Cells and Cell Division (Biology)

Cells and Cell Division Almost everything in the world is made up of smaller things. Houses are built out of individual bricks and pieces 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 are made of cells, 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 Cell Theory. 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. Some organisms, like bacteria or paramecium, are only one cell big. These are called unicellular organisms (uni=one). Other organisms are multicellular: that means they are made up of more than one cell (multi=more than one). For example, the human body consists of billions of cells! 2. Cells only arise from pre-existing cells. A cell can make copies of everything it has inside it, then divide itself in two, making two new cells. This process is called mitosis, or cell division. In this way, organisms can keep growing or replace damaged or old cells. For example, the formation of new cells is what allows your body to grow,

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, the molecules that make up the parts of the cell, such as sugars, fats and proteins are not alive. The separate regions of the cell are not alive on their own. Life can only be reduced down to the cellular level-thus cells are the smallest unit of life!

The Cell and Its Organelles Even the cell is made up of smaller parts. These parts are call organelles (little organs). They divide up all the work that the cell has to do. In the human body, we have different organs to do different jobs that help us live: for example, our lunges help us breathe while our brain helps us think. It’s the same in a cell: the different organelles have different jobs, and together they help the cell live.

In a unicellular organism, one cell does all the jobs the being needs to survive, and the cell divides up these jobs among its organelles. In multicellular organisms, many cells come together to make a living being. Just like in unicellular organisms, the cells of a multicellular organism have organelles which divide up the cell’s work.

Make a Cell We just learned that a cell contains different organelles to help it divide up the work it has to do. Let’s learn more about those organelles by building a cell of our own? 1. Your TA will give you a Styrofoam bowl filled with jello. This is your empty cell that you will need to add the organelles to.

2. Using the spoon, scoop out a small hole in the center for the gumball. This is the nucleus. The nucleus is the control center of the cell. It houses all the genetic information, DNA in the form of chromatin, that tells the cell what to do. DNA is like the recipe for the cell: all the instructions are there, and the organelles of the cell help to read it and build the final products: proteins! When the cell reads its DNA recipe in its nucleus, it converts these instructions to another form called messenger RNA (mRNA), which is like translating from one language to another in a process called transcription.

3. Now carve out a slit for the red fruit roll up. This is the endoplasmic reticulum (ER). The ER is like a little maze of tubes that are hollow inside. Add a few cake sprinkles right next to the ER. These are ribosomes. After mRNA is made in the nucleus, it is sent to the ribosomes on the ER. The ribosomes are responsible for reading the mRNA message and making the proper protein according to its instructions. This process is called translation. As a protein is made, or “translated,” the ribosomes pushes it into the maze of the ER. A second 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 Golgi Body. The proteins made by the ribosomes that are inside the ER are sent to the Golgi for finishing touches and distribution. Here, the protein may be packaged or changed: it’s like putting the paint on a car being made in a factory before it is sent out to the car dealer!

5. The powerplant of the cell is the mitochondria. Using the spoon, scoop out two holes for the red hot tamales. The mitochondria gets fuel from the food that you eat, like sugar. It then converts the fuel to useful forms of energy for the cell. 6. When performing their actions, cells make waste. But where does it go? To the lysosome, which is full of molecules that can break down cellular waste. Using your spoon, scoop out a hole for the Junior Mint, which serves as the lysosome. Lysosomes are the garbage dumps of the cell—they break down waste and dispose of it properly. 7. How does the cell stay together? They are housed in a doublelayered coating called the plasma membrane, that gives the cell its shape. This membrane helps control what goes in and out of the cell, and helps protect the cell from damaging things in the environment. The white Styrofoam bowl serves as the plasma membrane. 8. Inside the plasma membrane is a gel-like fluid called the cytosol that surrounds the organelles. That’s 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 before you eat it!

Mitosis Every organism starts out as one cell. In order to become a multicellular organism, cells must grow and divide. The ability to grow and divide is one of the most unique characteristics of the cell. Every cell, whether a unicellular organism or a single cell in a complex multicellular organism, arises from a pre-existing parental cell by a process known as cell division. Your TA will lead you to the next room, where you will be able to view the first cell(s) of a frog. Every frog starts out as zygote. A zygote is a single cell that is 1.6 million times bigger than a single cell of an adult frog. The zygote will undergo millions of divisions before it becomes an adult frog. Look at the zygote on the TV screen, which is connected to the microscope. Identify on the screen the parts of the zygote:

It takes 20 to 30 minutes for the zygote to divide. Your TA will bring you back to see the progress of the zygote. First you get to learn more about the process of cell division called mitosis. For now, skip the next page 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

division, it enters the 8-cell stage. Find a dividing frog egg that looks interesting 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 the dividing 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 simply making more of the cellular molecules and organelles. This period of growth is called interphase. During interphase, the cell makes copies of its DNA. Once the cell has copied its

DNA and is big enough, it divides. Mitosis is the name given to the period during which the cell divides. During mitosis, DNA sequences that were duplicated during interphase must be precisely divided, such that the two daughter cells receive exactly the same genetic information. During mitosis, the DNA information condenses into tightly packed coils called chromosomes. Scientists use a dye that stains the chromosomes for viewing under a microscope. We will be using this dye today. Mitosis occurs in steps that, with the help of the DNA dye, can be seen with the help of a microscope. These are the steps of mitosis: PROPHASE: The DNA, which is in a loosely-packed form called chromatin, condenses into chromosomes. Under the microscope, this looks like a change from a tangled mass of thin threads to shorter, thicket units. The chromosomes are composed of two paired sister chromatids that are held together by a centromere. The nuclear membrane disappears so that the chromosomes can be divided. METAPHASE: The chromosomes line up at the middle of the cell.

