Water Potential (IB Topic D2.3)

Essential Idea(s): Water potential explains the movement of water in biological systems, driven by differences in solute concentration and pressure, affecting cell stability and function in various environments.

Unit Length: 3 Lessons (+2 AHL)

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Guiding Questions

◊ What factors affect the movement of water into or out of cells?

◊ How do plant and animal cells differ in their regulation of water movement?

Materials:

Teaching Slides (SL) / Teaching Slides (AHL)	Quizlet Vocab Set (SL) / Quizlet Vocab Set (AHL)
	Notes Template (SL) / Notes Template (AHL)

IB Statement(s) and Objective(s)

D2.3.1: Solvation with water as the solvent

Define solvation
Draw a molecular example of solvation (such as salt dissolving in water)

D2.3.2: Water movement from less concentrated to more concentrated solutions

Define osmosis
Define osmolarity, isotonic, hypotonic and hypertonic
State the units of osmolarity

D2.3.3: Water movement by osmosis into or out of cells

Explain what happens to cells when placed in isotonic, hypotonic and hypertonic solutions

D2.3.4: Changes due to water movement in plant tissue bathed in hypotonic and those bathed in hypertonic solutions

Determine the concentration of solutes in a plant tissue given changes in plant tissue mass and/or length when placed in solutions of various tonicities
Explain the change in mass and/or volume of plant tissues placed in either hypotonic or hypertonic solutions

D2.3.5: Effects of water movement on cells that lack a cell wall

Define osmoregulation
Outline the role of the contractile vacuole in freshwater unicellular organisms

D2.3.6: Effects of water movement on cells with a cell wall

See D2.3.3

D2.3.7: Medical applications of isotonic solutions

Outline the use of normal saline in medical procedures

Additional Higher Level Topics

D2.3.8: Water potential as the potential energy of water per unit volume

Define water potential
State the symbol and unit for water potential
Explain why it is impossible to measure the absolute quantity of the potential energy of water
Outline how water potential measurements become positive and negative

D2.3.9: Movement of water from higher to lower water potential

Explain the movement of water from higher to lower water potential

D2.3.10: Contributions of solute potential and pressure potential to the water potential of cells with walls

Describe the impact of solute potential and pressure potential on the total water potential of cells with walls
Explain the movement of water in plant cells bathed in hypotonic solutions and hypertonic solutions (in terms of solute and pressure potentials)

D2.3.11: Water potential and water movements in plant tissue

State the general trend for ΨP inside cells
Give one example of a cell/tissue type that is typically under negative pressure potential


Activities: ⓟ = podcast / ⍰ = inquiry 5 / ⓦ = Write it / Ӕ = The academy / Ⓡ = Read it
Ⓛ (required): Lab Report: Osmosis & Osmolarity (💁) This lab will be broken down into steps and will culminate with a summative assessment on Oct Nov. 7. You will begin by writing a method with the following goal: *Identify the osmolarity of cells in a potato. You may work in pairs to conduct the experiment, but each student must write their own method without the help of the internet.* Post your data results here …have no idea what you’re doing and you kinda/sorta want to cheat? Watch this video (only as a last resort!!) As practice for your upcoming summative lab (in testing conditions), you will be completing a “front end” lab report, which will include your method (already written), along with a short introduction, variables section, background information, data table, and graph. Need help writing a good experiment? Use this writing guide Need help with experimental design vocab? Practice this Quizlet review set Need help with graphing? Use this graphing guide Want to know how you’re going to be graded? Here’s the rubric ⓟ/ⓦ: Case Studies in Hyponatremia (Death by Osmosis) (💁/ 👭 max 2) Osmosis has a reputation for being one of the more boring topics in Bio, but every so often it comes out as the murder weapon in some pretty grotesque cases. Read the case studies in this article, then answer the questions that follow at the end. Post your responses to G. Classroom. Ⓛ: Death by Osmosis (an interactive lab) (💁/👭 max 2) Use this guide to work your way through an interactive murder investigation. Extra Practice: Old School Worksheet #1 (Practice problems with osmosis) Old School Worksheet #2 (Practice problems with tonicity/osmosis)