4. 10: Studying Cells - Biology

4. 10: Studying Cells - Biology

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4. 10: Studying Cells

4. 10: Studying Cells - Biology

cell 'sel n 1 : the basic unit of structure & function in living things

In just a second we'll review some of the dudes who were among the first to study cells. In order for any of these guys to make any observations or discoveries, there had to have been certain technological tools available to them. The biggest of these tools was certainly the compound light microscope. An understanding of the microscope is "a must" in any biology course.
I have dedicated a page to the microscope in my "LAB REVIEW" Pages. To look at that now, click here .

For now, here is a quick exercise to review some important tools & techniques related to cell study. Match the tool or technique with its description.

Tools & Techniques
For Cell Study
compound microscope
electron microscope
microdissection apparatus
phase-contrast microscope
simple microscope

1. microscope composed of one lens
2. microscope that creates an image using two lenses
3. adding a chemical that makes certain cell structures easier to see, usually kills the cells
4. a high resolution microscope used to study living cells
5. microscope that provides images of the greatest magnification & resolution
6. microscope with two oculars, usually used during dissections to observe relatively large structures in more detail
7. small tools used to remove or transplant cell organelles
8. machine that can be used to separate cell organelles according to their densities

After you've done your best, check your answers < herE >.

OK, let's continue our review/study of the cell by reviewing the guys who first studied the cell. Number from 1-7 on a piece of paper & match each dude with his claim to fame.

Anton van Leeuwenhoek (1670)
Robert Hooke (1665)
Robert Brown (1831)
Matthias Schleiden (1838)
Theodor Schwann (1838)
Johannes Purkinje (1839)
Rudolf Virchow (1858)

  • the exact wording of the cell theory may vary depending on what textbook you use, but it's always composed of those 3 ideas
  • the "life functions" referred to in statement #2 are the same ones covered on my life functions page
  • if you peek back to the scientists review, you may notice that statements #1 & 2 are primarily a combo of Schleiden & Schwann's research, & statement #3 is Virchow's big idea
  • keep in mind that The Cell Theory is based on over 300 years of scientific investigations, beginning with Hooke in 1665 and continuing through today
  • some notable questions or "exceptions" to the Cell Theory do exist

Exceptions to the Cell Theory :

1. Viruses - are they alive ?
According to the Cell Theory we have to say "no" because a virus is not a cell. Viruses are made of two chemicals, protein & nucleic acid, but have no membranes, nucleus, or protoplasm. They appear to be alive when they reproduce after infecting a host cell.
2. Mitochondria & chloroplasts.
These cell organelles (small structures inside the cell) have their own genetic material & reproduce independently from the rest of the cell.
3. Where did the first cell come from ?
According to statement #3 of the cell theory, all cells come from other living cells. So how did the first cell ever appear ? It's the old "chicken & egg" dilemma. We will investigate this question (& its possible answer) in more detail during the Evolution Unit.


In this course we concern ourselves mostly with the differences between prokaryotic cells & eukaryotic cells, and between animal cells & plant cells.

The prokaryotic-eukaryotic difference is easy prokaryotic cells do not have a nucleus & eukaryotic cells do. Remember that all prokaryotic organisms are classified in the Moneran Kingdom. The organisms in the other four Kingdoms have eukaryotic cells.
(If you want to review the 5 Kingdoms, check out my "5 Kingdoms Page".)

The animal-plant cell differences aren't too bad either. Basically, some organelles are found in plant cells and not animal cells & vice versa. More on that in a minute.



chromosomes (DNA)
endoplasmic reticulum
golgi body
plasma membrane

Check here to click your work ---
I mean, click here to check your work.

Before we label a plant cell, let's take a
sTudY BReaK .

OK, time to label a typical plant cell (notice the green?). Usually, plant cell diagrams focus on structures that distinguish plant cells from animal cells. So some of the organelles that animal & plant cells have in common (like ribosomes, golgi bodies, endoplasmic reticulum) get left out all together. Label the diagram below & see what I mean .


cell wall
plasma membrane
vacuole (large)


If you can label diagrams of a plant or animal cell, then you pretty much know what the differences are between them.

