Mitosis Lesson Plan

Subject:  Biology

Grade Level:  9^th grade

Lesson Duration:  75 minutes

Benchmark: 

5c Cells:  Before a cell divides, the instructions are duplicated so that each of the two new cells gets all the necessary information for carrying on. 

State Benchmark: 12.A.4b

Describe the structures and organization of cells and tissue that underlie basic life functions including…reproduction. [Sample benchmark indicator: Explain asexual reproduction (mitosis)]

Objectives:

1.      The students will be able to identify specific stages of mitosis from illustrations and from animal cells on slides under a microscope. 

2.      The students will be able to draw and label a cell in each stage of mitosis (prophase, metaphase, anaphase, and telophase). 

3.      The students will be able to explain how both of the new cells produced in mitosis contain identical genetic information.

4.      Students should be able to predict what would be happen if there were an error in mitosis. 

Students Background:

The students should have a solid understanding of the structure of a cell.  Students need to know what chromosomes are and understand that they carry the genetic information of an individual.  They also need to know that every cell in an organism must have the same chromosomal DNA.  I would precede this lesson with a discussion on why cells need to divide.  The students must also have a working knowledge of how to properly use a microscope.  Students will also need to have pre-assigned lab partners and lab jobs. 

Materials Needed:

• 15 light microscopes
• 15 prepared slides of the stages of mitosis (from real cells, but separated so that the students can see each distinct stage)
• 30 Mitosis illustrations worksheets (appendix 1)
• Overhead of the mitosis illustrations worksheet (appendix 1)
• Computer with internet access hooked up to a TV or projector
• Many pairs of different colored socks.  No two pairs can look alike.  The exact amount really doesn’t matter as long as there are enough to allow the students understand what is going on.  I suggest about 10 different pairs, although more or less could be used. 

Activity Overview:

This lesson is designed to teach students the steps of mitosis and how  the genetic material changes and moves to create two new identical cells.  There are three different activities in this lesson. 

First, the class will do the sock activity.  This activity will help the students see how the chromosomes of the cell move throughout mitosis and finally end up with two genetically identical cells.  Chromosomes (visibly different pairs of socks) will be in the nucleus (a large circle on the floor) of a cell.  The class will assume that the cell has already replicated its chromosomes.  Each pair of socks will be a pair of chromatids.  (Note:  Do not fold the socks as you would if you had just done the laundry.  Simply place them next to each other so that the students can see that they are paired.)

Second, the class will watch a computer animation of mitosis.  I will hook the computer up to a TV or projector so that all the students can watch at the same time.  I will go to the website:  http://www.sci.sdsu.edu/multimedia/mitosis/.  This particular animation can be paused, watched frame by frame, or sped up.  This will allow me to point out things in the middle of the animation and allow students to ask questions.  At the same website, there is a video of an actual cell dividing.  I will show this several times as well. 

Last, the students will pair up and observe prepared slides of the stages of mitosis under a light microscope.  They will identify and sketch out what they see. A worksheet with examples of each of the stages of mitosis will be provided.  The students will take these sheets home and briefly explain what is happening in each stage. 

Introduction:  (10 minutes)

Teacher (T):  Last class we were discussing cells and why they need to divide.  Who can tell me why our cells divide?  (I will allow wait time after every question.)

Student (S):  Well, we are made of trillions of cells and we only start out from one.  The cells must divide for us to grow. 

T:  That’s good.  Are there any other reasons why cells might divide?

S:  Sometimes cells die and we need to make new ones. 

T:  That could be another reason.  There is one more major reason that a cell might divide, can anyone tell me what it is?

S:  Cells have a volume to surface area ratio that they must keep low.  If the cell gets too big in volume, then it has too little surface area for it to let enough things in and out of the cell and it would not work very well. 

T:  Very good!  So we know that cells need to divide.  Let’s imagine that we have a cell that has reached its volume to surface area ratio and it needs to divide to remain properly functional.  This cell needs to divide up evenly and both new cells need all of the same things that the large cell has.  This means that somehow, this cell needs to make sure that each new cell has the same genetic information.  If they do not have the exact same genetic information, the cell will not function properly.  How do cells do this?  That’s what we are going to discover today!

Body of Lesson:

Sock Activity (20 minutes)

T:  If everyone could come over to this side of the room we will begin our first activity. 

» Have the 10 (or however many) visibly different pairs of socks scattered on the floor within a large circle of tape (the cell wall).  Have matching pairs next to each other, but not folded together.   I will also have a copy of the stages of mitosis (appendix 1) on the overhead.  I will cover the stages with a sheet of paper and uncover them as we go along. 

