Cell Adhesion

Plants absorb water from soil. This water enters through roothairs and reaches the xylem bundles. Through xylem bundles water moves upward and reaches the leaves. The water in leaves is required for photosynthesis and also for transpiration. This upward movement of waier against the gravitational pull, is explained by Cohesion theory.

Major Biomes on earth Cohesion Theory

It says that transpiration from leaf surface leads to water loss in mesophyll cells, which in turn take up water from adjacent cell with higher water concentration. This process continues and loss of water is replaced by Xylem bundles. Now, water loss in xylem bundles creates a tension down to the roots, which again absorb water. Thus the water column moves upward. The water molecules have a tendency to stick together, which is called cohesion. This helps in maintain the water column.

Adhesion:

The walls of xylem vessels are made up of ligno cellulose, which have strong attraction for water molecules. This affinity is called adhesion. Due to adhesion, xylem vessels attract water molecules and water molecules attract other water molecules by cohesion. These two strong forces make the water column move upward. This theory explains the upward antigravity movement of water in tallest trees.

Cell to Cell binding through special Integrins

Integrins are also trans membrane binding glycol proteins that usually bind cells to matrix. However, they also may bind cells to cells. Binding is calcium dependent. Binding is from an integrin to a specific ligand on the target cell Binding may involve actin filaments, but is not associated with a cell junction Integrins contain an alpha and a beta subunit: Most cell to cell interactions involve integrins with an alpha and a beta-2 subunit

Examples:

Integrins on white blood cells allow tighter binding to endothelial cells before they migrate out of the blood stream to tissue. LFA-1 (white blood cells); Mac-1 (macrophages) Humans with a genetic disease called "leucocyte adhesion deficiency" are unable to synthesize the Beta-2 subunit. Thus, the white blood cells lack the entire family of beta-2 receptors needed to bind to endothelial cells. They suffer repeated bacterial infections