3.1.3 Transport in Plants

Question 1

what substances do plants transport over long distances

Answer 1

diffusion not sufficient = diffusion distance is too large
water, mineral ions: from roots to leaves (remain turgor, photosynthesis, cooling mechanisms)
sucrose, amino acids: transported from source to sink

Question 2

what substances do plants transport over short distances

Answer 2

oxygen, carbon dioxide
leaves are thin = short diffusion distance = can rely on diffusion
plants are not very active = have lower metabolic rates than animals = lower demand for oxygen
leaves and roots are adapated for gas exchange

Question 3

explain, using examples of transported substances, why multicellular plants need transport systems

Answer 3

large size req. transport over long distances
diffusion distance too great so cannot rely of diffusion alone
small SA: V ratio
transport water/ions from roots to leaves/other parts of the plant
transport sucrose from source to sink
transport hormones produced in one part to the site of action

Question 4

four types of cells that compose the xylem tissue

Answer 4

xylem vessles - dead
xylem tracheids - dead
xylem fibres - dead
xylem parenchyma - living

Question 5

xylem vessles

Answer 5

dead
water conducting cells: transport water and mineral ions from roots to leaves
lignen = structural support function within plants
continuous tube - no end walls
more effecient at water conduction than tracheids

Question 6

xylem tracheids

Answer 6

dead
water conducting cells: transports water and mineral ions from roots to leaves
lignen = structural support function within plants
tapered ends with perforations in end walls
less efficient at water conduction - used for water storage

Question 7

xylem fibres

Answer 7

dead
elongated cells - lignified
support functions
no water transport functions

Question 8

xylem parenchyma

Answer 8

living
packing tissue
support functions
no water transport functions

Question 9

functions of the xylem

Answer 9

transport of water and minerals
provide mechanical support (lignification of cellulose cell walls)

Question 10

lignified vs non lignified cellulose cell wall

Answer 10

L - impermable to water
NL - normally permeable

Question 11

lumen of xylem vessel

Answer 11

hollow - less/no resistance to flow of water

Question 12

thick lignified wall of xylem vessel

Answer 12

lignin adds strength + rigidity
prevents collapse under the large tension/ negative pressure/ transpiration pull
waterproof, impermeable to water so it doesn’t leak out of xylem

Question 13

non lignified pit of xylem vessel

Answer 13

no lignin
allows lateral flow of water netween xylem vessels
allows water to leave xylem or bypass a blockage

Question 14

spirals of lignin running around lumen of xylem

Answer 14

provides flexibility to prevent stem breakage during growth and movement

Question 15

companion cells

Answer 15

service and maintain sieve tube elements

Question 16

function of plasmodesmata

Answer 16

connect companion cells and sieve tube elements
facilitat movement of substances between cells
enables cell signalling

Question 17

vascular tissue

Answer 17

comprised of xylem and phloem

Question 18

how is vascular tissue in the stem adapted to its function

Answer 18

lignin - provides support, prevents collapse, prevents water loss
spiral thickening - allows flexibility
hollow vessels - minimises resistance to the flow of water
bordered pits - allows passage of water between vessels