Biology: cells. Structure, purpose, functions

The biology of the cell is generally known to each of the school curriculum. We invite you to remember what you once learned, as well as discover something new about her. The name "cage" was proposed as early as 1665 by the Englishman R. Hooke. However, it was only in the 19th century that it began to be studied systematically. Scientists were interested, among other things, and the role of the cell in the body. They can be in the composition of many different organs and organisms (eggs, bacteria, nerves, erythrocytes) or be independent organisms (protozoa). Despite all their diversity, there is much in common in their functions and structure.

Cell Functions

They are all different in form and often in function. Cells of tissues and organs of one organism can differ quite strongly. However, cell biology distinguishes functions that are inherent in all their varieties. This is where protein synthesis always takes place. This process is controlled by the genetic apparatus. A cell that does not synthesize proteins is essentially dead. A living cell is one whose components are constantly changing. However, the main classes of substances remain unchanged.

All processes in the cell are carried out using energy. These are nutrition, respiration, reproduction, metabolism. Therefore, a living cell is characterized by the fact that energy exchange takes place in it all the time. Each of them has a common most important property - the ability to store energy and spend it. Other functions include division and irritability.

All living cells can respond to chemical or physical changes in their environment. This property is called excitability or irritability. In cells, when excited, the rate of decay of substances and biosynthesis, temperature, and oxygen consumption change. In this state, they perform the functions inherent to them.

Cell structure

cell biology

Its structure is quite complex, although it is considered the simplest form of life in a science such as biology. The cells are located in the intercellular substance. It provides them with breathing, nutrition and mechanical strength. The nucleus and cytoplasm are the main building blocks of every cell. Each of them is covered with a membrane, the building element for which is a molecule. Biology has established that the membrane is composed of many molecules. They are arranged in several layers. Due to the membrane, substances penetrate selectively. In the cytoplasm are organelles - the smallest structures. These are the endoplasmic reticulum, mitochondria, ribosomes, cell center, Golgi complex, lysosomes. You will have a better understanding of what cells look like by studying the pictures presented in this article.


parts of the cage

When examining a plant cell under a microscope (for example, an onion root), you will notice that it is surrounded by a rather thick shell. The squid has a giant axon, the shell of which is of a completely different nature. However, it does not decide which substances should or should not be allowed into the axon. The function of the cell membrane is that it is an additional means of protecting the cell membrane. The membrane is called the "fortress wall of the cage". However, this is true only in the sense that it protects and protects its contents.

Both the membrane and the inner contents of each cell usually consist of the same atoms. These are carbon, hydrogen, oxygen and nitrogen. These atoms are at the beginning of the periodic table. The membrane is a molecular sieve, very fine (its thickness is 10 thousand times less than the thickness of a hair). Its pores resemble long narrow passages made in the fortress wall of some medieval city. Their width and height are 10 times less than their length. Moreover, the holes in this sieve are very rare. In some cells, pores occupy only one millionth of the entire membrane area.


living cell

Cell biology is also interesting from the point of view of the nucleus. It is the largest organoid, the first to attract the attention of scientists. In 1981, the cell nucleus was discovered by Robert Brown, a Scottish scientist. This organoid is a kind of cybernetic system, where information is stored, processed, and then transferred to the cytoplasm, the volume of which is very large. The nucleus is very important in the process of heredity, in which it plays a major role. In addition, it performs the function of regeneration, that is, it is able to restore the integrity of the entire cellular body. This organoid regulates all the most important functions of the cell. As for the shape of the nucleus, most often it is spherical, as well as ovoid. Chromatin is the most important component of this organoid. This is a substance that stains well with special nuclear dyes.

A double membrane separates the nucleus from the cytoplasm. This membrane is associated with the Golgi complex and with the endoplasmic reticulum. The nuclear membrane has pores through which some substances easily pass, while others are more difficult to do. Thus, its permeability is selective.

Nuclear juice is the inner content of the nucleus. It fills the space between its structures. Necessarily in the nucleus there are nucleoli (one or more). Ribosomes are formed in them. There is a direct relationship between the size of the nucleoli and the activity of the cell: the larger the nucleoli, the more actively the protein biosynthesis occurs; and, on the contrary, in cells with limited synthesis, they are either completely absent or small.

The nucleus contains chromosomes. These are special threadlike formations. In addition to genital, there are 46 chromosomes in the nucleus of a human cell. They contain information about the hereditary inclinations of the organism, which is passed on to the offspring.

The cells usually have one nucleus, but there are also multinucleated cells (in muscles, in the liver, etc.). If the nuclei are removed, the remaining parts of the cell will become unviable.


what cells look like

The cytoplasm is a colorless, mucous, semi-liquid mass. It contains about 75-85% water, about 10-12% amino acids and proteins, 4-6% carbohydrates, 2 to 3% lipids and fats, as well as 1% inorganic and some other substances.