This table summarizes the differences :

centrioles visible none (not visible)
cell wall none present
chloroplasts none present
vacuole small large


Now that you know what each organelle looks like, it's time to get the functions of each organelle to stick to your brain somewhere. Choose an organelle from the word bank for each description in #1-15.

cell membrane
cell wall
endoplasmic reticulum
golgi apparatus
nuclear membrane

  • Some organelles have two names : golgi apparatus = golgi bodies cell membrane = plasma membrane.
  • The organelles that you, an average biology student, would see in lab using a compound light microscope would be : the cell membrane, cell wall, nucleus, nucleolus, chloroplasts, large vacuoles. Other organelles require higher magnification and better resolution microscopes that typical high schools don't have on hand.
  • You should know a few more details about the plasma (cell) membrane. It is composed of lipids (fat molecules) & protein in what is described as the "Fluid Mosaic Model".

Now that you know everything there is to know about cells, may I suggest you brush up on your understanding of the microscope ?
Check out my Microscope Page.

Back to Biology Topics Outline

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Answers to "Tool & Techniques for Cell Study" :
1. simple microscope
2. compound microscope
3. staining
4. phase-contrast microscope
5. electron microscope
6. stereomicroscope
7. microdissection apparatus
8. ultracentrifuge
<-- back

Answers to "Cell Scientists Matching" :
1) J. Purkinje
2) R. Hooke
3) R. Virchow
4) A. von Leeuwenhoek
5) M. Schleiden
6) M. Schwann (has an "a" in last name - animal cells)
7) R. Brown

Answers to "Animal Cell Diagram" :

1. lysosome
2. endoplasmic reticulum
3. chromosome (DNA)
4. golgi body (apparatus)
5. vacuole
6. mitochondria
7. ribosome
8. nucleolus
9. nucleus (nuclear membrane would also be OK)
10. centrioles
11. plasma membrane
12. cytoplasm

Answers to "Plant Cell Diagram":

1. nucleus
2. nucleolus
3. plasma membrane
4. cytoplasm
5. cell wall
6. vacuole
7. chloroplast

ANSWERS to "Organelle Functions" Matching :
1. cytoplasm
2. cell membrane
3. nucleus
4. cell wall
5. ribosomes
6. endoplasmic reticulum
7. golgi apparatus
8. mitochondria
9. vacuole
10. nuclear membrane
11. nucleolus
12. lysosome
13. centrioles
14. centrosome
15. chloroplast
<-- back

Cells: Activities for Learning

These learning activities cover all of the understandings and skills in the IB guide for this topic. Lesson plans include resources to use on an interactive whiteboard and worksheets to print. There is a mix of laboratory work, theory lessons, and assessment materials with model answers.

Cells planning 1.1 Introduction to cells

This simple sheet sets out the learning objectives, essential questions and some ideas for assessment for the following activities.

Cell Theory Investigation

Time: 1h A practical Biology lesson that will illustrate the discovery of cells in the history of Biology and teach students how to use microscopes to measure the cell sizes.

Measuring size in Biology - units and the size of cell components

Time: 0.5h How many µm make a mm? This activity gives students clear examples of biological objects to cover sizes from 1mm to 1nm. Students watch a short video clip, investigate a visual biological data base using a slider and make a display which illustrate the huge range of sizes between tiny fleas and the miniscule molecules.

Calculating Magnification and Size

Time: 1h Student activities to illustrate the sizes of different cell components and to show students how to calculate cell sizes from electron micrographs. The lesson incorporates an online magnification animation and a downloadable worksheet.

SA to Volume practical activity

Time: 1h A practical laboratory in which students can visualise diffusion into blocks of different sizes. This will teach students some essential skills for internal assessment, and illustrate the concept of surface area to volume ratio.

Measuring Equipment - IA skills training

Time: 1h There are some important new skills to learn in IB Biology when it comes to the simple skill of measuring. Professional biologists and IB students are expected to know how precise their measurements are.

This series of short experiments illustrates SI units and the skills a student needs to achieve high grades in data collection and processing.

Critical Thinking about stem cells

Time: 1-2h This lesson plan contains a range of ides for activities to encourage students to engage with the ethical issues which surround the use of stem cells and therapeutic cloning.

