A whole galaxy of outstanding scientists of the past - Robert Hooke, Anthony van Leeuwenhoek, Theodor Schwann, Mathias Schleiden, with their discoveries in the field of nature study, paved the way for the formation of the most important branch of modern biological science - cytology. It 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.
Scientific discoveries made in them completely changed the face of the planet and led to the emergence of clones, genetically modified organisms and artificial intelligence. Our article will help you understand the basic methods of cytological experiments and find out the structure and functions of cells.
How a cell is studied
Like 500 years ago, the light microscope is the main instrument that helps to study the structure and properties of the cell. Of course, its appearance and opticalcharacteristics cannot be compared with the first microscopes created by father and son Janssens or Robert Hooke in the middle of the 16th century. The resolving power of modern light microscopes increases the size of cell structures by 3000 times. Raster scanners can capture images of submicroscopic objects such as bacteria or viruses, the latter so small that they are not even cells. In cytology, the method of labeled atoms is actively used, as well as in vivo study of cells, thanks to which the features of cellular processes are clarified.
Centrifugation
To separate 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 part of the same name in washing machines. By creating centrifugal acceleration, the device accelerates the cell suspension, and since the organelles have different densities, they settle in layers. At the bottom are large parts, such as nuclei, mitochondria or plastids, and in the upper nozzles of the distillation grate of the centrifuge, microfilaments of the cytoskeleton, ribosomes and peroxisomes are located. The resulting layers are separated, so it is more convenient to study the features of the biochemical composition of organelles.
Cell structure of plants
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 through the eyepiece of a microscope, will find features of difference. It's geometriccorrect contours, the presence of a dense cellulose membrane and large vacuoles, characteristic of plant cells. And one more difference that completely distinguishes plants in the group of autotrophic organisms is the presence in the cytoplasm of clearly visible oval green bodies. These are chloroplasts - the visiting card of plants. After all, it is they who are able to capture light energy, convert it into the energy of macroergic bonds of ATP, and also form organic compounds: starch, proteins and fats. Photosynthesis thus determines the autotrophic properties of the plant cell.
Independent synthesis of trophic substances
Let's dwell on the process due to which, according to the outstanding Russian scientist K. A. Timiryazev, plants play a cosmic role in evolution. There are approximately 350 thousand plant species on Earth, ranging from single-celled algae like chlorella or chlamydomonas to giant trees - sequoias, reaching a height of 115 meters. All of them absorb carbon dioxide, turning it into glucose, amino acids, glycerol and fatty acids. These substances serve as food not only for the plant itself, but are also used by organisms called heterotrophs: fungi, animals and humans. Such properties of plant cells as the ability to synthesize organic compounds and form a vital substance - oxygen, confirm the fact of the exclusive role of autotrophs for life on Earth.
Classification of plastids
It's hard to remain indifferent, contemplating the extravaganza of colors of blooming roses or the autumn forest. The color of plants is due to special organelles - plastids, characteristic only for 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 process of photosynthesis. They can also transform into chromoplasts. We observe this phenomenon, for example, in autumn, when the green leaves of trees turn gold, purple or crimson. Leucoplasts can transform into chromoplasts, for example milky tomatoes ripen to orange or red. They are also able to pass into chloroplasts, for example, the appearance of green color on the peel of potato tubers occurs when they are stored in the light for a long time.
Mechanism of plant tissue formation
One of the distinguishing features of higher plant cells is the presence of a hard and strong shell. It usually contains macromolecules of cellulose, lignin or pectin. Stability and resistance to compression and other mechanical deformations distinguish plant tissues into the group of the most rigid natural structures that can withstand heavy loads (recall, for example, the properties of wood). Between its cells, a lot of cytoplasmic strands arise, passing through holes in the membranes, which, like elastic threads, sew them together.between themselves. Therefore, strength and hardness are the main properties of a cell of a plant organism.
Plasmolysis and deplasmolysis
The presence of perforated walls responsible for the movement of water, mineral s alts and phytohormones can be detected due to the phenomenon of plasmolysis. Place a plant cell in a hypertonic saline solution. Water from its cytoplasm will diffuse outward, and under a microscope we will see the process of exfoliation of the parietal layer of hyaloplasm. The cell shrinks, its volume decreases, i.e. plasmolysis occurs. You can return the original form by adding a few drops of water to a glass slide and creating a concentration of the solution lower than in the cytoplasm of the cell. H2O molecules will enter inside through the pores in the shell, the volume and intracellular pressure of the cell will increase. This process was called deplasmolysis.
Specific structure and functions of animal cells
The absence of chloroplasts in the cytoplasm, thin membranes devoid of an outer shell, small vacuoles that perform mainly digestive or excretory functions - all this applies to animal and human cells. Their varied appearance and heterotrophic feeding habits are another distinguishing feature.
Many cells, which are separate organisms, or are part of tissues, are capable of active movement. These are phagocytes and spermatozoa of mammals, amoeba, infusoria-shoe, etc. Animal cells are combined into tissues due to the supra-membrane complex - the glycocalyx. Heconsists of glycolipids and proteins associated with carbohydrates, and promotes adhesion - adhesion of cell membranes to each other, leading to the formation of tissue. Extracellular digestion also occurs in the glycocalyx. The heterotrophic way 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 - an obligatory 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 looks like numerous disparate structural units. Both plant and animal somatic cells divide by mitosis, while gametes divide by meiosis.
So, we have established that the properties of cells of various groups of living organisms will depend on the features of the microscopic structure and functions of organelles.
