A great summary to understand what a cell is, what types there are and why they are so important.
Every living being is made up of cells , some of them by only one, while other organisms are made up of millions of them (as the cell theory that developed in the 19th and 20th centuries affirms).
In the human body, for example, there are between 75 and 100 billion cells, all of them with specific functions but that complement each other.
A cell is the smallest morphological and functional unit of any living organ, be it a human being or a bacterium. These always have their origin from another cell, that is, they do not appear by spontaneous generation.
Cells are open systems, so they always exchange both energy and matter with the environment. This is what allows them to capture food and oxygen from the outside and eliminate those substances that are not necessary, such as sweat or toxins in the form of excrement.
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cell size
The size of these units is expressed in micrometers or microns (µm) . To get an idea, it is one thousandth of a millimeter (10-3 millimeters). Although cells are generally associated with microscopic sizes , their size can actually vary.
It is possible to find bacteria of 1 and 2 microns in length, but especially in the human body, variety is important. The size of red blood cells is 7 microns, liver cells about 20 microns and oocytes 150 microns. Now, some cells, those that are formed in the brainstem and travel throughout the spine, can measure up to a meter.
In the animal kingdom, it is also possible to find this variability. An ostrich egg measures around 7 cm, and cells that extend through the giraffe’s neck can measure up to 10 meters.
cell shape
As well as the size of the cells, the shape they present can also be very varied . In fact, there are some that do not offer a fixed form.
The cells can be spindle-shaped, star-shaped, flattened, rounded, etc. It is possible to find cells with a rigid wall and others with a wall that allows them to emit pseudopods to move and get nutrients. Similarly, there are cells that, despite not having pseudopodia, have cilia or flagella that allow their movement.
Cells may or may not be joined together to form tissues. In fact, there are organisms that are unicellular, such as bacteria or algae.
Prokaryotic and eukaryotic cells: what are they?
There are different types of cells . If we make a more general classification, it is necessary to distinguish between prokaryotic and eukaryotic cells. In this last group, we can find plant and animal cells.
Prokaryotic cells are unicellular organisms that do not have a defined nucleus and in which the DNA is scattered throughout the cytoplasm. They are more primitive and it is believed that they are the origin of the more developed eukaryotic cells, and that they have a well-defined nucleus that is delimited by a double lipid layer. They contain a well organized cytoplasm.
- More information: “The 7 differences between DNA and RNA”
Similarities and Differences Between Eukaryotic and Prokaryotic Cells
Although there are differences between eukaryotic and prokaryotic cells, they also have aspects in common: both contain genetic material, a cell membrane that covers them and both have similar chemical structures, composed of proteins, carbohydrates, fats, minerals and vitamins. Also, both contain ribosomes, which synthesize proteins.
Eukaryotic and prokaryotic cells reproduce, although in different ways. Logically, both need energy to survive. In both, it is possible to find cytoplasm and a cytoskeleton.
Now, despite these similarities, scientists have discovered important differences . We describe them below.
1. Core
Genetic information can be found stored within the nucleus of eukaryotic cells . The nucleus of these structures is well defined, something that does not occur with prokaryotic cells.
2. Origin
Prokaryotic cells originated around 3.7 billion years ago, while eukaryotic cells 2 billion years ago.
3. Size
The size of both cells can vary; however, prokaryotes are smaller.
4. Cell organization
While prokaryotic cells are usually unicellular, eukaryotic cells are multicellular.
5. Genetic material
The genetic material in prokaryotic cells is scattered throughout the cytoplasm . Instead, the genetic material in eukaryotic cells is stored in the nucleus. As for the DNA of the former, it is circular. In the case of eukaryotes, it is linear and is associated with histones.
Prokaryotic cells have a single chromosome, while prokaryotes have multiple.
6. Plasma membrane
The plasma membrane of eukaryotic cells is composed of sterols. In prokaryotes there are no sterols (except in mycoplasmas).
Furthermore, the plasma membrane of prokaryotic cells is composed of peptidoglycan or murein, while eukaryotic cells are composed of phospholipids.
7. Organelles
Eukaryotic cells contain organelles such as the Golgi apparatus, mitochondria, or lysosomes. This is not the case for prokaryotic cells.
8. Playback
Both types of cells reproduce, reproduction in prokaryotic cells occurs by binary fission in an asexual manner.
animal and plant cells
Within eukaryotic cells, we can find animal-type cells and plant-type cells . As in the previous case, there are similarities and differences.
Both contain a well-defined nucleus in which the DNA is found. The reproductive processes are similar and include mitosis and meiosis. To get energy they need to breathe. Both share some cellular components such as ribosomes, the endoplasmic reticulum and the Golgi apparatus, among others.
As for the differences, plant cells do not store energy in the form of glycogen as is the case with animal cells, but rather store it in the form of starch. The former usually have a rectangular shape and are usually larger than the animals.
Plant cells are capable of synthesizing all amino acids, unlike animal cells. In terms of size, the latter are usually smaller. If we refer to the shape of plant cells, it is usually rectangular.
cell functions
Cells can perform a series of functions that allow and guarantee their survival.
- Metabolism : It is the process by which cells obtain energy, either by anabolism or synthesis of new materials, or by catabolism; that is, by the destruction of previously used materials.
- Excitability : Refers to how cells are able to respond to changes in their environment.
- Growth : It is the process by which the cell forms material to increase its size.
- Capture : Through capture, she takes advantage of materials from the surrounding environment.
- Elimination : Expulsion of toxins or waste.
- Reproduction : Formation of new cells that replace the old ones.
In summary, cells perform three basic functions:
- Nutrition : It is the introduction and transformation of food (heterotrophic cells) and the assimilation of the substances necessary to form its own organic matter (autotrophic cells).
- Relationship : The action of collecting information from the environment to respond to the stimuli captured.
- Reproduction : Formation of new cells. In the case of eukaryotes and specifically in humans, reproduction is by Meiosis (occurs in the sexual organs with the aim of the continuity of the species) or Mitosis (occurs in any part of the body for the formation of new tissues, organs and allows the growth of the individual).
The cells are grouped according to their specialization for the creation of tissues. These create organs, and the union of organs forms systems. For example, muscle cells join together to form muscle tissues. These join together to form the muscle which, in turn, forms the muscular system after the union of several of them.
Bibliographic references
- Buicán, Denis (1995). History of biology, Madrid, Editorial Accent.
- Otto, James H. and Towle, Albert. (1992). modern biology. [11th ed.]. McGraw Hill / Inter-American of Mexico. Mexico City, Mexico.
- VV. AA. (2004). General Biology [4th ed.]. University of Navarra Editions. Baranain, Spain.
To the classic question “what do you do?” I always answer “basically I am a psychologist”. In fact, my academic training has revolved around the psychology of development, education and community, a field of study influenced my volunteer activities, as well as my first work experiences in personal services.