Movement Of Substances Across a Membrane

PASSIVE TRANSPORT

Diffusion is the net movement of material from an area of high concentration to an area with low concentration. The difference between the two area is often term as the concentration gradient and diffusion will continue until this gradient has been eliminated.

Facilitated diffusion also called carrier-mediated diffusion, is the movement of molecule across the cell membrane via special transport protein that are embedded within the cellular membrane. Many large molecules, such as glucose, are insoluble in lipids and too large to fit through the membrane pores. Therefore, it will bind with its specific carrier proteins, and the complex will then be boned to a receptor site and move through the cellular membrane.

Osmosis is the diffusion of water molecule from a area of low solute concentration to area of high solute concentration. Examples of movement of water via asmosis in organisms include:

water absorption from the intestine, water reabsorption from the kidney tubules, water uptake from the soil by the root hairs

ACTIVE TRANSPORT



Water and minerals get into the root hair of plants from the soil. The concentration of minerals in the root hair is higher than that in the soil. That makes it easy for the water to move in via osmosis. The minerals, however, get into the root of  hair via active transport after they dissolve in water in the soil. This requires energy provided by ATP.