T:  This is our cell that needs to divide.  The different socks are the cell’s different chromosomes.  Can someone remind the class what chromosomes are?

S:  Chromosomes are condensed pieces of DNA in a cell. 

T:  That’s right.  The chromosomes in this particular cell have already replicated or copied themselves.  As you can see, each chromosome is made of two identical pieces.  These are the identical copies of the cells DNA.  There are many different chromosomes and they all are made of 2 identical copies of DNA.  If you look at the overhead, you can see that this stage of cell division is called prophase.  Now before we go on, can someone tell us what each of these socks represent?

S:  Each pair of matching socks is a chromosome.  Each chromosome is made of two identical copies of the same DNA.  That is what each individual sock is. 

T:  Exactly.  So now we can move on to the next step.  In this step, all of the chromosomes line up down the middle of the cell like this.  (I will move the socks to line up down the middle of the circle.)  This stage is called metaphase.  (I will uncover metaphase on the overhead.)  This is getting the chromosomes ready to split up and move to either side of the cell.  So now, what happens in metaphase?

S:  The chromosomes line up down the center of the cell. 

T:  Yes.  Now we can see what happens to the chromosomes.  An apparatus in the cell is formed called the spindle fibers.  The spindle fibers are just like pieces of string from either side of the cell that reach out to each chromosome and pull the identical pieces in opposite directions.  The spindle fibers attach to the centromere, or the center of each chromosome.  Then, they begin to pull half of the chromosome to each side of the cell.  (I will begin to separate the pair of socks by moving one sock of each pair in either direction.)  This stage is called anaphase.  (I will uncover anaphase on the overhead.)  Okay, there were some key terms and ideas in this stage.  First, can someone explain what the spindle fibers do?

S:  The spindle fibers come from two opposite ends of the cell and reach out and pull the chromosomes apart.

T:  That’s good.  Does anyone remember where the spindle fibers attach to the chromosomes?

S:  The center of the chromosome.  That’s called the centromere. 

T:  Very good.  You can see the centromeres more clearly on the overhead.  There are the little circles in the center of the chromosomes.  (I will point them out).  Now the chromosomes are separating out equally to opposite sides of the cell.  The chromosomes finish moving and then the cell actually needs to divide into two separate cells.  (I will finish moving the chromosomes apart and then put a new piece of tape down the middle separating it into two new cells.)  This stage is called telophase.  (I will uncover telophase on the overhead.)  All of these stages together are what happens during cell division.  All of these steps together is called mitosis.  So we have gone through four different steps to mitosis.  Can someone start us at the beginning and tell us what happens?  Feel free to show us with the socks.

S:  Well, first it starts in prophase where the DNA is already replicated and is condensed into chromosomes. 

T:  And what are the chromosomes composed of?

S:  Two identical copies of DNA.  Each sock in the chromosome represents a copy. 

T:  Great.  So we have replicated DNA in the form of chromosomes.  Can someone else tell us what happens next?

S:  The chromosomes line up down the middle in the next step called metaphase. 

T:  Exactly.  And then what happens?

S:  The chromosomes separate into the two separate copies and move to opposite sides of the cell. 

T:  Great.  What are the things that pull the chromosomes apart called?

S:  Spindle fibers.

T:  And the spindle fibers attach where on the chromosome?

S:  The centromere. 

T:  Exactly.  And this all happens in which step?

S:  Anaphase.

T:  What happens after anaphase?

S:  Telophase.

T:  Yes, that is right, and what happens in telophase?

S:  The chromosomes finish dividing and the cell splits into two separate cells. 

T:  That’s right.  And what happens after that?

S:  That’s the end.

T:  Well, it’s the end of this cell division, but the cell will work and grow and then it will need to divide.  After awhile each of these new cells will go through mitosis too!  Now that we have looked at mitosis using socks, we are going to see a short animation and video of mitosis.  Please take your seats.

Computer Animation and Video: (10 minutes)

» I would set up the computer and TV or projector ahead of time.  I would also test it to make sure that everything is working well.  The website address is: http://www.sci.sdsu.edu/multimedia/mitosis/

T:  Now I have an animation that we will watch.  First we will watch the whole thing.  It shows us the stages of mitosis.  Now before we start, let’s make sure that we all understand what we are looking at.  Can someone tell me what the red and blue x’s in the middle are?

S:  They are the chromosomes. 

T:  Right.  And like the pairs of socks, they are already replicated or copied.  You can see two halves on each chromosome.  Those are the identical copies of DNA.  Now let’s watch the whole thing. 

