Notes: Movement of Material across the Cell Membrane Passive Transport Passive Transport- the movement of material across a cell membrane without the use of energy. Three types of passive transport include: Diffusion, osmosis & facilitated diffusion

Diffusion Diffusion: The process in which molecules of a substance move from areas of higher concentration to an area of lower concentration.

Equilibrium is reached when the concentration is equal throughout. -The glass on the left has not reached equilibrium. The bottom of the glass is more concentrated than the top (which is dilute). -If left alone, the molecules will diffuse throughout the glass until equilibrium is reached (like the glass on the right)

How does diffusion affect a cell? Cell membranes are described as being selectively permeable since they allow some substances to pass through, but not others. The ovals represent a cell Dots in the diagram are solute (salt)

How does diffusion affect a cell? Cell membranes are described as being selectively permeable since they allow some substances to pass through, but not others. The ovals represent a cell Dots in the diagram are solute (salt)

In the example, the inside of the cell has a higher solute concentration than the solution outside of it. If the solute is small enough to pass across the cell membrane, which direction would it move? The solute would move out of the cell (to spread out). Draw an arrow on the diagram to show the movement of the solute. Always label your arrows, so that you know what is moving across the cell membrane. Solute(dots)

The solute would move out of the cell (to spread out). In the example, the inside of the cell has a higher solute concentration than the solution outside of it. If the solute is small enough to pass across the cell membrane, which direction would it move? The solute would move out of the cell (to spread out). Draw an arrow on the diagram to show the movement of the solute. Always label your arrows, so that you know what is moving across the cell membrane. Solute(dots)

If there is a difference in the concentration of the two solutions, we say there is a concentration gradient. The larger the difference, the greater the gradient.

2. FACILITATED DIFFUSION (Facilitate=to help) -Facilitated diffusion- molecules are moved across a membrane from an area of higher concentration to lower concentration with the help of a carrier protein.

Proteins are usually needed to move solute across the cell membrane when the solute is too large or charged and can’t pass between the phospholipids. The carrier protein or channel simply opens up a larger hole in the cell membrane and allows the solute to flow from one side of the cell membrane to the other (does not require energy). Solute (dots)

3. Osmosis Osmosis- The diffusion (movement) of water molecules across a selectively permeable membrane. The goal of the water molecules is to get the substance on either side of the membrane to be at equilibrium (same concentration on both sides).

The dots are the solute (sugar). Water Draw an arrow on the diagram to show the movement of the water. Make sure that you always label your arrows, so that you know what is moving across the cell membrane. The dots are the solute (sugar). The water is represented by the space around the dots. Since water is a small molecule, it is able to move across the cell membrane very quickly. Water moves into the area of higher solute concentration to dilute it.

Important Terms to Know! Hypertonic- a solution with a higher concentration than another solution. Hypotonic- a solution with a lower concentration than another solution. Isotonic- a solution that has an equal concentration to another. Cytolysis- the bursting of an animal cell when placed in a hypotonic solution. Plasmolysis- the shrinking of a plant cell placed in a hypertonic solution. Turgor Pressure- the force that pushed out on a plant’s cell wall when it is placed into a hypotonic solution.