3.1.3 Transport in plants

NOT FINISHED

Why do plants need transport systems

Large surface area to volume ratio

Rate of diffusion into plant tissues is too slow

High metabolic rate

What are the vascular tissues

Xylem

Phloem

Found vascular bundles

What does the xylem transport

Water and soluble minerals upwards

What does the phloem transport

Sugar up or down

How vascular bundle arranged in leaf

Xylem on top

Phloem underneath

How vascular bundle arranged in stem

Phloem towards outside

Xylem in middle

What's in between the xylem and the phloem

Vascular Cambium

What does the vascular cambium contain

Meristem cells

(differentiate into phloem (pushed outside) or xylem (pushed inside))

How vascular bundle arranged in root

x/ star shape = xylem

between branches = phloem bundles

What is transpiration

Evaporation of water from the stomata (through leaves)

What is the transpiration stream

The movement of water up the xylem (from roots to leaves)

How does water leave plant

• Osmosis from xylem to the mesophyll

• Evaporation from the surface of the mesophyll into air spaces in leaf (spongy mesophyll)

• Diffusion out of the stomata

Factors that impact transpiration

Temperature

Humidity

Light intensity

Air movement

Number, size & position of stomata

Presence of a waxy cuticle

Water availability

How does temperature impact transpiration

Higher temp = higher kinetic energy in water

= more evaporation of water vapor through the stomata

How does humidity impact transpiration

More water vapor surrounding the stomata = less steep diffusion gradient = less water leave by evaporation

How does light intensity impact transpiration

Higher light intensity = higher rate of photosynthesis = more gas exchange needed

O2 diffuses out of stomata and CO2 diffuses in

Stomata open more to exchange gases - evaporation

How does air movement impact transpiration

More wind/ air movement = less water vapor will surround the stomata (= blown away)

Therefore steeper water vapor gradient

& more water will stomata (evaporation)

How does number, size and position of stomata impact transpiration

More stomata & Bigger stomata = more water leave by evaporation

(Some plants have stomata on top and bottom of leaf) - More stomata on top of leaf = more water leave by evaporation (bottom = build up of water vapor = lose less)

How does the presence of a waxy cuticle impact transpiration

Waxy cuticle = waterproof

Thicker = less water leave through evaporation

How does water availability impact transpiration

More water available = doesn't matter how much water lost

How to set up a potomter

Select healthy plant (Cut stem underwater (stop air bubbles getting into xylem)

Cut at angle (increase SA for xylem)

Dry leaves (avoid reduction in transpiration - if leaves = wet)

Use same age/ species of plant

Same SA and no. of leaves

Why does potometer not measure rate of water uptake accurate

Some water used in turgor pressure, some in photosynthesis

Calculate rate of water uptake

(SA of circle {diameter or radius} x length bubble has moved) / time

How does water get into the plant through the roots

Lower water potential in the root hair cells

Due to a higher conc. of solutes (active transport of minerals.. into cell)

Water moves into the root hair cells

By osmosis

Where does water travel in the apoplastic pathway

Through the cell wall untill reaches caspariean strip (in endodermis)

What does the casperian strip do

Forces water to move inside cell, inside xylem

Where does water travel in the symplastic pathway

Through cytoplasm.

Water travels from cell to cell via plasmodesmata

What is the cohesion adhesion tension theory

High hydrostatic pressure in roots

Low hydrostatic pressure in leaves

Water evaporates through the stomata

=Creates tension in the xylem

Water moves up the xylem along the hydrostatic pressure gradient

In a continuous column

By cohesion

Adhesion

Capillary action

By mass flow (bulk mov.)

What are xerophytes

Plants adapted to reduce water loss

e.g Cacti and marram grass

WATER VAPOR

Why do xerophyte plants have rolled leaves

Reduced surface area for evaporation

Trap a layer of WATER VAPOR

Creating a higher WATER VAPOR potential outside the stomata

Reducing the WATER VAPOR potential gradient

Reduces evaporation of WATER VAPOR from the leaf

What are the adaptations that xerophytes have

• Rolled leaves

• Hairy leaves

• Sunken stomata

• Needle like leaves

• Dense spongy mesophyll

Why do xerophyte plants have hairy leaves

Trap a layer of WATER VAPOR

Creating a higher WATER VAPOR potential outside the stomata

Reducing the WATER VAPOR potential gradient

Reduces evaporation of WATER VAPOR from the leaf

Why do xerophyte plants have sunken stomata

Trap a layer of WATER VAPOR (isn't taken away by wind easily)

Creating a higher WATER VAPOR potential outside the stomata

Reducing the WATER VAPOR potential gradient

Reduces evaporation of WATER VAPOR from the leaf

Why do xerophyte plants have needle like leaves

Reduces the surface area of the leaf therefore less evaporation of WATER VAPOR

Why do xerophyte plants have dense spongy mesophyll layer

Smaller surface area for evaporation

(dense = closely compact)

What's different about xerophyte plants stomata

Less stomata

Closed in the day

Found in lower surface of leaves to reduce evaporation

What's different about xerophyte plants waxy cuticle

Thicker

= Waterproof &prevents water leaving through evaporation

What's different about xerophyte plants root system

Long deep roots to take up water

High solute conc. in root hair cells (= reduces water potential inside)

What are hydrophytes

Plants that live in areas of high water conc

E.g water lilies

What are the adaptations that hydrophytes have

• Aerenchyma

• Large surface area

• Pneumatophore

What is aerenchyma in hydrophytes

Plant tissue with air paces

What does aerenchyma do in hydrophytes

Allows buoyancy

Why do hydrophyte plants have a large surface area

To increase the rate of photosynthesis

(water is not a limiting factor)

What are pneumatophore in hydrophytes

Special roots that grow out of the water

What does pneumatophore do in hydrophytes

Aids gas exchange

Increases rate of photosynthesis

(water not limiting factor, gas exchange is - the gases needed)

What's different about pneumatophore plants stomata

lots of stomata (water not limiting)

Open most of the time

Found on upper surface of leaf = increase rate of gas exchange (bottom side = facing water)

What's different about pneumatophore plants waxy cuticle

Thinner waxy cuticle

= water loss doesn't need to be prevented

What's different about pneumatophore plants root system

Short root system = not damaged by currents

Plant can meet requirements for water - live in water

What does the phloem transport

Assimilates from source to sink

What are assimilates

Sucrose or amino acid (products of photosynthesis)

(sucrose not glucose = less reactive)

What is a source

Where sugars are made or released from a carbohydrate source (starch)

Therefore high in conc.

E.g leaf or roots

What is a sink

Where the sugars are used in respiration (anywhere in plant) or converted for storage (starch in roots)

Therefore in a low conc.

TRANSLOCATION FLASHCARDS NEEDED!!!!!!!!!!1

TRANSLOCATION FLASHCARDS NEEDED!!!!!!!!!!1

How assimilates get into phloem

• Active loading

What is active loading

• H+ ions in the companion cells are actively transported out into surrounding tissues

• H+ ion move back into companion cell with a sucrose OR an amino acid, using a cotransporter protein = Facilitated diffusion

• Sucrose diffuses through the plasmodesmata into the sieve tube elements

• Sucrose diffuses through the plasmodesmata into the sieve tube elements

What is mass flow hypothesis