Spoonpods, flagella and cilia.
Spoonpods, or pseudopodia (from Greek pseudodos- not real, podos– leg) are formed as a result of the flow of cytoplasm. In this case, processes of different shapes are formed. Characteristic of many unicellular (amoebas, foraminifera, radiolarians, etc.), animal leukocytes. Pseudopodia provide envelopment of solid nutrient particles - a process phagocytosis .
Cilia And flagella consist of microtubules of contractile proteins arranged in a special way. In a cross section, they have nine double microtubules at the periphery and two in the center. Cilia and flagella are covered with a plasma membrane. They have a diameter of about 0.25 microns. They differ in length (cilia are short, flagella are long) and in the nature of movement (in flagella it is spiral, in cilia it is ciliated and wavy). The movements of the cilia are coordinated.
They are found in unicellular organisms and in multicellular tissue cells (flagellum in sperm, cilia in ciliated epithelium). Functions of cilia and flagella: movement of unicellular organisms, provision of food (flagella of hydra digestive cells, etc.), tactile and protective functions (cilia of mucous membrane cells, etc.).
Basal bodies - special structures deepened into the cytoplasm that underlie cilia and flagella. Interconnected with the peripheral part of flagella or cilia and attached to the plasma membrane of the cell. Each cilium is based on one basal body. Their peripheral bundles (9 microtubules) are collected in groups of three. They are absent in the central part.
Ribosomes
They consist of two subunits - large and small. Chemical composition: ribosomal RNA and protein in almost equal proportions form a single ribonucleoprotein complex. Ribosomes are formed in the nucleolus.
Subunits under the influence of certain ions (calcium) and biologically active compounds can be separated or connected. The large and small subunits join together outside the nucleus, at the sites where the protein will be synthesized. There are ribosomes, both free and membrane-bound, forming a rough ER. First, the small subunit on the EPS membrane combines with an mRNA molecule, then combines with the large subunit.
The number of ribosomes depends on the intensity of protein synthesis processes.
Functions of ribosomes
Protein synthesis.
Cell center
Has or does not have centrioles . Centrioles are two mutually perpendicular cylinders that are formed from microtubules ordered in a certain way. They consist of nine bundles of microtubules, three in each, located along the periphery. The structure is similar to basal bodies. Centrioles are located in a section of the light cytoplasm. Microthreads extend radially from it in different directions. There are no centrioles in the cells of higher plants, some fungi, algae and protozoa.
Functions of centrioles
They take part in the formation of the spindle, cilia and flagella, and microtubules of the cytoplasm. If absent, all these processes occur without them. Other functions have not been fully clarified.
Inclusions
Inclusions – these are unstable structures that can appear and disappear in the process of life, mainly reserve substances. They are located in the cytoplasm and are also found in mitochondria, plastids, and cell sap of plant cell vacuoles. They can decompose under the action of enzymes into compounds that enter into the processes of metabolism, growth, flowering, fruit ripening, etc.
They come in a liquid state in the form of droplets (lipids) or a solid state - in the form of granules (starch, glycogen, etc.), crystals (oxalic acid salts, etc.).
There are organic and inorganic.
Organic inclusions
Organic : most often carbohydrates (starch, glycogen), fats, less often - proteins, pigments. Starch, which accumulates in leukoplasts, ruptures cell membranes and enters the cytoplasm, where it is stored in the form of grains. Protein granules (legumes, cereals) and fats (peanuts) can accumulate in plant cells of storage tissue. Glycogen in the form of grains or fibers is stored in animal cells and fungal cells. Many proteins and lipids are stored in the cytoplasm of animal eggs.
Inorganic inclusions
Inorganic : salts (sodium oxalate, uric acid, etc.). Inorganic inclusions are often found in the form of insoluble compounds.
Inclusions can appear in the form of structures that act as an intracellular skeleton in some unicellular animals. They are structures of a certain shape without a surface membrane. For example, radiolarians have a spherical capsule made of a horn-like compound, an intracellular skeleton made of silicon dioxide or strontium sulfate, and Giardia has a rod made of organic matter.
Plant cells contain the same structures as animal cells. But they are characterized by special structures that animal cells do not have.
