An organelle is a permanent formation in a cell that performs certain functions. They are also called organelles. An organelle is what allows a cell to live. Just as animals and humans are made up of organs, so every cell is made up of organelles. They are diverse and perform all the functions that ensure the life of the cell: this is the metabolism, and their storage, and division.
What are the organelles?
An organelle is a complex structure. Some of them may even have their own DNA and RNA. All cells contain mitochondria, ribosomes, lysosomes, a cell center, the Golgi apparatus (complex), and the endoplasmic reticulum (reticulum). Plants also have specific cell organelles: vacuoles and plastids. Some also refer to microtubules and microfilaments as organelles.
An organelle is a ribosome, a vacuole, a cell center, and many others. Let's take a closer look at the structure and functions of organelles.
Mitochondria
These organelles provide the cell with energy - they are responsible for They are found in plants, animals, and fungi. These cell organelles have two membranes: outer and inner, between which there is an intermembrane space. What is inside the shells is called the matrix. It contains a variety of enzymes - substances necessary to speed up chemical reactions. The inner membrane has folds - cristae. It is on them that the process of cellular respiration takes place. In addition, the mitochondrial matrix contains mitochondrial DNA (mDNA) and mRNA, as well as ribosomes, almost similar to those possessed by
Ribosome
This organelle is responsible for the process of translation, in which protein is synthesized from individual amino acids. The structure of the ribosome organelle is simpler than mitochondria - it does not have membranes. This organoid consists of two parts (subunits) - small and large. When the ribosome is idle, they are separated, and when it begins to synthesize protein, they unite. Several ribosomes can also come together if the polypeptide chain synthesized by them is very long. This structure is called a "polyribosome".
Lysosomes
The functions of organelles of this type are reduced to the implementation of cellular digestion. Lysosomes have one membrane, inside of which there are enzymes - catalysts for chemical reactions. Sometimes these organelles not only break down but also digest whole organelles. This can happen during a long starvation of the cell and allows it to live for some more time. Although if the nutrients still do not begin to flow, the cell dies.
and features
This organelle consists of two parts - centrioles. These are formations in the form of cylinders, consisting of microtubules. The cell center is a very important organelle. It is involved in the process of formation of the fission spindle. In addition, it is the center of microtubule organization.
golgi apparatus
It is a complex of disk-shaped membranous sacs called cisterns. The functions of this organoid are sorting, storing and converting certain substances. Here, mainly carbohydrates are synthesized, which are part of the glycocalyx.
The structure and functions of the endoplasmic reticulum
It is a network of tubules and pockets surrounded by a single membrane. There are two types of endoplasmic reticulum: smooth and rough. Ribosomes are located on the surface of the latter. Smooth and rough reticulum perform different functions. The first is responsible for the synthesis of hormones, storage and conversion of carbohydrates. In addition, the rudiments of vacuoles are formed in it - organelles characteristic of plant cells. The rough endoplasmic reticulum contains ribosomes on its surface that produce a polypeptide chain from amino acids. Then it enters the endoplasmic reticulum, and here a certain secondary, tertiary and quaternary structure of the protein is formed (the chain twists in the right way).
Vacuoles
These are organelles. They have one membrane. They accumulate cell sap. The vacuole is essential for maintaining turgor. It also participates in the process of osmosis. In addition, there are They are found mainly in unicellular organisms living in water bodies, and serve as pumps that pump out excess fluid from the cell.
Plastids: varieties, structure and functions
These are also organelles. They are of three types: leukoplasts, chromoplasts and chloroplasts. The former serve to store spare nutrients, mainly starch. Chromoplasts contain various pigments. Thanks to them, the petals of plants are multi-colored. This is necessary for the body in the first place in order to attract pollinating insects.
Chloroplasts are the most important plastids. Most of them are found in the leaves and stems of plants. They are responsible for photosynthesis - a chain of chemical reactions in which the body receives organic substances from inorganic substances. These organelles have two membranes. The chloroplast matrix is called the stroma. It contains plastid DNA, RNA, enzymes, and starch inclusions. Chloroplasts contain thylakoids - membrane formations in the form of a coin. Inside them, photosynthesis takes place. It also contains chlorophyll, which serves as a catalyst for chemical reactions. The thylakoids of chloroplasts are combined into piles - grana. Also in the organelles are lamellae, which connect individual thylakoids and provide a connection between them.
