chapter 9 - plant transport

Question 1

xylem

Answer 1

transports water and soluble mineral ions up the plant

Question 2

phloem

Answer 2

transports assimilates eg sucrose up and down the plant

Question 3

endodermis

Answer 3

sheath of cells surrounding the vascular bundle - has a key role in getting water into xylem vessels

Question 4

pericycle

Answer 4

layer of meristem cells - undifferentiated cells able to divide for new growth of tissues

Question 5

cambium

Answer 5

layer of meristem cells - able to produce new xylem and phloem

Question 6

parenchyma

Answer 6

packing and support tissue capable of cell division

Question 7

collenchyma

Answer 7

cells provide structural support, in growing shoots and leaves

Question 8

xylem vessels

Answer 8

columns of fused hollow (dead) cells which transport water and mineral ions up the plant

Question 9

fibres

Answer 9

long, dead cells with thick cell walls; provide support

Question 10

pits

Answer 10

gaps in the lignin where there is only cellulose

Question 11

adaptations of xylem vessels

Answer 11

• continuous column
• hollow
• lignin prevents walls from collapsing inwards and allows for adhesion for water molecules
• pits allow sideways movement into and out of vessels

Question 12

sieve tube elements

Answer 12

columns of cells that transport the assimilates

Question 13

companion cells

Answer 13

linked to the sieve tubes, contain dense cytoplasm and carry out the metabolic reactions required for transport

Question 14

adaptations of sieve elements

Answer 14

• thin layer of cytoplasm
• no nucleus or ribosomes
• thin cell walls
• end cell walls are perforated

Question 15

adaptations of companion cells

Answer 15

• linked to sieve elements by many plasmodesmata
• have dense cytoplasm with large nucleus
• more mitochondria and ribosomes than normal
• infoldings of cell surface membrane to increase the surface area

Question 16

water and mineral ion uptake from the soil

Answer 16

• mineral ions are absorbed by active transport into root hair cells
• these minerals lower the water potential of the cytoplasm in root hair cells
• water moves by osmosis

Question 17

movement of water across the root

Answer 17

• water moves into the root hair cell by osmosis down the water potential gradient
• the cell becomes turgid
• the adjacent cell will have a lower water potential than the root hair cell
• water will continue moving from cell to cell by osmosis

Question 18

the symplast pathway

Answer 18

water travels through the cytoplasm of cells and through plasmodesmata to neighbouring cells

Question 19

the apoplast pathway

Answer 19

water moves through the gaps in the cellulose cell wall; stops at the casparian strip in the endodermis

Question 20

the casparian strip

Answer 20

band of waterproof material made from waxy suberin; blocks the apoplast pathway and forces water into cells via the symplast pathway

Question 21

how does water move up the stem: root pressure

Answer 21

as water enters the roots by osmosis, water is forced up the stem

Question 22

how does water move up the stem: transpiration pull

Answer 22

water molecules are attracted to each other by cohesive forces which forms a long column of water in the xylem; as water is lost at the top via transpiration, the column is pulled through the xylem

Question 23

how does water move up the stem: capillary action

Answer 23

adhesive forces between water molecules and lignin in the narrow walls of the xylem help pull the water up the xylem vessels

Question 24

transpiration

Answer 24

the loss of water vapour from the upper parts of the plant, especially the leaves

Question 25

transpiration stream

Answer 25

the flow of water through a plant from the roots to the leaves in the xylem vessels

Question 26

process of transpiration

Answer 26

- water enters the leaves travelling in the xylem and then passes into the mesophyll cells by osmosis - water evaporates from the surface of the mesophyll to form water vapour which collects in the air space raising the water vapour potential - water molecules diffuse out of the leaf through the stomata and is carried away by air movements

Question 27

affect of relative humidity on transpiration rate

Answer 27

very high humidity will lower rate of transpiration because of the reduced water vapour potential gradient between inside the leaf and the air

Question 28

how to estimate the rate of transpiration

Answer 28

measure water uptake using a potometer

Question 29

xerophytes

Answer 29

plants that are adapted to dry conditions eg cacti and marram grass

Question 30

adaptations of xerophytes

Answer 30

- leaves reduced to spines - hairs to create a microclimate of still, humid air - rolled leaves - thick waxy cuticle - reduced number of stomata

Question 31

hydrophytes

Answer 31

plants that are adapted to live in water

Question 32

adaptations of hydrophytes

Answer 32

- wide, flat leaves - aerenchyma (specialised parenchyma with many air spaces) for buoyancy - stomata on upper surface - very thin/no waxy cuticle - small roots

Question 33

translocation

Answer 33

the movement of assimilates up and down the plant in the phloem (source to sink)

Question 34

source (with examples)

Answer 34

where assimilates are loaded into the phloem eg photosynthesising green leaves, storage organs at the start of growth season, seeds when they germinate

Question 35

sink (with examples)

Answer 35

where assimilates are removed from the phloem eg roots when growing, buds/any actively dividing meristems, storage organs flowers/fruits developing

Question 36

mass flow at source

Answer 36

sucrose is actively loaded into sieve tube element reduced water potential of sap water follows the sucrose moving down a water potential gradient increases hydrostatic pressure

Question 37

mass flow at sink

Answer 37

sucrose diffuses out of sieve tube elements increases water potential of sap water follows sucrose out of sieve element moving down a water potential gradient decreases hydrostatic pressure in phloem at the sink

Question 38

mass flow in translocation

Answer 38

water moving in at source and out at sink creates a hydrostatic pressure difference which forces the sap to move from source to sink by mass flow

Question 39

loading sucrose into phloem: symplast route

Answer 39

sucrose moves from photosynthesising mesophyll cells to companion cells through plasmodesmata

Question 40

loading sucrose into phloem: apoplast route

Answer 40

sucrose passes across the cell walls which involves the movement of hydrogen ions

Question 41

active transport of sucrose into companion cells

Answer 41

hydrogen ions pumped out of the companion cells using ATP leads to higher conc of H+ ions outside the cell than inside H+ ions can move back into the companion cells carrying sucrose molecules down the concentration gradient through co-transporter proteins

Question 42

unloading sucrose from the phloem

Answer 42

occurs in tissues that need sucrose likely that sucrose moves into the tissues by facilitated diffusion once in tissues, sucrose is converted into something else by enzymes

Question 43

invertase

Answer 43

converts sucrose into glucose and fructose