CellSizeLimitations_Diffusion
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Transcript CellSizeLimitations_Diffusion
Investigation 5.3
WHEN YOU FINISH YOUR QUIZ:
1) TURN IT IN TO YOUR HW BIN
2) GET OUT YOUR TEXTBOOK
3) OPEN TO PAGES 120-121
4) READ PROCEDURE FOR INV 5.3
Lab Write-Up
Purpose: To discover the relationship between cell
size and diffusion
Data Table:
Cube
Dimensions
3x3x3 cm
2x2x2 cm
1x1x1 cm
0.1x0.1x0.1 cm
Surface
Area (cm2)
Volume Surface Area to
(cm3)
Volume Ratio
Diffused
Distance (cm)
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)
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
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
Cell Size Limitations
WHY ARE CELLS SO SMALL?
HINT FOR NOTE-TAKING:
WRITE ONLY WHAT IS
UNDERLINED
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?
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?
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
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
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.
Think of a mouse and an elephant
Mice are always cold
Elephants are too hot
Osmosis and Diffusion
WHAT IS OSMOSIS AND HOW DOES IT
AFFECT CELL DIFFUSION?
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
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