Movement organelles
They are characteristic mainly of unicellular organisms. These include flagella and cilia. The first are present in euglena, trypanosomes, chlamydomonas. Flagella are also present in animal spermatozoa. Cilia are found in ciliates and other unicellular organisms.
microtubules
They provide the transport of substances, as well as the permanent shape of the cell. Some scientists do not classify microtubules as organelles.
Body protozoan is made up of cytoplasm and one or more cores. The nucleus is surrounded by a double membrane and contains chromatin, which includes deoxyribonucleic acid (DNA), which determines the genetic information of the cell. Most protozoa have a vesicular nucleus with a small amount of chromatin collected along the periphery of the nucleus or in an intranuclear body, the karyosome. Micronuclei of ciliates are massive nuclei with a large amount of chromatin. Common cell components of most protozoa include mitochondria and the Golgi apparatus.
Surface bodies of amoeboid forms(sarcodal, as well as some stages of the life cycle of other groups) is covered with a cell membrane about 100 A thick. Most protozoa have a denser, but elastic shell, the pellicle. The body of many flagellates is covered with a periplast formed by a series of longitudinal fibrils fused with the pellicle. Many protozoa have special supporting fibrils, such as the supporting fibril of the undulating membrane in trypanosomes and Trichomonas.
Thick and hard shells have resting forms of protozoa, cysts. Shell amoeba, foraminifera and some other protozoa are enclosed in houses or shells.
Unlike cells of a multicellular organism the cell of the simplest is a complete organism. To perform the diverse functions of the body in the body of the simplest, structural formations, organelles, can specialize. According to their purpose, the organelles of protozoa are divided into organelles of movement, nutrition, excretion, etc.
Very diverse protozoan movement organelles. Amoeboid forms move through the formation of protrusions of the cytoplasm, pseudopodia. This type of movement is called amoeboid and is found in many groups of protozoa (sarcode, asexual forms of sporozoans, etc.). Flagella and cilia serve as special organelles for movement. Flagella are characteristic of the class of flagellates, as well as gametes of representatives of other classes. They are few in most forms (from 1 to 8). The number of cilia, which are the organelles of the movement of ciliates, can reach several thousand in one individual. An electron microscope study showed that flagella and cilia in Protozoa, Metazoa and plant cells are built according to a single type. Their basis is a bundle of fibrils, consisting of two central and nine paired, peripheral ones.
tourniquet surrounded by a shell which is an extension of the cell membrane. Central fibrils are present only in the free part of the tourniquet, and peripheral fibrils go deep into the cytoplasm, forming a basal grain - blepharoplast. The tourniquet can be connected to the cytoplasm for a considerable distance by a thin membrane - an undulating membrane. The ciliary apparatus of ciliates can reach considerable complexity and differentiate into zones that perform independent functions. The cilia often coalesce in groups, forming spikes and membranellae. Each cilium starts from a basal grain, a kinetosome, located in the surface layer of the cytoplasm. The collection of kinetosomes forms the infracilia. Knetosomes reproduce only by dividing in two and cannot arise anew. With a partial or complete reduction of the flagellar apparatus, the infracilia remains and subsequently gives rise to new cilia.
The type of protozoa includes animals, the ancient forms of which were the progenitors of the entire diverse animal world. In this regard, the study of protozoa is of great importance for understanding the evolution of the animal world. The type under consideration includes up to 40,000 species. The simplest are widespread on our planet and live in various environments - in the seas and oceans, fresh waters, and some species - in the soil. Many protozoa have adapted to living in the body of other organisms - plants, animals, humans. All of them perform various functions: they actively participate in the cycle of substances, purify water from bacteria and decaying organic matter, affect soil-forming processes, and serve as food for larger invertebrates. Many marine unicellular organisms have hard mineral skeletons. For tens of millions of years, the microscopic skeletons of dead animals sank to the bottom, forming powerful deposits of limestone, chalk, and green sandstone there. The skeletons of some protozoa are used in the practice of geological exploration to determine oil-bearing layers.
The simplest are microscopically small animals of various shapes, the sizes of which range from 2-3 to 50-150 microns and even up to 1-3 mm. The largest representatives of this type, for example, shell rhizopods living in the polar seas off the coast of Russia, and fossil nummulites reach a diameter of 2-3 cm.
The body of protozoa consists of the same components as a multicellular cell - the outer membrane, cytoplasm, nucleus and organelles, and at the same time morphologically corresponds to one cell. Because of this, protozoa are often called unicellular animals (Monocytozoa). However, in physiological terms, they cannot be equated with individual cells of multicellular (Metazoa), since their body performs all the functions characteristic of multicellular animals. The only cell, which is the organism of the simplest, moves, captures food, multiplies, defends itself from enemies, that is, it has all the properties of the whole organism and physiologically corresponds to it. Therefore, protozoa are now called organisms at the cellular level or "non-cellular" organisms.
