Cells and Cell Division R20071012A

8/14/2019 Cells and Cell Division R20071012A

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Cells and Cell Division

Almost everything in the world is made up of smaller

things. Houses are built out of individual bricks andpieces of wood. Cars are built out of pieces of metal,plastic, and rubber. Think about your favorite toy.What parts make up your favorite toy?

The Cell Theory

One very important similarity among all living things is that they aremade ofcells, the smallest units of life. In 1838, two biologists,Schleiden and Schwann, studied many cells and made some conclusions.From their observations they developed what is known as the CellTheory. Since then, this theory has been central to our understanding of

biology. This theory states that:

1. All life forms are made from one or more cells. Someorganisms, like bacteria or paramecium, are only one cell big. These arecalled unicellular organisms (uni=one). Other organisms aremulticellular: that means they are made up of more than one cell(multi=more than one). For example, the human body consists ofbillions of cells!

2. Cells only arise from pre-existing cells. A cell can make copiesof everything it has inside it, then divide itself in two, making two newcells. This process is called mitosis, orcell division. In this way,organisms can keep growing or replace damaged or old cells. Forexample, the formation of new cells is what allows your body to grow,


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or what replaces your damaged skin when you fall and skin your knee,making you good as new!

3. The cell is the smallest form of life. There is nothing smaller

that is alive, and life requires what is inside a cell. For example, themolecules that make up the parts of the cell, such as sugars, fats andproteins are not alive. The separate regions of the cell are not alive ontheir own. Life can only be reduced down to the cellular level-thus cellsare the smallest unit of life!

The Cell and Its Organelles

Even the cell is made up of smaller parts. These parts are callorganelles (little organs). They divide up all the work that the cell hasto do. In the human body, we have different organs to do different jobsthat help us live: for example, our lunges help us breathe while our brainhelps us think. Its the same in a cell: the different organelles havedifferent jobs, and together they help the cell live.


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In a unicellular organism, one cell does all the jobs the being needs tosurvive, and the cell divides up these jobs among its organelles. Inmulticellular organisms, many cells come together to make a livingbeing. Just like in unicellular organisms, the cells of a multicellular

organism have organelles which divide up the cells work.

Make a Cell

We just learned that a cell contains different organelles to help it divideup the work it has to do. Lets learn more about those organelles bybuilding a cell of our own?

1.Your TA will give you a Styrofoam bowl filled with jello. This isyour empty cell that you will need to add the organelles to.


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2.Using the spoon, scoop out asmall hole in the center forthe gumball. This is thenucleus. The nucleus is the

control center of the cell. Ithouses all the geneticinformation, DNA in theform of chromatin, that tellsthe cell what to do. DNA islike the recipe for the cell: allthe instructions are there, andthe organelles of the cell help

to read it and build the finalproducts: proteins! When the cell reads its DNA recipe in itsnucleus, it converts these instructions to another form calledmessenger RNA (mRNA), which is like translating from onelanguage to another in a process called transcription.


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3.Now carve out a slit for thered fruit roll up. This is theendoplasmic reticulum

(ER). The ER is like a littlemaze of tubes that arehollow inside. Add a fewcake sprinkles right next tothe ER. These areribosomes. After mRNA is

made in the nucleus, it is sent to the ribosomes on the ER. Theribosomes are responsible for reading the mRNA message and

making the proper protein according to its instructions. Thisprocess is called translation. As a protein is made, ortranslated, the ribosomes pushes it into the maze of the ER. Asecond type of ER, called the smooth ER is where fats are formed.It is called smooth ER because it has no ribosomes on it.

4.Carve out another slit for the other fruit roll up. This is the GolgiBody. The proteins made by the ribosomes that are inside the ERare sent to the Golgi for finishing

touches and distribution. Here,the protein may be packaged orchanged: its like putting the painton a car being made in a factorybefore it is sent out to the cardealer!


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5.The powerplant of the cell is themitochondria. Using the spoon, scoop outtwo holes for the red hot tamales. The

mitochondria gets fuel from the food thatyou eat, like sugar. It then converts the fuelto useful forms of energy for the cell.

6.When performing their actions, cells makewaste. But where does it go? To the lysosome,which is full of molecules that can break downcellular waste. Using your spoon, scoop out a

hole for the Junior Mint, which serves as thelysosome. Lysosomes are the garbage dumpsof the cellthey break down waste and dispose of it properly.

7.How does the cell stay together? They are housed in a double-layered coating called the plasma membrane, that gives the cellits shape. This membrane helps control what goes in and out of thecell, and helps protect the cell from damaging things in theenvironment. The white Styrofoam bowl serves as the plasma

membrane.

8. Inside the plasma membrane is a gel-like fluid called the cytosolthat surrounds the organelles. Thats the jello in your cell!

9.Now put the lid on your jello cell and write your name on the top.Make sure to tell your parents each of the different parts beforeyou eat it!


