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Biology is the science of life, the living organisms that live on Earth.
Biology studies the structure and activity of living organisms, their diversity, the laws of historical and individual development.
The area of distribution of life is a special shell of the Earth - the biosphere.
The branch of biology that deals with the relationship of organisms to each other and to their environment is called ecology.
Biology is closely connected with many aspects of human practical activity - agriculture, medicine, various industries, in particular food and light industries, etc.
Living organisms on our planet are very diverse. Scientists distinguish four kingdoms of living beings: Bacteria, Fungi, Plants and Animals.
Every living organism is made up of cells (viruses are an exception). Living organisms feed, breathe, excrete waste products, grow, develop, reproduce, perceive environmental influences and react to them.
Every organism lives in a specific environment. Everything that surrounds a living being is called a habitat.
There are four main habitats on our planet, developed and inhabited by organisms. These are water, ground-air, soil and the environment inside living organisms.
Each environment has its own specific living conditions to which organisms adapt. This explains the great diversity of living organisms on our planet.
Environmental conditions have a certain influence (positive or negative) on the existence and geographical distribution of living beings. In this regard, environmental conditions are considered as environmental factors.
Conventionally, all environmental factors are divided into three main groups - abiotic, biotic and anthropogenic.
Chapter 1
The world of living organisms is very diverse. To understand how they live, that is, how they grow, feed, reproduce, it is necessary to study their structure.
In this chapter you will learn
About the structure of the cell and the vital processes occurring in it;
About the main types of tissues that make up organs;
On the device of a magnifying glass, a microscope and the rules for working with them.
You will learn
Prepare micropreparations;
Use a magnifying glass and a microscope;
Find the main parts of a plant cell on a micropreparation, in the table;
Schematically depict the structure of the cell.
§ 6. The device of magnifying devices
1. What magnifying devices do you know?
2. What are they used for?
If we break a pink, unripe fruit of a tomato (tomato), watermelon or apple with loose pulp, we will see that the pulp of the fruit consists of tiny grains. it cells. They will be better seen if you examine them with magnifying instruments - a magnifying glass or a microscope.
Loupe device. magnifying glass- the simplest magnifying device. Its main part is a magnifying glass, convex on both sides and inserted into the frame. Magnifiers are manual and tripod (Fig. 16).
Rice. 16. Manual magnifier (1) and tripod (2)
hand magnifier increases items by 2-20 times. When working, it is taken by the handle and brought closer to the object at such a distance at which the image of the object is most clear.
tripod magnifier increases items by 10-25 times. Two magnifying glasses are inserted into its frame, mounted on a stand - a tripod. An object table with a hole and a mirror is attached to the tripod.
The device of a magnifying glass and examining with its help the cellular structure of plants
1. Consider a hand magnifier. What parts does it have? What is their purpose?
2. Examine with the naked eye the pulp of a semi-ripe fruit of a tomato, watermelon, apple. What is characteristic of their structure?
3. Examine the pieces of fruit pulp under a magnifying glass. Sketch what you see in a notebook, sign the drawings. What shape are the fruit pulp cells?
Light microscope device. With a magnifying glass, you can see the shape of the cells. To study their structure, they use a microscope (from the Greek words "micros" - small and "scopeo" - I look).
The light microscope (Fig. 17) that you work with at school can magnify the image of objects up to 3600 times. into the telescope, or tube, this microscope has magnifying glasses (lenses) inserted. At the top end of the tube is eyepiece(from the Latin word "oculus" - eye), through which various objects are viewed. It consists of a frame and two magnifying glasses.
At the lower end of the tube is placed lens(from the Latin word "objectum" - an object), consisting of a frame and several magnifying glasses.
The tube is attached to tripod. Also attached to the tripod object table, in the center of which there is a hole and under it mirror. Using a light microscope, one can see an image of an object illuminated with the help of this mirror.
Rice. 17. Light microscope
To find out how much the image is enlarged when using a microscope, you need to multiply the number indicated on the eyepiece by the number indicated on the object used. For example, if the eyepiece is 10x and the objective is 20x, then the total magnification is 10 × 20 = 200 times.
How to work with a microscope
1. Place the microscope with the tripod facing you at a distance of 5–10 cm from the edge of the table. Aim the light with a mirror into the opening of the stage.