The nucleus is an essential part of the body of protozoa. Usually there is one core. However, there are also multi-core forms. Ciliates always have two nuclei: a large vegetative - macronucleus and a small generative - micronucleus. The nucleus regulates life processes and plays an important role in reproduction and the transfer of hereditary properties to offspring.
Most of the body of the protozoan is made up of protoplasm. Under a microscope, one can distinguish in it an outer dense, transparent, homogeneous (homogeneous) layer - ectoplasm and a usually granular endoplasm located inside of a more liquid consistency. Protoplasm serves as the main substrate of life activity.
The surface of ectoplasm in most forms is represented by a thin elastic shell - pellicle (Latin pellicula - skin), consisting of proteins and fat-like substances. Possessing the semi-permeable property, the shell regulates the flow of substances from the external environment (water, salts, oxygen, etc.). The pellicle is part of the living protoplasm. In some species, a thick shell develops on the surface of the body (pellicles) - the cuticle (Latin cuticula - skin), which plays a protective and supporting role. The cuticle does not have the properties of living protoplasm.
In the endoplasm, in addition to the nucleus, there are general-purpose organelles - mitochondria, the endoplasmic reticulum, the reticulum apparatus, etc. In addition, in accordance with the functions inherent in the whole organism, protozoa have special-purpose organelles that perform the functions of movement, nutrition, excretion, protection, etc.
Special purpose organelles
In connection with nutrition, excretion, movement and other functions in the body of protozoa, separate sections of protoplasm are isolated, which perform certain vital functions of unicellular organisms as independent organisms. These areas are collectively known as organelles, or organelles. In protozoa, special-purpose organelles are isolated in accordance with their functions, unlike any other cells that have organelles of general importance (mitochondria, centrosomes, ribosomes, etc.)
Food organelles have a different structure. Depending on the type of assimilation and the mode of nutrition, protozoa are divided into several groups (Fig. 1).
The first group consists of autotrophic protozoa. They feed like green plants, absorbing carbon dioxide, water and mineral salts from the external environment (holophytic nutrition). Assimilation organelles in them are chromatophores containing chlorophyll. In sunlight, with their participation, carbohydrates are synthesized. Autotrophic protozoa do not need ready-made organic substances. They synthesize carbohydrates, fats and proteins from inorganic substances.
The second group consists of heterotrophic protozoa that do not have chlorophyll. They can only use ready-made organic matter for food. Most of them feed on bacteria, algae, protozoa. This way of eating is called holozoic (animal). At the same time, food is digested in special organelles - digestive vacuoles that look like a bubble. Vacuoles form in the protoplasm around an ingested food particle. If there is a lot of food, several vacuoles appear simultaneously in the body of the simplest. Digestion of food occurs with the participation of digestive juices coming from the protoplasm. Many protozoa have organelles that serve to enter food particles into their body and throw undigested food debris out. These include the cell mouth - the cytostome, the cell pharynx - the cytopharynx, and the anal pore.
Organelles of excretion. Most freshwater species have special pulsating vacuoles. They look like bubbles, to which a system of tubules approaches from the protoplasm. Pulsating vacuoles gradually fill with liquid, after which, rapidly contracting, they throw the liquid out. In this way, the protozoa are freed from excess water, which, when living in a freshwater reservoir, according to the law of osmosis [show] all the time enters their body. If water is not removed, swelling and death of the protozoan will occur.
The phenomenon of osmosis is as follows: if two solutions with different concentrations are separated by a semi-permeable membrane, then the solvent (water) passes from a solution with a lower concentration to a solution with a higher concentration.
Organelles of movement in protozoa (Fig. 2) they serve:
- pseudopodia or pseudopodia (Greek pseudos - false, podos - leg), which are temporary protoplasmic protrusions; occur in an amoeba anywhere on its body. The movement is carried out due to the current of protoplasm, which gradually overflows into one of the pseudopodia; while the opposite end of the body is shortened.
- flagella (or scourges) - permanent organoids that look like long protoplasmic filaments, usually starting at the anterior end; They produce helical movements.
- cilia are permanent organelles, which are numerous short protoplasmic filaments. Their movements consist of quick swings in one direction and a slow subsequent straightening.