The content of the cell in the cytoplasm is able to move. Thanks to this, organelles are optimally placed, and biochemical reactions proceed better, as well as the process of excretion of metabolic products. Different formations are presented in the cytoplasmic layer: superficial outgrowths, flagella, cilia. The cytoplasm is permeated by the reticular system (vacuolar), consisting of flattened sacs, vesicles, tubules, communicating with each other. They are associated with the outer plasma membrane.

Endoplasmic reticulum

cell biology test

This organoid was named so because it is located in the central part of the cytoplasm (from the Greek the word "endon" is translated as "inside"). EPS is a very branched system of vesicles, tubules, tubules of various shapes and sizes. They are delimited from the cytoplasm of the cell by membranes.

There are two types of EPS. The first is granular, which consists of cisterns and tubules, the surface of which is dotted with granules (grains). The second type of EPS is agranular, that is, smooth. Granas are ribosomes. It is curious that mainly granular EPS is observed in the cells of animal embryos, while in adult forms it is usually agranular. As you know, ribosomes are the site of protein synthesis in the cytoplasm. Based on this, it can be assumed that granular EPS occurs predominantly in cells where active protein synthesis occurs. The agranular network is believed to be represented mainly in those cells where active synthesis of lipids, that is, fats and various fat-like substances, takes place.

Both types of EPS do not just take part in the synthesis of organic substances. Here these substances are accumulated, and also transported to the necessary places. EPS also regulates the metabolism that occurs between the environment and the cell.


These are cellular non-membrane organelles. They are composed of protein and ribonucleic acid. These parts of the cell are still not fully understood from the point of view of the internal structure. In an electron microscope, ribosomes look like mushroom-shaped or rounded granules. Each of them is divided into small and large parts (subunits) by a groove. Several ribosomes are often linked together by a strand of special RNA (ribonucleic acid) called i-RNA (informational). Thanks to these organelles, protein molecules are synthesized from amino acids.

Golgi complex

biology cell composition

The products of biosynthesis enter the lumens of the tubules and cavities of the EPS. Here they are concentrated in a special apparatus called the Golgi complex (in the picture above it is designated as the golgi complex). This apparatus is located near the nucleus. He takes part in the transfer of biosynthetic products that are delivered to the cell surface. Also, the Golgi complex is involved in their removal from the cell, in the formation of lysosomes, etc.

This organoid was discovered by Camilio Golgi, an Italian cytologist (years of his life - 1844-1926). In honor of him, in 1898, he was named the Golgi apparatus (complex). The proteins produced in the ribosomes enter this organoid. When they are needed by some other organoid, part of the Golgi apparatus is detached. Thus, the protein is transported to the desired location.


Talking about how cells look and what organelles are part of them, it is imperative to mention lysosomes. They are oval in shape, surrounded by a single-layer membrane. Lysosomes contain a set of enzymes that destroy proteins, lipids, and carbohydrates. If the lysosomal membrane is damaged, enzymes break down and destroy the contents inside the cell. As a result, she dies.

Cell Center

It is found in cells that are capable of dividing. The cell center consists of two centrioles (rod-shaped bodies). Being near the Golgi complex and the nucleus, it participates in the formation of the spindle of division, in the process of cell division.


molecule biology

Energy organelles include mitochondria (pictured above) and chloroplasts. Mitochondria are a kind of energy stations in every cell. It is in them that energy is extracted from nutrients. Mitochondria are variable in shape, but most often they are granules or filaments. Their number and size are not constant. It depends on what is the functional activity of a particular cell.

If you look at an electron micrograph, you can see that mitochondria have two membranes: an inner and an outer one. The inner one forms outgrowths (cristae) covered with enzymes. Due to the presence of cristae, the total mitochondrial surface increases. This is important in order for the activity of enzymes to proceed actively.

In mitochondria, scientists have found specific ribosomes and DNA. This allows these organelles to reproduce on their own during cell division.


As for chloroplasts, in shape it is a disk or a sphere with a double shell (inner and outer). Inside this organelle, there are also ribosomes, DNA and grains - special membrane formations associated both with the inner membrane and among themselves. Chlorophyll is found precisely in gran membranes. Thanks to it, the energy of sunlight is converted into chemical energy adenosine triphosphate (ATP). In chloroplasts, it is used for the synthesis of carbohydrates (formed from water and carbon dioxide).

Agree, the information presented above you need to know not only in order to pass the test in biology. The cell is the building material of which our body is made. And all living nature is a complex collection of cells. As you can see, there are many components that stand out in them. At first glance, it may seem that studying the structure of a cell is not an easy task. However, if you look at it, this topic is not that difficult. You need to know it in order to be well versed in such a science as biology. The composition of the cell is one of its fundamental themes.

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