Transport mechanisms

Passive Transport

This includes osmosis, diffusion, and facilitated diffusion- processes that don’t require additional energy from the plant.
Osmosis is the movement of water from an area of high water potential to an area of low water potential, across a selectively permeable membrane.
Diffusion is the random movement of particles from an area of high concentration to an area of low concentration.
Facilitated diffusion involves carrier proteins to move large solute molecules across the plasma membrane.

Active Transport

This involves energy to move substances against a concentration gradient or for uphill transport.
The root cells use active transport to absorb mineral ions from a very dilute solution in the soil.
Proton pumps push protons out of the cell, creating a concentration gradient which allows the movement of nutrients into the cell against their concentration gradient.
This process uses ATP as the source of energy to facilitate the movement.

Translocation

It’s the process of transport of solutes within a plant.
Occurs in the phloem and moves substances from sources (areas of production such as leaves) to sinks (areas of storage or use).
Powered by the energy released by respiration and is an active process.
It involves the loading and unloading of sugars from the sieve tubes by active transport.

Transpiration

Loss of water through the plant surfaces, mainly the leaves.
Creates a pull or tension that draws water up from the roots to the leaves in the xylem tissue.
Governed by the opening and closing of the stomata in the leaves, which in turn is controlled by the turgidity of guard cells.
Environmental factors such as humidity, temperature, light intensity and wind speed can affect the rate of transpiration.

Mass Flow Theory

Explains the mechanism of transport of soluble organic materials through the phloem.
Sugars are loaded into the sieve tube elements by active transport, decreasing the Ψ (water potential).
As a result, water enters from adjacent tissues by osmosis, generating a hydrostatic pressure gradient.
This gradient causes the movement or ‘mass flow’ of the content of the sieve tubes from sources to sinks.

Make sure you can explain and distinguish these different transport mechanisms, understanding the energy requirements and involved cell structures for each.