What Does Célula Mean
The structural and functional unit of all organisms is known as a cell . The cell is the smallest and simplest form of biological organization , that is, the smallest orderly and living structure known (most viruses are smaller than a cell, but there is disagreement among scientists regarding their origin and whether or not they are "living beings").
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It is said that the cell is the functional unit of all living beings because all of them are capable of carrying out the functions of nutrition , relationship and reproduction .
The cell is said to be the structural unit of living beings because all organisms are made up of cells. Some organisms are made up of a single cell and are called unicellular organisms while others, called multicellular organisms , are made up of a large number of cells of different types (which are usually specialized in specific functions).
The size of cells can vary enormously: some can be practically visible with the naked eye , although the vast majority of them are microscopic, that is, they can only be seen using a microscope . An average cell is around 10 µm (micrometers), but cell size varies widely: there are some that are as low as 1 µm and others 100 µm.
Cells can reproduce by two possible mechanisms: division by mitosis , which gives rise to two identical daughter cells, and division by meiosis , which allows the formation of gametes (sex cells). In meiosis there is an exchange of genetic information and four different daughter cells are produced, with half the genetic content of the initial cell.
Inside cells there are organelles or organelles , simpler structures that have specialized and differentiated shapes and structures. Within the organelles the various biochemical functions necessary for cell survival and functioning are carried out.
The discovery of the cell is considered the foundational step of the modern study of life ( biology ), since it allowed us to understand the enormous complexity of the body of living beings and allowed the emergence of many later sciences and disciplines .
See also: Eukaryotic cell
Cell types
The most important classification of cells has to do with the presence or absence of a cell nucleus . This distinction is fundamental in the history of evolution, as it allows us to distinguish the two great super-kingdoms or domains of living beings:
- Prokaryotic cells . These cells have a simple basic structure without membrane organelles and do not have a nucleus, so their genetic material is dispersed within the cell ( cytoplasm ). Prokaryotic cells are the smallest and are between 1–5 µm in size. Prokaryotic cells were the first life forms on Earth , and these organisms are much simpler than eukaryotes. All living things made up of prokaryotic cells are unicellular.
- Eukaryotic cells . Eukaryotic cells have a more complex structure than prokaryotes and have specialized membrane organelles in their cytoplasm. The main characteristic of this type of cell is that it has a defined nucleus, where its genetic material is found. Eukaryotic cells are larger than prokaryotic cells, but have sizes that can vary widely between 10-100 µm. These cells appeared later than prokaryotes in Earth's history and constitute a step forward in the specificity of life, as they allow a greater range of complexity. Eukaryotic cells are usually part of complex and multicellular organisms, although they can also be unicellular organisms (such as yeast).
Within the group of eukaryotic cells there are two main types: animal cells and plant cells. Although both have structures in common, they also have some differences (in relation to the functions they perform), as shown below.
- Both animal and plant cells have mitochondria , which are the organelles where cellular respiration takes place, a reaction that allows the cell to obtain energy for all its functions.
- The cell nucleus is another characteristic shared by both types of cells. The cell's genetic material (DNA) is housed in this membranous structure.
- Plant cells have a rigid cell wall, composed mainly of cellulose. This structure gives shape to the cell and gives support to the plant ( plant organisms do not have skeletons like animals). In addition, plant cells have a large vacuole that stores water and nutrients and, by occupying a large part of the cell volume, gives these cells rigidity.
- Plant cells have chloroplasts, organelles where photosynthesis takes place, a process by which the plant makes its own food. These organelles are unique to plant cells.
- Animal cells do not have a cell wall and are highly varied and often irregular in shape. For their part, plant cells are usually larger and prismatic in shape.
- Animal cells have two unique structures (that is, they are not found in plant cells): centrioles, which participate in cell division, and lysosomes, which are small vesicles that contain digestive enzymes and are involved in the degradation of cell structures. .
Parts of a cell
Cells have various organelles and delimited sectors:
- The plasma membrane . It is a biological border that delimits the cell and distinguishes its interior from the exterior. It is formed by a double layer of phospholipids, which separates the content of the cell from the environment that surrounds it and allows the entry and exit of substances . Thus, it can let in certain nutrients and excrete its wastes.
- Cellular wall. It is a thick and stable barrier, in addition to the plasma membrane , which confers certain rigidity and resistance to the cell. The cell wall is present in prokaryotic cells and in eukaryotic organisms it is only found in plant and fungal cells . The cell wall is manufactured based on various resistant materials and is variable in each type of organism.
- Core . This structure is limited by a nuclear envelope formed by a double membrane. The nucleus is an exclusive organelle of eukaryotic cells and inside it contains most of the cell's genetic material ( DNA ).
- Cytoplasm . It is the gelatinous substance that fills the interior of the cell, located between the plasma membrane and the nucleus (when present), and made up of water, salts, proteins and other substances. The main function of the cytoplasm is to support the organelles of the cell and help in the metabolic processes that occur within it.
- Organelles They are internal structures found in the cell that perform specific roles. Some of them are:
- Mitochondria . They are the structures where cellular respiration takes place, a reaction that allows the cell to obtain energy .
- Lysosomes They deal with digestion and the use of nutrients.
- Chloroplasts. They are structures (exclusive of plant cells) that contain chlorophyll, essential for the photosynthesis reaction that takes place inside.
- Ribosomes. They deal with the synthesis of proteins, a process necessary for cell growth and reproduction.
- Flagella. They are organelles present in certain cells and serve to propel themselves in the environment . They are typical of unicellular beings or mobile cells such as sperm.
Functions of a cell
Cells can have very diverse and complex functions:
- Structural functions. Build tissues, such as fat , muscle, and bone , that support the body and its organs.
- Secretory functions. Generate substances essential for life and self-regulation of the body, as do the mucous membranes or glands.
- Metabolic functions. Break down nutrients or transport them throughout the body, as digestive cells in the intestine and red blood cells do in the blood, respectively.
- Defensive functions. Help the body defend itself from external agents and eliminate them, or fight diseases, as do white blood cells.
- Control functions. Coordinate the enormous diversity of processes in the body, transporting information and generating specific reactions to certain stimuli (such as neurons ).
- Reproductive functions. Combine with other sex cells from another organism of the same species to give rise to a new individual ( sexual reproduction ), or divide (on their own) by mitosis to produce a new individual identical to the parent ( asexual reproduction ).