2. Place the prepared preparation on the stage and fix the glass slide with clamps.
3. Using the screw, slowly lower the tube so that the lower edge of the objective is 1–2 mm from the preparation.
4. Look into the eyepiece with one eye, without closing or closing the other. While looking into the eyepiece, use the screws to slowly raise the tube until a clear image of the object appears.
5. Put the microscope back in its case after use.
A microscope is a fragile and expensive device: you need to work with it carefully, strictly following the rules.
The device of the microscope and methods of working with it
1. Examine the microscope. Find the tube, eyepiece, lens, stage stand, mirror, screws. Find out what each part means. Determine how many times the microscope magnifies the image of the object.
2. Familiarize yourself with the rules for using a microscope.
3. Work out the sequence of actions when working with a microscope.
CELL. Magnifier. MICROSCOPE: TUBE, EYECOOLER, LENS, STAND
Questions
1. What magnifying devices do you know?
2. What is a loupe and how much magnification does it give?
3. How is a microscope made?
4. How do you know what magnification a microscope gives?
Think
Why is it impossible to study opaque objects with a light microscope?
Tasks
Learn the rules for working with a microscope.
Using additional sources of information, find out what details of the structure of living organisms allow you to see the most modern microscopes.
Do you know that…
Light microscopes with two lenses were invented in the 16th century. In the 17th century Dutchman Anthony van Leeuwenhoek designed a more advanced microscope, giving an increase of up to 270 times, and in the 20th century. The electron microscope was invented, magnifying the image by tens and hundreds of thousands of times.
§ 7. The structure of the cell
1. Why is the microscope you work with called a light microscope?
2. What is the name of the smallest grains that make up the fruits and other plant organs?
You can get acquainted with the structure of the cell using the example of a plant cell, examining a preparation of onion scales under a microscope. The preparation sequence is shown in Figure 18.
On the micropreparation, oblong cells are visible, tightly adjacent to one another (Fig. 19). Each cell has a dense shell With pores which can only be seen at high magnification. The composition of the membranes of plant cells includes a special substance - cellulose, giving them strength (Fig. 20).
Rice. 18. Preparation of the onion peel preparation
Rice. 19. Cellular structure of onion skin
Under the cell wall is a thin film membrane. It is easily permeable to some substances and impermeable to others. The semi-permeability of the membrane is maintained as long as the cell is alive. Thus, the shell maintains the integrity of the cell, gives it a shape, and the membrane regulates the flow of substances from the environment into the cell and from the cell into its environment.
Inside is a colorless viscous substance - cytoplasm(from the Greek words "kitos" - vessel and "plasma" - formation). With strong heating and freezing, it is destroyed, and then the cell dies.
Rice. 20. The structure of a plant cell
The cytoplasm contains a small dense nucleus, in which one can distinguish nucleolus. Using an electron microscope, it was found that the cell nucleus has a very complex structure. This is due to the fact that the nucleus regulates the life processes of the cell and contains hereditary information about the body.
In almost all cells, especially in old ones, cavities are clearly visible - vacuoles(from the Latin word "vacuus" - empty), limited by a membrane. They are filled cell sap- water with sugars and other organic and inorganic substances dissolved in it. When cutting a ripe fruit or other juicy part of a plant, we damage the cells, and juice flows out of their vacuoles. Cell sap may contain dyes ( pigments), giving a blue, purple, crimson color to the petals and other parts of plants, as well as autumn leaves.
Preparation and examination of the preparation of onion scales under a microscope
1. Consider in Figure 18 the sequence of preparation of the onion skin preparation.
2. Prepare the glass slide by carefully wiping it with gauze.
3. Pipette 1-2 drops of water onto a glass slide.
Using a dissecting needle, carefully remove a small piece of transparent skin from the inner surface of the onion scales. Place a piece of skin in a drop of water and flatten with the tip of a needle.
5. Cover the skin with a coverslip as shown.
6. View the prepared preparation at low magnification. Note which parts of the cell you see.
7. Stain the slide with iodine solution. To do this, put a drop of iodine solution on a glass slide. With the filter paper on the other hand, pull off the excess solution.
8. Examine the stained preparation. What changes have taken place?
9. View the specimen at high magnification. Find on it a dark stripe surrounding the cell - a shell; under it is a golden substance - the cytoplasm (it can occupy the entire cell or be near the walls). The nucleus is clearly visible in the cytoplasm. Find a vacuole with cell sap (it differs from the cytoplasm in color).