Ultrastructure of cells - planning sheet

This simple sheet sets out the learning objectives, essential questions and some ideas for assessment for the following activities.

Eukaryotic Cell Ultrastructure

Time: 1h Students will learn how to draw and label a diagram of the ultrastructure of a liver cell as an example of an animal cell. Using a webcast and revision flashcards the teacher has more freedom to assist students individually.

Prokaryote cell structure & function

Time: 1h Students learn how to draw and label a diagram of the ultrastructure of Escherichia coli (E. coli) as an example of a prokaryote. Using a webcast and revision flashcards the teacher has more freedom to assist students individually. .

Mobile phone bacteria experiment

Time: 1h Students takes samples from their mobiles phones and grow prokaryote colonies on agar plates. They investigate the hypothesis that mobiles phones harbour colonies of prokaryotes, and that touch screen smartphones are more hygienic than phones with buttons? This activity is combined with a 'webquest' to perfect prokaryote diagrams.

Cell Types Detective Activity

Time: 1h A Problem Based Learning activity - to challenge students to compare different types of cells and to outline differences between plant and animal eukaryote cells and prokaryote cells.

Membrane Structure and Transport - planning sheet

This simple sheet sets out the learning objectives, essential questions and some ideas for assessment for the following activities.

Membrane Structure and function

Time: 1h Students will learn how to draw and label a diagram of the fluid mosaic model of membranes. Using a webcast and revision flashcards the teacher has more freedom to assist students individually.

Falsification of membrane structures

Time: 1h The accepted model of membrane structure today is the fluid-mosaic model but this has not always been so. The evidence has supported, step by step, a succession of new models each a little closer to the real structure of membranes in nature. The story of this progress illustrates many ideas about the nature of science, especially those connected with exploration and discovery.

Further Membrane Structure

Time: 1h In this activity students see for themselves the wonderful interactions which occur inside cells and between cells using a wonderful short animation from Harvard university. The roles of some membrane proteins are clarified as well as the function of cholesterol in the cell membrane.

Time: 1h U sing all that we know about molecules and about the structure of the cell membranes students are challenged to illustrate the transport of four very different molecules through the membrane using play-doh, spaghetti, food and sweets. Protein pumps, protein channels, and the phospholipid bilayer are central to the story.

Membrane Permeability Experiment

Time: 1h This experiment is a good first assessment of the new analysis criteria. Students measure the diffusion of pigments out of beetroot cells. By increasing the temperature of the heat treatment the leakage through the plasma membrane changes. The intensity of the colour of the leaked betalin pigments can be measured using a colorimeter.

Onion cell plasmolysis experiment

Time: 1h Students use skills learned earlier in the topic to prepare slides of onion cells, collect data in different solute concentrations, and use a scatter graph of the results to identify the concentration for 50% plasmolysis in each type of onion. This is good introduction to data processing and data analysis questions in IB exams.

The origin of cells and cell division - planning sheet

This simple sheet sets out the learning objectives, essential questions and some ideas for assessment for the following activities.

Mitosis and the Cell Cycle

Time: 1h Mitosis is a miraculous process. In the making of the three trillion cells of our bodies it manages to faithfully share the chromosomes equally between the daughter cells. This lesson focuses on the key details which help students achieve high marks in exams and the activities help students to make sense of these details in the context of the whole process of mitosis.

Mitotic index & cancer

Time: 1h This is a great online activity. Students are first guided through the identification of cells in different stages of mitosis using an online simulation. Once they are confidence students count and record the number of cells undergoing mitosis and those which aren't in a range of cell samples. They count the cells, calculate the mitotic index and use this as a prognostic tool to answer some questions.

Control of cell cycle & cancer

Time: 1h The control of the cell cycle is essential for the normal functioning of the body. Cyclins have a key role in this control. Oncogenes have the opposite effect and effectively remove the control of the cell cycle and the cells divides to form a tumor. This activity introduces students to these concepts without getting too complicated.

Capturing cellular trajectories

This interplay of environment and cellular identity means that cancer cells might look stem-like under some experimental conditions but not in others, or might express different sets of genes depending on their neighbours. They also lack universal surface markers, making it even trickier to tag and study them. But researchers have devised a range of alternative strategies to track the cells’ trajectories, many of which are borrowed from the developmental-biology toolset.

