TRANSPORT IN PLANTS OVERALL

GCSE RECAP:

What is the role of Xylem?

What is the role of phloem?

What is the equivalent to vascular tissues in animals?

a) helps with transport of water and dissolves minerals and is made of dead cells

b) helps with transport of sugar and water

c) Blood

Xylem

Tissue in plants conducting water and dissolved materials upwards

Parenchyma:

• Often have a large vacuole for storage

• Association with photosynthetic sections of plants.

• Living tissue - made of cellulose

Collenchyma

• growing sections of plants,

• the cell wall is thickened with cellulose and pectin to resist bending

• living tissue

Sclerenchyma:

• composed of dead cells with very thick cell walls

• support tissue in plants

  • lignified - make them waterproof.

Root:

Xylem vessels are arranged in an x-shape in centre of ________ ________, surrounded by phloem. This provides support to withstand pulling forces which roots are exposed. Vascular bundle surrounded by ___________ which is an out layer of cells which supply xylem vessels with ________. Inside layer of the endodermis is a layer of meristem cells called ________.

vascular bundle

endodermis

water

pericycle

Stem:

Vascular bundles located near _______ ______ of stem. Xylem found towards _________ of each vascular bundle & phloem towards __________. Arrangement provides _________ & _________ to withstand bending forces that stems & branches are exposed. Layer of __________ in between xylem and phloem which is a layer of __________ cells that divide to produce new xylem & phloem tissue.

outer edge

inside

outer

strength

flexibility

cambium

meristem

Leaf:

Vascular bundles form _______ and _______ of a leaf. ______________ leaves have a branching network of _______ that starting at midrib and spreading outwards. These are involved in transport and support of leaves.

midribs veins

Dicotyledonous

veins

Apoplast

space between cells

Symplast:

space inside cells

Casparian Strip

impermeable to water and mineral ions

XYLEM:

Xylems carry _______

• Thick walls lined by ___________.

• Lignin walls proofs the walls and ______________ the vessel.

• Lignin deposit in walls in spiral. __________ or reticulate.

water

lignin

strengthens

annular

Vessels are found in ______________ plants (angiosperms). Lignin tends to laid down in _______ patterns. As tissue develops, the end walls _______ _______ leaving a hollow tube.

flowering

spiral

break down

Tracheid - found in ferns, conifers, and ______________.

They are not found in _______ as this _______ how tall mosses as they can’t transport ______________ any distance.

angiosperms

mosses, limits

water

What are the xylem adaptations:

• Lignin in cell walls

• Narrow tubes

• Pits in lignified cells

• Dead cells end to make a continuous column

• Lignin in spiral, annular or reticulate patterns

• No end walls, no cell contents.

Lignin in cell walls:

strength, support, waterproofing

Narrow tubes:

Allows adhesion with walls of xylem

Pits in lignified cells:

Water can travel to other vessels.

Dead cells end to make a continuous column:

cohesion of water molecules

Lignin in spiral, annular or reticulate patterns

stems can bend without breaking

No end walls, no cell contents

No resistance to upward flow of water

Phloem

Plant tissue containing sieve tube elements and companion cells, translocating sucrose and amino acids from the leaves to the rest of the plant

What is phloem made out of?

made of various cell types

What is bulk?

sieve tubes elements which are the main conducting cells and companion cells

What are other cell types of phloem tissue

Parenchyma

What does parenchyma do?

storage and strengthening fibres

What does mature phloem contain

living cells

Sieve tubes

lose their nucleus and organelles to create space for efficient transport of sugars and other organic compounds

Companion cells

connect to sieve tubes by plasmodesmata

very biochemically active

Apoplast

space between cells

through cells

Symplast

space within cells

through cytoplasm

What is an advantage of apoplast

it is quicker and there is no resistance

Osmosis

the net (passive) movement of water molecules from a region of high water potential to low water potential.

What is the plasmodesmata

strands of cytoplasm through pits in the cell wall joining adjacent cells

Endodermis

A single layer of cells around the pericycle and vascular tissue of the root. Each cell has an impermeable waterproof barrier in its cell wall

Casparian Strip

Impermeable to water and mineral ions so it blocks the movement of water in the apoplast so it moves into the cytoplasm

Water absorption in root hair cells.

For water to be constantly absorbed there needs to be a _____________ concentration gradient.

