Cell Theory

Topics: Bacteria, Cell, DNA Pages: 11 (2348 words) Published: November 23, 2008
Biology HL Portfolio

The Cell and Cell Theory


The cell

The word cell comes from the Latin word “cellula”, which means a small room. The cell is the smallest unit of a living organism, also known as “the building block of life”. Every living organism is consisted of a cell. There are bacteria (unicellular organisms), and multicellular organisms. There are different types of cells, prokaryotic and eukaryotic cells. All cells come from preexisting cells. “Every cell is self-maintaining; it takes in nutrients, converts them into energy, carries out special functions and reproduces itself if necessary.” The descriptive name for the smallest living biological structure was given by Robert Hooke in a book, which he published in 1665, while discovering “small units” in a cork. After that the research of the cell has progressed greatly.

Cell structure


Prokaryotic and Eukaryotic cells

There are two types of cells. While they are still cells which make them have a lot of similarities, they are also very different. The main difference between them is that a prokaryotic cell does not consist of a nucleus nor a nuclear membrane, while the eukaryotic on the other hand does. There are two types of prokaryotic cells, bacteria and archaea. The plasma membrane of the cell protects it from the outside environment. Most of them also have cell walls, but there are exceptions to that. Since the cells don’t have a nucleus the DNA is stored in the nucleoid. [pic]


The eukaryotic cell looks like this. They are around 10 times bigger than the prokaryotic cell. Unlike the prokaryotes they have a cell nucleus, where the cell’s DNA is stored, and a cell membrane. All of it’s chromosomal DNA is stored in the cell nucleus. The mitochondria in the eukaryotic cell also contain some of the DNA.

Cell Functions

“There are several main functions that the cell has to carry out: molecule transport, reproduction, and energy conversion.” 1

Molecule Transport
There are two types of molecule transport: active transport and passive transport. The passive transport is used for molecules such as oxygen, ethanol, and carbon dioxide. To transport proteins, polynucleotides and polysaccharides, cells rely on active transport. [pic]


Active transport is divided into two basic types of it. Exocytosis and endocytosis. “Exocytosis involves sending macromolecules out of the cell, while the opposite applies to endocytosis.” 2

Cellular Metabolism

Every day the cell has to go through tens of thousands of chemical reactions. But to go through them, they need energy. We can divide cellular metabolism into two categories anabolism and catabolism. The purpose of catabolism is to break down large molecules, while anabolism on the other hand uses the energy to make parts of cells such as proteins and nucleic acids.



1 http://library.thinkquest.org/C004535/basic_cell_functions.html 2 http://library.thinkquest.org/C004535/molecule_transport.html


The main goal of all living organisms is to survive. This is why it is needed for cells to reproduce. Cells reproduce in two ways, mitosis and meiosis. “Mitosis is mostly used by somatic cells (cells of the body). Meiosis is a form of sexual reproduction and only occurs in gametes (reproductive cells).” 1

To continue the race of an organism, it must reproduce. The cell division starts with interphase, and then it goes through prophase, metaphase, anaphase, and telophase.


“Meiosis starts with diploid cells, or...

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