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Mitosis

Every organism starts out as one cell. In order to become a multicellularorganism, cells must grow and divide. The ability to grow and divide isone of the most unique characteristics of the cell. Every cell, whether aunicellular organism or a single cell in a complex multicellularorganism, arises from a pre-existing parental cell by a process known ascell division.

Your TA will lead you to the next room, where you will be able to viewthe first cell(s) of a frog.

Every frog starts out as zygote. A zygote is a single cell that is 1.6million times bigger than a single cell of an adult frog. The zygote willundergo millions of divisions before it becomes an adult frog.

Look at the zygote on the TV screen, which is connected to themicroscope. Identify on the screen the parts of the zygote:

It takes 20 to 30 minutes for the zygote to divide. Your TA will bringyou back to see the progress of the zygote. First you get to learn moreabout the process of cell division called mitosis. For now, skip the nextpage of your workbook.

THE SECOND VISIT

Once the zygote goes through one cell division, it enters the 2-cell stage.After the second division, it enters the 4-cell stage. After the third


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division, it enters the 8-cell stage. Find a dividing frog egg that looksinteresting to you and draw it below:

What stage is it in? ________________________________________

THE THIRD VISIT

If there is enough time, your TA will bring you back to look at thedividing frog egg again. Pick out one you like and draw it below:

How many cells does the one you drew have? _______________

Looking at Mitosis

Cell growth can occur by simplymaking more of the cellular moleculesand organelles. This period of growthis called interphase. Duringinterphase, the cell makes copies of itsDNA. Once the cell has copied its


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DNA and is big enough, it divides. Mitosis is the name given to theperiod during which the cell divides.

During mitosis, DNA sequences that were duplicated during interphase

must be precisely divided, such that the two daughter cells receiveexactly the same genetic information. During mitosis, the DNAinformation condenses into tightly packed coils called chromosomes.Scientists use a dye that stains the chromosomes for viewing under amicroscope. We will be using this dye today. Mitosis occurs in stepsthat, with the help of the DNA dye, can be seen with the help of amicroscope. These are the steps of mitosis:

PROPHASE: The DNA, which isin a loosely-packed form calledchromatin, condenses intochromosomes. Under themicroscope, this looks like achange from a tangled mass of thinthreads to shorter, thicket units.The chromosomes are composed oftwo paired sister chromatids that

are held together by a centromere.The nuclear membrane disappearsso that the chromosomes can be divided.

METAPHASE: The chromosomesline up at the middle of the cell.

ANAPHASE: The sister


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chromatids are separated and move to opposite ends of the cell.

TELOPHASE: The chromosomesuncoil, going back to chromatin, andnuclear membranes reform aroundthe two new nuclei.

CYTOKINESIS: The cytoplasm

divides, completing the cell division.What started as one parent cell isnow two daughter cells.

The Microscope

Always carry the microscope with one hand under the base and one

hand holding the arm.


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BASE: supports the microscope

ARM: supports the body of the microscope

STAGE: the surface where the object you are looking at is placed

DIAPHRAGM: regulates the size of the light beam which enters theobjective lens

LIGHT: shines light through the object you are looking at to make iteasier to see

OBJECTIVE LENS: magnifies (makes bigger) the object you arelooking at

EYEPIECE: allows you to see the magnified objectFOCUS KNOBS: lower or raise the stage so that the image is in focus

Proper Handling of the Microscope

1.Clean the eyepieces with lens paper, never use anything else likeKleenex, cheesecloth, or handkerchief

2.Always start with the 4X objective (also known as the scanningobjective) when looking at a slide with your illumination set at 2 or3.

3.Always center the specimen in the field of view before switchingto the next higher objective.

4.Always use a coverslip when examining a wet-mount preparation.5.Do not spill any fluids on the microscope stage. If you do, clean

and dry the stage with a Kimwipe immediately.6.When you are done, leave the microscope ready for the next personby:

a. Return the 4X objective to the viewing position.b.Remove the slide from the stage.c. Clean off the immersion oil.d.Lower the stage to its lowest level.


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e. Turn off the light switch.f. Wrap the cord securely around the microscope.

7.Ask your TA if you have any questions!

In this next exercise, you are going to have the opportunity to lookfor the different stages of mitosis. Your TA will give you a preparedslide taken from a growing plant root. Why do you think it is necessaryto use an actively growing plant to look at dividing cells?

1.Place the slide on the stage of your compound microscope andlocate the tip using the 4X objective.

2.Switch to the 10X objective for a more detailed examination of theroot tip. You should be able to see dividing cells. Switch the 45X

to observe interesting cells more closely.

3.Locate and draw a cell in interphase

4.Locate and draw a cell in prophase


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5.Locate and draw a cell in metaphase

6.Locate and draw a cell in anaphase

7.Locate and draw a cell in telophase

What do you See?


