1. When you finish your quiz:
Investigation 5.3
When you finish your quiz:
Turn it in to your HW bin
Get out your Textbook
Open to pages
Read procedure for inv 5.3

2. Lab Write-Up
Purpose: To discover the relationship between cell size and diffusion
Data Table:
Cube
Dimensions
Surface Area (cm2)
Volume (cm3)
Surface Area to Volume Ratio
Diffused Distance (cm)
3x3x3 cm
2x2x2 cm
1x1x1 cm
0.1x0.1x0.1 cm

3. Lab Procedure
We will use “cells” of different sizes to test diffusion rates
Cells are made of agar
Agar comes from seaweed: it is the main substance in Jello
How will we test diffusion?
Agar also contain phenolphthalein solution
What is phenolphthalein?
It is an indicator for the presence of a base
Changes color in the presence of a base
What will we use as the diffusion substance?
A base: Sodium Hydroxide (NaOH)

5. Lab Write-Up
Hypothesis: Which cube size will be the best at diffusing chemicals? Why?
Cube size ____ will be best at diffusing chemicals because…
Discussion:
Questions 1,2,4,7,8 (pg. 121)
Conclusion:
Parts A-E
Side note: You only get ONE CUBE of agar per group!
Old Carpenter’s saying: Measure TWICE, cut ONCE

6. When you are done: Turn your quiz into the HW bins
Switch lab books with your partner
Grade your partner’s Investigation 5.3 Write-Up
Make sure both your names and the total points (out of 10) are on the top
Open textbooks to pg 119: Investigation 5.2
and pre-read the procedure

7. Cell Size Limitations Hint for Note-taking: write only what is
Why are cells so small?
Hint for Note-taking:
write only what is
underlined

8. Cell Size and Diffusion
ALL cells had a diffusion distance of around 0.5 cm
This took about 10 minutes
Would this work for an actual cell?

9. Most cells are between 2µm and 200µm
A micrometer is 1 millionth of a meter!
Too small to be seen with naked eye
Why can’t organisms be one big giant cell?

10. Diffusion (passive transport)
Particles (molecules and atoms) move from HIGH concentration to a LOWER concentration.
This is random movement.
The cell does not have to work or expend energy, so no ATP is used.
Diffusion in Action

11. Limits to Cell Size Diffusion limits cell size
Movement of food or wastes is from higher concentration to lower concentration
The larger the distance, the slower the diffusion rate
A cell 20 cm across would require months for nutrients to get to the center

12. Volume vs. Surface Area
As an object like a cube gets bigger, volume increases more rapidly than surface area.
When the cell size doubles (for example from 1 cm3 to 2 cm3), there will be 8x as much volume as before, but only 4x as much surface area as before.

13. Think of a mouse and an elephant
Mice are always cold
Elephants are too hot

14. What is osmosis and how does it affect cell diffusion?
Osmosis and Diffusion
What is osmosis and how does it affect cell diffusion?

15. What is Osmosis? Osmosis: Diffusion of water across a membrane
Different types of membranes will allow some, none, or all particles to move across them
When water moves across, this is osmosis

16. Types of Membranes
Permeable: Allows particles to pass through in either direction
Semi-Permeable: Only allows some particles to pass through
Impermeable: Does not allow particles to pass through
Differentially Permeable: Allows particles to pass through in only ONE direction based on osmotic differential