Chapter 1. Cell Lab

Home

In this lab we will explore the most basic unit of life itself: the cell. Though the cell is the smallest possible living unit, do not think of it as simple or dull. Today you will take on the role of a cytologist—a scientist who specializes in the structure and function of cells. We will learn about the different cell types and the many different structures found inside our own, human cells.

In the first part of this lab, we will explore different types of cell and organisms. Some will be very large with few parts, while others will be large and multifaceted. We will look at single-celled organisms and multicellular tissues. In the second part of the lab, we will examine the wide variety of human cells and discover how your body contains a diversity of cells, each with a different makeup and specialized set of organelles. In the final portion of the lab we will explore several cell-related diseases. Cells are complicated structures, and if they are not properly formed in the body it can have very drastic consequences!

First, you will read background information regarding cells and complete the Pre-Lab Prep questions before proceeding with your experiments.

Click "Next" to get started.

1.1 Background

Before we let you loose to use a microscope, you’ll have to understand the background material covering microscopes, the types of cells, and cellular structures. Read this material thoroughly, and then answer the questions that follow.

Why are cells called cells? In 1665, Robert Hooke built a very simple microscope. One of the things that he looked at was a thin slice of cork. Although they don’t look like living things, corks are made from the outer bark of cork oak trees. Hooke thought that the compartments he saw resembled a monk’s room, or cell, and so the cell got its name.

[insert fig 1: what Hooke saw]

Currently, researchers estimate that the human body contains somewhere between 50-100 trillion cells. That is 100,000,000,000,000 individual cells! Some of them die and are replaced (like skin cells) but most of them are permanent.

[insert fig 2: types of cells]

As microscopes became more powerful, it became clear that a single cell contains many smaller structures within it that perform different functions. These structures are like the organs of the human body: for example, the heart has its role, while the liver has another role, and the stomach does something completely different. Every organ is essential: just try to live without a stomach! Because of this similarity, these subcellular structures are called organelles (little organs).

There are also many different kinds of cells, both within an organism (heart cells are very different than liver cells) and among different kinds of organisms (plants are very different from animals, and this is partly due to the cells of which they are made). These differences can be used to classify organisms, which is one of the things you will be doing in this lab.

But let’s start with the similarities first. All living cells have certain features in common.

• The plasma membrane: the plasma or cell membrane encloses the contents of the cell. It is made up of a mixture of proteins and phospholipids. Lipids are fats; phospholipids are fat molecules with a phosphate group (PO₄) attached to one end of the molecule. The plasma membrane is made of a bilayer of phospholipids. One of its major roles is to control what enters and what leaves the cell.
• DNA: all living cells must contain genetic material. The genes within DNA provide the cell with instructions for making the many different proteins it needs to live.
• Cytoplasm: the interior of the cell is filled with a gelatinous material. This material consists primarily of dissolved molecules and ions, protein fibers, and water. The organelles of the cell are embedded within the cytoplasm.

[insert fig 3 - Human skin cell, magnified 400X (photo taken by author)]

Now for the differences. In the photo, what is one of the most obvious things you can see in the cell? In many cells, the DNA is enclosed within its own membrane. This forms an organelle called the nucleus. This leads us to one of the biggest distinctions between different types of cells.

Prokaryotic cells have DNA, but it is not inside a nucleus. Instead, it is found in the cytoplasm. There are other unique things about prokaryotes. They are very small cells, they have ribosomes but no other organelles, and they are all single-celled organisms. All prokaryotes are bacteria. They represent the oldest life on earth, and they are the simplest cells on earth.

All other organisms consist of one or more eukaryotic cells. Eukaryotes have a nucleus and many other organelles; they are much larger than prokaryotes.

[ins fig 4 - anatomy of a prokaryote]

[ins fig 5 - anatomy of a eukaryote with size comparisons to prokaryotic cells]

Certain organelles are found in all eukaryotic cells

As you might predict, specific organelles are essential for cell metabolism. Metabolism refers to the chemical reactions that are necessary for life and that continuously take place in all cells. Each organelle makes a different contribution to the metabolism of the cell. Both plant and animal cells must contain this set of organelles.