10. Draw 2-3 onion skin cells. Designate the membrane, cytoplasm, nucleus, vacuole with cell sap.
The cytoplasm of a plant cell contains numerous small bodies. plastids. At high magnification, they are clearly visible. In the cells of different organs, the number of plastids is different.
In plants, plastids can be of different colors: green, yellow or orange and colorless. In cells of the skin of onion scales, for example, plastids are colorless.
The color of certain parts of them depends on the color of plastids and on the dyes contained in the cell sap of various plants. So, the green color of the leaves is determined by plastids called chloroplasts(from the Greek words "chloros" - greenish and "plastos" - fashioned, created) (Fig. 21). Chloroplasts contain a green pigment chlorophyll(from the Greek words "chloros" - greenish and "fillon" - leaf).
Rice. 21. Chloroplasts in leaf cells
Plastids in Elodea leaf cells
1. Prepare a preparation of elodea leaf cells. To do this, separate the leaf from the stem, put it in a drop of water on a glass slide and cover with a coverslip.
2. Examine the specimen under a microscope. Find chloroplasts in cells.
3. Sketch the structure of an elodea leaf cell.
Rice. 22. Forms of plant cells
The color, shape, and size of the cells of different plant organs are very diverse (Fig. 22).
The number of vacuoles in the cells, plastids, the thickness of the cell membrane, the location of the internal components of the cell varies greatly and depends on what function the cell performs in the plant body.
ENVELOPE, CYTOPLASMA, NUCLEUS, NUCLEOL, VACUOLES, PLASTIDS, CHLOROPLASTS, PIGMENTS, CHLOROPHYLL
Questions
1. How to prepare an onion skin preparation?
2. What is the structure of a cell?
3. Where is cell sap located and what does it contain?
4. In what color can dyes found in cell sap and plastids stain different parts of plants?
Tasks
Prepare cell preparations of fruits of tomatoes, mountain ash, rose hips. To do this, transfer a particle of pulp to a drop of water on a glass slide with a needle. Divide the pulp into cells with the tip of a needle and cover with a coverslip. Compare the cells of the pulp of fruits with the cells of the skin of onion scales. Note the coloration of the plastids.
Draw what you see. What are the similarities and differences between onion skin cells and fruits?
Do you know that…
The existence of cells was discovered by the Englishman Robert Hooke in 1665. Looking at a thin section of cork (cork oak bark) through a microscope he designed, he counted up to 125 million pores, or cells, in one square inch (2.5 cm) (Fig. 23). In the core of the elder, the stems of various plants, R. Hooke found the same cells. He called them cells. Thus began the study of the cellular structure of plants, but it did not go easily. The cell nucleus was discovered only in 1831, and the cytoplasm in 1846.
Rice. 23. R. Hooke's microscope and the cut of cork oak bark obtained with it
Quests for the curious
You can make your own "historical" preparation. To do this, put a thin section of a light cork in alcohol. After a few minutes, start adding water drop by drop to remove air from the cells - “cells”, darkening the preparation. Then examine the section under a microscope. You will see the same thing as R. Hooke in the 17th century.
§ 8. Chemical composition of the cell
1. What is a chemical element?
2. What organic substances do you know?
3. Which substances are called simple, and which are complex?
All cells of living organisms consist of the same chemical elements that are included in the composition of objects of inanimate nature. But the distribution of these elements in cells is extremely uneven. So, about 98% of the mass of any cell falls on four elements: carbon, hydrogen, oxygen and nitrogen. The relative content of these chemical elements in living matter is much higher than, for example, in the earth's crust.
About 2% of the mass of the cell is accounted for by the following eight elements: potassium, sodium, calcium, chlorine, magnesium, iron, phosphorus and sulfur. Other chemical elements (for example, zinc, iodine) are contained in very small quantities.
Chemical elements combine to form inorganic and organic substances (see table).
Inorganic substances of the cell- this is water and mineral salts. Most of all, the cell contains water (from 40 to 95% of its total mass). Water gives the cell elasticity, determines its shape, and participates in metabolism.
The higher the metabolic rate in a particular cell, the more water it contains.
Chemical composition of the cell, %
Approximately 1–1.5% of the total cell mass is made up of mineral salts, in particular salts of calcium, potassium, phosphorus, etc. Compounds of nitrogen, phosphorus, calcium and other inorganic substances are used to synthesize organic molecules (proteins, nucleic acids, etc.). With a lack of minerals, the most important processes of cell vital activity are disrupted.
organic matter are part of all living organisms. They include carbohydrates, proteins, fats, nucleic acids and other substances.