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Your TA will give you several different things you may have comeacross in your everyday life. Pick one thing and put it under themicroscope.

Look at it using the 4X objective. What do you see?


Look at it using the highest power objective. What do you see?

Pick another item.



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Look at it using the highest power objective. What do you see?


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How Do Scientists Do Science?

Almost all scientists follow the Scientific Method when performingscience experiments. The scientific method has 5 steps, all of which arevery important.

1.OBSERVATION: Scientists observe the world around us. Thereare many different types of scientists that observe different aspectsof the world. Zoologists observe animals and botanists observeplants. If you were a scientist, what kind of things would you wantto observe?

2.ASK A QUESTION: After making observations,a scientist will ask himself or herself a questionsabout something. For instance, what makesdogs drool? It is important that scientists askquestions that can be answered. What is aquestion you have about something you haveobserved?

3.FORM A HYPOTHESIS: A hypothesis is aprediction about the answer to the question. Inthis case, the scientist might predict that only


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food will make the dog drool. What is your hypothesis for yourquestion?

4.PROCEDURE: Once the scientist has identified a question, he orshe must decide how to go about answering the question. To findout what makes dogs drool, a scientist might decide to put differentthings in front of the dog, like food, water, or dog biscuits, and

record the dogs reaction. Can you think of a way to answer yourquestion?

5.DATA COLLECTION: After deciding on a procedure, a scientistwill follow the procedure. The observations collected from theprocedures are called data. In the example above, the scientist

would make a list of the things placed in front of the dog and markdrool or no drool next to each thing. What kind of data wouldyou collect from your procedure?


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6.CONCLUSION: Based on the data collected, you will eitherconfirm or not confirm your hypothesis. If only food made the dogdrool, then the scientist can confirm the hypothesis. If somethingelse made the dog drool, the scientist did not confirm thehypothesis. Usually, the scientist will make a new hypothesis, andstart all over again.

An extremely important part of science experiments is something calleda control. A control is used to show that the data you collected is

because of your procedure. For example, the scientist performing theexperiment above would have a control by noting that the dog does notdrool when nothing is placed in front of it. If the dog drools whennothing is in front of it, the scientists data dont mean anything!

Your Turn to be a Scientist!

Over the four weeks of LABS, you will be able to use the ScientificMethod. Your group, with the help of your TA, will ask a questionabout plant growth, make a hypothesis, outline a procedure, collect data,and make a conclusion.

STEP 1: OBSERVATIONThink about what you know about plants and how they grow. Write

down anything you can think of. (Hints: What do plants need to grow?What makes them grow best?)


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STEP 2: ASK A QUESTIONHave you ever wondered how different things affect plant growth?

Discuss different questions with your group and your TA. Make surethat it is a question that can be answered. Decide on a question andwrite it below:

STEP 3: MAKE A HYPOTHESISWhat do you think is the answer to your question? Decide as a group ona hypothesis. Write it below:

STEP 4: DESIGN A PROCEDUREHow can you answer your question? Your group will have bean plantsto use to test your hypothesis. Make sure to have a control!! Write yourprocedure below:


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STEP 5: COLLECT DATAOver the next two weeks, your group will collect data as stated in yourprocedure. Remember to put it in the data sheet your TA will give you.

STEP 6: CONCLUSIONDuring week 3, your group will come to a conclusion about yourhypothesis.

Take Home Science

When you leave today, you will take both your jello cell and agar plateswith you.

Before you eat your cell, share what you learned with your parents.After you tell your parents about each organelle, eat that organelle.Finally, eat all the cytosol (jello) and throw away the plasma membrane(styrofoam bowl).

Bacteria are unicellular organisms that are everywhere, but are usuallyinvisible. Over the next week, you will have the chance watch bacteriagrow by dividing over and over again.

Using the sterile cotton swabs, find a place in your house you thinktheres a lot of bacteria and rub the cotton swab on it (door knobs, faucethandles, etc.). Then rub the swab on the agar plates. Over the week,look at the plates. Every other day, look at the plates and observe whatis going on. Write down what you think might be happening on the twoplates.

DAY OBSERVATIONS


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Data Sheet

DATE Height of Condition 1:

_____________

Height ofCondition 2:

_____________

Height ofCondition 3:

_____________

April 26, 2003

May 3, 2003

May 10, 2003

May 17, 2003

Acknowledgements

Thanks to everyone who made today possible!


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Dr. John Mordacq and Sue Fox for your ideas and supportthroughout the year.

Joyce and Rick Morimoto for making this amazing program

possible and support throughout the year.

Kate Veraldi for handling all the administrative work.

The Doi family for sotring the lab coats and helping with snacks.

The TAs and JTAs for making the kids experiences better.

The Labonne lab, especially Elizabeth, for the frog eggs.

References

www.axcessexcellence.comBiology 210 Lab Manual

Cells and Cell Division R20071012A

Documents

Transcript of Cells and Cell Division R20071012A