» I will show the animation in its entirety.  I would show it at about 2 frames per second.  At this speed, I can tell the students which stage the cell is in. 

T:  I hope everyone was able to follow along.  Now we can go through it frame by frame and talk about what it happening. 

» I will start going through the animation frame by frame.

T:  When the chromosomes are moving toward the center, which step is this?  (I would have the animation stopped on a frame showing metaphase.)

S:  Metaphase.

T:  (Continue with the animation frame by frame.)  Now what is pulling the chromosomes apart here in anaphase?

S:  The spindle fibers. 

T:  And where do the spindle fibers attach?

S:  The centromeres.

T:  Exactly.  You can see the centromeres here.  And you can see them splitting up as the chromosomes separate.  (Continue with animation.)  And now at then end of telophase, what do we have?

S:  Two genetically identical new cells.

T:  Good job class.  You seem to be understanding mitosis.  The other part of this animation is a video of a real cell undergoing mitosis.  Let’s watch that.  (I will show the video of mitosis.)  I know that went by really fast, but that’s what it looks like in a real cell.  Let’s watch it again.  (I would show the video 2 or 3 more times depending on student interest.)  Great, now we can look at some slides of real cells going through mitosis.

Microscope Activity: (30 minutes)

T:  You need to sit next to your lab partner and have the materials person go get you two a microscope.  The other partner needs to get out two sheets of paper.  I will hand out the slides.  

» Allow time for students to get their microscopes.  Hand out the pre-made slides of the stages of mitosis. 

T:  Now that you all have microscopes and paper, you all should be able to observe the different stages of mitosis on your slide.  Go ahead and look at your slide and see what is on it.  (I will pause for the students to focus on their slides.)  There are 4 separate cells on the slide.  Each cell is frozen in a specific stage of mitosis.  I want you to sketch out each stage on a sheet of paper.  The sketch doesn’t need to be very detailed, I simply what you to identify where the chromosomes are in each of the stages and what they look like.  I will come around to each group to see if you are finding the stages and to see your drawings.  What is it that you need in your sketches?

S:  We need to draw the cell and where the chromosomes are in each stage.

T:  Right.  You can just draw four circles and then fill them in with the positions of the chromosomes.  Go ahead and get started.  I will be coming around. 

» I will walk around the classroom making sure that everyone is on task.   I will check the microscope image to make sure that they are seeing what they need to be seeing.  I will also look at their sketches and help them if they are not doing it right. 

  T:  We are running out of time.  You have about 3 minutes to wrap up your sketches and put away your microscopes.  Please bring your slides up to the front of the room and set them on my desk. 

Closure:  (5 minutes)

T:  For one last time, let’s walk through the stages of mitosis using everything we have learned today.  Can someone tell me what happens first in prophase?

S:  In prophase, the DNA has already copied itself and is condensed into chromosomes.  The chromosomes are made of identical copies of DNA. 

T:  Good, and then what happens next?

S:  The chromosomes line up down the middle in metaphase.

T:  That’s right.  What happens next?

S:  Anaphase is next.  The spindle fibers attach to the centromeres of the chromosomes and begin to pull the chromosomes apart.  One copy of each chromosome goes to each opposite side of the cell. 

T:  Great!  Who can tell me what happens after that?

S:  The chromosomes reach opposite ends of the cell and then the cell splits apart and makes two new cells.  This is called telophase. 

T:  You all really seem to understand this.  What is so special about the two new cells that have been made?

S:  They have identical genetic material. 

T:  Wonderful!  It seems like you all have a fairly good grasp on mitosis now.  For your homework, I want you all to take the sketches that you have drawn from the slides, and write a short explanation of what is happening with the chromosomes in  each step.  Also be sure to write the name of the stage of each sketch if you haven’t already.  That will be due at the beginning of the next class.  Have a great day!

Assessment: 

• The homework is a form of assessment.  I will be able to see if students understand what is happening with the chromosomes during mitosis.  I will also see if they are using the students are using the terminology that they learned in class. 
• For a summitive assessment I would give a quiz.  

1.      What is the purpose of mitosis?  What are the end products?  (be specific)

2.      Here are the four stages of mitosis (I would have unlabeled diagrams of prophase, metaphase, anaphase and telophase out of order.)  Please name them and put them in order (1-4). 

3.      Imagine that a cell is going through mitosis.  During anaphase, one of the chromosomes does not separate properly.  The entire chromosomes is pulled to one side of the cell.  This new cell that forms from this side has the entire chromosome (both identical copies of DNA).  What might happen to the other cell that is produced in this particular mitotic division?