Plastids - organelles that are unique to plant cells. In addition, each plant cell has a cell wall, which contains cellulose. Plant cells are characterized by special large vacuoles that provide support for turgor pressure. The cytoplasms of plant cells are connected to each other through pores in the cell walls using plasmodesmata , form a single whole - simplast .
Animal cells have a supra-membrane structure, the glycocalyx, which is absent in plant cells.
The cells of all living organisms have a related structure. They all consist of a plasma membrane, a shell around it (glycocalyx in animals or a cell wall: in fungi - from chitin, in plants - from cellulose), cytoplasm (organelles are located in it, any of which performs its functions, the cell center, for example, participates in division) and the nucleus, which protects DNA (not counting prokaryotes).
Cell organelles
These include ribosomes, lysosomes, mitochondria, Golgi complex, endoplasmic reticulum and cell center. Plant cells also contain special organelles unique to them - vacuoles. They accumulate unnecessary substances, plastids (chromoplasts, leucoplasts, chloroplasts, in the latter the process of photosynthesis occurs). The functions of the cell center, mitochondria, ribosomes and other structures are very important. Mitochondria play the role of typical energy production stations; the process of intracellular respiration occurs in them. Ribosomes are responsible for the production of proteins, synthesizing them from individual amino acids in the presence of mRNA, which contains information about the substances needed by the cell. The functions of lysosomes are to break down chemical compounds with the help of enzymes that are contained inside the organelle. The Golgi complex accumulates and stores certain substances. The endoplasmic reticulum is also involved in metabolism.
Cellular center - structure and functions
This organelle is also called a centrosome. The functions of the cell center can hardly be overestimated - without this organelle, cell division would be impossible. It consists of 2 parts. In this, the cell center is identical to the ribosome, the structure of which also contains two halves. The parts of the centrosome are called centrioles, each of them looks like a hollow cylinder formed from microtubules. They are placed perpendicular to each other. The functions of the cell center include the formation of a spindle by centrioles during the process of meiosis or mitosis.
How is a cell divided?
There are two main methods - meiosis and mitosis. Cell center functions appear in both processes. In both the first and second cases, division occurs in several stages. The following stages are distinguished: prophase, metaphase, anaphase, telophase. 
Meiosis usually involves two alternating cell divisions, the time between them is called interphase. As a result of this process, from a cell with a diploid set of chromosomes (double), several with a haploid (single) appear. During the process of mitosis, the number of chromosomes is not miniaturized - the daughter cells also have a diploid set. There is also a division method called amitosis. In this case, the nucleus, and then the entire cytoplasm, simply divides in two. This species is not nearly as widespread as the first two; it is found more among the simple ones. The cell center is not involved in this process.
The role of the cell center in division
Prophase involves preparation for the process of mitosis or meiosis, during which the nuclear membranes are destroyed. During metaphase, the cell center separates into two separate centrioles. They, in turn, spread to the opposite poles of the cell. At this same stage, the chromosomes line up along the equator. Then they are attached to the centrioles by the filaments of the spindle in such a way that the different chromatids of each chromosome are attached to the reverse centrioles. During metaphase, any of the chromosomes is split into separate chromatids, which are pulled by the centrioles to the opposite poles by the threads. 
During telophase, nuclear membranes are formed, the cytoplasm is divided, and daughter cells are completely formed.
