Transport in plants

Transports water and minerals

Consists of cells specialised for transporting fluids by mass flow

Transports dissolved assimilates

Layer of dividing cells (called pericycle)

Plants with 2 seed leaves and a branching pattern of veins in the leaf

Cells that help to load sucrose into sieve tubes

Make up the tubes in phloem tissue that carry sap up and down plant

Tubes which carry water up a plant

Gaps in cell wall containing cytoplasm that connects two cells

Device that can measure rate of water uptake as a leafy stem transpires

The loss of water vapour from the aerial parts of a plant, mostly through stomata in leaves

The attraction between water molecules and the walls of the xylem vessel

The attraction between water molecules caused by hydrogen bonds

A plant adapted to living in water or where ground is very wet

Plant adapted to living in dry conditions

Substances that have become part of the plant

Part of plant that loads materials into transport systems

The transport of assimilate throughout a plant

Part of plant where assimilates are removed from transport system

Puncture experiments

Ringing experiments

Radioactive tracers

Aphid stylet experiments

If phloems punctured, sap oozes out showing there's a high pressure in phloem

If xylem punctured, airs sucked in showing low pressure in xylem

Waters pulled up xylem, sap pulled up phloem

Ring of phloem and bark removed. Swelling above ring, reduced growth below ring, leaves unaffected. Shows sugars are transported down phloem

Radioactive isotopes can trace movement of sugars, ions or water and their rate of transport

Aphids suck phloem sap through stylets. Due to high pressure, once punctured, sap moves out of phloem into xylem

Photosynthesis transported into sieve tube from comp cells by ATP

Decreases causing H2O to move in by osmosis from xylem

Hydrostatic pressure in phloem

Moves down phloem to areas of less pressure

Removed from phloem by AT

Xylem, xylem have lower WP

Back into xylem from phloem by osmosis

Up xylem by tension from transportation

In phloem

Sugars (sucrose) and AA

Source

Part of the plant that loads assimilates into sieve tubes

Sink

Part of the plant that removes assimilates from sieve tubes

H+ ions actively pumped out of comp cells using energy from ATP

High conc of H+ ions causes facilitated diffusion back into comp cells. Sucrose carried with H+ ions through cotransport proteins in plasma membrane

Increasing conc of sucrose in comp cells causes it to diffuse through plasmodesmata into sieve tube elements

Active as involves use of ATP in comp cells

Causes an increase in conc outside cell and decrease inside comp cell, as result creating conc gradient

The proteins only allow the movement of H+ ions into the cell if accompanied by sucrose molecules

Secondary A.T

As results from A.T of the H+ ions into cell and moves sucrose against conc gradient

Mass flow

Up or down as required

Difference in hydrostatic pressure between the 2 ends of the tube which produces pressure gradient

Enters at source, increasing hydrostatic pressure

Leaves at sink, reducing hydrostatic pressure

Makes WP inside sieve tube more negative

As result, water molecules move into elements by osmosis form surrounding tissue which increases the hydrostatic pressure in sieve tube at source

Leaves are source as photosynthesise

Root is sink as stores sugars

Roots are source as stores sugars

Leaves are sinks as uses sugar for growth

Flowers

Roots

Fruits

Buds

Leaves

Respiration and growth or converted to starch for storage

Makes WP less negative so water moves out of sieve tube into surrounding cells, reducing the hydrostatic pressure in phloem at sink

1. Loaded into sieve tube element and reduces WP

2. Osmosis and increases hydrostatic pressure in elements

3. Tube from higher hydro pressure at source to lower at sink

4. Sieve tube by surrounding cells and increases WP in tube

5. Out of tube and reduces hydro pressure

Entering - Increases hydrostatic pressure

Leaving - decrease hydrostatic pressure

Therefore pressure gradient along tube and sap flows from higher to slower pressure

Rolled leaves

Reduces leaf SA

Thick waxy cuticle

Deep root system

Sunken stomata

Hairy leaves

Accumulation of solutes in leaves

Many large air spaces in leaves

Stomata on upper epidermis

Stems have large air spaces

Specialised structures (hydathodes) which release water droplets

Reducing water loss

Replacing water loss

Plants living on land

Access to water

By transpiration as plants exchange gases with atmosphere via stomata

Waxy cuticle on leaf - reduces H2O loss by evaporation through epidermis

Stomata found on under surface - reduces evaporation due to direct heating from sun

Stomata closed at night when no light for photosynthesis

Deciduous plants lose leaves in winter when temp too low for photosynthesis

Sand dunes

Harsh conditions as H2O drains quickly, sand salty and exposed to windy conditions