[ins fig 6 - animal cell]

There is a smaller structure within the nucleus called the nucleolus. Ribosomes are tiny organelles that make proteins; they will be discussed more below. Ribosomes are made in the nucleolus.

The mitochondrion is the power plant of the cell. The cell uses a molecule called adenosine triphosphate (ATP) as its main energy source. Almost all ATP used by the cell is made in the mitochondrion.

A group of organelles are involved in the production of proteins. The cell has to make a wide variety of proteins to survive. Proteins are made of small molecules called amino acids. A string of amino acids has to be bonded together, folded into the correct shape, and then sent to its final destination in order for the protein to do its job in the cell.

• The ribosome forms the chain of amino acids. Some ribosomes float free in the cytoplasm, while others are attached to the surface of the rough endoplasmic reticulum.
• The rough endoplasmic reticulum (rough ER) is where theamino acid chain is modified and then folded into its final shape. This is a critical step; if a protein is not the right shape it will not be able to function.
• From the rough endoplasmic reticulum, the protein is sent to the Golgi apparatus. If the rough ER is like a factory, the Golgi apparatus is like a post office: its job is to ship the protein to its final destination. This protein may go to another part of the cell, or it may be released from the cell.

[ins fig 7 - figure is to illustrate the path that a protein takes through the endomembrane system from ribosome to rough ER to Golgi]

The smooth endoplasmic reticulum (smooth ER) is a set of folded membranes that are not covered with ribosomes. Clearly, the smooth ER is not involved in protein synthesis. Instead, it plays a major role in lipid synthesis, including making new membranes. It is also important for drug detoxification – any drug that enters the body will be broken down here.

The lysosome is an organelle that contains enzymes that can catalyze the breakdown of carbohydrates, fats, proteins, and nucleic acids—every type of molecule that we find in a cell. For single-celled organisms, the lysosome acts as a kind of digestive system, breaking down the food particles that the organism consumes. In the human body, white blood cells engulf and destroy bacteria with lysosomal enzymes. The lysosome is also a recycling center: molecules and organelles that are not functional can be broken down and their parts can be reused.

Lastly, the cytoskeleton is a complex web of strong, tough, and interlocking proteins that give the cell shape and structural support. These long strands are found throughout the cytoplasm. Just like the human skeleton gives the body shape, helps it stay upright, and enables it to move, the cytoskeleton carries out the same functions for the cell.

Some organelles are only found in plant cells

Every eukaryotic cell contains the organelles we’ve just covered. But some organelles are more limited. This is a clue that the organelle does something that not every cell needs to do. This is most obvious when we compare animal cells with plant cells.

[ins fig 8 - plant cell, illustrating the chloroplast, central vacuole, and cell wall]

As you can see, this plant cell contains all the same organelles as the animal cell plus a few more. The biggest difference between plants and animals is photosynthesis. Animal cells cannot simply capture sunlight energy and use it to make sugars. Plant cells can do that because they contain chloroplasts. Chloroplasts contain chlorophyll and other molecules that are necessary for photosynthesis. Plants are green because the chlorophyll inside their chloroplasts is green.

[ins fig 9 - chloroplasts]

Plant cells contain a large organelle called the central vacuole. The major role of the central vacuole is the storage of water. The water stored here helps support the plant. The central vacuole may also be used to store other molecules. For example, red pigment stored in the central vacuole produces a red flower.

The cell wall is not really an organelle, but it is a structure that animal cells do not have. The cell wall surrounds the plasma membrane of a plant cell. It is made mostly of cellulose fibers, which protect the cell and help support the body of the plant. Plant cells are often rectangular or boxy in shape because of their cell walls.

Plant, Animal, or Protozoan?

