Lesson Plan for - Why Cells Are Small

8/3/2019 Lesson Plan for - Why Cells Are Small

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Frederick R. Logan

[email protected]

Title of lesson:

Why Cells are Small.

Content Area:

State of California Science Content Standards, Cell Biology 1a and 1e.

Background:

The purpose of the lesson is to demonstrate the following

- There is a limit to cell size.

- The relationship of cell size to homeostasis.

- Why cells need to divide.- Why are larger organism made out of many smaller cells as opposed to one or a few large cells.

Introduction:

Before the students work on this lab have them read pages 13-21 in their science book (Focus on

Life Science, California Edition.).

Before starting the lab go over with the students using overheads, white boards, or a chalk board the

following points (making sure to write the information down before speaking/lecturing and having

the students copy the notes):

Cell are the basic unit of structure and function for all life. In other words, cells are thesmallest unit of life that is able to carry out all the function associated with life (Respond to

Stimulus, Homeostasis, Need for Energy, Reproduction, etc..).

Materials from outside the cell are needed to support these functions/requirements as well as

the need for the cell to get rid of waste products formed as a result of thesefunctions/requirements.

Materials used during cell activity enter the cell from the outside through the cell membraneand must travel through the cytoplasm to their destination. This destination might be directly

in the center of the cell (or close to it). Waste products travel through the cytoplasm to the

cell surface to the outside. If materials are not able to reach a destination in a certain time, the cell might not be able to

function properly or possibly die.
mailto:[email protected]:[email protected]


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Materials:

Each group of four students should get one each of the following:

For the Lab Exercise

1 set of Phenolphthalein Agar Blocks (PAB) - (A set consist of 1 3cm3 , 1 2cm3, and 1 1cm3 PABblocks).*

100 ml of 0.4% NaOH (CAUTION: NaOH or Sodium hydroxide is caustic and can burn the skin, mucusmembranes, and eyes.)1 Plastic Spoon

1 self sealing snack size plastic bag (Zip-lock style)

4 Safety Goggles

4 Pairs of GlovesMillimeter Ruler

Paper Towels

4 Lab Sheets.1 Knife (options: a razor blade or a 10 cm piece of thin fishing line tied between two bamboo skewers).

1 stopwatch (optional)

For the assessment:

1 Set of Starch Agar Blocks (SAB) (3cm X 3cm X 3cm , 3cm X 2cm X 4cm, and 3cm X 1cm X 5cm).+

100ml of 0.1% Iodine Solution.

(all other materials will be the same as for the lab exercise).

*The Phenolphthalein Agar Blocks (PAB) are made by using 10gs of Agar and 2 gs of Phenolphthalein per1000 ml of H2O. 2500 ml of finished solution will fill a standard 9x11 cake pan up to 3ml deep.

Boil the water, add the agar, stir well (do not allow to boil).

When the agar has fully dissolved turn of the heat source. After taking the solution off the heat source, add the Phenolphthalein and stir well. The solution should

not turn pink (if it does, add a few drops of HCL to neutralize the color).

Pour the solution into the pan before it starts to set. (It actually sets very quickly once it starts to cool).

+ Starch Agar Blocks (SAB) are made by using 10gs of Agar and 2 gs of starch per 1000 ml of H2O.

Boil the water, add the agar, stir well (do not allow to boil).

When the agar has fully dissolved turn of the heat source.

After taking the solution off the heat source, dissolve the starch in a small amount of cold water, add to

the agar solution and stir well.

Pour the solution into the pan before it starts to set. (It actually sets very quickly once it starts to cool).


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Through (Procedure):

1) Have the student form groups of four students with the following responsibilities (have this done before

handing out materials:

- Timer - Person who measures and sketches the PABs.

- Person who uses the spoon to place the PABs into the plastic bag and pours the 0.4%NaoH solutioninto 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 lab sheets.

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 25 minutes)

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

8) Show the students how to calculate the total surface area of each of the three cell models using the

following formula: Surface area of a cube is = 6 x (length x width x height), that is, the total surface area is

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 the following

formula: Volume of a cube is = length x width x height. Ask the students which cube has the greatest

volume.

10) Show the students how to calculate the Surface Area to Volume Ratio for each cube. To do this, foreach 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 volume of 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 in the

quickest.

12) After 20 minutes has lapsed, have the students take the cubes out of the solution, dry off the cubes with

a paper towel, and cut the cubes in half.

13) Measure the distance the color has traveled.

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

15) After cleaning up, have the entire group go before class and present their results. After presenting have

them write their results on a class graph on an overhead, white-board, or chalk board.


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16) Have the entire class write down the class graph and ask for volunteers to make some generalizations

about

Beyond (Homework):

Have the students answer the following questions that have been written down on an overhead, white-board,

or chalk board.

1) On your worksheet, which column in your lab worksheet represents the amount of cell membrane

around a cell?

2) On your worksheet, which column in your lab worksheet represents the contents of the cell

(cytoplasm and nucleus)?3) As the cell grows larger, does the Surface Area to Volume Ratio become larger, smaller, or stay the

same?

4) Which cell has the greatest total surface area to volume ratio?5) Which cell has the greatest chance of survival?

6) What do cells in your body do when they get too big to for materials to get in and out of the cell fast

enough to function properly?

Assessment:

1. Ask the students to predict which of the following cells will have the greatest chance for survival:

1) 3cm x 3cm x 3cm

2) 3cm x 2cm x 4cm3) 3cm x 1cm x 5cm

2. The students need to back up their prediction based upon the Surface Area to Volume ratios.

3. Give the students in groups of four the material for the assessment (All the material will be the same withthe exception of using SAB and Iodine).

4. Have the students follow the same procedure for the PABs, except tell them that they will allow the

blocks to sit in the solution for 30 minutes.

5. At the end of 30 minutes, have one of the students take out the three blocks, dry them off, cut them in half

lengthwise, then examine them to determine if the pattern of color penetration supported the students

prediction.

6. After cleaning up, have the entire group go before class and present their results. Have them share their

predictions they made before testing the three blocks and if their results supported their original predictions.

This lesson has information derived from the following sources:

Diffusion in Simulated Agar Cells by Kathryn Dishaw (www.bctf.bc.ca/BCScTA/)

Cell Size Lab by Shannon Tice (http://chem.lapeer.org/bio1docs/CellSize.html)

Cell Size and Division by Nicholas DiGiovanni (http://www.iit.edu/~smile/bi9226.html)
http://www.bctf.bc.ca/BCScTA/http://chem.lapeer.org/bio1docs/CellSize.htmlhttp://www.iit.edu/~smile/bi9226.htmlhttp://www.bctf.bc.ca/BCScTA/http://chem.lapeer.org/bio1docs/CellSize.htmlhttp://www.iit.edu/~smile/bi9226.html


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Modifications for ESL Students:

1. Provide copies of all notes and lectures to ESL students for them to compare their own

notes to those presented by the instructor during the exercise.

2. Use graphic organizers to show relationships of concepts to each other. (An example of a

graphic organizer is included)

They

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Lesson Plan for - Why Cells Are Small

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