Cell Membrane and Transport

Ariel Sacco

Ashlee Heidgerd Sidney Hardie

Cell Membrane• It is composed of lipids, proteins, and

carbohydrates.• It is a bilayer of phospholipids molecules.• The water soluble phosphates are the

heads on the membrane.• The water insoluble fatty acids are the tails

inside the membrane.• Proteins function as receptors on the

surface and form passageways for ions and molecules.

• It is the outermost layer of the cell.

Fluid Mosaic Membrane Model

Hydrophobic Region

Hydrophilic Region

Carbohydrate Side Chain

Glycoprotein

Integral Protein

Phospholipid

Hydrophobic Region

Hydrophilic Region

Transmembrane Protein

Diffusion• In the body, diffusion exchanges

oxygen and carbon dioxide.• It’s the movement of molecules

of ions from higher concentration to lower concentration

Facilitated Diffusion

• Special carrier molecules move substances through the membrane.

• It moves substances from higher concentration to lower concentration

Osmosis• The diffusion of water molecules

from higher water concentration to lower water concentration through a permeable membrane.

• The osmotic pressure increases as the number of particles are dissolved.

• Cells lose water when in hypertonic solutions and gain water in hypotonic solutions.

• The Na K pump is an example of endocytosis and exocytosis because during this process potassium ions are diffusing out of the cell and the sodium ions are diffusing in to the cell.

PUMP

Endocytosis• It conveys relatively large particles into a cell.• It occurs in three forms which are pinocytosis,

phagocytosis, receptor mediated endocytosis.– Pinocytosis – cells take in tiny droplets of

liquid from their surroundings– Phagocytosis – the cell takes in solids from

their surroundings– Receptor mediated endocytosis – protein

molecules are drawn into the cell by receptors

Exocytosis• It releases substances that were

stored in the cell.• Transcytosis – it combines

endocytosis and exocytosis to transport a particle across the cell.

The End