Cell theory facts for kids
In biology, cell theory is a big idea that explains what living things are made of. It was first thought of in the mid-1800s. This theory says that all living things are made of tiny building blocks called cells. It also says that cells are the basic units of life, and that every new cell comes from a cell that already existed. Cells are super important for how all organisms are built and how they reproduce.
The three main ideas of cell theory are:
- All living things are made of one or more cells.
- The cell is the basic unit of how living things are built and how they work.
- All cells come from cells that were already there.
Most scientists agree with cell theory. However, some biologists think that things like viruses are alive, even though they are not made of cells. This makes them question the first idea of cell theory. Since there isn't one perfect way to define life, this discussion continues!
Contents
How We Discovered Cells
For a long time, people didn't know about cells because they were too small to see. But as microscopes got better, we could finally see these tiny parts of life. The discovery of cells is mostly thanks to a scientist named Robert Hooke. This started a whole new area of science called cell biology, which is the study of cells.
When Hooke looked at a piece of cork through his microscope, he saw many tiny holes. He was surprised because no one had seen these before! Later, two other scientists, Matthias Schleiden and Theodor Schwann, studied cells from both plants and animals. They found important differences between plant and animal cells. This showed that cells were not just important for plants, but for animals too.
The Amazing Microscope
The invention of the microscope made it possible to discover cells. People in ancient Rome learned how to make glass and noticed that objects looked bigger when seen through it. In the 12th century, an Italian named Salvino D’Armate made a piece of glass that fit over one eye, which made things look bigger.
Later, in the 13th century, people started using lenses more often in eyeglasses. This probably led to more use of simple microscopes, which are like magnifying glasses. Around 1620, compound microscopes appeared in Europe. These microscopes use two lenses to make things look much, much bigger.
In 1665, Robert Hooke used a microscope about six inches long. It had two curved lenses inside. He looked at different things under a light and wrote about what he saw in his book, Micrographia. Hooke also used a simpler microscope with one lens for clearer images.
Antonie van Leeuwenhoek was another scientist who did a lot of work with microscopes. He was a fabric seller who became interested in microscopes after seeing one in 1648. He learned how to grind lenses and made his own special microscope with a single lens. This small glass sphere could magnify things 270 times! This was a huge step forward, as microscopes before could only magnify up to 50 times.
After Leeuwenhoek, there wasn't much progress in microscope technology for about 200 years. Then, in the 1850s, Carl Zeiss, a German engineer, started making better lenses for microscopes. The quality of these lenses got even better in the 1880s when he worked with Otto Schott and Ernst Abbe.
Optical microscopes can only see objects that are about the size of a wavelength of light or larger. This meant scientists still couldn't see very tiny things. But in the 1920s, the electron microscope was invented. This new type of microscope could see objects much smaller than what optical microscopes could see, opening up even more possibilities in science!
The First Look at Cells
The cell was first discovered by Robert Hooke in 1665. He wrote about it in his book Micrographia. In this book, he described 60 detailed "observations" of different objects seen through his microscope. One of his observations was from very thin slices of bottle cork.
Hooke found many tiny pores that he called "cells." This name came from the Latin word Cella, which means 'a small room' (like where monks lived), and Cellulae, which meant the six-sided cells of a honeycomb. However, Hooke didn't know what their real structure or job was. What Hooke thought were cells were actually the empty walls of dead plant tissues. Because microscopes at that time didn't magnify much, Hooke couldn't see the other parts inside the cells. So, he didn't think these "cellulae" were alive. His observations didn't show the nucleus or other organelles found in most living cells.
Antonie van Leeuwenhoek was another scientist who saw cells soon after Hooke. He used a microscope with much better lenses that could magnify objects 270 times. With these microscopes, Leeuwenhoek found tiny moving objects. In a letter in 1676, he said that since these objects could move, they must be living organisms. Over time, he wrote many more papers describing different kinds of microorganisms. Leeuwenhoek called these "animalcules," which included tiny creatures like protozoa and bacteria.
Even though he didn't have much formal education, Leeuwenhoek was the first to accurately describe red blood cells. He also discovered bacteria after studying "pepper water" in 1676. He was also the first to find sperm cells in animals and humans. After discovering these cells, Leeuwenhoek realized that for a new life to start, a sperm cell needs to enter an egg cell. This helped to disprove the old idea that living things could just appear out of nowhere, which was called spontaneous generation.
It was harder to see cells in animal tissues than in plants. This was because animal tissues were very delicate and easily torn, making it hard to prepare thin slices for study. Scientists believed there was a basic unit of life, but they weren't sure what it was. It took more than a hundred years for this basic unit to be linked to the cell structure in both animals and plants. This idea was finally put forward by Henri Dutrochet. He said that the cell was not just a building block, but also a unit that performed life functions.
In 1804, Karl Rudolphi and J.H.F. Link proved that cells had their own cell walls. Before this, people thought that cells shared walls and that fluids passed between them that way.
The Cell Theory Takes Shape
Two scientists, Theodor Schwann and Matthias Jakob Schleiden, are usually given credit for developing cell theory. Another scientist, Rudolf Virchow, also helped a lot.
In 1839, Schleiden suggested that every part of a plant was made of cells or came from cells. He also thought that cells were formed by a process like crystallization, either inside other cells or from outside. However, this idea was not new, and another scientist named Barthelemy Dumortier had said it years before. This idea of cells forming from crystallization is no longer accepted in modern cell theory.
In the same year, 1839, Theodor Schwann stated that animals, like plants, are also made of cells or products of cells. This was a huge step forward because not much was known about animal structure compared to plants at that time. From these ideas about plants and animals, the first two main parts of cell theory were formed:
- All living organisms are made of one or more cells.
- The cell is the most basic unit of life.
Schleiden's idea that cells formed by crystallization was proven wrong in the 1850s by Robert Remak, Rudolf Virchow, and Albert Kolliker. In 1855, Rudolf Virchow added the third main idea to cell theory. In Latin, he said Omnis cellula e cellula. This means:
- All cells come only from cells that were already there.
However, the idea that all cells come from pre-existing cells had actually been suggested by Robert Remak earlier. Some people think Virchow used Remak's idea without giving him credit. Remak had published his observations on cell division in 1852. He said that new animal cells were made by binary fission, a process first described by Dumortier. Once this third idea was added, the basic cell theory was complete!
Modern Cell Theory
The modern version of cell theory includes a few more important ideas:
- Cells are where energy is made and used.
- The information that tells cells how to work and grow (DNA) is passed from one cell to the next.
- All cells have the same basic chemical makeup.
Types of Cells
Cells can be divided into two main types:
- Prokaryotes: These are small cells that have a plasma membrane around them and a cell wall. Prokaryotes do not have a nucleus (but they do have their DNA in a circular or linear shape). They also don't have other parts called organelles that are surrounded by membranes, though they do have ribosomes. The inside of a prokaryote cell contains its DNA and the cytoplasm. Bacteria and Archaea are two types of prokaryotes.
- Eukaryotes: These are more complex cells. Over a long time, these cells gained a special partner called a mitochondrion, and later developed a nucleus. These changes, among others, are the big differences between prokaryotes and eukaryotes.
Animals have developed many more different types of cells (100–150 different kinds) in their multicellular bodies compared to plants, fungi, and protoctista, which have about 10–20 different types.
Images for kids
-
A Prokaryote cell.
-
A Eukaryote cell.
See also
In Spanish: Teoría celular para niños
