A cell is understood to be a structural and functional unit of all organisms. The cell is the smallest and simplest form of biological organization, that is, the smallest orderly and living structure that is known (it should be noted that most viruses are smaller than a cell, however there is a discrepancy among scientists from according to their origin and whether or not they are “living beings”.
The cell is considered to be the functional unit of all living beings, since they are the only ones capable of carrying out the functions of nutrition, reproduction and relationship.
It is the structural unit of every living being because all living organisms are made up of cells. There are several organisms that are only made up of one cell and these are called unicellular organisms, while others, called multicellular organisms, are made up of a large number of cells of various types (which are usually specialized in specific functions).
The size of the cell can change drastically: some can become practically invisible to the naked eye; however, most of them are microscopic, meaning that they can only be seen by a microscope.
An average cell is about 10 µm (micrometers), but cell size varies many times: there are some that are only 1 µm and others are 100 µm.
Cells can reproduce through two possible mechanisms: division by meiosis that allows the formation of gametes (sex cells) and division by mitosis, which has two identical daughter cells. In meiosis there are genetic information exchanges and four different daughter cells are generated from each other, these present the amount of genetic content of the initial cell.
Inside there are organelles or organelles, they are simple formations that have specialized and differentiated shapes and structures. In organelles, various biochemical functions vital for cell survival and function are carried out.
Parts of a cell
- The plasma membrane: it is a biological barrier that delimits the cell and separates its interior and exterior. It is composed of a phospholipid bilayer, which divides the cell’s content from the environment that surrounds it and allows substances to enter and exit. In this way, certain nutrients are introduced and their waste is secreted.
- Cell wall : it is a thick and stable barrier, attached to the plasma membrane, which provides rigidity and rigidity to the cell. The wall is located in prokaryotic cells and in eukaryotic organisms they are only present in plant and fungal cells, the cell wall is built around various resistant materials, it varies in each type of organism.
- Nucleus : this formation is limited by a nuclear envelope formed by a double membrane. The nucleus is a characteristic organelle of eukaryotic cells and inside it contains most of the genetic material of the cell (DNA).
- Cytoplasm : it is a gelatinous substance that covers the interior of the cell, located between the plasma membrane and the nucleus (if present), and made up of water, proteins, salts and other substances. The vital function of the cytoplasm is to support the cell’s organelles and help all the metabolic processes that take place in the cell.
- Organelles: they are structures that are inside the cell and that carry out specific functions. Several of them are:
Mitochondria: are structures where cellular respiration takes place, this reaction allows the cell to obtain energy.
Lysosomes: they are based on digestion and the use of nutrients.
Chloroplasts: they are structures (only in the plant cell) they have chlorophyll, vital for the photosynthesis reaction that takes place inside.
Ribosomes : carry out protein synthesis, an important process for cell growth and reproduction.
Flagella: they are organelles that exist in certain cells, whose function is to propel themselves in the environment. They are present only in unicellular beings and mobile cells such as sperm.
Examples of cell functions
Cells can carry out diverse and very complex functions:
- Secretory functions: they produce substances vital to life and the body’s self-regulation, just as the glands or mucous membranes do.
- Structural functions: building tissues, such as fat, muscle, and bone, whose function is to support the body and its organs.
- Defensive functions: allows the body to defend itself against external agents and eliminate them, or attack diseases, just as white blood cells do.
- Reproductive functions: linking with other sex cells from other organisms of the same species, in order to give rise to a new entity (sexual reproduction) or separate (on their own) through mitosis to generate a new individual similar to the parent ( asexual reproduction ).
- Metabolic functions: transporting nutrients or transporting them throughout the body, just as red blood cells act in the blood and digestive cells in the intestine.