The need for transport systems

Specialisations of xylem vesselsLignified To provide waterproofing and to increase mechanical strength Dead A result of the lignification, this means that cytoplasmic contents are absent

The need for transport systems

Why do large organisms have specialised

transport systems while smaller ones do not?

With large size comes a small SA:vol ratio The consequence of this is specialised organs of

exchange and with these come a need to

transport materials between the cells and these sites of exchange which is met with a transport

Achievements of plant transport

Water transport

From roots to leaves

Achievements of plant transport

Water transport

From roots to leaves

Nutrient (sucrose / amino acid) transport

From leaves throughout the plant

Achievements of plant transport

Water transport

From roots to leaves

Nutrient (sucrose / amino acid) transport

From leaves throughout the plant

Ion transport

From roots to growing points

• The term ‘xylem’ refers to a tissue made up

from the following cell types: vessels, fibres,

tracheids and xylem parenchyma

• Xylem vessels transport water (the

‘transpiration stream’) and mineral ions

absorbed by the roots.

• Flow is unidirectional (upward) ‘pulled’ by evaporation from the leaves

Specialisations of xylem vessels

Lignified To provide waterproofing and to increase mechanical strength

Dead

A result of the lignification, this means that cytoplasmic contents are absent thus reducing resistance to water flow

Pitted To allow lateral movement of water from the xylem

Made from fused cells

which have lost their

internal walls

To reduce resistance to water flow and to allow the cohesive and adhesive forces between water molecules to aid transpiration

Distributed around the

periphery of the stem

To increase resistance of the stem to bending (lateral) forces

Held in the middle of the

root To increase resistance to pulling forces

Held in the midrib of To provide support and help present a flat surface for

photosynthesis

Specialisations of xylem vesselsLignified To provide waterproofing and to increase mechanical strength

Dead

A result of the lignification, this means that cytoplasmic contents are absent thus reducing resistance to water flow

Pitted To allow lateral movement of water from the xylem

Made from fused cells

which have lost their

internal walls

To reduce resistance to water flow and to allow the cohesive and adhesive forces between water molecules to aid transpiration

Distributed around the

periphery of the stem

To increase resistance of the stem to bending (lateral) forces

Held in the middle of the

root To increase resistance to pulling forces

Specialisations of xylem vesselsLignified To provide waterproofing and to increase mechanical strength

Dead

A result of the lignification, this means that cytoplasmic contents are absent thus reducing resistance to water flow

Pitted To allow lateral movement of water from the xylem

Made from fused cells

which have lost their

internal walls

To reduce resistance to water flow and to allow the cohesive and adhesive forces between water molecules to aid transpiration

Distributed around the

periphery of the stem

To increase resistance of the stem to bending (lateral) forces

Held in the middle of the

root To increase resistance to pulling forces

Held in the midrib of To provide support and help present a flat surface for

photosynthesis

Specialisations of xylem vesselsLignified To provide waterproofing and to increase mechanical strength

Dead

A result of the lignification, this means that cytoplasmic contents are absent thus reducing resistance to water flow

Pitted To allow lateral movement of water from the xylem

Made from fused cells

which have lost their

internal walls

To reduce resistance to water flow and to allow the cohesive and adhesive forces between water molecules to aid transpiration

Distributed around the

periphery of the stem

To increase resistance of the stem to bending (lateral) forces

Held in the middle of the

root To increase resistance to pulling forces

Specialisations of xylem vesselsLignified To provide waterproofing and to increase mechanical strength

Dead

A result of the lignification, this means that cytoplasmic contents are absent thus reducing resistance to water flow

Pitted To allow lateral movement of water from the xylem

Made from fused cells

which have lost their

internal walls

To reduce resistance to water flow and to allow the cohesive and adhesive forces between water molecules to aid transpiration

Distributed around the

periphery of the stem

To increase resistance of the stem to bending (lateral) forces

Held in the middle of the

root To increase resistance to pulling forces

Held in the midrib of To provide support and help present a flat surface for

photosynthesis

Specialisations of xylem vesselsLignified To provide waterproofing and to increase mechanical strength

Dead

A result of the lignification, this means that cytoplasmic contents are absent thus reducing resistance to water flow

Pitted To allow lateral movement of water from the xylem

Made from fused cells

which have lost their

internal walls

To reduce resistance to water flow and to allow the cohesive and adhesive forces between water molecules to aid transpiration

Distributed around the

periphery of the stem

To increase resistance of the stem to bending (lateral) forces

Held in the middle of the

root To increase resistance to pulling forces

Specialisations of xylem vesselsLignified To provide waterproofing and to increase mechanical strength

Dead

A result of the lignification, this means that cytoplasmic contents are absent thus reducing resistance to water flow

Pitted To allow lateral movement of water from the xylem

Made from fused cells

which have lost their

internal walls

To reduce resistance to water flow and to allow the cohesive and adhesive forces between water molecules to aid transpiration

Distributed around the

periphery of the stem

To increase resistance of the stem to bending (lateral) forces

Held in the middle of the

root To increase resistance to pulling forces

Held in the midrib of To provide support and help present a flat surface for

photosynthesis

Exchanging water between

A closer look at the cell

boundaries…

Cellulose cell wall

Cell membrane Cytoplasm

Vacuole membrane (tonoplast)

Vacuole Plasmodesmata

Middle lamella

• Small holes in the cell walls between adjacent cells

• Membrane flows through from cell to cell

• Cytoplasm is continuous between the cells

• Some have threads of smooth ER passing

through increasing communication further

Three modes of water transfer

between cells…

Apoplast route

Three modes of water transfer

between cells…

Apoplast route

Water flows within the cell walls

Cellulose if freely permeable to water

Relies on the cohesive forces of water (H-bonds).

cell has no control over water movement since the water never enters the living contents of the cell

(protoplasm).

