Transport in Plants
Features of transport systems
A suitable medium in which to carry materials liquid based on water readily
dissolves substances
Form a mass of flow transport transport medium is moved in bulk over large
distances
System of tubular vessels forms a branching network distributing to all parts
Mechanism for moving the transport medium within vessels
Animals muscular contractions of body muscles and heart
Plants evaporation of water and differences in solute concentration
Means of controlling the flow of the transport medium
Transport systems in plants
No need to transport respiratory gases in bulk because:
Most gases used/made are produces/required by the leaves usually has a large
surface area as gases diffuse directly in and out through the stomata
Do not move place to place low energy requirement reduced need for ATP
O2 required for respiration is produced during photosynthesis and CO 2 required is
produced during respiration as well as from the atmosphere
Exchange between organisms and the environment
For exchange to be effective, the surface area of the organism must be large
compared to its volume
Features for specialised exchange systems
Large surface area to volume ratio increases the rate of exchange
Very thin diffusion distance is short materials can cross the exchange
surface rapidly
Partially permeable allow selected materials to cross without obstruction
Movement of the environmental medium e.g. air to maintain a concentration
gradient
Movement of the internal medium e.g. water/sucrose to maintain a
concentration gradient
Features of root hairs
Each root hair is a tiny extension of a root epidermal cell
The root hairs remain functional for a few weeks before dying back to be replaced by
others growing near the tip
The provide a large surface area because they are very long extensions and occur in
their 100s on each of the branches of the root
They have a thin cell surface membrane across which materials can move
They are permeable the epidermal cell is not covered by a waxy cuticle and the
thin cellulose wall is no barrier to the movement of water and ions
The cell surface membrane has specialised protein channels called aquaporins to
allow water to pass through more easily/rapidly
Water enters the root hairs via osmosis soil solution has a high-water potential and
the vacuole and cytoplasm have a high concentration of ions, sugars and organic acids
which lowers its water potential
, The concentration of ions in the root hairs is normally higher than in the soil solution so
movement takes place against a concentration gradient special carrier proteins in the
cell membrane allows movement active transport with help of ATP
Distribution of vascular tissues
Dicotyledonous plants
Vascular tissues form a network of tiny vascular bundles throughout the lamina (blade of
the leaf)
Form a series of side veins that run parallel with one another
These side veins then merge into a central main vein
The main vein runs along the centre of the leaf increasing g in diameter towards the
petiole (leaf stalk)
Within each vein there is an area of xylem towards the upper surface of the leaf and an
area of phloem towards the lower surface
Each vascular bundle consists of:
A cap of sclerenchyma fibres for mechanical support
Outer phloem tissue for transporting organic material\inner xylem tissue to
transporting water and mineral salts and also for mechanical support
A thin layer of tissue called the cambium between the phloem and the xylem
A root
A vascular tissue is situated centrally roots are subject to pulling forces only
Vertical forces are better resisted by a central column of supporting tissue
Xylem is a single star-shaped block of tissue at the centre of the root with phloem
situated in separate groups between each of the points of the star-shaped xylem
A Stem
Vascular bundles are arranged to the outside of the stem
Together with associated sclerenchyma tissue it provides support in herbaceous stems
and transports material
The main forces acting on stems are lateral ones action of wind outer cylinder of
non-continuous tissue supports the stem
Xylem is towards the inside and phloem is towards the outside cambium (layer
between them) is a layer of dividing cells which forms xylem and phloem
Structure and Function of Xylem
Sclerenchyma fibres in the xylem contribute to support whereas the vessels and
tracheids have both support and transport roles
Tracheids are elongated cells with tapering ends. They conduct water but are less well
adapted then vessels. They do not have open ends, so water has to pass from cell to cell
via pits. Usually found in the finest branches of the xylem tissue in the leaves and roots
Xylem vessel elements:
Vary in structure depending on the type and amount of thickening of their cell walls
All are hollow and elongated
As they mature their cell walls become impregnated with lignin, which causes them
to die the end walls break down cells form a continuous tube
Sometimes the lignin forms rings (annular thickening) around the vessel, other times
it forms a spiral or network (reticular thickening)
