Two major ways that molecules enter & exit cells Diffusion & Osmosis Two major ways that molecules enter & exit cells

Diffusion & Osmosis Write this down and answer it after paying close attention to this lecture: Explain why the following things occur using what you learn about osmosis and diffusion: - Blood cells in pure water would absorb water and eventually burst! - Blood cells in salty water would shrivel.

Diffusion Movement of particles from areas of higher concentration to areas of lower concentration Occurs spontaneously – requires no energy from the cell Movement is driven by the kinetic energy (KE) of the particles All particles have KE; KE increases as temp. increases

Example: A chamber is filled with two gases, one from the left & one from the right. What will happen over time? = gas molecule

Molecules will diffuse due to their own KE & become evenly distributed = gas molecule

In cells, small molecules (O2, CO2, etc In cells, small molecules (O2, CO2, etc.) will diffuse across a membrane from areas of high concentration to low concentration

(High concentration of molecules) (Low concentration of molecules) Example: (High concentration of molecules) (Low concentration of molecules)

Transport protein Larger molecules will also diffuse but may require the help of a transport protein

Osmosis A specific type of diffusion Refers to water diffusing across a semi-permeable membrane

Water molecules Solute molecules (non-water) In this scenario, more water will move to the right than to the left. Why? The concentration of water molecules is greater on the left, and they will move from higher concentration to lower concentration

Example: Semi-permeable membrane (only water can move across) Ask yourself:   1. Which side has a greater concentration of water molecules? Water + Sugar Pure water A B Side B

membrane (only water can move across) Example: Semi-permeable membrane (only water can move across) Ask yourself:   2. Which side will have more water molecules colliding with the membrane? Water + Sugar Pure water A B Side B

membrane (only water can move across) Example: Semi-permeable membrane (only water can move across) Ask yourself:   3. Which side will have more water molecules moving across the membrane? Water + Sugar Pure water A B Side B

The net (overall) movement of water will be greater from B to A Example: Semi-permeable membrane   Water + Sugar Pure water A B The net (overall) movement of water will be greater from B to A

AFTER:   Water + Sugar Pure water A B Eventually, equilibrium is reached where amount of water moving across is equal

Ask yourself: Cell The cell Cell Example: 1. Which side has a greater concentration of water molecules? Saturated Salt Solution Cell The cell Cell membrane

Saturated Salt Solution Cell Example: Ask yourself: 1. Which side will have more water molecules colliding with the membrane? Saturated Salt Solution Cell The cell Cell membrane

Saturated Salt Solution Cell Example: Ask yourself: 3. Which side will have more water molecules moving across the membrane? Saturated Salt Solution Cell The cell Cell membrane

The net (overall) movement of water will be out of the cell. Cell Example: Saturated Salt Solution Cell The net (overall) movement of water will be out of the cell.

Saturated Salt Solution After: Saturated Salt Solution Cell The cell will shrink as it loses water until water movement reaches equilibrium.

Also: Saturated Salt Solution Cell The salt water is now more dilute while the cell is less watery.

What do you think would happen to blood cells in pure water? concentrated salt solution?

Blood cells in pure water would absorb water and eventually burst! Blood cells in conc. salt solution would shrivel

In plant cells, the cell wall keeps the cell from exploding in pure water.