A whole galaxy of outstanding scientists of the past - Robert Hook, Anthony van Levenguk, Theodor Schwann, Matthias Schleiden, with their discoveries in the field of the study of nature, paved the way for the formation of the most important branch of modern biological science - cytology. She studies the structure and properties of the cell, which is the elementary carrier of life on Earth. The fundamental knowledge gained as a result of the development of cell science has inspired researchers to create disciplines such as genetics, molecular biology, and biochemistry.
The scientific discoveries made in them completely changed the face of the planet and led to the appearance of clones, genetically modified organisms and artificial intelligence. Our article will help to understand the basic methods of cytological experiments and to determine the structure and function of cells.
How to study a cell
Like 500 years ago, a light microscope is the main instrument that helps to study the structure and properties of cells. Of course, its appearance and optical characteristics cannot be compared with the first microscopes created by father and son Jansens or Robert Hook in the middle of the 16th century. The resolution of modern light microscopes increases the size of cell structures by 3,000 times. Scanning raster instruments can capture images of submicroscopic objects such as bacteria or viruses, the latter being so small that they are not even cells. In cytology, the method of labeled atoms is actively used, as well as the intravital study of cells, thanks to which the features of cellular processes are clarified.
Centrifugation
In order to divide the cell contents into fractions and study the properties and functions of the cell , cytology uses a centrifuge. It works on the same principle as the homonymous part in washing machines. Creating a centrifugal acceleration, the device accelerates the cell suspension, and since the organelles have different densities, they settle in layers. Large parts, such as nuclei, mitochondria, or plastids, appear at the bottom, and microfilaments of the cytoskeleton, ribosomes, and peroxisomes are located in the upper nozzles of the centrifuge rectification lattice. The resulting layers are separated, so it is more convenient to study the characteristics of the biochemical composition of organelles.
Plant cell structure
The properties of a plant cell are in many ways similar to the functions of animal cells. However, even a schoolboy, examining fixed preparations of plant, animal or human cells in the microscope’s eyepiece, will find differences. These are geometrically regular contours, the presence of a dense cellulose membrane and large vacuoles, characteristic of plant cells. And another difference that completely distinguishes plants into a group of autotrophic organisms is the presence in the cytoplasm of well-visible green oval bodies. These chloroplasts are the business card of plants. After all, it is they who are able to capture light energy, translate it into the energy of ATP macroergic bonds, and also form organic compounds: starch, proteins and fats. Photosynthesis thus determines the autotrophic properties of plant cells.
Self-synthesis of trophic substances
Let us dwell on the process due to which, according to the outstanding Russian scientist K. A. Timiryazev, plants play a cosmic role in evolution. On Earth, there are approximately 350 thousand species of plants, ranging from unicellular algae like chlorella or chlamydomonas and ending with giant trees - sequoias, reaching a height of 115 meters. All of them absorb carbon dioxide, turning it into glucose, amino acids, glycerin and fatty acids. These substances serve as food not only to the plant itself, but are also used by organisms called heterotrophs: mushrooms, animals, and humans. Such properties of plant cells as the ability to synthesize organic compounds and the formation of a vital substance - oxygen, confirm the fact of the exceptional role of autotrophs for life on Earth.
Plastid classification
It is difficult to remain indifferent, contemplating the extravaganza of the colors of blooming roses or autumn forest. The color of plants is due to special organoids - plastids, characteristic only of plant cells. It can be argued that the presence of special pigments in their composition affects the functions of chloroplasts, chromoplasts and leukoplasts in metabolism. Organelles containing the green pigment, chlorophyll, determine the important properties of the cell and are responsible for the photosynthesis process. They can also turn into chromoplasts. We observe this phenomenon, for example, in the fall, when the green leaves of the trees turn golden, purple or crimson. Leukoplasts can transform into chromoplasts, for example, milk-ripened tomatoes ripen to orange or red. They are able to pass into chloroplasts, for example, the appearance of green color on the peel of potato tubers occurs during their long-term storage in the light.
The mechanism of formation of plant tissues
One of the hallmarks of the cells of higher plants is the presence of a solid and durable shell. It usually contains macromolecules of cellulose, lignin or pectin. Stability and resistance to compression and other mechanical deformations, distinguish plant tissues in the group of the most rigid natural structures that can withstand heavy loads (recall, for example, the properties of wood). Between its cells there are many cytoplasmic strands passing through holes in the shells, which, like elastic threads, sew them together. Therefore, strength and hardness are the main properties of a plant cell.
Plasmolysis and deplasmolysis
The presence of perforated walls responsible for the movement of water, mineral salts and phytohormones can be detected due to the phenomenon of plasmolysis. Place the plant cell in a hypertonic solution of sodium chloride. Water from its cytoplasm will diffuse outward, and under a microscope we will see the process of exfoliation of the parietal layer of the hyaloplasm. The cell shrinks, its volume decreases, i.e. plasmolysis occurs. You can return to its original form by adding a few drops of water to the glass slide and creating a solution concentration lower than in the cell cytoplasm. H 2 O molecules will enter through the pores in the membrane; the volume and intracellular pressure of the cell will increase. This process was called deplasmolysis.
Specificity of the structure and functions of animal cells
The absence of chloroplasts in the cytoplasm, thin membranes deprived of the outer shell, small vacuoles, performing mainly digestive or excretory functions - all this refers to animal and human cells. Their diverse appearance and heterotrophic mode of nutrition is another distinguishing feature.
Many cells, which are separate organisms, or that are part of the tissues, are capable of active movement. These are phagocytes and spermatozoa of mammals, amoeba, ciliates, etc. The union of animal cells in tissue is carried out thanks to the supmembrane complex - glycocalyx. It consists of glycolipids and proteins associated with carbohydrates, and promotes adhesion - the adhesion of cell membranes to each other, leading to tissue formation. Extracellular digestion also occurs in glycocalyx. The heterotrophic method of nutrition determines the presence in the cells of a whole arsenal of digestive enzymes, concentrated in special organelles - lysosomes, which are formed in the Golgi apparatus - the mandatory single-membrane structure of the cytoplasm.
In animal cells, this organelle is represented by a common network of channels and cisterns, while in plants it has the appearance of numerous disconnected structural units. Both plant and animal somatic cells divide by mitosis, and gametes divide by meiosis.
So, we have established that the characteristics of the cells of various groups of living organisms will depend on the features of the microscopic structure and functions of the organelles.