3.3.2 transport tissues

Question 1

function of xylem vessels

Answer 1

transport water & mineral ions from root to leaves/other parts of plant

Question 2

how structure relates to function of xylem vessels

Answer 2

consists of:
- vessels = carry water & dissolved mineral ions
- fibres = support plant
- living parenchyma cells = act as packing tissue to separate/support vessels

Question 3

impact of lignin on the xylem vessel

Answer 3

• as xylem vessels develop, lignin impregnates the walls which makes them waterproof & kills cells
• end walls & cell contents decay
• leaves long column of dead cells

Question 4

describe the role of lignin within xylem vessels

Answer 4

• make them waterproof
• strengthens vessel walls & prevents collapse
• keeps vessel open even when water in short supply
• lignin thickening forms patterns which prevent vessel becoming too rigid & allows some flexibility
• some places: lignification incomplete = gaps in cell wall (pits/bordered pits)

Question 5

patterns formed by lignin

Answer 5

• spiral
• annular (rings)
• reticulate (network of broken rings)

Question 6

what do pits/bordered pits in xylem vessels allow

Answer 6

• bordered pits in 2 adjacent vessels aligned to allow water to leave 1 & pass to another
• allow water to leave xylem & pas into living parts of plant

Question 7

adaptations of xylem to function

Answer 7

• made from dead cells aligned end to end = continuous column
• tubes are narrow = water column doesn’t break easily & capillary action is effective
• bordered pits (lignified walls) = water move sideways 1 vessel to another
• lignin deposited in spiral/annular/reticulate patterns = xylem can stretch as plant grows & enables stem/branch to bend

Question 8

why is the flow of water not impeded in xylem vessels

Answer 8

• no cross-walls
• no cell contents, nucleus or cytoplasm
• lignin thickening prevents wall collapsing

Question 9

structure/function of phloem

Answer 9

• tissue used to transport assimilates (eg. sucrose, amino acids)
• sucrose dissolved in water forming sap
• consists of sieve tubes (made up of sieve tube elements & companion cells)

Question 10

structure/function of sieve tube elements in phloem vessels

Answer 10

• elongated sieve tube elements lined end to end = sieve tubes
• contain no nucleus & little cytoplasm = space for mass flow of sap
• ends of sieve tube elements = perforated cross-walls called sieve plates
• perforations in sieve plates = movement of sap from 1 element to next
• sieve tubes have thin walls

Question 11

structure/function of companion cells in phloem vessels

Answer 11

• in between sieve tubes
• large nucleus & dense cytoplasm
• numerous mitochondria producing ATP for active processes
• carry out metabolic processes needed to load assimilates actively into sieve tubes