata - trapping water vapour

Question 2

Explain the role of the phloem (1)

Answer 2

• transports carbonhydrates / sugars / products of photosynthesis / sucrose / amino acids

Question 3

Explain the role of the xylem (1)

Answer 3

Transports water and dissolved mineral ions

Question 4

Explain how the enedodermis carries out its function in the uptake of water and minerals in the plant (4)

Answer 4

• waterproof casaprian sstrip made of suberin whch is hydrophobic
• blocks apoplast pathway
• active transport of minerals by endodermis cells
• into symplast pathway
• active transport of minerals into pericycle
• water follows via osmosis
• water and minerals move into xylem vessles

Question 5

Explain what is meant by transpiration. Describe the factors affecting transpiration. (7) Describe how you could use a potometer to investigate one of the factors (3)

Answer 5

Transpiration
* transpiration is the evaporation of water vapour from inside the leaves of the plant
* through stomata
* down a water potential gradient
* high temperature increases the rate of transpiration
* increased kinetic energy of water molecules
* increases air movement increases the rate of temperature increasing the diffusion gradient
* high humidity decreases rate of transpiraation decreasing the diffusion gradient
* high light intersity increases rate of transpiration
* because of stomatal opening
* sset up under water make sure air cannot get in
* volumer of water taken up per unit of time
* control of wind speed by using a fan
* to give a close approximation of transpiration rate

Question 6

State the bame of the process by which plants lose water from their leaves (1)

Answer 6

Transpiration

Question 7

Describe one theory that would explain how w\ter moves up the stem of the leafy shoot (3)

Answer 7

• water lost by leaves via transpiration
• causing tension on water molecules
• cohesive forces between water molecules
• adhesive forces between water molecules and and xylem
• water molecules pulled up into xylem

Question 8

describe the rolee of potassium ions in guard cells closing the stomata (1)

Answer 8

pumpers out of guard cells

Question 9

describe the rolee of water potential of cells in guard cells closing the stomata (1)

Answer 9

increases water potential so water moves out

Question 10

describe the role of unevenly thickened cell walls in guard cells closing the stomata (1)

Answer 10

decreased water so decreases volyne of cell causing walls to move together

Question 11

How dos the effect of increased humidity effect rate of transpiration (2)

Answer 11

• decreases effect on rate of water loss
• reduces the diffusion gradient so water potential gradient between iside and outside of leaf

Question 12

Describe the uptake of water by plants form the soil into xylem (7) explain the role of ions in this process (3)

Answer 12

• water absorbed by root hair cells
• water can be absorbed into cell walls
• moves across cortex via apoplast route
• can also move across plasma membrane into cytoplasm bia omossis
• water moves from the cytoplasm of one cell to the next via plasmodesmata
• cells the ymplast route
• water can also move through cytoplasm and vacoules via vacuoular route
• casparian strip in endodermal walls
• made of suberin
• stops apoplast route water forced into symplast route
• ions absorbed into root hair cells by active transport
• ions lowering water potential in root hair cells
• at endodermic ions absorbed into cytoplasm by active transport
• ions travel through pericylce into xylem
• lowers water potential in the xylm
• lower water potential in root hair cells or xylem increasing osomotic gradient between soil and cell contents

Question 13

State two practical measures which should be taken when setting up the apparatus to ensure the potometer functions correctly give reasons fro your answers (4)

Answer 13

• shoot cut under water to prevent air enertering
• shoort with large number of leaves ensure measurable rate of transpiration
• ensure leves are dry reduces rate of transpiration
• leave time for apparatus to settle down allow plant to equilibriate
• seal joint with vaseline to prevent air entering apparature
• ensure bubble set at approprate position to enable reading being taken

Question 14

Name the original source of energy that moves wwater through a plant (1)

Answer 14

Sunlight

Question 15

Explain how water moves up the xylem (2)

Answer 15

• molecules of water moving together because of cohesion of molecules
• adhesion to walls of xylem
• root pressure pushes water upwards

Question 16

Explain the difference of diagrams of cross section of roots and stems

Answer 16

• xylem is at centre in root
• no vascualr bundles in stem
• endodermis not visible in root

Question 17

tissue external to xylem is removed by ringing why did an accumulation of sucrose occur (3)

Answer 17

• sucrose is produced in leaf
• sucrose travels in phloem
• phlowm is removed by rining
• sucrose cannot flow to roots

Question 18

Name the other type of organic molecules likely to accumulate with sucrose in ringing (1)

Answer 18

amino acids/ hormones / florigen

Question 19

If growing points of shoots of plants are removed from ringing there is a greater accumulaion of sucrose why (2)

Answer 19

• sucrose used for cell wall formation
• less sucrose used by sinls as they have been removed
• therefore more will pass down stem

Question 20

Explain fully the likely effect of the removal of the ring of tissue in the concentration of sucrose below the ring (3)

Answer 20

• sucrose not replaced from above
• so concentration decreases
• as movement towards root continues
• and sucrose used in respiration / sotrage / converted to starch / growth / active transport

Question 21

State the function of sieve tube cell (1)

Answer 21

• translocation of sucrose from source to sink

Question 22

State the function of companion cells (1)

Answer 22

Carry out metabolism to suppy sieve cells with energy contains lots of mitochondria

