Long distance transport

How does transport in plants take place?

Long-distance transport involve xylem and pholem for water, minerals and foods are moved.

• Long distance transport food
•  diffusion is a slow process move for Short distance.

Bulk or mass flow is different from diffusion.

Mass flow or bulk flow.

Movement of substance through the pressure difference.

Movement of substance in bulk or mass form.

Diffusion

It is a slow process and dependent on concentration.

Bulk flow can be achieved through

Positive hydrostatic pressure gradient. Example garden hose.

Negative hydrostatic pressure gradient example suction through a straw.

Plant absorb water through.

Water is absorbed  root hairs through two distinct pathways.

• Apoplast pathway
• Symplast pathway

Apoplast pathway

Movement of water from the adjacent cell wall.

Except casparian strip of the endodermis in the roots.

Feature of apoplastic pathway

Water is moved through intercellular space

Apoplast does not involve crossing the cell membrane.

Dependent on water potential gradient.

Apoplastic movement of water

Water evaporation from the intercellular space and tension develop.

Mass flow of water adhesion and cohesion are developed.

Symplast pathway

Movement of water from interconnected protoplast.

Neighbouring cell are connected  cytoplasmic stands through plasmodesmata.

Characteristics of symplest pathway.

Movement of  through cytoplasm.

Symplast pathway involve crossing the cell membrane.

Symplest movement occurs down a potential gradient.

Facts

Water absorption directly through xylem vessel.

Ascent of Sap.

Movement of water through vascular bundle.

Transpiration pull

transpiration pull is negative hydrostatic pressure developed in area parts due to evaporating loss of water.

Rate of ascent of Sap in plants is 15meter per hour.

transpiration pull is referred to cohesive- tension transpiration pull model of water transport.

Cohesion

Mutual attraction between water molecules.

Adhesion

Attraction of water molecules to polar surface

Surface tension

Water molecules are attracted to each other in liquid phase more than the gas phase.

High tensile strength

High capillarity

transpiration can create pressure sufficient to lift a xylem size column of water over 130 metre high.

Root pressure

Actively transported ions in vascular tissue create a potential gradient and increase the pressure inside the xylem, this positive pressure is called the root pressure.

Condition for root pressure

Low rate of evaporation and transpiration

High atmospheric humidity.

Root pressure exist from evening.

Application of root pressure

Pushing up water to a small height in a stem

Guttation

Water transport.

Facts

Root pressure do not play a major role in water movement of tall tree.

Guttation

Loss of xylem Sap in the form of a liquid drop from the uninjured margin of leaves is called guttation.

Guttation is driven by root pressure

Guttation drop contain dissolve organic and inorganic substance

Phloem transport

Food is transport from source to sink

Source

Part of plant where synthesis or stored the food for example leaves.

Sink

Part of plant that need food

Chemical nature of phloem sap is alkaline.

Food in phloem transported in bi directional.

Pressure flow or mass flow hypothesis given by munch.

• Glucose is prepared 
• Transport in sucrose
• Stored in starch.

Sucrose is move in companion cell and then into living phloem sieve tubes cells by active transport.

How transport in plants ?