Carbohydrates are an important group of organic substances, as a result of the breakdown of which cells receive the energy necessary for their vital activity. Carbohydrates are part of the cell membranes, giving them strength. Storage substances in cells - starch and sugars also belong to carbohydrates.
Proteins play an essential role in the life of cells. They are part of a variety of cellular structures, regulate life processes and can also be stored in cells.
Fats are stored in cells. When fats are broken down, the energy necessary for living organisms is also released.
Nucleic acids play a leading role in the preservation of hereditary information and its transmission to descendants.
The cell is a "miniature natural laboratory" in which various chemical compounds are synthesized and undergo changes.
INORGANIC SUBSTANCES. ORGANIC SUBSTANCES: CARBOHYDRATES, PROTEINS, FATS, NUCLEIC ACIDS
Questions
1. What are the most abundant chemical elements in a cell?
2. What role does water play in a cell?
3. What substances are classified as organic?
4. What is the importance of organic matter in a cell?
Think
Why is the cell compared to a "miniature natural laboratory"?
§ 9. Vital activity of the cell, its division and growth
1. What are chloroplasts?
2. In what part of the cell are they located?
Life processes in the cell. In Elodea leaf cells, under a microscope, one can see that green plastids (chloroplasts) smoothly move along with the cytoplasm in one direction along the cell membrane. By their movement, one can judge the movement of the cytoplasm. This movement is constant but sometimes difficult to detect.
Observation of the movement of the cytoplasm
You can observe the movement of the cytoplasm by preparing micropreparations of the leaves of elodea, vallisneria, root hairs of water color, hairs of stamen filaments of Tradescantia virginiana.
1. Using the knowledge and skills gained in previous lessons, prepare micropreparations.
2. Examine them under a microscope, note the movement of the cytoplasm.
3. Sketch the cells, arrows indicate the direction of cytoplasmic movement.
The movement of the cytoplasm contributes to the movement of nutrients and air in the cells. The more active the vital activity of the cell, the greater the speed of movement of the cytoplasm.
The cytoplasm of one living cell is usually not isolated from the cytoplasm of other living cells nearby. The threads of the cytoplasm connect neighboring cells, passing through the pores in the cell membranes (Fig. 24).
Between the shells of neighboring cells is a special intercellular substance. If the intercellular substance is destroyed, the cells separate. This is what happens when potatoes are boiled. In ripe fruits of watermelons and tomatoes, crumbly apples, the cells are also easily separated.
Often living growing cells of all plant organs change shape. Their shells are rounded and sometimes move away from each other. In these areas, the intercellular substance is destroyed. Arise intercellular spaces filled with air.
Rice. 24. Interaction of neighboring cells
Living cells breathe, feed, grow and multiply. Substances necessary for the life of cells enter them through the cell membrane in the form of solutions from other cells and their intercellular spaces. The plant receives these substances from the air and soil.
How does a cell divide? The cells of some parts of plants are capable of dividing, due to which their number increases. As a result of cell division and growth, plants grow.
Cell division is preceded by the division of its nucleus (Fig. 25). Before cell division, the nucleus increases, and bodies, usually cylindrical in shape, become clearly visible in it - chromosomes(from the Greek words "chrome" - color and "soma" - body). They transmit hereditary traits from cell to cell.
As a result of a complex process, each chromosome, as it were, copies itself. Two identical parts are formed. During division, parts of the chromosome diverge to different poles of the cell. In the nuclei of each of the two new cells, there are as many of them as there were in the mother cell. All content is also evenly distributed between the two new cells.
Rice. 25. Cell division
Rice. 26. Cell Growth
The nucleus of a young cell is located in the center. In an old cell, there is usually one large vacuole, so the cytoplasm, in which the nucleus is located, is adjacent to the cell membrane, and young cells contain many small vacuoles (Fig. 26). Young cells, unlike old ones, are able to divide.
INTERCELLULAR. INTERCELLULAR SUBSTANCE. CYTOPLASMA MOVEMENT. CHROMOSOMES
Questions
1. How can you observe the movement of the cytoplasm?
2. What is the importance of the movement of cytoplasm in cells for a plant?
3. What are all plant organs made of?
4. Why don't the cells that make up the plant separate?
5. How do substances enter a living cell?
6. How does cell division take place?
7. What explains the growth of plant organs?
8. Where are the chromosomes located in the cell?
9. What role do chromosomes play?
10. What is the difference between a young cell and an old one?
Think
Why do cells have a constant number of chromosomes?
