B9 - transport in plants

Question 1

metabolic demands = reason for transport system

Answer 1

water - transport medium, turgor, photosynthesis
mineral ions- nitrates, magnesium
hormones- made in one part of plant, needed in another
sugars - made in photosynthesis, needed for respiration

Question 2

phloem

Answer 2

• living tissue
• transport assimilates
• flows up & down
• companion cells w/ lots of mitochondria provide energy for sieve tube elements
• perforated walls form sieve plates
• organelles break down when cells join

Question 3

xylem structure

Answer 3

• thick lignified wall
  -non-lignified pits = water leave to surrounding cells
• lignin spirals around lumen of xylem vessels so don’t collapse under transpiration pull

Question 4

symplast pathway

Answer 4

LIVING plant cell cytoplasm connected through plasmodesmata

• water diffuse into RHC from soil
• cells further up from roots have lower water potential.
• water moves into sap in the vacuole through the tonoplast of adjacent cells
• water leaves to next cell = water potential drops = more water follows in behind = maintain steep concentration gradient.

Question 5

apoplast pathway

Answer 5

movement through DEAD cell wall & intercellular spaces
- as more water enters xylem, more water pulls through the apoplast behind due to cohesion of water molecules
- creates tension & continuous water flow through cell wall.

Question 6

endodermis

Answer 6

cells surrounding vascular tissue

Question 7

casparian strip

Answer 7

waterproof layer of suberin (waxy) that runs around endodermal cells
- apoplast pathway forced into symplast pathway, so toxic solutes can’t pass through selectively permeable cell surface membranes as have no receptors on carrier proteins.

Question 8

endodermal -> xylem

Answer 8

• endodermal cells more dilute
• mineral ions actively transported into xylem
• lowers water potential so water follows by osmosis
• cause root pressure & pushes water up xylem

Question 9

issues with potometer

Answer 9

• can’t directly measure transpiration/water evaporation from leaves
• measures rate of water uptake
• But some water used by cells in photosynthesis = not accurate

Question 10

Why is glucose made in photosynthesis transported around plant as sucrose?

Answer 10

sucrose = non-reducing & less reactive = less liable to enzyme breakdown

Question 11

aerenchyma

Answer 11

specialised parenchyma
- large air spaces formed from apoptosis in parenchyma, making stem/leaves more buoyant
- in hydrophytes