If you look at Robert Hooke’s drawing, it becomes clear that he was only looking at the cell walls of dead cork cells. The next step in understanding living cells came about 20 years later. Anton van Leeuwenhoek used his microscope to examine pond water, and found that it was teeming with life. Leeuwenhoek called the organisms that were swimming around on his slide “animalcules,” or little animals.

[ins fig 10 - Leeuwenhoek’s drawings of animalcules]

In the 19^th century, the term protozoan was invented to describe these organisms. This term comes from the Greek words “first animals”. However, protozoans are not animals, nor are they plants: they are their own unique form of life. For example, they are all unicellular organisms (the whole organism is made of just one cell), while plants and animals are multi-cellular. However, protozoans are sometimes described as “plant-like,” meaning they have green chloroplasts and can absorb light energy, or “animal-like,” meaning they must capture and eat other living organisms for energy. The protozoan Amoeba, for example, loves to feast on bacterial cells.

How do the protozoans move and capture prey? There are three major ways, and they help us classify the protozoan:

1. Cilia are short, hair-like structures that cover the surface of the cell. As they bend, the cell moves through the water. They also create water currents that can help pull prey towards the protozoan.
2. Flagella are longer structures, more like tails, that are used for swimming.
3. Pseudopodia are extensions out from the main part of the cell. They are used for crawling and for wrapping around prey.

[ins fig 11 - figure should focus on cilia, flagella, and pseudopods]

Now that you know so much about cells, it is time to use your knowledge. In today’s lab you will be identifying and classifying newly discovered cells. You will also be examining abnormal cells in a multicellular organism (a human in this case)—what happens when an organelle is missing or damaged?. You should be able to predict the effects on the cell and on the person.

1.2 Pre-Lab Quiz

Answer the following comprehension questions before proceeding with the lab.

1.3 Experiment Notebook

Developers: Sections 1.3.1 - 1.3.3 should be formatted as smaller sub-tabs under this primary tab.

Section 1.3.1: Types of Cells

In this section of lab, you will be provided with a sample collected as part of an ecological survey of the Great Lakes of North America. A healthy aquatic environment will contain a diverse collection of microorganisms. In this sample you should be able to find prokaryotic cells (e.g. bacteria) and eukaryotic cells (e.g. plant cells, animal cells, and protozoa).

Instructions and tips for this activity:

Begin by placing a couple of drops of the sample on a microscope slide. First click the pipette, then click the specimen jar. This will suck a few drops of sample into the pipette. Then click one of the slides to place this liquid on the slide so you can view it on the microscope. Lastly, click and drag a coverslip to the slide with your sample liquid on it. The coverslip will ensure that none of the lake water gets onto our microscope’s lenses.

Once your slide is prepared, click and drag it to the microscope to begin the examination. You will need to adjust the focus to make the microscope image crisp and clear. Drag the focus bar to the left and/or right until the image you see is in focus.

We will begin with the 4x objective, which gives the lowest magnification power. You should be able to see many different microorganisms in the water even at this level of magnification. Use the left/right and up/down arrows to move around the slides and look at different areas.

Identifying the Microorganisms

There are 9 different microorganisms that can commonly be found in the waters of the Great Lakes. Your job is to find examples of all 9. As you find and click on these organisms, they will be automatically identified on the microscope (look at the Identification box near the top of the screen). As each organism is identified, you will have to characterize it as either prokaryotic or eukaryotic. For those types of cells that you label as eukaryotic, you will then have to subcategorize them as plants, animals, or protozoa. Review the information in the background materials to help you determine how to categorize the cells.

You can change the magnification, or “zoom in” on a microorganism in two ways. The box on the top right of the screen shows you which objective is currently being used to view the slide. Clicking any of these objectives will automatically change the magnification level to 10x, 40x, or 100x magnification. The higher the number, the greater the magnification—the more the image is enlarged and the more details you can see. However, the low power 4x objective is the best one to use to “search” the slide for microorganisms to study.

