1. How this reading relates to what we are doing in class
Science is not just about facts (verifiable observations and measurements).
The POWER lies in how those facts come together in a story to explain how and why a natural phenomenon works the way it does.
We are constructing those stories using facts (or evidence) to construct evidence-based explanatory models of how cells work.

2. How this reading relates to what we are doing in class
Uncertainty is a BIG part of science!
Scientists are out to discover the unknown.
Make hypotheses (educated guesses)
Gather information to test those hypotheses
Make revisions of hypotheses that include the new information
We are doing this in our online discussions, in our reading guides, in our explanatory models, and even in our quizzes!!!

3. Unit #2: Flow of Energy through a Cell!
Introduction
Initial Ideas
Whiteboards (10 min)
Whole-class discussion (5 min)
Any questions that we have about how energy flows through a cell
Photo credit:

4. Membrane Function
Working cells control the transport of materials to and from the environment with membranes.
Transport
of materials

5. Membrane Function A closer look at our membranes Hydrophobic region
Hydrophilic
region

6. How do molecules cross a cellular membrane?
Many small non-polar molecules can pass through (or permeate) by diffusion
Oxygen (O2), Carbon Dioxide (CO2)
Water (H2O), although polar, is small enough to pass through
Other charged and larger polar molecules cannot pass through (or permeate) and need membrane transport processes to do so.
Ions: K+, Na+, H+
Small hydrophilic molecules like glucose, amino acids, nucleotides
Macromolecules like proteins and RNA
Therefore, our cellular membranes are
selectively permeable!!!

7. Passive Transport: Diffusion Across Membranes
Molecules contain heat energy.
They vibrate and wander randomly - Brownian Motion.
Diffusion is one result of the movement of molecules.
Molecules tend to spread into the available space.
Diffusion is passive transport; no energy is needed.
Water and small non-polar molecules like O2, CO2 travel across cell membranes through passive diffusion.

9. Osmosis and Water Balance in Cells
Osmosis is the passive transport of water across a selectively permeable membrane.
[solute]
[water]
= [solute]
= [water]
[solute]
[water]

10. Water Balance in Cells
Plasmolysis

11. Turgid Flaccid Osmoregulation is the control of water balance.
Sodium-potassium pump essential to regulate cell volume through control of osmosis in many animal cells.
Water balance in plant cells is different.
They have rigid cell walls.
They are at the mercy of the environment.
Turgid Flaccid

12. Lab 3 - Osmosis and Diffusion
Here we will be going through an exercise of hypothesis-driven science.
Brownian motion
Selectively Permeable Membrane
Hypothesis - educated guess, an idea you can test
Making Predictions:
If …[organize what you think you know and how you are testing your idea]
Then …[predict what experimental result you would get]
Because …[general principles; Ex: diffusion,membranes]
Diffusion

13. Lab 3 - Osmosis and Diffusion
We will go through this on Tuesday!
Constructing a scientific argument
Re-state your claim/hypothesis
Support or refute it with evidence or counter-evidence from
Verifiable observations,
Verifiable measurements, and/or
Reliable resources, other people’s data
If claim/hypothesis refuted, state an alternative hypothesis

14. Lab 3 - Osmosis and Diffusion
Osmosis evidence - the Egg!
Hypothesis:
The solution that is hypertonic relative to the egg will…
The solution that is hypotonic relative to the egg will…
Prediction:
If …[organize what you know and how you are testing your idea]
Then …[predict your experimental result - what data will you actually have?]
Because …[general principles about osmosis]

15. Lab 3 - Osmosis and Diffusion
We will go through this on Tuesday!
Constructing a scientific argument
Re-state your claim/hypothesis
Support or refute it with evidence or counter-evidence from
Verifiable observations,
Verifiable measurements, and/or
Reliable resources, other people’s data
If claim/hypothesis refuted, state an alternative hypothesis

16. Lab 3 - Osmosis and Diffusion
Plasmolysis
View of Elodea cells