Moving Cellular Materials Types of Transport

Cell membrane The cell membrane is referred to as semi-permeable because it allows some substances to enter the cell while keeping other out of the cell. It is made of two phospholipid layers. The head of the lipids are hydophilic (attracted to water). The tails are hydrophobic (afraid of water).

Part I. Passive transport Passive transport is a type of transport that moves materials through the membrane that DOES NOT require energy. All materials pass from an area of high concentration to an area of low concentration. This means materials go with the concentration gradient. This would be like traveling down stream in a boat.

Types of Passive Transport There are three types of transport: diffusion, osmosis, and facilitated diffusion. All three will be explained in the following slides.

Oxygen and other small gas molecules use this type of transport. The random movement of molecules from an area of high concentration (where there is relatively more of them) to an area of low concentration (where there is relatively less of them). Oxygen and other small gas molecules use this type of transport. Diffusion

Equilibrium Molecules of a substance will continue to move until the relative number of molecules is equal in the two areas. Equilibrium is the equal balance of molecules between two areas.

Osmosis Osmosis is the diffusion of water through the membrane. Water moves from an area of high concentration of solute to an area of low concentration of solute.

From which side will the move? Why? Side A Side B

Different Movements of Water Hypotonic: the solute concentration is high inside the cell and water must move inside the cell Hypertonic: the solute concentration is high outside the cell and water must move out Isotonic: the solute concentrations are the same inside and outside the cell; no net water movement

Facilitated Diffusion The diffusion of larger molecules (like glucose) across the membrane with the help of transport proteins. Molecules move from high to low concentrations.

Part II. Active Transport Active transport is when energy (ATP) is required to move molecules across the cell membrane. The reason energy is required is because molecules move from low concentration to high concentration gradients. This would be like trying to return to your stadium seat to get your jacket when thousands of fans are leaving.

Moving Molecules with Energy Active transport moves individual molecules like minerals in the soil. Minerals move into the root system of plant even if the roots contain more minerals than the surrounding soil.

Endocytosis Endocytosis is the process of taking large substances into the cell by surrounding it with the cell membrane. Large protein molecules, food molecules, and even bacteria use this form of transport.

How does it work? 1. The cell membrane folds itself around the item, enclosing it in a sphere called a vesicle. 2. The vesicle pinches off and enters the cytoplasm. 3. The vesicle transports the substances to the part of the cell that needs it.

Exocytosis The opposite of endocytosis, exocytosis is when the vesicles fuses with the cell membrane and its contents are released outside the cell.