Movement is closely connected with irritability and often serves as its external manifestation. Irritability is the ability of the organism to respond to the influence of the external and internal environment with certain active reactions.
The simplest are irritable. They respond to the action of various mechanical, light, chemical or other environmental stimuli with a directed movement, called taxis (Greek taxis - arrangement in order). Taxis are distinguished, directed either towards the stimulus or away from it, and depending on the stimuli, thermo-, photo-, hydro, chemo-, galvanotaxis, etc. are distinguished. One of the forms of movement characteristic of taxis is amoeboid movements associated with the deformation of the cell by the formation of protoplasmic protrusions in the form of pseudopodia. In the formation of pseudopodia, the ability of protoplasm to pass from the state of gel to sol and vice versa is manifested. Flickering movements are carried out by flagella and cilia.
Some species have special organelles for the perception of stimuli. These include photosensitive eyes, tactile bristles, etc.
Skeletal formations are found in the body of protozoa. The outer skeleton is often represented by calcareous or flint shells. Of the internal skeletal formations, we should mention a special axial rod - axostyle (Gech. acson - axis, stylos - stick).
Protection organelles. Some protozoa have protective devices - trichocysts - short sticks located in the ectoplasm under the pellicle. When irritated, the trichocysts shoot out, turning into a long elastic thread that strikes the enemy or prey.
reproduction
Protozoa reproduce asexually and sexually. Asexual reproduction occurs both in the form of division into two parts, and in the form of multiple division (Fig. 3).
In the form of division into two parts, it begins with the division of the cell nucleus. In this case, the nuclear structures are evenly distributed between the two newly formed nuclei (mitosis). Following the nucleus, the protoplasm divides, after which the two newly emerged daughter individuals begin an independent life.
In most protozoa, it proceeds in the form of copulation, in ciliates - in the form of conjugation (Fig. 4).
During copulation (lat. copulare - to connect), two individuals approach each other, their protoplasm and nuclei merge, forming one individual - a zygote, which then reproduces asexually.
Conjugation (Latin conjagatio - conjugation, copulation) is a form of sexual reproduction characteristic of ciliates. During conjugation, two ciliates are applied to each other with their bodies. Their nuclei undergo complex restructuring. The macronuclei of both partners are destroyed and disappear. Micronuclei after double fission and destruction of a part of the nuclear material form a stationary and wandering nucleus in each ciliate. The first remains in place, and the second, moving, passes into a partner, where it merges with its stationary core. Then the partners diverge, and their nuclei after division form a micro- and macronucleus. Conjugation is a kind of fertilization and is associated with the combination of hereditary factors (genes) of two individuals.
encysting
If the encysted individual again finds itself in favorable conditions, excystation occurs; the animal leaves the cyst, turns into a vegetative form and resumes active life. Encystation of pathogenic protozoa plays an important role in the spread of protozoan diseases.
Life cycle
In the life cycle of some protozoa, morphologically different forms alternate. There are vegetative, sexual and encysted forms. The former are characterized by active nutrition and growth. They usually reproduce asexually. The latter are represented by micro- and macrogametes. Their appearance precedes the sexual process. The encysted forms (cysts) are characterized by resistance to adverse environmental conditions.
Classification
The division of the type of protozoa into classes is based mainly on the structure of the organoids of movement and the characteristics of reproduction. The classification is generally accepted, according to which all protozoa are divided into 4 classes.
Cell organelles, they are also organelles, are specialized structures of the cell itself, responsible for various important and vital functions. Why all the same "organelles"? It's just that these components of the cell are compared with the organs of a multicellular organism.
What organelles make up the cell
Also, sometimes organelles are understood exclusively as permanent cell structures that are in it. For the same reason, the cell nucleus and its nucleolus are not called organelles, nor are cilia and flagella. But the organelles that make up the cell include: complex, endoplasmic reticulum, ribosomes, microtubules, microfilaments, lysosomes. In fact, these are the main organelles of the cell.
If we are talking about animal cells, then their organelles also include centrioles and microfibrils. But the number of plant cell organelles still includes only plastids characteristic of plants. In general, the composition of organelles in cells can differ significantly depending on the type of cell itself.
A drawing of the structure of a cell, including its organelles.
two-membrane cell organelles
Also in biology there is such a phenomenon as two-membrane cell organelles, these include mitochondria and plastids. Below we describe their inherent functions, however, like all other major organelles.
