Cage plants. Features of plant cells

The bodies of living organisms can be a single cell, their group or a huge cluster of billions of such elementary structures. Most of the higher plants belong to the latter . The study of the cell - the main element of the structure and functions of living organisms - is engaged in cytology. This section of biology began to develop rapidly after the discovery of the electron microscope, the perfection 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.

The discovery of R. Hooke's cell

The theory of the tiny elements of the structure of all living things has passed the path of development, measured by hundreds of years. The structure of the shell of plant cells was first seen in his microscope by the British scientist R. Hooke. General provisions of the cellular hypothesis were formulated by Schleiden and Schwann, before similar conclusions were made by other researchers.

The Englishman R. Hook examined in a microscope the slice of an oak plug and presented the results at a meeting of the Royal Society in London on April 13, 1663 (according to other sources, the event occurred in 1665). It turned out that the bark of the tree consists of tiny cells called Hooke "cells". The walls of these chambers, forming a pattern in the form of honeycombs, the scientist considered a living substance, and the cavity was recognized as a lifeless, auxiliary structure. Later it was proved that inside the cells of plants and animals contain a substance, without which their existence is impossible, and the activity of the whole organism.

Cell theory

An important discovery of R. Hooke was developed in the works of other scientists who studied the structure of cells of animals and plants. Similar elements of the structure 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, the representatives of the biological science of Germany M. Schleiden and T. Schwann formulated a hypothesis, which later became a cellular 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 are the basis of the vital activity of most organisms on the Earth. An important addition was made by R. Virchow in 1855, noting that cell division is the only way of their multiplication. The Schleiden-Schwann theory with refinements has become generally accepted in biology.

Cell - the smallest element of the structure and vital activity of plants

According to the theoretical statements of Schleiden and Schwann, the organic world is one that proves a similar microscopic structure of animals and plants. In addition to these two kingdoms, cellular existence is characteristic for fungi, bacteria, and there are no viruses. The growth and development of living organisms is provided by the emergence of new cells in the process of dividing the existing ones.

A multicellular organism is not just a cluster of structural elements. Small units of structure interact with each other, forming tissues and organs. Unicellular organisms live in isolation, which does not prevent them from creating colonies. The main signs of the cell are:

• Ability to 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 by means of a protective membrane. Communication has survived, because separately these structures can not exist. At present, two super-kingdoms - nuclear-free and nuclear organisms - are singled out. The second group consists of plants, mushrooms and animals, which are studied by the relevant sections of science and biology in general. The cell of the plant has a nucleus, cytoplasm and organelles, which will be discussed below.

Variety of plant cells

On the rupture of a ripe watermelon, apple or potato, structural "cells" filled with liquid can be seen with the naked eye. These are parenchyma cells of fruits, having a diameter of up to 1 mm. Bast fibers are elongated structures, the length of which considerably exceeds the width. For example, a plant cell, which is called cotton, reaches a length of 65 mm. The fibers of linseed and hemp have linear dimensions of 40-60 mm. Typical cells are much less than -20-50 microns. To consider such tiny structural elements is possible only under a microscope. Features of the smallest units of the structure of the plant organism are manifested not only in differences in shape and size, but also in the functions performed in the tissue.

Cage plant: the main features of the structure

The nucleus and the cytoplasm are closely interrelated and interact with each other, which is confirmed by studies of scientists. These are the main parts of the eukaryotic cell, all the other elements of the structure depend on them. The nucleus serves to accumulate and transmit the genetic information necessary for protein synthesis.

British scientist R. Brown in 1831 first noticed in the cell plants of the family of orchids a special body (nucleus). It was a nucleus surrounded by a semiliquid cytoplasm. The name of this substance means in literal translation from the Greek "primary cell mass". It can be more liquid or viscous, but necessarily covered with a membrane. The outer shell of the cell consists mainly of cellulose, lignin, wax. One of the signs that distinguish plant and animal cells is the presence of this strong cellulose wall.

The structure of the cytoplasm

The inner part of the plant cell is filled with the hyaloplasm with the fine granules suspended in it. Closer to the shell, the so-called endoplasm passes into a more viscous exoplasm. It is these substances that fill the plant cell that serve as a place for the flow of biochemical reactions and transport of compounds, the placement of organoids 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 final 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, which is located in the cytoplasm and occupies up to 20% of its volume. The Englishman R. Brown, who for the first time considered this most important and constant component of all eukaryotes under the microscope, gave him the name from the Latin word nucleus. The appearance of nuclei usually correlates with the shape and size of cells, but sometimes differs from them. Mandatory elements of the structure - the membrane, karyolymph, nucleolus and chromatin.