The second way to increase the magnification is to click on any of the organisms on the slide. The microscope will automatically magnify that organism using the 10x magnification level. You can zoom in further by clicking the 40x or 100x objectives in the box on the top left of the screen. Using the 100x objective you should be able to see the individual cells of the organism.

HINT: The prokaryotic bacteria cells are too small to see at 4x or even 10x magnification. Try increasing the magnification without clicking on any of the organisms to see what you can find.

You should have found three types of protozoa in the water sample: Paramecium, Euglena, and Amoeba. Look again at these three species very closely. Each of them exemplifies a different way protozoa move and capture their prey.

In a different sample of pond water, you come across the following types of cells (shown at 10x magnification).

A colleague just identified a new organism in some samples she collected from the Great Lakes. Using your new cell classification skills, can you help her identify it? She’s worried it may be an invasive species—an organism that is rapidly becoming more and more common in an area where it’s not normally found.

As a cytologist, it is your job to characterize it so we can begin the identification process.

Launch your experiment module, and let's take a look at the collected samples.

In the next part of the lab, we will look at all of these different types of human cells to see what makes them so different.

Section 1.3.2: Cellular Organelles and Their Function

Now that you have some cytological experience, we will examine several different types of human cells to see how they have specialized structures to carry out their different functions.

In this section of the lab, we will examine the following types of human cells:

• Liver Cells
• Insulin-producing Pancreas Cells
• White Blood Cells
• Muscle Cells
• Nerve Cells

We also have fluorescent dyes for the following types of organelles found in human cells:

• Nucleus
• Rough Endoplasmic Reticulum (Rough ER)
• Smooth Endoplasmic Reticulum (Smooth ER)
• Golgi Apparatus
• Lysosomes
• Mitochondria
• Plasma membrane
• Cytoskeleton

First, let’s design our hypotheses for this experiment. Remember, a hypothesis is your educated prediction about the outcome of the experiment. For this experiment, we need to determine what types of organelles will be needed in EACH type of cell to best enable it to carry out its function.

Now that you have some idea of what will happen, let’s see if your predictions are correct.

As you will note after launching the experiment module, the cells we will use in this experiment have all been stained with specific fluorescent dyes that each bind to a different organelle inside the cell. To detect these dyes we will have to use a fluorescent microscope—a microscope specifically designed to detect different colors of fluorescent light. This microscope can detect each of the dyes we used independently, so we can examine the organelles of the cells one at a time. (NOTE: chemicals have also added that stain the cytoplasm and other parts of the cell to make the overall structure clearer under the microscope. However, you only need to focus on the fluorescing or glowing parts.) To begin, drag the tray of slides to the fluorescent microscope. You will then be able to use the microscope to examine the organelles in each type of cell.

You will use the interactive interface to select a) the type of cells you want to view, and also b) the fluorescent stained organelles in each cell. Make sure to look at ALL the different organelles for each cell type, and then answer the questions that follow.

You are on your way to becoming a human cytology expert! However, so far we’ve only looked at healthy, normal cells. Unfortunately, that is not always the case. In the next and final section of the lab, you will have to apply everything that you have learned so far to help determine the cellular organelle-based causes of various human diseases.

Section 1.3.3: Diseases of the Cell

Sometimes certain genetic or developmental problems cause specific cells or cellular organelles to be malformed in an individual. This can create all sorts of diseases and disorders. In the final section of the lab, we will examine several diseases caused by cellular problems.

There are five separate cases available for you to explore, but you are only going to focus on one of them. After reading through the brief descriptions of each patient’s case, select one patient to examine more thoroughly. You will be provided with samples of some of that patient’s cells to analyze. It is your job as a cytologist to examine the cells and determine which type of cell is affected by the disease. Once you find the abnormality, you can deduce what is causing it.

(Once you have made your diagnosis, be sure to read about the other cases to better understand each disease. You will need this information when completing your Lab Report at the end of this activity!)