ANAPHASE: The sister

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

TELOPHASE: The chromosomes uncoil, going back to chromatin, and nuclear membranes reform around the two new nuclei. CYTOKINESIS: The cytoplasm divides, completing the cell division. What started as one parent cell is now two daughter cells.

The Microscope

Always carry the microscope with one hand under the base and one hand holding the arm.

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 the objective lens LIGHT: shines light through the object you are looking at to make it easier to see OBJECTIVE LENS: magnifies (makes bigger) the object you are looking at EYEPIECE: allows you to see the magnified object FOCUS 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 like Kleenex, cheesecloth, or handkerchief 2. Always start with the 4X objective (also known as the scanning objective) when looking at a slide with your illumination set at 2 or 3. 3. Always center the specimen in the field of view before switching to 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 person by: 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.

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 look for the different stages of mitosis. Your TA will give you a prepared slide taken from a growing plant root. Why do you think it is necessary to use an actively growing plant to look at dividing cells?

1. Place the slide on the stage of your compound microscope and locate the tip using the 4X objective. 2. Switch to the 10X objective for a more detailed examination of the root 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

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?

Your TA will give you several different things you may have come across in your everyday life. Pick one thing and put it under the microscope. Look at it using the 4X objective. What do you see?

Look at it using the 10X objective. What do you see?

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

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

Look at it using the 10X objective. What do you see?

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

How Do Scientists Do Science? Almost all scientists follow the Scientific Method when performing science experiments. The scientific method has 5 steps, all of which are very important. 1. OBSERVATION: Scientists observe the world around us. There are many different types of scientists that observe different aspects of the world. Zoologists observe animals and botanists observe plants. If you were a scientist, what kind of things would you want to observe?

2. ASK A QUESTION: After making observations, a scientist will ask himself or herself a questions about something. For instance, what makes dogs drool? It is important that scientists ask questions that can be answered. What is a question you have about something you have observed?

3. FORM A HYPOTHESIS: A hypothesis is a prediction about the answer to the question. In this case, the scientist might predict that only

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

4. PROCEDURE: Once the scientist has identified a question, he or she must decide how to go about answering the question. To find out what makes dogs drool, a scientist might decide to put different things in front of the dog, like food, water, or dog biscuits, and record the dog’s reaction. Can you think of a way to answer your question?

5. DATA COLLECTION: After deciding on a procedure, a scientist will follow the procedure. The observations collected from the procedures are called data. In the example above, the scientist would make a list of the things placed in front of the dog and mark “drool” or “no drool” next to each thing. What kind of data would you collect from your procedure?

6. CONCLUSION: Based on the data collected, you will either confirm or not confirm your hypothesis. If only food made the dog drool, then the scientist can confirm the hypothesis. If something else made the dog drool, the scientist did not confirm the hypothesis. Usually, the scientist will make a new hypothesis, and start all over again. An extremely important part of science experiments is something called a control. A control is used to show that the data you collected is because of your procedure. For example, the scientist performing the experiment above would have a control by noting that the dog does not drool when nothing is placed in front of it. If the dog drools when nothing is in front of it, the scientist’s data don’t mean anything!

Your Turn to be a Scientist! Over the four weeks of LABS, you will be able to use the Scientific Method. Your group, with the help of your TA, will ask a question about plant growth, make a hypothesis, outline a procedure, collect data, and make a conclusion. STEP 1: OBSERVATION Think 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?)

STEP 2: ASK A QUESTION Have you ever wondered how different things affect plant growth? Discuss different questions with your group and your TA. Make sure that it is a question that can be answered. Decide on a question and write it below:

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

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

STEP 5: COLLECT DATA Over the next two weeks, your group will collect data as stated in your procedure. Remember to put it in the data sheet your TA will give you. STEP 6: CONCLUSION During week 3, your group will come to a conclusion about your hypothesis.

Take Home Science When you leave today, you will take both your jello cell and agar plates with 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 usually invisible. Over the next week, you will have the chance watch bacteria grow by dividing over and over again. Using the sterile cotton swabs, find a place in your house you think there’s a lot of bacteria and rub the cotton swab on it (door knobs, faucet handles, 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 what is going on. Write down what you think might be happening on the two plates. DAY

OBSERVATIONS

Data Sheet DATE

Height of Condition 1: _____________

Height of Condition 2: _____________

April 26, 2003 May 3, 2003 May 10, 2003 May 17, 2003

Acknowledgements Thanks to everyone who made today possible!

Height of Condition 3: _____________

Dr. John Mordacq and Sue Fox for your ideas and support throughout 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.com Biology 210 Lab Manual