To study stem cells in embryonic mammary glands, Fre and her team used a strain of mice called Confetti, so named because the cells can express four different fluorescent reporters. When the researchers treated animals with a chemical to induce reporter-protein expression at different times during development, the proteins were activated in various locations. Using fluorescence microscopy, the team could then see where cells of different lineages ended up in adult tissues. Vermeulen and colleagues have used a similar fluorescence-based approach to understand how the environment controls colon-cancer stem cells in cell culture studies 5 .

Genetic barcodes are another option for tracking cells when they acquire mutations and diverge into different subgroups. The approach gives each population of cells a fixed genetic barcode as the populations divide, the barcodes evolve. By sequencing all the barcodes in the population and comparing them, researchers can then work out how the different cells relate to one another, and their relative contribution to the growth of the tumour.

Early variants of this approach relied on static barcodes carried inside lentiviruses, used as a way to insert the sequences into a pool of cells at random. Now, the gene-editing tool CRISPR is improving the process.

In CRISPR-based lineage tracing, researchers insert an array of CRISPR target sequences into cells’ genomes. The Cas9 enzyme then periodically cuts into these targets, triggering DNA-repair processes and leaving a genetic scar that acts as a unique identifier for a cell and its progeny. Unlike lentiviral barcodes, this system generates unique barcodes dynamically, potentially every time the cells divide, allowing researchers to reconstruct how different cells and their progeny are related 6 . “Changes accumulate over time,” says stem-cell biologist Alexander van Oudenaarden at the Hubrecht Institute in Utrecht, the Netherlands. “It’s fundamentally different from the lentiviral barcodes that were used earlier.”

Cancer research with a human touch

Another approach couples the sequence for a fluorescent protein to a repetitive piece of DNA — a long repeat of cytosine and adenine bases that cells see as problematic. As cells divide, they periodically ‘repair’ this repetitive sequence by trimming it, ultimately bringing the sequence for the fluorescent protein into a position in the genome where it can be expressed. This fix happens once in every 10,000 cells or so, Vermeulen says, sending up a tiny genetic flare that’s visible under the microscope. The advantage, he says, is that this sort of fluorescent label doesn’t require a chemical to activate it. “It’s a way of lineage tracing that leaves the cell completely untouched,” he says.

Each of these strategies has its pros and cons. Some CRISPR sequences are more prone to scarring than others, for instance, introducing bias into a theoretically unbiased process. And both microscopy and sequencing-based strategies require advanced computational and technical skills. Still, coupled with single-cell RNA sequencing, the labels provide powerful tools to assess the relative importance of individual cells in a tumour.

“If a tumour is driven by cancer stem cells, only a few labelled cells will proliferate and become large clones,” Vermeulen points out. “But in a tumour that depends on many cell types, most cells will expand. When the data are put into a mathematical model, you can actually identify to what extent it’s one mode of growth versus the other.”

Career Connection

CytotechnologistHave you ever heard of a medical test called a Pap smear (Figure)? In this test, a doctor takes a small sample of cells from the uterine cervix of a patient and sends it to a medical lab where a cytotechnologist stains the cells and examines them for any changes that could indicate cervical cancer or a microbial infection.

Cytotechnologists (cyto- = “cell”) are professionals who study cells via microscopic examinations and other laboratory tests. They are trained to determine which cellular changes are within normal limits and which are abnormal. Their focus is not limited to cervical cells they study cellular specimens that come from all organs. When they notice abnormalities, they consult a pathologist, who is a medical doctor who can make a clinical diagnosis.

Cytotechnologists play a vital role in saving people’s lives. When abnormalities are discovered early, a patient’s treatment can begin sooner, which usually increases the chances of a successful outcome.

These uterine cervix cells, viewed through a light microscope, were obtained from a Pap smear. Normal cells are on the left. The cells on the right are infected with human papillomavirus (HPV). Notice that the infected cells are larger also, two of these cells each have two nuclei instead of one, the normal number. (credit: modification of work by Ed Uthman, MD scale-bar data from Matt Russell)

Watch the video: Cell Biology. Cell Structure u0026 Function (May 2022).