Cell Membrane: A deeper look

Lets say we soak our egg in pesticide and the membrane does NOT let the endocrine disruptors in. Does this mean that no molecules will move at all?

Passive Transport – Osmosis Definition: diffusion of water across a selectively permeable membrane Important in maintaining the cell’s homeostasis (equilibrium) No energy needed for passive transport

What controls osmosis? Concentration gradient Type of solution Unequal distribution of particles on either side of a membrane Type of solution Isotonic Hypotonic Hypertonic

Solutions All substances important to life are most often part of a solution. A solution is made of 2 parts… 1. Solvent – liquid of the solution 2. Solute – the part dissolved within the solution Ex. Salt Water - (Solvent – water) (Solute – salt)

Types of Solutions- Important!!! Isotonic Concentration of dissolved substances in the solution is the same as the concentration of inside the cell they retain natural shape Normal body fluids are isotonic.

Types of Solutions- Important!!! Hypotonic Concentration of dissolved substances in the solution is lower than the concentration inside the cell Low solute in solution, higher water concentration Cells swell

Types of Solutions- Important!!! Hypertonic Concentration of dissolved substances in the solution is higher than the concentration inside the cell High solute in solution, lower water concentration Cells shrink

Water Diffusing

Isotonic Solution

Hypotonic Solution

Hypertonic solution

Types of Solutions…

Which cell is which?

Consider this experiment: You place an animal cell in a container of distilled water. What will happen? Make a hypothesis with your neighbor.

CQ#4: What do you predict will happen when you place an animal cell in a container of distilled water? Water will not move. Water will move from the cell into the beaker holding the experiment. Water will move into the cell for a while. Water will move into the cell and the cell will explode!

Water will move into the cell and the cell will explode! Why? Start: concentration of water is higher outside the cell than inside, so water moves in. As time passes: the concentration of water inside the cell increases, but it never gets as high as the distilled water. The water moving in increases the cell’s volume until it can’t handle the volume and explodes.

Now consider this: You place a plant cell in the same solution. The animal cell has exploded, but the plant cell never does. Why not? (Group work!)

CQ#5: The plant cell doesn’t explode because … Plants are tougher than animals. Plants have a cell wall that pushes back against the increased cell volume. Plants don’t let water cross membranes. We have no idea.