By far the most significant route (accounts for ~80%

of water flow between cells)

The Apoplast Route

Cellulose cell wall

Cell membrane Cytoplasm

Vacuole membrane (tonoplast)

Vacuole Plasmodesmata

Middle lamella

Three modes of water transfer

between cells…

Apoplast route

Symplast route

Three modes of water transfer

The Symplast Route

Cellulose cell wall

Cell membrane Cytoplasm

Vacuole membrane (tonoplast)

Vacuole Plasmodesmata

Three modes of water transfer

between cells…

Apoplast route

Symplast route

Vacuolar route

Three modes of water transfer

The Vacuolar Route

Cellulose cell wall

Cell membrane Cytoplasm

Vacuole membrane (tonoplast)

Vacuole Plasmodesmata

Middle lamella

The transpiration stream

Evaporation of water from the spongy mesophyll

tissue…

…draws water across the leaf by apoplast, symplast and vacuolar routes…

…and out of the xylem in the leaves.

This pulls water up the continuous column of water in the xylem (cohesive forces stop the column from

The endodermis

Root cortex

Endodermis Xylem vessel

The endodermis

• Endodermal cells have a waterproof layer

(made of suberin) impregnated into their cell wall called the Casparian strip

Band of suberin

The endodermis

• The Casparian strip blocks the apoplast route and

so any water passing though the endodermis

must pass through symplast route.

• This gives the plant control of water and mineral uptake since both must pass across a membrane

Major water loss is an unavoidable consequence of leaf

function

• Gas exchange is critical for photosynthesis

• Gas exchange requires a huge, moist surface area (provided by the spongy mesophyll)

• The gas exchange surface must be ventilated (achieved by diffusion though air spaces and open stomata)

Major water loss is an unavoidable consequence of leaf

function

• Gas exchange is critical for photosynthesis

• Gas exchange requires a huge, moist surface area (provided by the spongy mesophyll)

• The gas exchange surface must be ventilated (achieved by diffusion though air spaces and open stomata)

Major water loss is an unavoidable consequence of leaf

function

• Gas exchange is critical for photosynthesis

• Gas exchange requires a huge, moist surface area (provided by the spongy mesophyll)

• The gas exchange surface must be ventilated (achieved by diffusion though air spaces and open stomata)

Measuring transpiration – the

potometer

• Measures uptake of water into a plant

• Makes the assumption that uptake is the same

as evaporative loss

• Some have syringes, used to calibrate or reset the apparatus

Measuring transpiration – the

– All joins must be air/water tight

– Bubbles are eliminated from capillary tube

Here’s one from an exam paper…

Environmental factors affecting

Can you make predictions on a graph like this?

Phloem – transverse section

Phloem within the

vascular bundle

Sieve tube

Phloem parenchyma

Phloem – longitudinal section

Most of the cytoplasmic contents of the sieve tube are removed and its metabolic

demands are met

by the companion cells associated with it

The sieve plates are responsible for

pumping materials from cell to cell

This process is

and controlled by threads of protein which pass through

Phloem – longitudinal section

The transfer cell

is a key cell in loading sieve tubes with sucrose

It has a highly folded membrane and many

mitochondria to aid active transport

into the sieve tube

Phloem loading

Mineral uptake and transport

Uptake

• Most minerals are taken up from the soil by

active transport by root hair cells

• These cells have a large surface area for

uptake

• In certain soils some ions are taken up

passively (e.g Ca2+ in lime soils)

Mineral uptake and transport

Mineral uptake and transport

Mineral uptake and transport

Mineral uptake and transport

Transport

to the endodermis

are transported in the transpiration stream

(lateral movement) for more selective transport

Analysing data - absorption of

mineral ions

• Root tissue from trees can be extracted and cultured in an ion-rich medium.

• Its mineral absorbing activity can be

measured by analysing the contents of the

cytoplasm over time.

• Two such groups of such tissue were cultured and their potassium (K+) content recorded

over a 150 minute period.

Analysing data - absorption of

mineral ions

• One group was cultured as above in air, a

Sealed chamber with controlled atmosphere

Root tissue blocks in culture solution

1) Compare the results of the two groups [3]

2) What is the K+ concentration of the culture

solution? Explain your answer [3]

3) List three factors, other than K+ concentration,

which must be controlled in this experiment [3]

4) Explain the differences in K+ absorption

between the two groups [4]