In the membrane separating the nucleus from the cytoplasm, there are pores. Through them, substances come from the nucleus to the cytoplasm and back. Cariolymph is a liquid or viscous nuclear content with chromatin sites. The nucleolus contains ribonucleic acid (RNA), which penetrates into the ribosomes of the cytoplasm to participate in protein synthesis. Another nucleic acid, deoxyribonucleic (DNA), is also present in large quantities. DNA and RNA were first discovered in animal cells in 1869, later found in plants. The nucleus is a "control center" for intracellular processes, a place for storing information about hereditary traits of the whole organism.

Endoplasmic reticulum (EPS)

The structure of cells of animals and plants has a significant similarity. Necessarily present in the cytoplasm are internal tubules filled with substances of different origin and composition. The granular variety of EPS differs from the agranular type by the presence of ribosomes on the membrane surface. The former is involved in the synthesis of proteins, the latter plays a role in the formation of carbohydrates and lipids. As the researchers established, the channels not only permeate the cytoplasm, they are associated with each organoid of a living cell. Therefore, the value of EPS is assessed very highly as a participant in metabolism, a system of communication with the environment.

Ribosomes

The structure of a plant or animal cell is difficult to imagine without these small particles. Ribosomes are very small, you can see them only in an electron microscope. The composition of the bodies is dominated by proteins and molecules of ribonucleic acids, there is an insignificant amount of calcium and magnesium ions. Almost the entire amount of RNA cells is concentrated in ribosomes, they provide protein synthesis, "collecting" proteins from amino acids. Then the proteins enter the channels of EPS and are carried by the network throughout the cell, they penetrate into the nucleus.

Mitochondria

These organelles of the cell are considered to be energy stations, they are visible when magnified in a conventional light microscope. The number of mitochondria varies within very wide limits, there may be one or thousands of them. The structure of the organoid is not very complex, there are two membranes and a matrix inside. Mitochondria consist of protein lipids, DNA and RNA, are responsible for the biosynthesis of ATP-adenosine triphosphate. For this substance, plant or animal cells are characterized by the presence of three phosphates. Cleavage of each of them gives the energy necessary for all processes of vital activity in the cell itself and in the whole organism. Conversely, the addition of phosphoric acid residues makes it possible to store energy and transfer 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 the green plastids (chloroplasts). We will talk about them.

Golgi Complex

A complex cellular organelle consists of granules, membranes and vacuoles. The complex was opened in 1898 and was named after the Italian biologist. Features of plant cells consist in the uniform distribution of Golgi particles throughout the cytoplasm. Scientists believe that the complex is necessary to regulate the water content and waste products, remove excess substances.

Plastids

Only cells of plant tissues contain organelles of green color. 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 through chemical reactions. The main types of plastids are:

• Orange and yellow chromoplasts formed by carotene and xanthophyll;
• Chloroplasts containing chlorophyll grains, - green pigment;
• Leucoplasts - colorless plastids.

The structure of plant cells is associated with the chemical reactions that occur in it, 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 due to chlorophyll, it is this substance that can capture the energy of the light beam. The presence of a green pigment explains the characteristic color of leaves, herbaceous stems, immature fruit. Chlorophyll is similar in structure to the hemoglobin of animals and humans.

Red, yellow and orange coloration of various plant organs is due to the presence of chromoplasts in the cells. Their basis is a large group of carotenoids, which play an important role in metabolism. Leukoplasts are responsible for the synthesis and accumulation of starch. Plastids grow and multiply in the cytoplasm, along with it move along the inner shell of the plant cell. They are rich in enzymes, ions, 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, corpuscles, granules and vesicles. Often there are different inclusions in the form of solid crystals of mineral substances, drops of oils, starch grains. Cells closely adjoin in the composition of plant tissues, life as a whole depends on the activity of these tiniest units of the structure that form the whole.

With a multicellular structure, there is a specialization that 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 us single out the basic elements of the comparison of the plant cell with the elementary units of the structure of other living organisms:

1. Dense shell, characteristic only for plants, is formed by cellulose (cellulose). In fungi, the membrane consists of strong chitin (a special protein).
2. The cells of plants and fungi differ in color due to the presence or absence of plastids. Such bodies as chloroplasts, chromoplasts and leukoplasts are present only in the plant cytoplasm.
3. There is an organoid that distinguishes animals - it's a centriole (cell center).
4. Only in the cell of the plant there is a large central vacuole, filled with liquid contents. Usually this cell juice is colored with pigments in different colors.
5. The main reserve compound of the plant organism is starch. Mushrooms and animals accumulate glycogen in their cells.

Algae are known for many single, free-living cells. For example, such an independent organism is chlamydomonas. Although plants differ from animals by the presence of a cellulose cell wall, but the sex cells are devoid of such a dense shell - this is yet another proof of the unity of the organic world.