AP Biology Discussion Notes

Thursday 10/9/2014

Goals for the Day

1. Be able to describe cell organelles and their functions.

2. Be able to describe and calculate water potential as well as water potential at equilibrium

Question of the DayWhat is the equation to figure out Water Potential, and what does that really tell us?

Question of the DayWhat is the equation to figure out Water Potential, and what does that really tell us?

– Measures the ability of water to do work (measure of it’s POTENTIAL energy)

Water Potential Calculations

Ψ= Ψp + Ψs

Water Potential Ψ= Ψp + Ψs

Water potential – physical property that predicts which direction water will flow.

Includes the effects of solute conc. and

physical pressure.

Water Potential Ψ= Ψp + Ψs

Water “potential” – potential refers to water’s potential energy, or water’s ability/capacity to do work.

Water Potential Ψ= Ψp + Ψs

Usually measured in MPa.

1MPa = 10x atmospheric pressure, so typical plant cell might have a pressure of .5MPa

Pure water in an open container under standard conditions has 0MPa

Water Potential Ψ= Ψp + Ψs

Solute Potential (Ψs)– directly proportional to molarity of the solution

Ψs of pure water is by definition 0

Water Potential Ψ= Ψp + Ψs

Solute Potential (Ψs)– solutes bind to water molecules, which reduces the capacity of water to move and do work (reduces )

As Molarity (amount of solute) increases the Ψs becomes more negative

Water Potential Ψ= Ψp + Ψs

Pressure Potential (Ψp)– physical pressure of a solution so it can be positive or negative relative to the atmosphere

Water in living cells is under positive pressure

Plasmolysis mini Lab

• Discussed answers and reviewed lab concepts, then handed lab in.

Organelles organized

• Went over answers to organelles organizer

• Also got another practice sheet for organelles, this time looking at structure and function.