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

Investigation 5.3

Lab Write-Up

Purpose: To discover the relationship between cell size and diffusion

Data Table: CubeDimensions

Surface Area (cm2)

Volume (cm3)

Surface Area to Volume Ratio

Diffused Distance (cm)

3x3x3 cm

2x2x2 cm

1x1x1 cm

0.1x0.1x0.1 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

JelloHow will we test diffusion?

Agar also contain phenolphthalein solutionWhat 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 partnerGrade 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

WHY ARE CELLS SO SMALL?

HINT FOR NOTE-TAKING: WRITE ONLY WHAT IS

UNDERLINED

Cell Size Limitations

Cell Size and Diffusion

ALL cells had a diffusion distance of around 0.5 cmThis 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

WHAT IS OSMOSIS AND HOW DOES IT AFFECT CELL DIFFUSION?

Osmosis and 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