UNIT 8: TRANSPORT IN PLANTS
Xylem vessels
Made of hollow, dead cells joined end to end, create
long tube
Contain no cytoplasm or nuclei
Walls are made of lignin, strong to keep the plant
upright
Water and minerals flow
upwards from the root to
the leaves
Thick cell walls
Phloem tube
Made of living cells joined end to end called sieve
tube element
Walls are not completely broken down, form sieve
plates which have small holes in them
Thin cells contain cytoplasm, no nucleus
Each sieve tube element has a companion cell
which has nucleus and other organelles to supply
Transport sucrose and amino acids up and down
Transpiration stream: path way of water
from root hairs of a plant up the root and stem
and out of leaves into the atmosphere
1. Water moves into a root hair cells by
osmosis
2. Cohesion/adhesion of water molecules
creates transpiration pull (tension)
3. Water moves up xylem, into leaves by osmosis, creating a transpiration
stream
4. Loss of water from leaf by transpiration lowers water potential + pressure at
top -> water flows up
5. Evaporation from surfaces of cells
Transpiration: the loss of water from plant leaves by evaporation of water at the
surface of the mesophyll cells followed by the loss of water vapour through the
stomata
Wilting occurs if water loss > uptake – cells become flaccid, tissues become
limp and plant is no longer supported -> decrease surface area, prevent water
loss, conserved for other processes
Structure Function
Xylem vessels
Made of hollow, dead cells joined end to end, create
long tube
Contain no cytoplasm or nuclei
Walls are made of lignin, strong to keep the plant
upright
Water and minerals flow
upwards from the root to
the leaves
Thick cell walls
Phloem tube
Made of living cells joined end to end called sieve
tube element
Walls are not completely broken down, form sieve
plates which have small holes in them
Thin cells contain cytoplasm, no nucleus
Each sieve tube element has a companion cell
which has nucleus and other organelles to supply
Transport sucrose and amino acids up and down
Transpiration stream: path way of water
from root hairs of a plant up the root and stem
and out of leaves into the atmosphere
1. Water moves into a root hair cells by
osmosis
2. Cohesion/adhesion of water molecules
creates transpiration pull (tension)
3. Water moves up xylem, into leaves by osmosis, creating a transpiration
stream
4. Loss of water from leaf by transpiration lowers water potential + pressure at
top -> water flows up
5. Evaporation from surfaces of cells
Transpiration: the loss of water from plant leaves by evaporation of water at the
surface of the mesophyll cells followed by the loss of water vapour through the
stomata
Wilting occurs if water loss > uptake – cells become flaccid, tissues become
limp and plant is no longer supported -> decrease surface area, prevent water
loss, conserved for other processes
Structure Function
