The cell

The cell is the structural and functional unit of all living things. It is the part of the living being (or even the living being if it is unicellular) that performs the three vital functions of living beings: nutrition, relationship and reproduction.

Although there are unicellular living beings, most are multicellular. Because the cells are very small, they could not be observed or studied until the techniques of observation allowed it with inventions such as the microscope.

In all cells these three basic structures are distinguished:

• The plasma membrane is a layer of lipids and proteins that surrounds the cell. It is responsible for regulating the passage of substances between the outside and the inside of the cell.
• The cytoplasm is the part of the cell that is surrounded by the membrane. It is formed by an aqueous medium (cytosol) in which the cellular organelles float. Organelles are structures responsible for carrying out various functions.
• The genetic material (DNA) is substance containing the hereditary information and controls the operation of the cell.

By No machine-readable author provided. Mortadelo2005 assumed (based on copyright claims). [Public domain], via Wikimedia Commons

Cell theory

The cell theory is based on the following postulates:

• The cell is the structural, functional and genetic unit of living beings.
• All living things are made up of one or more than one cell.
• The cell is the functional unit of living beings. It is the minimum unit of a living being that can carry out the basic vital functions: nutrition, relationship and reproduction .
• Every cell comes from a previous cell.
• Every cell has DNA with the specific characteristics of the living being and they are transmitted to their descendants.

Interactive activity: Parts of the eukaryotic cell.

Interactive activity: Prokaryotic and eukaryotic cell.

Interactive activity: Cell anatomy viewer.

The cell as a functional unit

The cell is the functional unit of living beings because the vital functions of living beings are carried out in it: nutrition, relationship and reproduction.

In the cell, a multitude of chemical reactions take place inside it, the so-called cellular metabolism, which allows it to stay alive and adapt to the environment.

Some cells, such as plants, have autotrophic nutrition and are capable of making their own organic matter (in chloroplasts) and oxidizing it for energy (in mitochondria). Others, like animals, have heterotrophic nutrition, and need to incorporate organic matter already made by other organisms.

Activity: Anabolism or Catabolism?

The cell as a genetic unit

The cell, in its DNA, contains all the hereditary information necessary to control its vital activity and that of the organism of which it is a part.

Every cell comes from another pre-existing cell, transmitting the hereditary characters contained in the chromosomes to subsequent generations.