Question 23

Name two other pathways by which water moves across the roote cortex except the vacoular pathway (4)

Answer 23

• Apoplast
• via cell walls
• symplast
• via cytoplasm / plasmodesmata

Question 24

How does the casparian strip affect the route of water takes into stele (1)

Answer 24

• Makes the water pass through (symplast) prevents it going through the apoplast

Question 25

Give one benefit of tranpiration to a plant (1)

Answer 25

* cooling effect * upply movement of minetal ions * maintains transpiration * required for photsynthesis

Question 26

Suggest why the end of the shoort should be cut under water before inserted into the potometer (2)

Answer 26

* prevent entry of air into xylem preenting formation of air bubble * whcih would break transpiration stream

Question 27

State what measurementsw ould have bee made in order to determine the rate of transpiration (2)

Answer 27

* diameter of capilalry tuber * distance travelle by bubble * time taken

Question 28

Explain how sunken stoma is able to reduce transpiration (3)

Answer 28

* High humidity in air chamber because water vapoyr removed by wind / water vapour trapped * this reduces the water potential gradient * between the inside of the leaf and air chamber/ inside and outside of the stoma

Question 29

Describe end explain two other adaptations whcih reduce the rate of transpiration in plants that live in very dry condition (2)

Answer 29

* rolle leaves reduce surface areaexposed to the environment * reduced number of stomata less openings for water to be lost through * hairs on leaves increase humidity reducing water potential gradient * thick cuticle reduce evaporation from ssurface of leaf

Question 30

Bame two other types of cells except companion cells and sieve tube element forund in phloem (2)

Answer 30

* pernchyma * phloem fibres

Question 31

Explain how two features of the sieve tube element enable the phloem to carry out its functio (4)

Answer 31

* sieve plates - permits biderectional flow * few organelles - no obsstruction to flow of solutes * plasmodesmata - allows transport of molecules from companion cell to sieve tube elements

Question 32

Suggest why the prescence of large numbers of mitochondira in the companion cells dows no support the mass flow theory (3)

Answer 32

* mass flow is a passive process * from hgih to low concentration * ATP not required since a passive process

Question 33

Describe the similarities and differences in the structure and functioning of arteries and xylem vessles (10)

Answer 33

* both tubular * both have movement by mas flow * both movement along pressure gradients * both movement in one direction only * artery transports bloow xylem water * arteries living xylem dead * movement of liquid pulastile in arteries smooth in xylem * pressure generated by heart in arteries no pump for xylem * xylem contains lignin * xylem has support dunction * adhesiv forces in xylem * arteries have muslce and elastic tiue * arteries recoil * smooth entoehrlium of artery reducing friction * artery walls composed of layers * remembers to use whereas

Question 34

State the term used to describe plants adapted for dry conditions (1)

Answer 34

xerophytes

Question 35

Name one source and one sink in plants (1)

Answer 35

* source - lead and sink - shoot tip or root

Question 36

Describe and explain the strucutral adaptations hwon by a water lily and marram grass that enable them to survive in environments that differ in terms of water availability (10)

Answer 36

Water lilly * it is a hydrophyte * access to water all year round * roots submerged in mude at bottom of a pond and floating leaves on surface * there are large air spaces present in leaves whcih allows them to float on the surface allowing oxygen to diffurse to roots for respiration * xylem tissue poorly developed as water provides support * stomata are found on upper epidermis of leaves to allow gas exchange with the air * they have a thin cuticle as water loss iss not a problem Marram grass * xerophyte * lives in habitats with low water availability * thick cuticle to reduce evaporation as waterproofing * stomatal pores on upper epidermis * rolled leaves reduce transpiration as trap water vapour * sunken stomata in pits * hair surround stomata trap water vapour * mainitaining humid air around stomata reducing water potential gradient

Question 37

Outline a method by which the density of stomata coul dhave been determines (3)

Answer 37

* coat surface of leaf with clear nail varnish * examine using light microscope * count number of stomata in field of view

Question 38

Why is it imporatnt that no air bubbles enter the potometer (1)

Answer 38

* block the xylem

Question 39

Explain why light intensity and temperature are controlled in a potometer investigation

Answer 39

* increase inn temperature increase in kinetic energy * increase in light intensity increases tomatal oopening * increasing evaporation of water vapour

Question 40

Why is less water vapour lose through stomata in xerophytes (3)

Answer 40

* sunken stomata cuase water vapour build up in pits * reduced diffusion gradient * rate of transpiration reduced * moving air can easily disrupt diffusion as blow away water vapour

Question 41

Suggest why it is difficult to calculate stomatal density in xerophytes (1)

Answer 41

* Stomat sunken in pits so will nto shown up in impression

Question 42

Explain why leaves where removed above region to be invesitgated in ringing experiment (2)

Answer 42

* reduces photsynthesis * reducing sugar production above experimental region

Question 43

State two variables which should have been controlled in rinign experiment (1)

Answer 43

* light intensity * wavelength species * temperature * surface area of leabes * humidity * air movement

Question 44

With reference to the role of the caspariant trip explain how cyanide would result in reduction of root pressure (3)

Answer 44

* stopes apoplast pathway * movement of ions into xylem requires active transport * Cyanise is a repisratory inhibitor preventing ATP synthesis * lower water potential gradient reducing root pressure