Quest for the curious
Study the effect of temperature on the intensity of cytoplasmic movement. As a rule, it is most intense at a temperature of 37 °C, but already at temperatures above 40–42 °C it stops.
Do you know that…
The process of cell division was discovered by the famous German scientist Rudolf Virchow. In 1858, he proved that all cells are formed from other cells by division. At that time, this was an outstanding discovery, since it was previously believed that new cells arise from the intercellular substance.
One leaf of an apple tree consists of about 50 million cells of different types. There are about 80 different cell types in flowering plants.
In all organisms belonging to the same species, the number of chromosomes in the cells is the same: in house flies - 12, in Drosophila - 8, in corn - 20, in garden strawberries - 56, in river cancer - 116, in humans - 46, in chimpanzees , cockroach and pepper - 48. As can be seen, the number of chromosomes does not depend on the level of organization.
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Using a new type of microscope invented and manufactured by the Marine Biological Laboratory (MBL), scientists were able to see and measure the density of heterochromatin (heterochromatin), an extremely compressed form of chromosomal material that is found in the nucleus of human cells and some other living beings. Until recently, this chromosomal "dark matter" was thought to contain non-coding DNA and inactive genes. However, according to some recent research, this DNA is not completely dormant.
Unfortunately, even the most modern methods of microscopy did not allow until now to make an in-depth study of "heterochromatic" DNA, which was required to understand its role in "cellular mechanics". And the magic wand in this case was a new type of microscope - OI-DIC (orientation-independent differential interference contrast), the possibility of which was justified back in 2000. "Our work is a demonstration of the successful collaboration and collaboration between biologists, scientific engineers and information technology professionals," said David Mark Welch, director of the Marine Biological Laboratory's Research Department.
Studies of heterochromatin using an OI-DIC microscope, according to scientists, are the first practical application of this technology. This technology is ideal for long-term studies of living cells and isolated organoids, which are not exposed to any aggressive external influences.
Traditional DIC technology has been widely used by life scientists since the 1970s for imaging live cells. In the 1980s, this technology was greatly improved, making it possible to obtain images of high quality and resolution. But the improvement did not rid the technology of its main drawback - to obtain a complete image, it is required to make several rotations of the sample at a strictly defined angle. Unlike DIC technology, the OI-DIC microscope illuminates the sample with several beams of light in succession and, based on many individual images, using complex algorithms, recreates the resulting image.
"The new microscope provides the best ratio of image resolution to its contrast to date. Now with this microscope we can see details as small as 250 nanometers," write scientists from the National Institute of Genetics, Japan, who took part in the development of the new microscope, - "We will soon complete the development of an improved data processing algorithm, which will allow us to increase the resolution of the microscope even more. And researchers from the University of Chicago will have completed the development of a new optical OI-DIC system by this time, which will allow us to obtain three-dimensional images of the objects under study."
Magnifier, microscope, telescope.
Question 2. What are they used for?
They are used to enlarge the object in question several times.
Laboratory work No. 1. The device of a magnifying glass and examining the cellular structure of plants with its help.
1. Consider a hand magnifier. What parts does it have? What is their purpose?
A hand magnifier consists of a handle and a magnifying glass, convex on both sides and inserted into a frame. When working, the magnifying glass is taken by the handle and brought closer to the object at such a distance at which the image of the object through the magnifying glass is the clearest.
2. Examine with the naked eye the pulp of a semi-ripe fruit of a tomato, watermelon, apple. What is characteristic of their structure?
The pulp of the fruit is loose and consists of the smallest grains. These are cells.
It is clearly seen that the pulp of the tomato fruit has a granular structure. In an apple, the flesh is a little juicy, and the cells are small and close to each other. The pulp of a watermelon consists of many cells filled with juice, which are located either closer or further away.
3. Examine the pieces of fruit pulp under a magnifying glass. Sketch what you see in a notebook, sign the drawings. What shape are the fruit pulp cells?
Even with the naked eye, and even better under a magnifying glass, you can see that the pulp of a ripe watermelon consists of very small grains, or grains. These are cells - the smallest "bricks" that make up the bodies of all living organisms. Also, the pulp of a tomato fruit under a magnifying glass consists of cells that look like rounded grains.
