Transport in plants

Question 1

Describe the structure of the root from the outer layer inwards

Answer 1

• epidermi
• exodermis
• cortc (parenchyma)
• endodermis
• phloem
• xylem

Question 2

Describe the structure of a stem from outwards in

Answer 2

• epidermis
• collenchyma
• parenchyma
• vascular bindle
• interfascicular cambium
• pith

Question 3

Describe the uptake of water into the xylem

Answer 3

• the endodermis is impregnated with areas of suberin called the casparian strip
• this blocks the apoplast pathway forcing water into the symplast pathway
• minerals are selected to move into the ymplasst by active transport
• this sets up a water potential gradient with lower water potential in the xylem so water moves in via osmosi resulting in a force called root pressure

Question 4

What is the apoplast pathway

Answer 4

from cell wall to cell wall

Question 5

Describe the symplast pathway

Answer 5

from cytoplasm to cytoplasm through plasmodesmata

Question 6

Describe the vacuolar pathway

Answer 6

• from vacoule to vacoule

Question 7

What is the structure of the xylem

Answer 7

• vessels
• tracheids
• fibres
• parenchyma

Question 8

Describe the function of xylem

Answer 8

• are dead cells that transport water and minerals up the plant and provide mechanical strength and support as they are strenghtened by waterproof lignin

Question 9

Describe te structure and the function of the phloem

Answer 9

• phloem sieve tubes carry sucroe and amino acids
• sieve elements end in sieve plates containing pores through which contain cytoplasmic filaments extend linking cells
• no other organelles are in the sieve elements
• companion cells contain many mitochondria for ATP and the organelles for proteins synthesis
• proteins and ATp are passed to the sieve elements through plasmodesmata

Question 10

What is transpiration

Answer 10

• loss of water as water vapour by evaporation and diffusion out of the open stomata from leaves of plants
• leads to transpiration stream

Question 11

What is the transportation stream

Answer 11

• water moves into the roote and enters the xylem (root pressure) cohesive forces between water molecules and adhesive forces between water molecule and hydrophilic lining of the xylem create a transpiration pull as the water leaving the xylem ito the leaf cells pull on molecules below
• this is cohesion tension theory

Question 12

What factors increase transpiration

Answer 12

• light intensity to a point
• high temperatures
• low humidity
• high air movement

Question 13

What is a hydrophyte

Answer 13

• water plants
• eg water lillies

Question 14

what are the adaptations of a hydrophyte

Answer 14

• little / no waxy cuticle no need to conserve water
• stomata on upper surface ass lower surface submerged
• porrly developed xylem no need to transport water
• large air spaces to provide buoyancy and acts as a resovoir of gas

Question 15

What is a mesophyte

Answer 15

• live with adequate water

Question 16

What are adaptations of mesophytes

Answer 16

• close stomata at ngiht to decrease water loss
• shed leaves in unfavourable conditions eg winter
• undergroup oran and dormant seeds survive winter

Question 17

What is a xerophyte

Answer 17

• water is scarce
• eg marram grass

Question 18

What are adaptations of a xerophyte

Answer 18

• thick waxy cuticle reduin water loss via evaporation from epidermal tissue
• sunken stomata increasing humidity in an air chamber above the stomata reducing diffusion gradient and therefore water loss
• rolles leaves - reduces area of leaf exposed directly to air
• stiff interlocking hairs trap water vapous inside rolled leaff and reducing water potential gradient and therefore water loss

Question 19

What is translocation

Answer 19

• the phloem transports the products of photosynthesis from the source (the leaf) to the sink (area of use or storage)
• bidirectional flow occurs

Question 20

What is ringing experiement evidence for translocation

Answer 20

• removal of phloem
• show accumulation of sucrose products on leaf side of the ring but none on the root side
• movement of sucrosse was blocked by removal of phloem
• therefore phloem is route of transport

Question 21

Describe how aphids are experimental evidence for translocation

Answer 21

• use aphis to sample sap from phloem
• aphid stylus extends into sieve tube elements
• if a laser is used to remove the stylis from the body the stylus then becomes a micropipeete and ap diereis out
• thiss can be analued to show that sucrose and amino acids are carried in the phloem both above and below leaves

Question 22

Describe radioactive leabelling is evidence for transloction

Answer 22

• of Co2 which will become incoroporated into sucrose can be used in cojuction with aphid technique to determine the rate of transport in the phloem

Question 23

Describe how source and sinks are evidence for translocatio

Answer 23

• sources and sinks can determine by autoradiography using radioactivley labelled carbon dioxide

Question 24

Describe for theory of mass flow

Answer 24

• sucrose made at source lowers water potential
• water enter cells and sucrose is forced into phloem (loading)
• this increases hydrostatic pressure and therfore mass flow occurs along the phloem to the root where sucrose is stored as starch, water potential is less negatic and water moves into the xylem

Question 25

Describe against mass low theory

Answer 25

• sieve plates impede flow
• translocation is fasted than expected with dissucion
• theory does not explain biirectional flow or differentt rates of flow of amino acids and sucrose
• not explain companion cell mitochondia, high O2 intake or stopping of translocation by cyanide