Passive Transport vs.

Active Transport

Remember that all cells have …

• Plasma or cell membranes that are selectively permeable and very fluid…

• (Click the animation below)

fluid membrane

Passive Transport• Does not require energy • Moves substances from a higher

concentration to a lower concentration

• Moves with the concentration gradient

Types of Passive Transport

• Diffusion • Osmosis• Facilitated Diffusion

Diffusion

• Movement of matter (particles) from a high concentration to a low concentration

• Moves particles that are small in size such as …

diffusion of particlesdiffusion of ink

wateroxygen

wastesions

Carbon dioxide

Food (glucose)

Osmosis

• Movement of water across a membrane from higher to lower concentration

Osmosis animation

How do cells react to different environments?

• Because cells have cell membranes they will be affected by various concentrations of substances in fluids. (think about the egg experiment)

There are three environmentsa. Isotonic- same concentrations of water in and

out of the cellb. Hypotonic- higher concentration of water

outside the cell than insidec. Hypertonic- lower concentration of water

outside the cell than inside

animations for various environments (click here to observe changes)

Facilitated Diffusion

• Passage of particles across the plasma membrane by means of transport proteins called channel or carrier proteins

• Used in the movement of small sugars and large amino acids across the cell membrane

faciitated diffusion animation

Facilitated Diffusion

carrier protein

Active Transport

• Requires energy in the form of ATP (adenosine triphosphate)

• Moves substances from a lower concentration to a higher concentration

• Moves molecules against the concentration gradient

Types of Active Transport

• Sodium-Potassium pump• Endocytosis• Exocytosis

Cell membrane pumps (ion pumps)

1. Transport proteins embedded in the plasma membrane act as “pumps”

2. Each pump can bond to a particular particle whose shape fits it.

3. Chemical energy (ATP) alters the shape of the pump and this releases the particle to the other side.

4. Once the particle is released, the pump returns to its original shape.

Sodium-Potassium Pump

• Animal cells have a high concentration or K+ ions and a low concentration of Na+ ions compared to the environment

• A pump maintains these concentrations by moving 2 K+ ions into the cell for every 3 Na+ ions that it moves out of the cell

sodium-potassium pump

EndocytosisThe membrane engulfs particles and takes in substances from the environment. Part of the

membrane breaks away and becomes a vesicle.

Phagocytosis: Engulfing food and particles, “cell eating”Pinocytosis: Engulfing liquids, “cell drinking”

Examples: large particles, cholesterol, bacteria, oil droplets pinocytosis animation phagocytosis animation

ExocytosisThe reverse of endocytosis. This is how the cell exports substances and gets rid of wastes.

Examples: toxic wastes, hormones, proteins, carbohydrates

exocytosis animation

An amoeba is a unicellular organism that eats by endocytosis and releases wastes by exocytosis.