To the question: What is the structure of the functions of the cell nucleus and cell center? given by the author Anyukha Sunyaykina the best answer is Cell nucleus The nucleus is the most important component of the cell. The cell nucleus contains DNA, i.e. genes, and, thanks to this, performs two main functions: 1) storage and reproduction of genetic information 2) regulation of metabolic processes occurring in the cell. A nuclear-free cell cannot exist for a long time, and the nucleus is also unable to to independent existence, therefore the cytoplasm and the nucleus form an interdependent system. Most cells have one nucleus. It is often possible to observe 2-3 nuclei in one, for example in liver cells. Multinucleate cells are also known, and the number of nuclei can reach several dozen. The shape of the nucleus depends largely on the shape of the cell; it can be completely irregular. There are spherical and multi-lobed kernels. Invaginations and outgrowths of the nuclear membrane significantly increase the surface of the nucleus and thereby strengthen the connection of nuclear and cytoplasmic structures and substances. Structure of the nucleus The nucleus is surrounded by a shell, which consists of two membranes with a typical structure. The outer nuclear membrane on the surface facing the cytoplasm is covered with ribosomes, the inner membrane is smooth. The nuclear envelope is part of the cell membrane system. The outgrowths of the outer nuclear membrane connect with the channels of the endoplasmic reticulum, forming a single system of communicating channels. Metabolism between the nucleus and the cytoplasm occurs in two main ways. Firstly, the nuclear envelope is penetrated by numerous pores through which molecules are exchanged between the nucleus and the cytoplasm. Secondly, substances from the nucleus into the cytoplasm and back can enter due to the release of invaginations and outgrowths of the nuclear membrane. Despite the active exchange of substances between the nucleus and the cytoplasm, the nuclear envelope limits the nuclear contents from the cytoplasm, thereby ensuring differences in the chemical composition of the nuclear sap and the cytoplasm. This is necessary for the normal functioning of nuclear structures.
The cell center, the mitotic center, a permanent structure in almost all animal and some plant cells, determines the poles of the dividing cell (see Mitosis). K. c. usually consists of two centrioles - dense granules 0.2-0.8 μm in size, located at right angles to each other. During the formation of the mitotic apparatus, the centrioles diverge to the cell poles, determining the orientation of the cell division spindle. Therefore, it is more correct to K. c. called a mitotic center, thereby reflecting its functional significance, especially since only in some cells of K. c. located in its center. During the development of the organism, the position of the blood cells changes. in cells, and its form. When a cell divides, each daughter cell receives a pair of centrioles. The process of their doubling occurs more often at the end of the previous cell division. The occurrence of a number of pathological forms of cell division is associated with abnormal division of K. c.
Answer from Caucasian[newbie]
I have 2 questions in connection with this text. 1. In the cells of higher plants there is no cell center. In this case, what structure (organelle) replaces it, for example, during cell division? 2. During cell division, does the cell center double or do its centrioles simply diverge to the poles, i.e. does it seem to split?
Hyaloplasma (cytoplasmic matrix) - a homogeneous fine-grained structure consisting of two phases - liquid and solid.
- What are the liquid and solid phases of hyaloplasm?
Liquid phase(cytosol) is a colloidal solution consisting of H 2 O, proteins, amino acids, RNA, lipids, carbohydrates, ions (Na +, K +, Mg 2+, C 1 -, HC0 3 -, HP0 4 2-). The cytosol is the internal environment of the cell in which many chemical processes occur, it unites all cellular structures and ensures chemical interaction between them, and is a container for substances necessary for the life of the cell.
Solid phase hyaloplasm (cytoskeleton) is represented by a system of thin protein filaments crossing the cytoplasm in various directions. The cytoskeleton is formed by three components: microtubules, microfilaments and intermediate filaments. The cytoskeleton is the framework of the cell, determines its shape, connects membrane organelles and plasmalemma into a single whole, organizes the placement of all structural components of the cell, ensures intracellular transport of substances and movement of organelles, changes the physical properties of hyaloplasm (sol-gel).
Organoids - These are permanent specialized areas of the cytoplasm that have a certain structure and perform certain functions in the cell.
Let's remember the classification of cell organelles. Let's return once again to the cards with the names of organelles. Divide them into groups
A) by structure
B) for its intended purpose in the cage
B) by participating in the exchange of goods
Classification of organelles:
I . By structure:
a) membrane structure - single-membrane (ER, CG, lysosomes, vacuoles), double-membrane (mitochondria and plastids);
b) non-membrane structure - ribosomes and cell center.
II . By purpose in the cage:
a) general purpose - are present in most cells, provide basic life processes (mitochondria, AG, EPS, ribosomes, cell center, lysosomes, plastids and vacuoles with cell sap);
b) special purpose - provide specialized functions: myofibrils - in muscle cells; organelles of movement (flagella and cilia), organelles of excretion (pulsating vacuoles and adductor canals), organelles of digestion (cell mouth, digestive vacuole and powder) - in protist cells.