Laboratory work No. 2. The device of the microscope and methods of working with it.
1. Examine the microscope. Find the tube, eyepiece, lens, stage stand, mirror, screws. Find out what each part means. Determine how many times the microscope magnifies the image of the object.
The tube is a tube that contains the eyepieces of a microscope. Eyepiece - an element of the optical system facing the eye of the observer, part of the microscope, designed to view the image formed by the mirror. The lens is designed to build an enlarged image with fidelity in terms of the shape and color of the object of study. The tripod holds the tube with the eyepiece and objective at a certain distance from the object table, which is placed on the test material. The mirror, which is located under the object table, serves to supply a beam of light under the object under consideration, i.e., improves the illumination of the object. Microscope screws are mechanisms for adjusting the most efficient image on the eyepiece.
2. Familiarize yourself with the rules for using a microscope.
When working with a microscope, the following rules must be observed:
1. Work with a microscope should be sitting;
2. Inspect the microscope, wipe the lenses, eyepiece, mirror from dust with a soft cloth;
3. Set the microscope in front of you, a little to the left, 2-3 cm from the edge of the table. Do not move it during operation;
4. Fully open the diaphragm;
5. Always start working with a microscope at a low magnification;
6. Lower the lens to the working position, i.e. at a distance of 1 cm from the glass slide;
7. Set the illumination in the field of view of the microscope using a mirror. Looking into the eyepiece with one eye and using a mirror with a concave side, direct the light from the window into the lens, and then maximally and evenly illuminate the field of view;
8. Put the micropreparation on the stage so that the object under study is under the lens. Looking from the side, lower the lens with a macro screw until the distance between the lower lens of the objective and the micropreparation is 4-5 mm;
9. Look into the eyepiece with one eye and turn the coarse adjustment screw towards yourself, smoothly raising the lens to a position at which the image of the object will be clearly visible. You can not look into the eyepiece and lower the lens. The front lens can crush the coverslip and scratch it;
10. Moving the preparation with your hand, find the right place, place it in the center of the microscope field of view;
11. Upon completion of work with a high magnification, set a low magnification, raise the objective, remove the preparation from the working table, wipe all parts of the microscope with a clean cloth, cover it with a plastic bag and put it in a cabinet.
3. Work out the sequence of actions when working with a microscope.
1. Place the microscope with a tripod towards you at a distance of 5-10 cm from the edge of the table. Aim the light with a mirror into the opening of the stage.
2. Place the prepared preparation on the stage and secure the slide with clips.
3. Using the screw, slowly lower the tube so that the lower edge of the lens is 1-2 mm from the preparation.
4. Look into the eyepiece with one eye, without closing or closing the other. While looking into the eyepiece, use the screws to slowly raise the tube until a clear image of the object appears.
5. Put the microscope back in its case after use.
Question 1. What magnifying devices do you know?
Hand magnifier and tripod magnifier, microscope.
Question 2. What is a loupe and what magnification does it give?
A magnifying glass is the simplest magnifying device. A hand magnifier consists of a handle and a magnifying glass, convex on both sides and inserted into a frame. It magnifies objects by 2-20 times.
A tripod magnifier magnifies objects 10-25 times. Two magnifying glasses are inserted into its frame, mounted on a stand - a tripod. An object table with a hole and a mirror is attached to the tripod.
Question 3. How does a microscope work?
Magnifying glasses (lenses) are inserted into the telescope, or tube, of this light microscope. At the top end of the tube is an eyepiece through which various objects are viewed. It consists of a frame and two magnifying glasses. At the lower end of the tube is placed a lens consisting of a frame and several magnifying glasses. The tube is attached to a tripod. An object table is also attached to the tripod, in the center of which there is a hole and a mirror under it. Using a light microscope, one can see an image of an object illuminated with the help of this mirror.
Question 4. How to find out what magnification the microscope gives?
To find out how much the image is magnified when using a microscope, multiply the number on the eyepiece by the number on the objective lens being used. For example, if the eyepiece is 10x and the objective is 20x, then the total magnification is 10 x 20 = 200x.
Think
Why is it impossible to study opaque objects with a light microscope?
The main principle of operation of a light microscope is that light rays pass through a transparent or translucent object (object of study) placed on the object table and enter the lens system of the objective and eyepiece. And light does not pass through opaque objects, respectively, we will not see the image.
Tasks
Learn the rules for working with a microscope (see above).
