movement across the membrane:

Plasma membrane:
• The plasma membrane (cell membrane) is made of two layers of phospholipids. The membrane has many proteins embedded in it.
• Proteins embedded within the phospholipid bilayer carry out the specific functions of the plasma membrane, including selective transport of molecules
• The plasma membrane regulates what enters and leaves the cell. Many molecules cross the cell membrane by diffusion and osmosis.
Molecules that pass through the phospholipid bilayer easily are :
a. Hydrophobic molecules (oil soluble) or nonpolar molecule – lipid, vitamin A, D,E and K
b. Small uncharged molecule – water, urea, carbon dioxide, glycerol, oxygen
Molecules that can’t pass through the phospholipid bilayer easily are:
a. Large uncharged – Glucose, amino acid
b. Polar molecules – Sucrose
c. Ions (charged) – H+ , Na+ , HCO3 , K+Ca2+ , Cl- , Mg2+

Diffusion of Across a Plasma Membrane:
a. Passive Transport of Water :- Osmosis:
– movement of water molecule across semi permeable membrane from less concentrated solution (high concentration of water molecules) to more concentrated solution (low concentration of water molecules)
- example: absorption of water into the root hair cells.
b. Facilitated diffusion
– movement of particles from areas of high concentration to areas of low concentration by using the transport protein but not require energy. Example: movement of glucose and amino acid into the cell across the membrane.
– example: absorption of amino acid and glucose into blood capillaries in small intestine
Active Transport Movement of substances such as ions across cell membrane against concentration gradient (Movement from low to high concentrations)
by using protein transport and energy to overcome the concentration gradient. example : movement of mineral ions from soil into root hair cells.