Cellular Transport

• Passive transport = molecules move across the cell membrane without the cell using energy
• Active transport = the cell uses energy (ATP) to move molecules across the cell membrane

Passive Transport

• Molecules move from an area of high concentration to low concentration
• Can also say that molecules move down a concentration gradient
• Concentration gradient = the difference in the amount of a substance between two places
• Molecules move until equilibrium is reached
• Equilibrium = the same amount in all areas

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• There are 3 types of passive transport
1. Diffusion = Molecules move across the cell membrane on their own
• Also called simple diffusion
2. Facilitated diffusion = molecules diffuse through protein channels in the cell membrane
• Molecules can’t cross on their own because they are polar, charged, or too big
3. Osmosis = the passive transport of water across the cell membrane

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• Example of simple diffusion
• Molecules are moving down a concentration gradient & crossing the membrane on their own

Active Transport

• Cells use active transport to maintain homeostasis (stable internal condition)
• Doesn’t always want to be equal with the environment
• Cells want their pH, temp., & concentrations of molecules to remain stable

• Molecules move from an area of low concentration to an area of high concentration
• Molecules move against (or up) their concentration gradient

• All types of active transport require the cell to use ATP
1. The cell moves molecules using protein pumps
• Protein pumps work like a lock & key system, each protein only moves certain molecules
2. Endocytosis = the cell uses vesicles to move molecules into the cell
• Once inside the cell the vesicle can fuse with lysosomes to break down the materials
3. Exocytosis = the cell uses vesicles to move molecules out the cell
• Once the vesicle fuses with the cell membrane the materials are released

Diagram of Endocytosis & Exocytosis

Osmosis

• Osmosis = the diffusion of water across the cell membrane
• Is a type of passive transport
• Gets its own name because water is so important to cells!
• The cytoplasm of a cell is mostly water
• Water can move through the cell membrane on its own or through special proteins called aquaporins

Types of Cell Environments

1. Hypertonic
• Environment = a lot of solutes, a little water
• Cell = few solutes, a lot of water
• Water moves…OUT of the cell
• The cell…SHRINKS

2. Hypotonic
• Environment = few solutes, a lot of water
• Cell = a lot of solutes, a little water
• Water moves…INTO the cell
• The cell…SWELLS, eventually can burst

3. Isotonic
• Equal amounts of solutes and water in the cell and the environment
• Water moves…IN and OUT of the cell equally
• The cell…STAYS THE SAME

Plant vs. Animal Cells

• Animal cells want to be in an isotonic environment
• Hypotonic environment can cause the cell to lyse (burst)
• Hypertonic environment can cause the cell to shrink
• Plant cells want to be in a hypotonic environment
• The cell wall prevents the cell from bursting
• The water entering the plant cell makes it firm & allows the plant to stand upright so it can get sunlight