Using additional sources of information, find out what details of the structure of living organisms allow you to see the most modern microscopes.
The light microscope made it possible to examine the structure of cells and tissues of living organisms. And now, it has already been replaced by modern electron microscopes, which allow us to examine molecules and electrons. A scanning electron microscope allows you to obtain images with a resolution measured in nanometers (10-9). It is possible to obtain data concerning the structure of the molecular and electronic composition of the surface layer of the surface under study.
If we break a pink, unripe fruit of a tomato (tomato), watermelon or apple with loose pulp, we will see that the pulp of the fruit consists of tiny grains. These are cells. They will be better seen if you examine them with magnifying instruments - a magnifying glass or a microscope.
magnifier device. A magnifying glass is the simplest magnifying device. Its main part is a magnifying glass, convex on both sides and inserted into a frame. Magnifiers are manual and tripod (Fig. 16).
Rice. 16. Manual magnifier (1) and tripod (2)
A hand magnifier magnifies objects 2-20 times. When working, it is taken by the handle and brought closer to the object at such a distance at which the image of the object is most clear.
A tripod magnifier magnifies objects 10-25 times. Two magnifying glasses are inserted into its frame, mounted on a stand - a tripod. An object table with a hole and a mirror is attached to the tripod.
The device of a magnifying glass and examining with its help the cellular structure of plants
- Consider a hand magnifier. What parts does it have? What is their purpose?
- Examine with the naked eye the pulp of a semi-ripe fruit of a tomato, watermelon, apple. What is characteristic of their structure?
- Examine the pieces of fruit pulp under a magnifying glass. Sketch what you see in a notebook, sign the drawings. What shape are the fruit pulp cells?
Light microscope device. With a magnifying glass, you can see the shape of the cells. To study their structure, they use a microscope (from the Greek words "micros" - small and "scopeo" - I look).
The light microscope (Fig. 17) that you work with at school can magnify the image of objects up to 3600 times. Magnifying glasses (lenses) are inserted into the telescope, or tube, of this microscope. At the upper end of the tube is an eyepiece (from the Latin word "oculus" - eye), through which various objects are viewed. It consists of a frame and two magnifying glasses. At the lower end of the tube is placed a lens (from the Latin word "objectum" - an object), consisting of a frame and several magnifying glasses.
The tube is attached to a tripod. An object table is also attached to the tripod, in the center of which there is a hole and a mirror under it. Using a light microscope, one can see an image of an object illuminated with this mirror.
Rice. 17. Light microscope
To find out how much the image is enlarged when using a microscope, you need to multiply the number indicated on the eyepiece by the number indicated on the object used. For example, if the eyepiece is 10x and the objective is 20x, then the total magnification is 10 x 20 = 200x.
How to work with a microscope
- Place the microscope with a tripod towards you at a distance of 5-10 cm from the edge of the table. Aim the light with a mirror into the opening of the stage.
- Place the prepared preparation on the stage and fix the glass slide with clamps.
- Using the screw, smoothly lower the tube so that the lower edge of the objective is 1-2 mm from the preparation.
- Look into the eyepiece with one eye, without closing or closing the other. While looking into the eyepiece, use the screws to slowly raise the tube until a clear image of the object appears.
- Put the microscope back in its case after use.
A microscope is a fragile and expensive device: you need to work with it carefully, strictly following the rules.
The device of the microscope and methods of working with it
- Examine the microscope. Find the tube, eyepiece, lens, stage stand, mirror, screws. Find out what each part means. Determine how many times the microscope magnifies the image of the object.
- Familiarize yourself with the rules for using a microscope.
- Work out the sequence of actions when working with a microscope.
New concepts
Cell. Magnifying glass. Microscope: tube, eyepiece, lens, tripod
Questions
- What magnifying devices do you know?
- What is a loupe and how much magnification does it give?
- How is a microscope made?
- How do you know what magnification a microscope gives?
Think
Why is it impossible to study opaque objects with a light microscope?
Tasks
Learn the rules for working with a microscope.
Using additional sources of information, find out what details of the structure of living organisms allow you to see the most modern microscopes.
Do you know that...
Light microscopes with two lenses were invented in the 16th century. In the 17th century Dutchman Anthony van Leeuwenhoek designed a more advanced microscope, giving an increase of up to 270 times, and in the 20th century. The electron microscope was invented, magnifying the image by tens and hundreds of thousands of times.