Functions of cell organelles
And now we will briefly describe the main functions of the organelles of an animal cell. So:
- The plasma membrane is a thin film around the cell, made up of lipids and proteins. A very important organelle that provides transportation of water, mineral and organic substances into the cell, removes harmful waste products and protects the cell.
- The cytoplasm is the internal semi-liquid environment of the cell. Provides communication between the nucleus and organelles.
- The endoplasmic reticulum is a network of channels in the cytoplasm. Takes an active part in the synthesis of proteins, carbohydrates and lipids, is engaged in the transport of nutrients.
- Mitochondria are organelles in which organic substances are oxidized and ATP molecules are synthesized with the participation of enzymes. In fact, mitochondria are a cell organelle that synthesizes energy.
- Plastids (chloroplasts, leukoplasts, chromoplasts) - as we mentioned above, are found exclusively in plant cells, in general, their presence is the main feature of the plant organism. They play a very important function, for example, chloroplasts, containing the green pigment chlorophyll, are responsible for the phenomenon in a plant.
- The Golgi complex is a system of cavities separated from the cytoplasm by a membrane. Carry out the synthesis of fats and carbohydrates on the membrane.
- Lysosomes are bodies separated from the cytoplasm by a membrane. The special enzymes present in them accelerate the reaction of splitting complex molecules. Also, the lysosome is an organoid that provides protein assembly in cells.
- - cavities in the cytoplasm filled with cell sap, a place of accumulation of reserve nutrients; they regulate the water content in the cell.
In general, all organelles are important, because they regulate the vital activity of the cell.
The main organelles of the cell, video
And finally, a thematic video about cell organelles.
The phylum Protozoa includes approximately 25,000 species of unicellular animals living in water, soil, or organisms of other animals and humans. Having a morphological similarity in the structure of cells with multicellular organisms, the protozoa differ significantly from them in functional terms.
If the cells of a multicellular animal perform special functions, then the cell of the simplest is an independent organism capable of metabolism, irritability, movement and reproduction.
The simplest are organisms at the cellular level of organization. Morphologically, the protozoan is equivalent to a cell, but physiologically it is a whole independent organism. The vast majority of them are microscopically small in size (from 2 to 150 microns). However, some of the living protozoa reach 1 cm, and the shells of a number of fossil rhizopods are up to 5-6 cm in diameter. The total number of known species exceeds 25 thousand.
The structure of the protozoa is extremely diverse, but they all have features characteristic of the organization and function of the cell. Common in the structure in the structure of protozoa are the two main components of the body - the cytoplasm and the nucleus.
cytoplasm
The cytoplasm is bounded by an outer membrane that regulates the flow of substances into the cell. In many protozoa, it is complicated by additional structures that increase the thickness and mechanical strength of the outer layer. Thus, formations such as pellicles and shells arise.
The cytoplasm of protozoa usually breaks up into 2 layers - the outer one is lighter and denser - ectoplasm and internal, equipped with numerous inclusions, - endoplasm.
General cellular organelles are localized in the cytoplasm. In addition, a variety of special organelles may be present in the cytoplasm of many protozoa. Various fibrillar formations are especially widespread - supporting and contractile fibers, contractile vacuoles, digestive vacuoles, etc.
Nucleus
The simplest have a typical cell nucleus, one or more. The nucleus of protozoa has a typical two-layer nuclear envelope. Chromatin material and nucleoli are distributed in the nucleus. The nuclei of protozoa are characterized by exceptional morphological diversity in terms of size, number of nucleoli, amount of nuclear juice, etc.
Features of the vital activity of protozoa
Unlike somatic cells, multicellular protozoa are characterized by the presence of a life cycle. It is composed of a series of successive stages, which are repeated in the existence of each species with a certain regularity.
Most often, the cycle begins with the stage of the zygote, which corresponds to the fertilized egg of multicellular organisms. This stage is followed by singly or repeatedly repeated asexual reproduction, carried out by cell division. Then sex cells (gametes) are formed, the pairwise fusion of which again gives a zygote.
An important biological feature of many protozoa is the ability to encystment. At the same time, the animals round out, shed or draw in the organelles of movement, secrete a dense shell on their surface, and fall into a state of rest. In the encysted state, protozoa can tolerate drastic environmental changes while remaining viable. When conditions favorable for life return, the cysts open and the protozoa emerge from them in the form of active, mobile individuals.
According to the structure of the organelles of movement and the characteristics of reproduction, the protozoan type is divided into 6 classes. The main 4 classes are Sarcodaceae, Flagellates, Sporozoans and Ciliates.