8/3/2019 Why Are Cells Small Pre-Lab Handout

1/4

Why Are Cells Small? Lab Activity

Name: ________________________________ Period;________________

Background InformationYou are going to investigate the question Why cells are small? using blocks of a porous materialcalled agar that allows a solution to enter freely into the inside of the blocks through a process calleddiffusion. These blocks will simulate cells of different sizes but of the same shape.

Agar or agar agar is a gelatinous substance obtained from the cell membranes of some species of redalgae or seaweed. The word agar comes from the Malay word agar-agar (meaning jelly). It is alsoknown as kanten, agal-agal (Ceylon agar), or China grass. Chemically, agar is a poly mer (poly = many)made up of many small units of the of the sugar galactose.

The agar blocks you will be using contain a color changing chemical called Phenolphthalein. In the presence of a basic solution the phenolphthalein will turn a very bright color. The Phenolphthalein Agar Blocks will be abbreviated in the future as as PAB.

The basic solution you will be using contains water and a chemical called Sodium Hydroxide. Asolution is a mixture of materials, one of which is usually a fluid. A fluid is a material that flows, such asa liquid or a gas. The fluid of a solution is usually the solvent. The material other than the solvent is thesolute. We say that we dissolve the solute into the solvent. The solution you will be using will have astrength of about 0.1%. It is dilute but can cause strong irritation if gotten in your eyes or on your skin.

In the image above, you have a drop of concentrated dye in the middle of the beaker with water. At the beginning the dye is only found in the middle, while the rest of the beaker contains water molecules.After time, the dye molecules spread out away from each other and becomes evenly dispersedthroughout the beaker of water.

8/3/2019 Why Are Cells Small Pre-Lab Handout

2/4

Safety concerns:It is important that you do not handle the Phenolphtahlein Agar Blocks (PABs) without gloves. If youwere to accidentally ingest (swallow) the Phenolphthalein, it could cause gastrointestinal distress or

extremely strong purging (diarrhea).

Sodium Hydroxide (NaOH) is used as a drain cleaner (37% or above). Although the solution we will beusing in class will be very dilute (0.1%), it can still hurt you if you are careless. Use goggles at all timesfor this activity! If you are caught with your goggles off, you will receive a ZERO for your labgrade.

Referenceshttp://www.chem4kids.com/files/react_acidbase.htmlhttp://www.chemtutor.com/solution.htmhttp://en.wikipedia.org/wiki/Agar

Question: Why is the human body composed of Trillions of very tiny cells vs a small group of very largecells?

Hypothesis: ___________________________________________________________________________________ ___________________________________________________________________________________ ___________________________________________________________________________________ ___

Methods and MaterialsMaterials (per lab group)3 blocks of PAB1 knife1 Metric ruler Paper towels1 glass jar with 0.1% NaOH solution

http://www.chem4kids.com/files/react_acidbase.htmlhttp://www.chemtutor.com/solution.htmhttp://en.wikipedia.org/wiki/Agarhttp://www.chem4kids.com/files/react_acidbase.htmlhttp://www.chemtutor.com/solution.htmhttp://en.wikipedia.org/wiki/Agar

8/3/2019 Why Are Cells Small Pre-Lab Handout

3/4

Procedure:

1) Each group will determine who will have the following responsibilities (have this done before the labstarts!):- Timer - Person who measures and sketches the PABs.- Person who uses the spoon to place the PABs into the plastic bag and pours the 0.1%NaoHsolution into the plastic bag.- Person who takes the PABs out to the plastic bag, dries them off, and cuts them in half.

2) Hand out the supplies.3) Have the students measure the dimensions of the blocks and record the measurements on their labsheets.

4) Have the students place the blocks in the plastic bag, using the spoon.

5) Have them carefully pour the 100ml 0.4%NaoH solution over the PABs.

6) Have the timer start the time (the blocks have to stay covered by the NaoH solution for 15 minutes)

7) Have the students record the following information on their worksheets.

8) After 15 minutes has lapsed, have the students take the cubes out of the solution, dry off the cubeswith a paper towel, and cut the cubes in half.

9) Measure the distance the color has traveled.

10) Have the students properly dispose of waste materials, wash their hands, and clean up.

8/3/2019 Why Are Cells Small Pre-Lab Handout

4/4

Day 2

8) Show the students how to calculate the total surface area of each of the three cell models using thefollowing formula: Surface area of a cube is = 6 x (length x width x height), that is, the total surface areais 6 times the surface area of one side. Ask the students which cube has the greatest surface area.

9) Show the students how to calculate the total volume of each of the three cell models using thefollowing formula: Volume of a cube is = length x width x height. Ask the students which cube has thegreatest volume.

10) Show the students how to calculate the Surface Area to Volume Ratio for each cube. To do this, for each cube size, divide its surface area by its volume (SA/V = Surface Area to Volume Ratio). The

number obtained can be expressed as a ratio. For example, a surface area of 24cm2 divided by a volumeof 3 cm3 = 24/3 = 8/1 = 8:1. 7.

11) After doing the calculations, ask the students which of the three cells will allow materials to move inthe quickest.