Transport in Angiospermatophyta. Outline of IS Leaf (tissue)

Transport in Angiospermatophyta

Outline of IS Leaf (tissue)

Outline of IS of stem (tissue)

Outline of IS Root (tissue)

Root system provide large surface area

• Branching and Root hairs• The cells with hairs have a greater cell wall size• To absorb-• Mineral ion• Water• Structure of cortex –facilitates water uptake

Plants absorb their nutrients in inorganic form

• N as Nitrate, Ammonium ion• K as potassium ion• P as Phosphate ion• Ca as Calcium ion.

Three main methods for the absorption

• Diffusion• Via fungal hyphae• Mass flow

Diffusion

• Some minerals are more concentrated in the soil than in the root and when dissolved in water will diffuse into the root

Fungal hyphae

• Fungus help many plant species to absorb minerals.

• The thread of fungus grow thru the soil and absorb M

• Some grow into the plant roots and transport these M in the root

• Fungus receives sugars from the plant• Ex. Mutualism.

• Ex., Oak, Beech and Birch all form ectomycorrhizal relationships with a number of fungi.

• Ectomycorrhiza

• In ectomycorrhizae– The mycelium of the fungus forms a dense sheath

over the surface of the root

In endomycorrhizaeMicroscopic fungal hyphae extend into roots

• Endomycorrhizae. No mantle forms around the root. Within the root cortex, the fungus makes extensive contact with the plant through branching of hyphae

• providing an enormous surface area for nutrient swapping

Agricultural Importance of Mycorrhizae

• Farmers and foresters– Often inoculate seeds with spores of mycorrhizal

fungi to promote the formation of mycorrhizae

Mass flow of water.

• The plant takes large volume of water which contains some dissolved minerals.

• Minerals dissolved in water form hydrogen bonds with water such that the movement of water towards the root 'drags' the minerals with the water.

Active transport

• plants can take up K+ from the soil against a ten-thousand-fold concentration gradient

• e.g., from as little as 10 µM in the soil to 100 mM in the cell.

Terrestrial plant

• Support themselves— - thickened cellulose - cell turgor -lignified Xylem

• Water and minerals can travel through a plant by one of three routes– Out of one cell, across a cell wall, and into another

cell– Via the symplast– Along the apoplast

Water and minerals ascend from roots to shoots through the xylem

• Plants lose an enormous amount of water through transpiration, the loss of water vapor from leaves and other aerial parts of the plant

• The transpired water must be replaced by water transported up from the roots

• Xylem sap– Rises to heights of more than 100 m in the tallest

plants

Pushing Xylem Sap: Root Pressure

• At night, when transpiration is very low– Root cells continue pumping mineral ions into the

xylem of the vascular cylinder, lowering the water potential

• Water flows in from the root cortex– Generating root pressure

Pulling Xylem Sap: The Transpiration-Cohesion-Tension Mechanism

• Water is pulled upward by negative pressure in the xylem

Transpirational Pull

• Water vapor in the airspaces of a leaf– Diffuses down its water potential gradient and

exits the leaf via stomata• Transpiration produces negative pressure

(tension) in the leaf– Which exerts a pulling force on water in the xylem,

pulling water into the leaf

Cohesion and Adhesion in the Ascent of Xylem Sap

• The transpirational pull on xylem sap– Is transmitted all the way from the leaves to the

root tips and even into the soil solution– Is facilitated by cohesion and adhesion

• The movement of xylem sap against gravity– Is maintained by the transpiration-cohesion-

tension mechanism

• Stomata help regulate the rate of transpiration• Leaves generally have broad surface areas– And high surface-to-volume ratios

• Both of these characteristics– Increase photosynthesis– Increase water loss through stomata

• Plants lose a large amount of water by transpiration

• If the lost water is not replaced by absorption through the roots– The plant will lose water and wilt

• Transpiration also results in evaporative cooling– Which can lower the temperature of a leaf and

prevent the denaturation of various enzymes involved in photosynthesis and other metabolic processes

• About 90% of the water a plant loses– Escapes through stomata

Each stoma is flanked by guard cellsWhich control the diameter of the stoma by changing shapeChanges in turgor pressure that open and close stomata

animation

• http://www.biologymad.com/resources/transpiration.swf

Abiotic Factors affect the rate of Trpn.

• Light• Temperature• Wind • Humidity

Xerophyte Adaptations That Reduce Transpiration

• Xerophytes– Are plants adapted to arid climates– Have various leaf modifications that reduce the

rate of transpiration• The stomata of xerophytes– Are concentrated on the lower leaf surface– Are often located in depressions that shelter the

pores from the dry wind