Xerophyte

Leaf rolled longitudinally so air trapped inside

Thick waxy cuticle on upper epidermis

Stomata on lower epidermis

Spongy mesophyll very dense with few air spaces

Outer epidermis contain small, thick walled cells

Tiny hairs

Stomata in pits in L.E

Air becomes humid which reduces H2O lost from leaf

Can roll more tightly in dry conditions

Reduces evaporation

Protected by enclosed air spaces

Reduces air movement and therefore loss of H20 vapour

Less S.A for evaporation

Trap water vapour, reducing WP gradient between leaf and air

Xerophyte

Succulent

Stores H2O in stem which becomes fleshy and swollen

Stem often rubbed or fluted to expand when H2O available

Leaves reduced to spikes - reduces SA so less water lost by transpiration

Green stem for photosynthesis

Roots widespread - take advantage of any rain that falls

Close stomata when low H2O availability - reduces H2O lost

Low WP inside leaf cells - achieved by maintaining high salt concentration in cells. Reduces evaporation of H2O as WP gradient between cells and lead air spaces reduced

Long tap roots which can reach water deep underground

Hard to get O2 to submerged tissues

Need to keep leaves in sunlight for photosynthesis

Many large air spaces in leaf

Stomata on upper epidermis

Leaf stem has many large air sapces

Keeps leaves afloat so in air and can absorb sunlight

Exposed to air to allow gaseous exchange

Helps with buoyancy and also allows O2 to diffuse quickly to roots for aerobic respiration

Into water or air with very high humidity

Transpiration stream stops and plants can't transport mineral ions up to leaves

Contains hydathodes at tips or margins of leaves which can release H2O droplets which then evaporate from leaf surface

Potometer

Water uptake/transpiration

Yes

200-250 micrometers

90%

10%

Waxy cuticle

It opens to allow gaseous exchange for photosynthesis

1. Xylem and moves by osmosis into cells of spongy mesophyll. May also pass along cell wall Vis apoplast pathway

2. Cell walls of spongy mesophyll

3. Diffusion out through open stomata - relies on difference in conc of vapour in leaf compared to outside (known as water vapour potential grad). Must be higher WP inside leaf than out

Transports useful mineral ions up plants

Maintains cell turgidity

Supplies H2O for growth, cell elongation and photosynthesis

Supies H2O that as evaporates, keeps plant cool

Light intensity

Temp

Relative humidity

Air movement (wind)

H2O availability

Atmospheric pressure

SA:V ratio

Thickness of cuticle

Stomata size

Stomata frequency

Position of stomata

πr²l

Decreasing atmospheric pressure= increased rate of transpiration a water vapourises more easily

In light, stomata opens for gaseous exchange. Higher intensity= higher rate as more open

Increases K.E

Higher temp increases rate in 3 ways:

1. ↑ rate of evaporation from cell surfaces so water vapour potential in leaf rises

2. ↑ rate of diffusion through stomata as H2O molecules have more KE

3. ↓ relative water vapour potential in air, allowing more rapid diffusion out of leaf

Lower humidity outside leaf = higher WP grad

Higher humidity in air decreases rate of loss as smaller H2O vapour potential grad between air sapces I'm leaf and air outside

Air moving outside will carry away vapour that's diffused out - will maintain high water vapour pot grad

If little water in soil, plant can't replace lost water. If insufficient water in soil, stomata close and leave wilt, guard cells flacid

Leaf needs higher WP than air

Transports water and minerals up plant

Xylem tubes help support plant

Dead cells

Vessels to carry water and dissolved mineral ions

Fibres to help support plant

Living parenchyma cells which act as packing tissue to seperate and support vessels

Lignin impregnates walls of cells making the walls waterproof

Kills the cells. End walls and contents of cell decay, leaving long column of dead cells with no contents (creating a xylem vessel)

Strengths vessel walls and prevents vessels from collapsing (keeps them open even when water may be in short supply)

Form patters in cell walls - either annular (rings) or spiral or reticulate (network of broken rings)

Prevents vessel from being too rigid and allows some flexibility in branch/stem

Leaves gaps in cell wall - gaps form pits of bordered pits

To allow water to leave one vessel and pass into next and allows water to leave xylem and pass into living parts of plant

1. Dead cells aligned end to end to form continuous column

2. So water column doesn't break easily and capillary action can be effective

3. Lignified walls allow water to move sideways from one vessel to another

4. Spiral, annular or reticulate patterns allow xylem to stretch as plant grows and enables stem/branch to bend

No cross walls

No cell content, nucleus or cytoplasm

Lignin thickening prevents wall from collapsing

By fine stands of cytoplasm through gaps in cell wall

Allows communication and flow of substances between the cells

Between sieve tubes

Carry out metabolic processes needed to load assimilates actively into the sieve tubes

Large nucleus

Dense cytoplasm

Many mitochondria (to produce ATP needed for active processes)