III . By participation in metabolism:
a) anabolic system (synthesis of substances) – EPS, CG and ribosomes, plastids;
b) catabolic system (breakdown of substances) - mitochondria, lysosomes and microbodies.
Cell center
Structural features: Located near the nucleus of animal cells and some plants. It consists of two small bodies - centrioles, perpendicular to each other. Each centriole consists of protein microtubules.
Functions performed: Participates in the construction of the cell division spindle. Lie at the base of flagella and cilia
Inclusions - these are unstable components of the cytoplasm, the content of which varies depending on the functional state of the cell. Distinguishtrophic , secretory and excretory inclusions. Inclusions may be surrounded by a membrane.
Trophic - reserves of nutrients in the cell: granules of proteins and starch or glycogen, drops of fat.
Secretory - in the cells of the glands, enzymes, hormones and other biologically active substances accumulate in them
Excretory - they accumulate waste products that must be removed from the cell (crystals of calcium oxalate, residual bodies).
Ribosomes - a spherical organelle of general importance, non-membrane structure, with a diameter of 17-35 nm; consists of r-RNA (40%) and proteins (60%).
It has 2 subunits: small and large, which are connected using Mg 2+. Subunits are formed in the nucleoli. Ribosomes are located freely in the cytoplasm or attached to the membranes of the ER and the outer nuclear membrane, and are also present in mitochondria and chloroplasts.
Have 2 active centers: aminoacyl (fixation of t-RNA with AK) and peptidyl (peptide bonds are formed between AK). Ribosomes form complexes - polysomes.
Functions: protein synthesis (translation)
It has been proven that the cells of eukaryotic organisms are represented by a system of membranes that form organelles of protein-phospholipid composition. However, there is an important exception to this rule. Two organelles (the cell center and the ribosome), as well as organelles of movement (flagella and cilia) have a non-membrane structure. How are they educated? In this work, we will try to find the answer to this question, and also study the structure of the cellular center of the cell, often called the centrosome.
Do all cells contain a cell center?
The first fact that interested scientists was the optional presence of this organelle. Thus, it is absent in lower fungi - chytridiomycetes - and in higher plants. As it turned out, in algae, in human cells and in most animals, the presence of a cell center is necessary for the processes of mitosis and meiosis. Somatic cells divide in the first way, and sex cells in the other. The centrosome is an obligatory participant in both processes. The divergence of its centrioles to the poles of the dividing cell and the tension between the spindle threads between them ensures the further divergence of the chromosomes attached to these threads and to the poles of the mother cell.
Microscopic studies revealed structural features of the cell center. It includes from one to several dense bodies - centrioles, from which microtubules fan out. Let's study in more detail the appearance, as well as the structure of the cell center.
Centrosome in an interphase cell
In the life cycle of a cell, the cell center can be seen during a period called interphase. Two microcylinders are usually located next to the nuclear membrane. Each of them consists of protein tubes assembled in threes (triplets). Nine such structures form the surface of the centriole. If there are two of them (which happens most often), then they are located at right angles to each other. During the period of life between two divisions, the structure of the cell center in the cell is almost the same in all eukaryotes.
Ultrastructure of the centrosome
It became possible to study in detail the structure of the cell center as a result of the use of an electron microscope. Scientists have found that centrosome cylinders have the following dimensions: their length is 0.3-0.5 microns, their diameter is 0.2 microns. The number of centrioles necessarily doubles before division begins. This is necessary so that the mother and daughter cells themselves, as a result of division, receive a cell center consisting of two centrioles. The structural features of the cell center lie in the fact that the centrioles that make it up are not equivalent: one of them - mature (maternal) - contains additional elements: the pericentriolar satellite and its appendages. The immature centriole has a specific region called the cart wheel.
Behavior of the centrosome in mitosis
It is well known that the growth of an organism, as well as its reproduction, occurs at the level of the elementary unit of living nature, which is the cell. The structure of the cell, the localization and functions of the cell, as well as its organelles, are examined by cytology. Despite the fact that scientists have conducted quite a lot of research, the cell center remains insufficiently studied, although its role in cell division has been fully elucidated. In the prophase of mitosis and in the prophase of the reduction division of meiosis, the centrioles diverge to the poles of the mother cell, and then the formation of a spindle filament occurs. They are attached to the centromeres of the primary constriction of chromosomes. Why is this necessary?
