Plant Physiology - Transport in Plants (Diffusion, Osmosis, Transpiration, Phloem Transport)

Diffusion is the passive movement of individual molecules from a region of higher concentration to a region of lower concentration, occurring until equilibrium is reached. It is influenced by the concentration gradient, temperature, and pressure.

Osmosis is a special type of diffusion involving the movement of solvent molecules (usually $H_2O$) through a semi-permeable membrane from a region of higher solvent chemical potential to lower chemical potential.

Water Potential ($\Psi_w$) is the potential energy of water per unit volume relative to pure water. Pure water has the highest potential, defined as $0$ $MPa$. Adding solutes decreases $\Psi_w$, making it negative.

Plasmolysis occurs when a plant cell is placed in a hypertonic solution, causing water to move out and the protoplast to shrink away from the cell wall. The cell becomes flaccid.

Transpiration is the loss of water in the form of water vapor from the aerial parts of the plant, primarily through stomata. It creates a 'Transpiration Pull' that facilitates the ascent of xylem sap.

The Cohesion-Tension Theory explains water movement in xylem through the cohesive force between $H_2O$ molecules, adhesive forces between water and xylem walls, and surface tension.

Phloem Transport involves the translocation of organic solutes (mainly sucrose) from 'Source' (leaves) to 'Sink' (roots/storage organs) via the Mass Flow Hypothesis or Pressure Flow Hypothesis.

Active Transport involves the movement of molecules against a concentration gradient using energy in the form of $ATP$ and specific membrane proteins.