Transport in plants

Question 1

why do plants need transport systems

Answer 1

.they have low SA:VOL ratio

.diffusion is too slow to meet metabolic needs

.substance must be moved over long distances

Question 2

what are the two main transport systems in a plant

Answer 2

xylem and phloem

Question 3

what is the role of the xylem

Answer 3

.transports water and mineral ions
.provides structual support

Question 4

how is the xylem tissue adapted

Answer 4

.elongated
.hollow tubes
.no end walls
.lack organelles
.wall thickened with lignin for support
.pits to allow movement of water and ions in and out of vessels

Question 5

role of phloem

Answer 5

transports sugars and amino acids

Question 6

adaptations of sieve tube elements

Answer 6

.connected end to end

.have sieve plates with pores to allow flow of sugars and amino acids

.lack nuclei and most organelles

.thin layer of cyto

Question 7

adaptation of companion cells

Answer 7

.connected to sieve tube elements through pores

.cyto contains large nucleus

.many mito to release energy for active transport through sieve tube elements

.many ribosomes for protein synthesis

Question 8

xylem and phloem in the root

Answer 8

.xylem forms a cross in the middle
.phloem are in the corners of the cross

Question 9

xylem and phloem in the stem

Answer 9

.xylem in the inside
.phloem on the outside

Question 10

xylem and phloem in the leaf

Answer 10

.xylem on the top
.phloem on the bottom

Question 11

what is transpiration

Answer 11

evaporation of water from plants as a side effect of gas exchange

Question 12

why does transpiration occur

Answer 12

.water evaporates from mesophyll cells

.stomata open so they can absorb CO2 for photo

.this provides a pathway for water vapour loss through the stomata

.water vapour moves down water potential gradient from the air spaces in the leaf into the atmosphere

Question 13

how does light effect transpiration rate

Answer 13

.high light intensity = stomata open for maximum CO2 absorption for photo

Question 14

how does temp effect transpiration rate

Answer 14

.high temp = evaportation of water faster due to higher kinetic energy

Question 15

how does humidity effect transpiration rate

Answer 15

.low humidity increases water vapour gradient between leaf and atomosphere

Question 16

how does wind speed effect transpiration rate

Answer 16

high wind speed = increase water vapour gradient between leaf and atmosphere

Question 17

how to use a photometer

Answer 17

.cut the shoot underwater at a slant to increase SA for water uptake
.assemble photometer with shoot submerged in water
.keep capillary tube end of photometer submerged
.check that apparatus is airtight
.dry leaves
.leave time for shoot to acclimatise
.shut the tap and record the position of the air bubble
.measure dist move by air bubble and time taken

Question 18

how to calculate rate of transpiration

Answer 18

.calculate area of capillart tube = pi r^2

.times the area by distance moved = volume of water uptake

.divide by time taken

Question 19

how does water move through plants

Answer 19

.enters plants root hair cells via osmosis
.moves through the cytoplasm or cell walls towards xylem
.xylem transports water from roots to leaves

Question 20

what is the apoplast pathway

Answer 20

.water moves through spaces in the cell walls and between cells

Question 21

what is the symplast pathway

Answer 21

.water moves from cell to cell through cytoplasm and plasmodesmata

Question 22

what does the casparian strip do

Answer 22

forces water molecules to take the symplast pathway to go to the xylem

Question 23

how does water travel upwards through the xylem

Answer 23

.cohesion = H-bonds causes water to stick together and move as one column

adhesion = H-bonds between water molecules and cellulose in xylem vessel walls pulls water upwards

.transpiration pull = from evaportaion of water at leaves

Question 24

leaf structure

Answer 24

.upper epidermis with waxy cuticle- reduces water loss from the surface
.palisade mesophyll cells- carry out photo
.spongy mesophyll cells- carry out photo
.stomata
.lower epidermis

Question 25

what are the adaptation of leaf for gas exchange

Answer 25

.air spaces =
.network for gases to quicly diffuse in and out and access photosynthesising cells

.mesophyll cells =
.provides large SA for gases to diffuse

.stomata =
.open up allowing inward diffusion of CO2 and outward diffusion of O2
.close to minimise water loss

Question 26

how do plants limit water loss

Answer 26

.waxy cuticle = waterproof
.guard cells = close stomata

Question 27

what are xerophytes

Answer 27

.plants that are adapted to live in dry enviroments

Question 28

adaptations of xerophytes

Answer 28

.thick waxy cuticle = reduces water loss
.rolling of leaves = encloses stomata to reduce air flow and evporation of water
.hairs = trap moist air
.sunken stomata in pits = reduce air flow and transpiration
.needle like leaves = reduce SA

Question 28

translocation steps

Answer 28

.at soruce, sucrose is actively loaded into sieve tube elements from companion cells
.this decreases water potential in sieve tube elements
.water enter sieve tube elements from xylem and companion cells via osmosis
.this increases hydrostatic pressure in sieve tube elements at the source
.at sink, solutes are actively removed from sieve tube elements
.this increases water potential in sieve tube elements in sink
.water leaves phloem by osmosis decreasing hydrostatic pressure at the sink
.this creates a pressure gradient, pushing solutes from source to sink

Question 28

how does active loading into the phloem work at the source

Answer 28

.hydrogen ions are actively transported out of companion cells into source cells

.H+ is co-transported along the concentration gradient back into companion cells with surcrose

.sucrose then diffuses along concentration gradient through plasemodesmata from companion cells to sieve tube elements