Transport in Plants

Question 1

why do plants require a transport system

Answer 1

to ensure all cells receive a strong supply of nutrients
important as substances travel against gravity up the stem

Question 2

relate the structure of xylem to its function

Answer 2

long continuous columns of dead tissue allowing transportation of water
pits allow water to move sideways between vessels
thickened with lignin providing structural support

Question 3

relate the structure of phloem to its function

Answer 3

sieve tube elements transport sugars around plant
companions cells designed for active transport of sugar into tubes
plasmodesmata allow flow of substances between cytoplasm of different cells

Question 4

describe the structure and function of vascular system in the roots

Answer 4

consists of xylem and phloem
xylem arranged in an x shape to provide resistance against force
surrounded by endodermis which are a water supply

Question 5

describe the structure and function of vascular system in stem

Answer 5

xylem on the inside bundle to provide support and flexibility
phloem on the outside
layer of meristem cells that produce new xylem and phloem

Question 6

describe the structure and function of vascular system in leaves

Answer 6

forms the midrib and veins
involved in transport and support

Question 7

define transpiration

Answer 7

evaporation of water from the leaves of plants
consequence of gas exchange as occurs when the stomata open to exchange o2 and co2

Question 8

name the factors that affect the rate of transpiration

Answer 8

increased light intensity increases transpiration
high temperature increases transpiration
increased wind increases transpiration increased humidity decreases transpiration
waxy cuticle prevents transpiration

Question 9

how can we measure transpiration

Answer 9

potometer
plant cutting is placed in a water filled tube with an air bubble
rate is calculated by measuring movement of air bubble over time

Question 10

explain the apoplast pathway

Answer 10

method of osmosis through root hair cells
water moves through cell walls and intercellular spaces
pathway can only be used up until the casparian strip

Question 11

explain the synplast pathway

Answer 11

water moves through cytoplasm via plasmodesmata
water must be actively transported into cells to begin this

Question 12

explain the cohesion tension theory

Answer 12

water molecules form hydrogen bonds with other molecules causing them to stick together
surface tension of water also creates effect
as water lost through transpiration, more can be drawn up stem

Question 13

give adaptations of xerophytes to live in dry conditions

Answer 13

small, rolled leaves
densely packed mesophyll
thick waxy cuticle
closed stomata
hairs to trap moisture

Question 14

give adaptations of hydrophytes to live in wet conditions

Answer 14

thin or no waxy cuticle
air spaces for buoyancy
open stomata
wide, flat leaves

Question 15

summarise translocation

Answer 15

sucrose produced in leaves actively loaded into sieve tube elements
lowers water potential causing water to move in to the phloem from the xylem creating high hydrostatic pressure mass flow of solutes down a pressure gradient to the sink

Question 16

describe the process of adhesion

Answer 16

attraction of water molecules to the impermeable walls of xylem tissue

Question 17

explain why large multicelluar plants need a transport system

Answer 17

long diffusion distance and diffusion isn’t fast enough
small surface area:volume

Question 18

explain the benefit to plants of internal transport systems

Answer 18

surface area:volume too small
ensures molecules reach all tissues
allows high metabolic rate

Question 19

what type of cell makes up the cambium

Answer 19

meristem

Question 20

explain how the casparian strip prevents ions from reaching xylem of the plant by apoplast pathway

Answer 20

casparian strip is impermeable to water so forces water to pass through cell surface membrane

Question 21

how does water enter the endodermis

Answer 21

ions enter against the concentration gradient by active transport which reduces water potential of endodermal cells
water moves by osmosis down the concentration gradient

Question 22

state one similarity between xylem and phloem

Answer 22

both made of cells joined end to end

Question 23

state two differences between xylem and phloem

Answer 23

xylem vessels contain lignin but phloem only contain cellulose
xylem have a wide lumen but phloem have a narrow lumen

Question 24

state the function of pits in xylem tissue

Answer 24

lateral movement of water

Question 25

how can a potometer be used to calculate a more accurate rate of transpiration

Answer 25

potometer is air tight and uses dry leaves
measures the rate of transpiration by measuring movement of air bubbles per time interval
stem cut underwater and mean volume of water loss is calculated

Question 26

suggest why it is beneficial for the plant for carbohydrates to be transferred throughout plant as sucrose

Answer 26

sucrose is soluble so can be transported in sap
sucrose is relatively metabolically inactive so none used up during active transport