By dissolving sucrose in water

Sieve tubes and comp cells

Very thin

No nucleus

Little cytoplasm

Allows more space for mass flow of sap to occur

Elongated elements lined up end to end

Perforated cross-walls called sieve plates

Allow movement of sap from one element to next

Pores and plasmodesmata

Smaller SA:V ratio

Regular supply of O2, H2O, nutrients and minerals

Low as plants not very active and respiration rate is low

By diffusion

High

Can absorb water and minerals but can't absorb sugars

Photosynthesis in leaves

To move:

H2O and minerals from roots to leaves

Sugars from leaves to rest of plant

Water and soluble mineral ions

Travel upwards

Phloem and xylem

Assimilates

Travel up or down

2 seed leaves

To give bundle strength and support

At centre

Xyelm in centre (x shape)

Phloem found around arms

Strength to withstand pulling forces to which roots are exposed

Endodermis - helps gets water into xylem vessels

Layer of meristem cells - pericycle

Outer edge of stem

Seperate and discrete

Seperate in young stems

Continuous ring in older stems

Arrangement provides strength and flexibility to withstand bending force which stems and branches are exposed

Xylem towards inside of bundle

Phloem towards outside

Cambium

Layer of meristem cells that divide to produce new phloem and xylem

Midrib and veins of leaf

Branching newtork of veins that get smaller as spread away from midrib

Xylem on top of phloem

Leaf

1. Xylem

2. Phloem

Root

1. Phloem

2. Xylem

Stem

1. Vascular bundle

2. Xylem

3. Phloem

4. Sclerenchyma

1. Transported into xylem - lowers WP in xylem and water follows by osmosis

2. Enables water to move by mass flow, pulled upwards by tension from above

3. Water out of xylem creates low hydrostatic pressure and thus tension

4. Moves water across leaf

5. Water from cell surface

6. Of water vapour out of leaf

Mass flow

Root pressure

Transpiration pull

Capillary action

Endodermis moving minerals into medulla and xylem by AT, drawing water into medulla by osmosis

Rest of medulla builds up and forces water into xylem

As xylem vessels narrow, the forces of attraction (adhesion) can pull the water up the sides of the vessel

Forces of cohesion

The molecules in a column

Pull creates tension which is why xylem needs to be strengthened with lignin as it prevents collapse unde tension

Cohesion between water molecules and tension in column of water

Plant maintaining unbroken column

If one xylem vessel broken, water column can still be maintained via bordered pits

Evaporates from cells lining the cavity above the guard cells (sub-stomatal air spaces)

Lowers the WP in these cells, causing water to enter them by osmosis from neighbouring cells

By osmosis

Pair of guard cells which regulates opening and closing

Small pore called stomatal aperture

1. ATPase to convert ATP to ADP

2. Transported from guard cells via proton pump

3. Potassium ion channels open and influx of K+

4. Cl-

5. Becomes more negative

6. Into guard cells by osmosis

7. Turgor pressure causes stomata to open

Movement of water from soil, through plant, to the air surrounding the leaves

WP grad between soil and air in leaf air spaces

When cells touching, water molecules can move from cell with higher WP to one with lower via osmosis

Cytoplasm and vacuole shrinks and cell no longer turgid

Membrane looses contact with wall (plasmolysis) and tissue now flaccid

Apoplast pathway

Symplast pathway

Vacuolar pathway

Osmosis

Turgid

Strong cellulose cell wall

Measure of tendency of H2O molecules to move from one place to another

0

Cytoplasm contains mineral ions and solutes

Apoplast

Symplast

Vascular

H2O passes through spaces in cell walls and between cells - use adhesion to stick to walls

Doesn't pass through plasma membrane into cell therefore moves by mass flow not osmosis

Evap of water in air spaces creates tension that pulls water from walls

Dissolved mineral ions and salts carried in water

Water enters cytoplasm through membrane then passes through plasmodesmata from one cell to next

Some water lost to air spaces

WP of cytoplasm lower

Water enters cytoplasm through membrane. Also passes through vacuoles

Water

Cytoplasmic bridges

Cell junctions (plasmodesmata) at which cytoplasm of one cell is connected to another through gap in cell wall

Root hair cells

Absorb mineral ions and water from soil

1. Actively absorbed from soil making WP of cytoplasm more -ve

2. Root hair cells by osmosis

3. Across root cortex by osmosis and via apoplast pathway

4. Actively transported into medulla making WP more -ve so water follows by osmosis

Blocked by casparian strip so must enter symplast

Layer cells surrounding medulla and xylem

Starch sheath - contains starch (sign energy's being used)

Between cortex and medulla

Ensures water and dissolved minerals have to pass into cytoplasm through membrane

Actively transports mineral ions from cytoplasm of cortex cells into medulla and xylem

Makes WP of medulla and xylem more -ve so water moves from cortex cells to medulla and xylem by osmosis

Pass back to cortex as apoplast blocked by casparian strip