Now that you have successfully diagnosed your patient, the experimental portion of this lab is complete. You have successfully analyzed all sorts of cells—cells from different organisms, cells with different types of organelles, and cells with different types of diseases. The only thing remaining is to write up your observations in a lab report.

1.4 Lab Report

Introduction:

Complete this partially written paragraph by choosing the correct words from the drop-down menus.

Methods: Put the steps from each of our experiments into the correct order.

1.5 Vocabulary List

Adenosine triphosphate (ATP): the molecule used for energy in the cell. Made in the mitochondria.

Amino acid: small molecule that is bonded to other amino acids to build proteins.

Bacteria: Very, very small, prokaryotic unicellular organisms. Many bacteria cause human diseases, while others are harmless. Some are required to maintain a healthy digestive system. Bacteria are the most common form of life on Earth.

Cell: the smallest unit of life. All living things are made of one or more cells.

Cell wall: a structure that surrounds the plasma membrane of a plant cell. It provides support and protection for the cell.

Central vacuole: organelle found only in plant cells for the storage of water and other substances. Helps support the plant.

Chloroplast: organelle found only in plant cells for photosynthesis.

Cilia: short, hair-like structures that cover the surface of some protozoans. They are used for movement and prey capture.

Cytologist: A scientist who studies cells – their shapes, structures, organelles, and functions.

Cytoskeleton: A web of interlocking protein strands and fibers that give the cell shape and structural support.

Cytoplasm: proteins and other molecules dissolved in water form a gel-like substance that fills the interior of the cell.

Deoxyribonucleic acid (DNA): the genetic material of all living cells. Genes provide instructions for making proteins.

Enzyme: protein that catalyzes chemical reactions so they happen more quickly.

Eukaryote: A cell that contains a nucleus and many other organelles. May be a single-celled or a multicellular organism.

Flagellum (plural, flagella): long tail used for swimming.

Florescent Dye: Chemicals that bind to certain chemicals in the cell. Different dyes can be used to stain different organelles. These dyes will then fluoresce, or glow, different colors when viewed through a florescent microscope.

Golgi apparatus: organelle that ships a protein to its destination.

Lysosome: organelle that contains digestive enzymes. These enzymes catalyze the breakdown of organic molecules, bacteria, and old organelles.

Metabolism: chemical reactions that are necessary for life and that are continuously taking place in all cells.

Mitochondrion (plural: mitochondria): produces chemical energy in the form of ATP.

Multicellular: An organism consisting of many cells working together. In complicated organisms like humans, the cells form tissues and organs. Plants and animals are multicellular organisms.

Nucleus: organelle that encloses the DNA in a eukaryotic cell.

Nucleolus: structure within the nucleus that synthesizes ribosomal RNA.

Objective: The magnifying lens of a microscope. Objectives come in different levels of magnification, e.g. 4x, 10x, 100x etc. The higher the number the greater the magnification (i.e. a 4x objective magnifies sometime four-times, but a 100x objectives magnifies it 100-times, making small structures like cells readily visible).

Organelle: a subcellular structure that contributes to the cell’s metabolism.

Peroxisome: organelle that contains enzymes for carbohydrate and fatty acid breakdown.

Plasma membrane: the phospholipid bilayer that encloses the cell content. Organelles also are bounded by a membrane.

Prokaryote: A cell that does not contain a nucleus. It has ribosomes, but no other organelles. All prokaryotes are bacteria.

Protozoan: single-celled organism that resembles an animal; it captures prey and swims rapidly.

Pseudopodium: extension out from the main part of a cell that it uses for crawling and prey capture.

Ribonucleic acid (RNA): ribosomes are made of this molecule.

Ribosome: structure that creates a string of amino acids to form a protein.

Rough endoplasmic reticulum: organelle that folds a protein into its final shape.

Smooth endoplasmic reticulum: organelle that synthesizes lipids and breaks down toxins.

Unicellular: Organism that are made of just one cell. Protozoan species are unicellular.