1. Passive and Active Transportation

2. Review
Cells have a semi-permeable membrane that allows some molecules to pass across the cell wall and keeps others out.
A cell is like a prison- the brick walls surrounding the prison act like the cell membrane keeping the inside protected. It is also similar to a semi-permeable membrane that allow some things to leave and keep other things inside.

3. Types of Transport Passive transport- does not require energy
Moves molecules across the cell membrane from area of high concentration to low
Diffusion- movement of molecules like oxygen, carbon dioxide
Osmosis- movement of water
Active transport- requires energy
Pulls molecules into areas of high concentration
accumulating high concentrations of molecules that the cell needs, such as ions, glucose and amino acids.
Endocytosis / Exocytosis- also requires energy
Moves large molecules (bulk) in and out of the cell.
Ex. White blood cells absorbing bacteria

4. Comparing Diffusion & Osmosis
What is it?
Diffusion is a spontaneous movement of particles from an area of high concentration to an area of low concentration.
Osmosis is the spontaneous net movement of water across a semipermeable membrane
Will continue until it equalizes concentrations on both sides of the membrane.
Process
** Movement of solutes**
**Movement of the solution (water)**

5. Comparing Diffusion & Osmosis
Importance
To create energy;
Helps in exchange of gases
In animals, osmosis influences the distribution of nutrients and the release of metabolic waste products.
Concentration Gradient
Goes from a high solute concentration gradient to a low concentration gradient
Moves down concentration gradient (from high to low) H2O concentration
Water
Doesn’t need water for movement
Needs water for movement
Examples
Perfume or Air Freshener where the gas molecules diffuse into the air spreading the aroma.
Movement of water into root hair cells.

6. Factors that Affect Movement
Factors that affect movement across a cell membrane
Concentration gradient – move from high to low
Molecule size- smaller molecules increase the rate of diffusion
Surface Area- the more the surface area to volume ratio of the cell, the more the substance will diffuse.

7. Cell Sizes Affect of Diffusion

8. Why are Cells Small?
Cells must exchange nutrients & other molecules within its environment.
The cell takes nutrients in and sends wastes out.
The cell membrane is the only way in and out of the cytoplasm.
The cell membrane has a limited surface area.

9. Volume vs Surface Area

10. Surface Area & Volume

11. SA /V Ratio
When talking about a cells ability to function (diffuse molecules across the membrane to get nutrients / remove wastes) we talk about a Surface area to volume ratio.
SA:V ratio describes the amount of surface area per volume unit of the cell.
**The SA determines how much gets in and our but the more volume there is the more materials there will be needed to get in and out of the cell.**
As the cell gets larger, the SA:V ratio decreases making the cell less effective at doing it’s jobs.

12. Math Formulas: Surface area (mm2) = Length X Width X 6 (# of sides)
Volume (mm3) = Length X Width X Height
Surface area to volume ratio (mm2)/(mm3) = Surface area (mm2) Volume (mm3)
Double the cell size (from 1 mm to 2 mm), and the surface area ↑ 4-fold or (increases 4 times)
Double the cell size (from 1 mm to 2 mm), and the volume ↑ 8-fold or (increases 8 times)

13. . . . so it will either be poisoned by its wastes or starve.
So.. Why are Cells Small?
As cell size increases, the surface area to volume ratio decreases.
Therefore, the rate of diffusion slows down....
thus a cell cannot get rid of wastes fast enough or get nutrients fast enough
. . . so it will either be poisoned by its wastes or starve.

14. Cell Size and Diffusion Lab
Background Information:
Potassium permanganate is an indicator for starch and turns dark purple/black.
Cells require nutrients in order to survive.
Cells must eliminate waste in order to survive.
Pretend that each potato cube is a single cell and the the potassium permanganate is the nutrients(food) for the cell.
Purpose: To provide evidence for why cells are so small.
Hypothesis: Make a statement as to which potato (cell) will have the nutrients diffuse the farthest proportionally (closest to the center of the cell) in 30 minutes, and why do you think so.

16. TONICITY & OUR CELLS
When cells are in isotonic solution, movement of water out of the cell is exactly balanced by movement of water into the cell.
A 0.9% solution of NaCl (saline) is isotonic to animal cells.

17. Effects of Osmosis on Living Tissue
Celery Lab
*You must include the definitions for the introduction in your lab report (1 per person)
*Follow Directions CAREFULLY
*Complete all of the Analysis.
Remember what Concentration Gradient means:
In passive transport substances move from a high concentration to a low concentration – this is the natural flow of the gradient

18. Scalpel Safety Hold a scalpel as you would a pencil.
Cut with a downward motion but never push down very hard to make a cut. (If extreme pressure is required, you have a dull scalpel or require a different instrument.)
Watch the placement of your specimen-holding hand. Do not cut toward your holding hand.

19. Exit Slip
Answer the following questions on a separate piece of paper. When you answer, think about the fact that cells have water in them, and how would they respond in hypertonic or hypotonic situations.
1) Why are you thirsty after eating a bag of potato chips?
2) After swimming in the ocean, your lips will be very dry. Explain why.
3) Describe the similarities and differences between osmosis and diffusion.
4) Compare and contrast passive and active transport (how are they the same, and how are they different?)

20. Potatoes lab

21. Osmosis http://www.youtube.com/watch?v=IaZ8MtF3C6M endo /exo
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