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Course: High school biology > Unit 2
Lesson 1: Introduction to cellsIntroduction to cells review
Key terms
| Term | Meaning |
|---|---|
| Cell | The smallest living unit of life |
| Cell theory | The explanation of the relationship between cells and all living organisms |
| Microscope | Instrument used to magnify objects too small to be seen with the naked eye |
| Simple light microscope | Microscopy tool that uses visible light and one lens to magnify an object |
| Compound light microscope | Microscopy tool that uses visible light and multiple lens to magnify an object |
| Electron microscope | Microscopy tool that uses a beam of electrons to create a magnified image |
Cell discovery and cell theory
| Time | Event |
|---|---|
| Early 1600s | Robert Hooke discovers dead cells using early microscope. |
| Late 1600s | Anton von Leeuwenhoek develops a more powerful microscope that allows him to see living cells like bacteria. |
| Early 1800s | Matthias Schleiden and Theodor Schwann conclude that all living organisms are made of cells, and that cells can be produced from other cells. |
| Mid 1800s | Rudolf Virchow confirms that all cells must come from pre-existing cells. (There is some evidence that this idea was stolen from Polish scientist Robert Remak.) |
These events gave way to the modern cell theory, which states:
- All living things are composed of one or more cells.
- The cell is the basic unit of life.
- New cells arise from pre-existing cells.
Viewing cells
In order to view cells, scientists must use magnifying tools called microscopes.
Simple light microscopes, such as magnifying glasses, generally are not powerful enough to view cells. Therefore, scientists need to use compound light microscopes or electron microscopes to see detailed cell structures or very small objects, such as viruses.
Comparing light microscopes and electron microscopes
| Light microscope | Electron microscope |
|---|---|
| Uses visible light | Uses beam of electrons |
| Lower resolution and magnification | Higher resolution and magnification |
| Cells can be alive or dead | Cells must be dead |
| Inexpensive, relatively small | Expensive, very large |
Common mistakes and misconceptions
- Not all cells are the same. Although cells are the basic units of life, there are many different kinds of cells that make up multicellular organisms. Some cells have specialized jobs that allow them to work with one another to perform an organism’s biological functions. Not all cells are the same shape or size either. For example, sperm cells are much smaller than, say, a muscle cell.
- Cells are the smallest living thing, but they are not the smallest thing. Cells are small enough that we need microscopes to view them, but they are much larger than some other substances that we have learned about. In fact, cells are made out of many atoms, so they are larger than macromolecules and viruses!
- Not all microscopes are just magnifying glasses! Magnifying glasses do qualify as simple microscopes since they have only one lens. However, there are also more complex microscopes. Microscopes with multiple lenses are known as compound microscopes, and they are able to bend light to produce a much more magnified image than a simple magnifying glass.
Want to join the conversation?
What happens when we use live cells in an electron microscope ?(23 votes)
electron microscopes produce electrons in an complete vacuum chamber, when live cells are placed in the chamber they would disintegrate due to vacuum(32 votes)
They say that cells are the smallest living unit. However, they also say that viruses are smaller. Aren't viruses considered living units as well?(17 votes)
It depends who you ask. Generally the answer is that viruses are not living units, for two reasons: The first reason is just that we've decided a cell is the basic unit of life, and viruses don't intrinsically contain cells, therefore they are not life. The second reason is that viruses are more like parasites, and are dependent on cells to "reproduce", so they aren't really living on their own.(21 votes)
why does the cell have to be dead in order for the electron microscope to work?(8 votes)
The reason for this is because the electrons destroy the living cells and when the cells are placed in the vacuum, there is no oxygen thus no life for the cells. Hope this helped clear any remaining doubts.(14 votes)
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According to cell theory all cells must come from preexisting cells, but then how did the first cell come about, and more importantly, why can't that happen again?(7 votes)
We actually do not know this answer for sure. Some theories suggest that the primordial Earth was the perfect place for chemical reactions to occur, with molecules eventually coming together to form the first cellular mechanisms. One theory suggests that amino acid (protein building blocks) chains were able to survive in the hellish conditions on the early Earth, and that their composition and characteristics eventually gave way to cells. One other theory suggests that cells evolved from viruses. There are several guesses in the community, and without our very own primordial Earth or time machine, what lead to the first cells is unknown.
On Earth, if a primordial cell were to develop again, it would likely die, due to the millions of other, fully developed cells that exist (competition and natural selection). However, should there be life on other planets, then it could be safely said that the process did happen again.
Does this help?(16 votes)
how many cells does a human have(8 votes)
There is a estimation of more than 37 trillion(10 votes)
Is there something called a micrometer ruler?(10 votes)
yes there is something called a micrometer ruler(5 votes)
- ¿En que año hicieron el primer microscopio ?(9 votes)
El primer microscopio se inventó en 1590, pero no está claro quién lo inventó realmente. La primera vez que se utilizó un microscopio para observar células muertas fue por Robert Hooke a principios del siglo XVII, si eso ayuda. ¡Espero que esto ayude!(7 votes)
can someone explain cells with detail and give more examples? thanks!(4 votes)
As mentioned in Cell Theory, all living things are composed of one or more cells, cells are the basic unit of life, and that new cells come from preexisting cells.
There are many kinds of cells, but generally, they can be classified in two broad groups: prokaryotic and eukaryotic. Prokaryotic cells tend to be simpler, with no nucleus or membrane-bound organelles. Some examples of prokaryotic cells include bacteria and archaea.
Eukaryotic cells, on the other hand, are more complex, with a nucleus and other membrane-bound organelles like mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus, lysosomes, etc. Eukaryotic cells can even be classified down to specific cells like animal, plant, fungi, and protists.
Even though I mentioned some of the main differences, keep in mind that there are organisms that are anomalies and may not strictly fit into one kind of classification.
This is a brief summary of what cells are, and I provided some examples of prokaryotic and eukaryotic organelles and organisms. If you are interested in learning more, I encourage you to do some more research yourself, or you can watch some videos here on Khan Academy.
I hope I answered your question as thoroughly as possible. Have an amazing day. :)(17 votes)
- In the introduction to cells review, three cell theories were given but in my biology textbook four cell theories were given which the last one is ( A cell contains information for its structural and functional development in its nucleic acid.This information is passed down from parent to offspring cells). so my question is how true is the fourth cell theory, should it be part of the cell theory or not?(8 votes)
Yes, I think so. Sal probably forgot to mention it.(8 votes)
- what would i use to examine the entercica cell(8 votes)
- You could use an electron microscope if you want to see the enterica cell clearly or you can use a complex microscope if you just want to see the overall picture and it's parts. Hope this helped to answer your question.(6 votes)
