The bodies of living organisms can be a single cell, a group of them or a huge accumulation, numbering billions of such elementary structures. The latter include most of the higher plants. The study of the cell - the main element of the structure and functions of living organisms - deals with cytology. This branch of biology began to develop rapidly after the discovery of the electron microscope, the improvement of chromatography and other methods of biochemistry. Consider the main features, as well as the features by which the plant cell differs from the smallest structural units of the structure of bacteria, fungi and animals.
Opening of the cell by R. Hooke
The theory of the tiny elements of the structure of all living things has passed the path of development, measured in hundreds of years. The structure of the plant cell membrane was first seen in his microscope by the British scientist R. Hooke. The general provisions of the cell hypothesis were formulated by Schleiden and Schwann, before that other researchers made similar conclusions.
The Englishman R. Hooke examined a section of an oak cork under a microscope and presented the results at a meeting of the Royal Society in London on April 13, 1663 (according toother sources, the event occurred in 1665). It turned out that the bark of a tree consists of tiny cells, called "cells" by Hooke. The walls of these chambers, forming a pattern in the form of a honeycomb, the scientist considered a living substance, and recognized the cavity as a lifeless, auxiliary structure. Later it was proved that inside the cells of plants and animals they contain a substance, without which their existence is impossible, and the activity of the whole organism.
Cell theory
The important discovery of R. Hooke was developed in the works of other scientists who studied the structure of animal and plant cells. Similar structural elements were observed by scientists on microscopic sections of multicellular fungi. It was found that the structural units of living organisms have the ability to divide. Based on the research, representatives of the biological sciences of Germany M. Schleiden and T. Schwann formulated a hypothesis that later became the cell theory.
Comparison of plant and animal cells with bacteria, algae and fungi allowed German researchers to come to the following conclusion: the “chambers” discovered by R. Hooke are elementary structural units, and the processes occurring in them underlie the life of most organisms on Earth. An important addition was made by R. Virchow in 1855, noting that cell division is the only way for their reproduction. The Schleiden-Schwann theory with refinements has become generally accepted in biology.
Cell is the smallest element in the structure and life of plants
According to the theoretical positions of Schleiden and Schwann,the organic world is one, which proves the similar microscopic structure of animals and plants. In addition to these two kingdoms, cellular existence is characteristic of fungi, bacteria, and viruses are absent. The growth and development of living organisms is ensured by the emergence of new cells in the process of division of existing ones.
A multicellular organism is not just an accumulation of structural elements. Small units of structure interact with each other, forming tissues and organs. Single-celled organisms live in isolation, which does not prevent them from creating colonies. The main features of the cell:
- capability for independent existence;
- own metabolism;
- self-reproduction;
- development.
In the evolution of life, one of the most important stages was the separation of the nucleus from the cytoplasm with the help of a protective membrane. The connection has been preserved, because these structures cannot exist separately. Currently, there are two super-kingdoms - non-nuclear and nuclear organisms. The second group is formed by plants, fungi and animals, which are studied by the relevant branches of science and biology in general. A plant cell has a nucleus, cytoplasm and organelles, which will be discussed below.
Diversity of plant cells
On the break of a ripe watermelon, apple or potato, you can see structural "cells" filled with liquid with the naked eye. These are fetal parenchyma cells with a diameter of up to 1 mm. Bast fibers are elongated structures, the length of which significantly exceeds the width. For example,the cell of a plant called cotton reaches a length of 65 mm. Bast fibers of flax and hemp have linear dimensions of 40–60 mm. Typical cells are much smaller -20–50 µm. Such tiny structural elements can only be seen under a microscope. Features of the smallest structural units of a plant organism are manifested not only in differences in shape and size, but also in the functions performed in the composition of tissues.
Plant cell: basic structural features
The nucleus and cytoplasm are closely interconnected and interact with each other, which is confirmed by the research of scientists. These are the main parts of the eukaryotic cell, all other structural elements depend on them. The nucleus serves to store and transmit the genetic information necessary for protein synthesis.
The British scientist R. Brown in 1831 first noticed a special body (nucleus) in the cell of a plant of the orchid family. It was a nucleus surrounded by semi-liquid cytoplasm. The name of this substance means in literal translation from Greek "the primary mass of the cell." It may be more liquid or viscous, but it is necessarily covered with a membrane. The outer shell of the cell consists mainly of cellulose, lignin, and wax. One feature that distinguishes plant and animal cells is the presence of this strong cellulose wall.
The structure of the cytoplasm
The inner part of a plant cell is filled with hyaloplasm with tiny granules suspended in it. Closer to the shell, the so-called endoplasm passes into a more viscous exoplasm. Exactlythese substances, with which the plant cell is filled, serve as a place for the occurrence of biochemical reactions and the transport of compounds, the placement of organelles and inclusions.
Approximately 70-85% of the cytoplasm is water, 10-20% is proteins, other chemical components - carbohydrates, lipids, mineral compounds. Plant cells have a cytoplasm, in which, among the end products of synthesis, there are bioregulators of functions and reserve substances (vitamins, enzymes, oils, starch).
Core
Comparison of plant and animal cells shows that they have a similar structure of the nucleus, located in the cytoplasm and occupying up to 20% of its volume. The Englishman R. Brown, who first examined this most important and constant component of all eukaryotes under a microscope, gave it a name from the Latin word nucleus. The appearance of the nuclei usually correlates with the shape and size of the cells, but sometimes differs from them. Mandatory elements of the structure are the membrane, karyolymph, nucleolus and chromatin.
