Cell

A cell is the basic structure of matter in a living organism. There are 2 types of cells: Eukaryotes and Prokaryotes. You can watch the video on the right by the Amoeba Sisters to know about cells if reading is not for you.

## A History of Cells

### The Discoveries of Robert Hooke

   In 1665, a scientist by the name of Robert Hooke first discovered cells through a compound microscope when he was looking at a thin slice of cork. He saw the deceased cells as empty rooms, and hence, the cell got its name. He described his findings in his book called Micrographia. The book had given 60 observations of various objects viewed under a compound microscope described in detail. Hooke had stated,"These pores, or cells, were not very deep, but consisted of a great many little boxes...." However, what fascinated Hooke the most was the quantity of cells that the cork contained.

### Anton van Leeuwenhoek's views with the microscope

Anton van Leeuwenhoek began to observe tiny objects with microscopes as well. Leeuwenhoek viewed drops of lake water, scrapings from teeth and gums, and water from rain gutters. He found a variety of unicellular organisms. He noted that several of the tiny organisms viewed moved. He called the moving organisms animalcules (little animals).

### The Cell Theory

The Cell Theory was created by Matthias Schleiden, Theodor Schwann, and Rudolf Virchow, 3 German scientists who made especially important contributions to people's knowledge about cells.

#### Schleiden's Discoveries

Matthias Schleiden declared that all plants are made of cells in 1838 based on his own research and the research of his predecessors. His discoveries would later be added to by Theodor Schwann, another German scientist.

#### Schwann's Discoveries

In the next year of Schleiden's discovery, Theodor Schwann concluded that all animals are also made up of cells, and thus, all living things are made up of cells.

#### Virchow's Discoveries

Rudolf Virchow, in 1855, proposed that new cells are formed only from cells that already existed. Virchow wrote, "All cells come from cells."

#### The Cell Theory

The three and many others helped develop the cell theory, which is a widely accepted explanation of the relationship between cells and living things. It is true for all living things, no matter how different they are. Cells are common to all living things, so they can provide access to information about the functions that living things do. It states that:

* All living things are composed of cells.
* Cells are the basic units of structure and functions in any living organism.
* All cells are produced from cells that existed before them.

## Parts of a Cell

Cells have structures called organelles, which perform specific functions that they are given.

Again, you can watch the video listed on the left if reading this is not your style. The video explains the parts of a cell in a song.

### Cell Wall

The cell wall, a rigid layer of nonliving material, is made of a strong material called cellulose and is only found in plant cells and other organisms except animal cells. It is used to protect and support the cell further than the cell membrane.

### Cell Membrane

The cell membrane is located just inside the cell wall. Both Prokaryotic and Eukaryotic cells have the cell membrane, which is described as selectively permeable, as it controls what goes in and out of the cell. In cells like animal cells, the cell membrane is the outside boundary of the cell. To survive, the cell membrane must allow helpful materials to enter the cell and harmful materials to leave the cell.

### Mitochondria (Mitochondrion when singular)

Mitochondria are membrane-bound organelles found only in Eukaryotic cells. They are best known as the powerhouse of the cell because the convert the chemical energy into the food the cell can use to live.

### Nucleus

The nucleus, also known as the cell's control center, directs all the cell's activities. It is a large oval structure which acts as the brain of the cell and contains chromosomes, or DNA. Like Mitochondria, it is also only found in Eukaryotic cells.

#### Nucelar Envelope

The nucleus is enveloped by a membrane called the nuclear envelope as it is a membrane-bound organelle. Materials pass in and out of the nucleus through pores in the nuclear envelope. It protects the nucleus like a mailing envelope protects a letter or a cell membrane protects the cell.

#### Nucleolus

The nucleolus is the center of the nucleus where ribosomes are made.

#### Chromatin

The chromatin are thin strands that contain genetic material, called chromosomes or DNA, which are the instructions for directing the cell's functions. This is how the nucleus "knows" how to direct the cell's activities.

### Chloroplasts

Found only in plant cells, chloroplasts capture energy from sunlight to produce food for the cell in a process called photosynthesis. Chloroplasts have chlorophyll, which makes them and the cells in the plant leaf so green.

### Lysosomes

Looking like small, round structures, lysosomes function as the trash can of the cell, but they are only found in animal cells and other cells. They contain chemicals that break down certain material in the cell. Basically, they are the clean up crew for the cell which rids the cell of unneeded unwanted substances.

### Cytoplasm

The cytoplasm is a clear, gel-like fluid between the cell membrane and the nucleus in which many organelles are found and float in. Both Prokaryotes and Eukaryotes have it.

### Golgi Apparatus

Golgi Apparatus, or Golgi Bodies as many would say, is a flattened sac-like organelle that receives proteins and other nutrients from the Endoplasmic Reticulum (ER) and distribute them to all parts of the cell.

### Vacuoles

Vacuoles are the storage areas of the cell which are filled with water. Plant cells have a single large vacuole, but some animal cells don't have vacuoles at all; others do. Vacuoles store food and other materials needed by the cell as well as waste products.

#### Cell Sap

The cell sap is the liquid inside the central vacuole of a plant cell that serves as storage of materials and provides mechanical support. It has a role in plant cell osmosis as well.

#### Tonoplasts

The tonoplast is a kind of cytoplasmic membrane that surrounds a vacuole, separating the vacuole's content from the cell's cytoplasm.

### Endoplasmic Reticulum

The endoplasmic reticulum looks like a long maze of passage ways connected to the nucleus. It could either be smooth or rough; the smooth ER produces other materials that are needed in the cell, the rough ER carries ribosomes, which produce proteins. The Endoplasmic Reticulum generally produces materials that are needed by other parts of the cell.