Features of transport systems
A suitable medium in which to carry materials liquid based on water readily
dissolves substances
Form a mass of flow transport transport medium is moved in bulk over large
distances
System of tubular vessels forms a branching network distributing to all parts
Mechanism for moving the transport medium within vessels
Animals muscular contractions of body muscles and heart
Plants evaporation of water and differences in solute concentration
Means of controlling the flow of the transport medium
Transport systems in plants
No need to transport respiratory gases in bulk because:
Most gases used/made are produces/required by the leaves usually has a large
surface area as gases diffuse directly in and out through the stomata
Do not move place to place low energy requirement reduced need for ATP
O2 required for respiration is produced during photosynthesis and CO 2 required is
produced during respiration as well as from the atmosphere
Exchange between organisms and the environment
For exchange to be effective, the surface area of the organism must be large
compared to its volume
Features for specialised exchange systems
Large surface area to volume ratio increases the rate of exchange
Very thin diffusion distance is short materials can cross the exchange
surface rapidly
Partially permeable allow selected materials to cross without obstruction
Movement of the environmental medium e.g. air to maintain a concentration
gradient
Movement of the internal medium e.g. water/sucrose to maintain a
concentration gradient
Features of root hairs
Each root hair is a tiny extension of a root epidermal cell
The root hairs remain functional for a few weeks before dying back to be replaced by
others growing near the tip
The provide a large surface area because they are very long extensions and occur in
their 100s on each of the branches of the root
They have a thin cell surface membrane across which materials can move
They are permeable the epidermal cell is not covered by a waxy cuticle and the
thin cellulose wall is no barrier to the movement of water and ions
The cell surface membrane has specialised protein channels called aquaporins to
allow water to pass through more easily/rapidly
Water enters the root hairs via osmosis soil solution has a high-water potential and
the vacuole and cytoplasm have a high concentration of ions, sugars and organic acids
which lowers its water potential
, The concentration of ions in the root hairs is normally higher than in the soil solution so
movement takes place against a concentration gradient special carrier proteins in the
cell membrane allows movement active transport with help of ATP
Distribution of vascular tissues
Dicotyledonous plants
Vascular tissues form a network of tiny vascular bundles throughout the lamina (blade of
the leaf)
Form a series of side veins that run parallel with one another
These side veins then merge into a central main vein
The main vein runs along the centre of the leaf increasing g in diameter towards the
petiole (leaf stalk)
Within each vein there is an area of xylem towards the upper surface of the leaf and an
area of phloem towards the lower surface
Each vascular bundle consists of:
A cap of sclerenchyma fibres for mechanical support
Outer phloem tissue for transporting organic material\inner xylem tissue to
transporting water and mineral salts and also for mechanical support
A thin layer of tissue called the cambium between the phloem and the xylem
A root
A vascular tissue is situated centrally roots are subject to pulling forces only
Vertical forces are better resisted by a central column of supporting tissue
Xylem is a single star-shaped block of tissue at the centre of the root with phloem
situated in separate groups between each of the points of the star-shaped xylem
A Stem
Vascular bundles are arranged to the outside of the stem
Together with associated sclerenchyma tissue it provides support in herbaceous stems
and transports material
The main forces acting on stems are lateral ones action of wind outer cylinder of
non-continuous tissue supports the stem
Xylem is towards the inside and phloem is towards the outside cambium (layer
between them) is a layer of dividing cells which forms xylem and phloem
Structure and Function of Xylem
Sclerenchyma fibres in the xylem contribute to support whereas the vessels and
tracheids have both support and transport roles
Tracheids are elongated cells with tapering ends. They conduct water but are less well
adapted then vessels. They do not have open ends, so water has to pass from cell to cell
via pits. Usually found in the finest branches of the xylem tissue in the leaves and roots
Xylem vessel elements:
Vary in structure depending on the type and amount of thickening of their cell walls
All are hollow and elongated
As they mature their cell walls become impregnated with lignin, which causes them
to die the end walls break down cells form a continuous tube
Sometimes the lignin forms rings (annular thickening) around the vessel, other times
it forms a spiral or network (reticular thickening)