Anaphase cell division spindle
The experiments of G. Boveri, A. Neil and other scientists made it possible to establish that the structure of the cell center and its functions are interconnected. The presence of two centrioles, bipolarly located in relation to the cell poles, and spindle filaments between them ensures uniform distribution of chromosomes connected to microtubules to each of the poles of the mother cell.
Thus, the number of chromosomes will be the same in the daughter cells resulting from mitosis, or half as many (in meiosis) as the original mother cell. Particularly interesting is the fact that the structure of the cell center changes and is correlated with the stages of the cell life cycle.
Chemical analysis of the organelle
To better understand the functions and role of the centrosome, we will study what organic compounds are included in its composition. As you might expect, proteins lead the way. Suffice it to remember that they also depend on the presence of peptide molecules in it. Note that proteins in the centrosome have contractile ability. They are part of microtubules and are called tubulins. While studying the external and internal structure of the cell center, we mentioned auxiliary elements: pericentriolar satellites and centriole appendages. They contain cenexin and myricitin.
There are also proteins that regulate the metabolism of the organelle. These are kinase and phosphatase - special peptides responsible for the nucleation of microtubules, that is, for the formation of an active seed molecule with which the growth and synthesis of radial microfilaments begins.
Cellular center as an organizer of fibrillar proteins
In cytology, the idea of the centrosome as the main organelle responsible for the formation of microtubules has finally been established. Thanks to the generalizing research of K. Fulton, it can be argued that the cell center ensures this process in four ways. For example: polymerization of spindle filaments, formation of procentrioles, creation of the radial system of microtubules of the interphase cell and, finally, synthesis of elements in the primary cilium. This is a special formation characteristic of the mother centriole. By studying the structure and functions of the cell membrane, scientists detect it under an electron microscope in the cell center after mitotic cell division or at the beginning of mitosis. During the G2 stage of interphase, as well as in the early stages of prophase, the cilium disappears. According to its chemical composition, it consists of tubulin molecules and is a mark by which a mature mother centriole can be identified. So how does centrosome maturation occur? Let's consider all the nuances of this process.
Stages of centriole formation
Cytologists have found that the daughter and mother centrioles that form the diplosome are not identical in structure. Thus, the mature structure is bordered by a layer of pericentriolar substance - a mitotic halo. Full maturation of the daughter centriole takes longer than one cell life cycle. At the end of the G1 stage of the second cell cycle, the new centriole already acts as an organizer of microtubules and is capable of forming spindle filaments, as well as the formation of special movement organelles. They can be cilia and flagella, found in unicellular protozoa (for example, green euglena, slipper ciliates), as well as in many algae, for example Chlamydomonas. Flagella, formed thanks to the microtubules of the cell center, are equipped with many spores in algae, as well as the germ cells of animals and humans.
The role of the centrosome in cell life
So, we are convinced that one of the smallest cellular organelles (occupies less than 1% of the cell volume) plays a leading role in regulating the metabolism of both plant and animal cells. Violation of the formation of the division spindle entails the formation of genetically defective daughter cells. Their chromosome sets differ from the normal number, leading to chromosomal aberrations. The result is the development of abnormal individuals or their death. In medicine, the fact of the relationship between the number of centrioles and the risk of developing cancer has been established. For example, if normal skin cells contain 2 centrioles, then a tissue biopsy for skin cancer reveals an increase in their number to 4-6. These results provide evidence for the key role of the centrosome in the control of cell division. Recent experimental data indicate the important role of this organelle in intracellular transport processes. The unique structure of the cell center allows it to regulate both the shape of the cell and its changes. In a normally developing unit, the centrosome is located next to the Golgi apparatus, near the nucleus, and together with them provides integrative and signaling functions in the implementation of mitosis, meiosis, as well as programmed cell death - apuptosis. That is why modern cytologists consider the centrosome to be an important unifying organelle of the cell, responsible both for its division and for the entire metabolism in general.
