Step into my elevator! When the elevator was crowded, what did all the people in the elevator want to do? WHY? When one more person was forced into the already crowded elevator did they find it was easy or difficult to get in? WHY?

Just like people entering or exiting an elevator, molecules move into or out of cells. Sometimes easily, sometimes with great effort.

Cell Transport Pages 80-85

There are two ways that molecules can move through a cell membrane 1. Passive Transport ex. Osmosis ex. Diffusion 2.Active Transport ex. Transport Proteins ex. Engulfing

Diffusion is the main method that small molecules move across a membrane It’s the process by which molecules move from an area of higher concentration to an area of lower concentration. Example – perfume bottle

What Does Concentration Mean? Taste the liquid in the three cups. Which cup has a lower concentration of water in it? (higher concentration of lemonade mix)? Which cup has a higher concentration of water molecules in it (lower concentration of lemonade mix)? More mix, less water molecules Less mix, more water molecules

Diffusion Across A Cell Membrane Cell Membrane OUTSIDE OF CELL INSIDE OF CELL

How do most small molecules move across the cell membrane? The cell membrane that surrounds the cell is selectively permeable. –Some substances can pass through the membrane while others cannot Ex. the balloon with vanilla Cells must get needed molecules in and expel waste Substances move in and out through pores.

What causes Diffusion? Molecules are always moving and bumping into each other. The more molecules there are the more collisions there will be. Collisions will cause the molecules to push away from each other until, over time, they will spread out evenly. –They meet a point of equilibrium.

OSMOSIS Like oxygen, water passes easily into and out of cells. Osmosis is the diffusion of water molecule. –Water moves from an area of higher concentration to an area of lower concentration. Cells cannot function without water, so most cell processes depend on osmosis.

Effects of Osmosis Normal blood cell at equilibrium. Concentration of water inside the cell is the same as outside. Hypertonic blood cell. Concentration of water inside the cell is higher than the outside.Water flows out of the cell, shrinking it. Hypotonic blood cell. Concentration of water inside the cell is lower than the outside. Water flows in the cell, swelling it.

ACTIVE TRANSPORT Diffusion and osmosis are forms of passive transport. –Movement of molecules without using cellular energy What if cells need to take in molecules that are found in a higher concentration? –The cell has to move molecules in the opposite direction. –Cells can do this, but they need to use their own energy Active transport is the movement of molecules using cellular energy.

Methods of Active Transport 1.Transport proteins – proteins that pick up molecules outside the cell and carry them in using energy. (ex. calcium, potassium, sodium) 2.Engulfing – Cell membrane surrounds the particle and forms a vacuole around it. The cell uses energy in this process.

In PASSIVE transport molecules (in this case, sugar) will move from a more concentrated area and will spread out to a less concentrated area throughout the beaker filled with water. Molecules NATURALLY want to move this way, so it does NOT require energy to happen. In ACTIVE transport molecules will move from a less concentrated area and will be taken into a more concentrated area. The cells need lots of energy in order to do this.