Plants absorb dissolved mineral ions through _________ ____________ to keep the solute potential high (__________________)

Water diffuses via ____________ into RHC

continuous

active transport

low water potential

osmosis

What are the methods through which water can move up the xylem

Root pressure

Cohesion - adhesion theory

Capillarity

Root pressure:

Ions moved into xylem by _______ _____________.

Lowers _______ _________ in xylem

More moves into _______ by osmosis, which creates ______ pressure

active transport

water potential

root

root

Cohesion Adhesion Theory:

• Water molecules are ________.

• _________ bonds form between water molecules which leads to _________.

• Hydrogen bonds form between water and molecules found in cellulose which leads to __________.

• Both processes come together for _______________.

• Root pressure ________ allows for transpiration

polar

Hydrogen

cohesion

adhesion

transpiration

further

Capillarity:

Cohesion between water molecules generates __________________.

Only operates over ________ distances

surface tension

short

Transpiration

evaporation of water vapour/molecules from the underside of the leaves (stomata)

Where other part of the leaf can the stomata evaporate from?

Epidermis

Where is stomata found

underside of leaves

What is each stomata surrounded by?

Guard Cells

What is the function of guard cells?

change shape to open or close the stomata

How can water enter the guard cells?

Osmosis

Turgid:

Active transport of K+ lowers ________ ____________.

Water enters by ________

Guard cells are ______ which causes the stoma to ______

water potential

osmosis

swollen

open

Flaccid

Guard cells __________ which causes them the stoma to _______

shrink

close

What genetic factors affect the rate of transpiration

Number, distribution and the size of the stomata

What environmental factors affect the rate of transpiration

Temperature

Humidity

Air Speed

Light Intensity

Temperature:

As temperature increases, it ______ the water potential of the atmosphere. it increases the __________ ________ of water molecules, accelerating their rate of ______________, from the walls of the mesophyll cells and if stomata are ______, it speeds up their rate of diffusion into the atmosphere. The ________ temperature causes the water molecules to ______ away from the leaf more quickly reducing _______ _________ around the leaf.

lowers

kinetic energy

evaporation

open

higher

diffuse

water potential

Humidity

The lower the humidity, the faster the rate of transpiration. If the air around the plant is dry, the concentration gradient between the leaf and the air is increased

Air movement

The windier it is, the faster the rate of transpiration. Lots of air movement blows away water molecules from the stomata. This increases the concentration gradient

Light Intensity

The higher the light intensity, the faster the rate of transpiration.

Stomata open allowing CO2 to enter the leaf to facilitate photosynthesis.

The rate of transpiration slows during the night due to this.

What is the formula for the rate of transpiration

Rate= Volume/Time

What is the formula for volume

3.14 x r² x h

What does the availability of water depend on?

where they live

What are the three types of plants

Xerophytes

Hydrophytes

Mesophytes

Xerophytes

plants that live in areas of water availability

Succulent thick leaves

store water

White leaves/spines

light colours reflect light and thereby cool the plant

Thick/waxy cuticles

reduce water loss from epidermal cells

Loss of leaves to form spines

in deserts, light is not usually a limiting factor, so photosynthesis can be carried out by the shoot.

Trichomes

create a more humid microenvironment, trapping water vapour close to the surface of the leaf to reduce the water potential gradient and therefore evaporative water loss.

Sunken stomata

like trichomes, a more humid microenvironment is created

CAM photosynthesis

stomata open during the night when it’s cooler, CO2 is fixed so that it can be used during the day for photosynthesis without having to open the stomata

Curled leaves

create a more humid microenvironment and therefore reduce water loss by transpiration. They also have all of the stomata facing inwards

Reduced number of stomata

fewer gaps for water to evaporate out through

Hydrophytes

plants that have adapted in water

Problems that may occur are:

CO2 supply may be limited for submerged parts of the plant

Light of the correct wavelengths for photosynthesis does not penetrate deep into water

Little/no waxy cuticle

no need to conserve water

Stomata on upper surface

as lower surface is submerged

Poorly adapted xylem

as no need to transport water

Large air spaces

provide buoyancy and acts as reservoirs of gas

Translocation

the phloem transports the products of photosynthesis from the source to the sink

Source

the leaf

Sinks

area/use of storage

Companion cells

where most cell organelles are

very biochemically active

where metabolic processes occur

Sieve tubes

filter and lose most cell organelles to make space for transport

What is the mass flow hypothesis

suggests there is a passive mass flow of sugars from the phloem of the leaf where there is a highest concentration (the source) to other areas such as growing tissues where there is a lower concentration (the sink)