Transport Through Cell Boundaries

Every living cell exists in a liquid environment that it needs to survive. In order to understand how water and particles move through the cell boundaries, we have to understand concentration.

The cytoplasm of a cell contains a solution of many different substances. The substances dissolved in the solution are called solutes.

Measuring concentration The amount of solute in a solution is called the concentration. Concentration is the mass of the solute in a given volume of solution. Ex. If you dissolve 12 grams of salt in 3 liters of water the concentration is 12 g/3 L = 4g/L

Passive Transport There are 3 ways in which particles or water move through the cell membrane which require no energy: -diffusion (particles) -osmosis (water) -facilitated diffusion (particles)

Diffusion Diffusion: When particles move from an area of higher concentration to an area of lower concentration. (See diagram on board.) Particles that move freely by diffusion are small non-polar molecules.

Diffusion Requires no energy. When the concentration of a solute is the same throughout a system (inside and outside the cell), the system has reached equilibrium.

Osmosis Osmosis is the passing of water through a selectively permeable membrane. Why does water do this? Again it all has to do with concentration.

Osmosis Water will tend to move across membranes until equilibrium is reached (when the concentration is the same on both sides of the cell membrane). This state is called isotonic (which means same strength). (See diagrams on board.)

A solution that is more concentrated is called hypertonic. A solution that is less concentrated is called hypotonic. When we are talking about a solution that is hypertonic or hypotonic, we always assume that the solution is outside the cell.

Osmotic Pressure Osmotic pressure is the force required to oppose osmosis.

Facilitated Diffusion There are hundreds of different protein channels that allow particular substances to diffuse across cell membranes. This diffusion through protein channels in the membrane is called facilitated diffusion.

In passive transport, molecules are said to move with the concentration gradient.

Sometimes molecules have to move against their concentration gradient? How? By using energy.

Sometimes cells must move materials from areas of lower concentration to areas of higher concentration. Active Transport

Ions requiring active transport: Calcium Potassium Sodium

Active Transport Requires Energy ATP Moves against the concentration gradient

ATP

Adenosine-5'-triphosphate is a multifunctional nucleotide used by the cell as a co-enzyme.

Endocytosis Taking material into a cell by the in folding of a membrane.

2 Types of Endocytoses Phagocytosis- Solid particles are ingested into the cell Pinocytosis – liquids taken into the cell.

Exocytosis Moves materials out of the cell The membrane of the vacuole fuses with the cell membrane, forcing the contents out of the cell.

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