There are pores in the membrane that separates the nucleus from the cytoplasm. They transport substances from the nucleus to the cytoplasm and vice versa. Karyolymph is a liquid or viscous nuclear content with areas of chromatin. The nucleolus contains ribonucleic acid (RNA) that enters the ribosomes of the cytoplasm to participate in protein synthesis. Another nucleic acid, deoxyribonucleic acid (DNA), is also present in large amounts. DNA and RNA were first discovered in animal cells in 1869 and subsequently found in plants. The nucleus is the centermanagement” of intracellular processes, a place for storing information about the hereditary characteristics of the whole organism.
Endoplasmic reticulum (ER)
The structure of animal and plant cells has a significant similarity. Necessarily present in the cytoplasm are internal tubules filled with substances of different origin and composition. The granular type of EPS differs from the agranular type by the presence of ribosomes on the membrane surface. The first is involved in the synthesis of proteins, the second plays a role in the formation of carbohydrates and lipids. As researchers have established, the channels not only penetrate the cytoplasm, they are associated with every organelle of a living cell. Therefore, the value of EPS is highly valued as a participant in metabolism, a system of communication with the environment.
Ribosome
The structure of a plant or animal cell is hard to imagine without these small particles. Ribosomes are very small and can only be seen with an electron microscope. Proteins and molecules of ribonucleic acids predominate in the composition of the bodies, there is a small amount of calcium and magnesium ions. Almost all of the cell's RNA is concentrated in ribosomes; they provide protein synthesis by "assembling" proteins from amino acids. Then the proteins enter the EPS channels and are carried by the network throughout the cell, penetrate into the nucleus.
Mitochondria
These organelles of the cell are considered its energy stations, they are visible when magnified in a conventional light microscope. The number of mitochondria varies over a very wide range, there may be units or thousands. The structure of the organoid is not very complex, there are twomembranes and matrix inside. Mitochondria are composed of protein lipids, DNA and RNA, are responsible for the biosynthesis of ATP - adenosine triphosphoric acid. This substance of a plant or animal cell is characterized by the presence of three phosphates. The splitting of each of them provides the energy necessary for all life processes in the cell itself and throughout the body. On the contrary, the addition of phosphoric acid residues makes it possible to store energy and transfer it in this form throughout the cell.
Consider the cell organelles in the figure below and name those that you already know. Note the large vesicle (vacuole) and green plastids (chloroplasts). We will talk about them later.
Golgi complex
Complex cellular organoid consists of granules, membranes and vacuoles. The complex was opened in 1898 and was named after the Italian biologist. Features of plant cells are the uniform distribution of Golgi particles throughout the cytoplasm. Scientists believe that the complex is necessary to regulate the content of water and waste products, remove excess substances.
Plastids
Only plant tissue cells contain green organelles. In addition, there are colorless, yellow and orange plastids. Their structure and functions reflect the type of plant nutrition, and they are able to change color due to chemical reactions. Main types of plastids:
- orange and yellow chromoplasts formed by carotene and xanthophyll;
- chloroplasts containing chlorophyll grains -green pigment;
- leucoplasts are colorless plastids.
The structure of a plant cell is associated with the chemical reactions of the synthesis of organic matter from carbon dioxide and water using light energy. The name of this amazing and very complex process is photosynthesis. Reactions are carried out thanks to chlorophyll, it is this substance that is able to capture the energy of a beam of light. The presence of green pigment explains the characteristic color of leaves, herbaceous stems, unripe fruits. Chlorophyll is similar in structure to hemoglobin in the blood of animals and humans.
The red, yellow and orange color of various plant organs is due to the presence of chromoplasts in the cells. They are based on a large group of carotenoids that play an important role in metabolism. Leucoplasts are responsible for the synthesis and accumulation of starch. Plastids grow and multiply in the cytoplasm, moving along with it along the inner membrane of the plant cell. They are rich in enzymes, ions, and other biologically active compounds.
Differences in the microscopic structure of the main groups of living organisms
Most cells resemble a tiny sac filled with mucus, bodies, granules and vesicles. Often there are various inclusions in the form of solid crystals of minerals, drops of oils, starch grains. Cells are in close contact in the composition of plant tissues, life as a whole depends on the activity of these smallest structural units that form a whole.
With a multicellular structure, there isspecialization, which is expressed in different physiological tasks and functions of microscopic structural elements. They are determined mainly by the location of tissues in the leaves, root, stem, or generative organs of the plant.
Let's highlight the main elements of the comparison of the plant cell with the elementary structural units of other living organisms:
- Dense shell, characteristic only for plants, is formed by fiber (cellulose). In fungi, the membrane consists of durable chitin (a special protein).
- Cells of plants and fungi differ in color due to the presence or absence of plastids. Bodies such as chloroplasts, chromoplasts and leukoplasts are present only in plant cytoplasm.
- There is an organoid that distinguishes animals - this is the centriole (cell center).
- Only in the plant cell there is a large central vacuole filled with liquid content. Usually this cell sap is colored with pigments in different colors.
- The main reserve compound of the plant organism is starch. Mushrooms and animals accumulate glycogen in their cells.
Among algae, many single, free-living cells are known. For example, such an independent organism is chlamydomonas. Although plants differ from animals in the presence of a cellulose cell wall, but germ cells lack such a dense shell - this is another proof of the unity of the organic world.
