Pear cells under a magnifying glass. Collection of laboratory works in biology. The device of a microscope and methods of working with it

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Biology is the science of life, of living organisms living on Earth.

Biology studies the structure and vital functions of living organisms, their diversity, and the laws of historical and individual development.

The distribution area of ​​life is special shell Earth - biosphere.

The branch of biology about the relationships of organisms with each other and with their environment is called ecology.

Biology is closely related to many aspects of human practical activity - agriculture, medicine, various industries, in particular food and light, 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 (with the exception of viruses). Living organisms eat, breathe, excrete waste products, grow, develop, reproduce, perceive influences environment and react to them.

Each organism lives in a specific environment. Everything that surrounds a living being is called its 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 impact (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. Cellular structure of organisms

The world of living organisms is very diverse. To understand how they live, that is, how they grow, feed, and 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;

About the structure of a magnifying glass, a microscope and the rules for working with them.

You will learn

Prepare microslides;

Use a magnifying glass and microscope;

Find the main parts of a plant cell on a micropreparation in the table;

Schematically depict the structure of a cell.

§ 6. Construction 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. This cells. They will be better visible if you examine them using magnifying devices - a magnifying glass or a microscope.

Magnifying device. Magnifier- the simplest magnifying device. Its main part is a magnifying glass, convex on both sides and inserted into the frame. Magnifiers come in handheld and tripod types (Fig. 16).

Rice. 16. Hand-held magnifying glass (1) and tripod magnifying glass (2)

Hand magnifier Magnifies objects by 2–20 times. When working, it is taken by the handle and brought closer to the object at a distance at which the image of the object is most clear.

Tripod magnifier Magnifies objects 10–25 times. Two magnifying glasses are inserted into its frame, mounted on a stand - a tripod. A stage with a hole and a mirror is attached to the tripod.

The device of a magnifying glass and using it to examine the cellular structure of plants

1. Examine a hand-held magnifying glass. What parts does it have? What is their purpose?

2. Examine with the naked eye the pulp of a semi-ripe tomato, watermelon, or apple. What is characteristic of their structure?

3. Examine pieces of fruit pulp under a magnifying glass. Draw what you see in your notebook and sign the drawings. What shape do the fruit pulp cells have?

The device of a light microscope. Using a magnifying glass you can see the shape of the cells. To study their structure, they use a microscope (from the Greek words “mikros” - small and “skopeo” - look).

The light microscope (Fig. 17) that you work with at school can magnify images of objects up to 3600 times. Into the telescope, or tube This microscope has magnifying glasses (lenses) inserted into it. At the upper end of the tube there is eyepiece(from 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” - object), consisting of a frame and several magnifying glasses.

The tube is attached to tripod. Also attached to the tripod stage, in the center of which there is a hole and below it mirror. Using a light microscope, you can see an image of an object illuminated by this mirror.

Rice. 17. Light microscope

To find out how much the image is magnified when using a microscope, you need to multiply the number indicated on the eyepiece by the number indicated on the object being used. For example, if the eyepiece provides 10x magnification and the objective provides 20x magnification, then the total magnification is 10 × 20 = 200x.

How to use a microscope

1. Place the microscope with the tripod facing you at a distance of 5–10 cm from the edge of the table. Use a mirror to shine light into the opening of the stage.

2. Place the prepared preparation on the stage and secure the slide with clamps.

3. Using the screw, smoothly lower the tube so that the lower edge of the lens is at a distance of 1–2 mm from the specimen.

4. Look into the eyepiece with one eye without closing or squinting the other. While looking through the eyepiece, use the screws to slowly lift the tube until a clear image of the object appears.

5. After use, put the microscope in its case.

A microscope is a fragile and expensive device: you must work with it carefully, strictly following the rules.

The device of a microscope and methods of working with it

1. Examine the microscope. Find the tube, eyepiece, lens, tripod with stage, 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. Practice the sequence of actions when working with a microscope.

CELL. MAgnifying glass. MICROSCOPE: TUBE, OCULAR, LENS, TRIPOD

Questions

1. What magnifying devices do you know?

2. What is a magnifying glass and what magnification does it provide?

3. How does a microscope work?

4. How do you know what magnification a microscope gives?

Think

Why can't we study opaque objects using a light microscope?

Tasks

Learn the rules of using a microscope.

Using additional sources of information, find out what details of the structure of living organisms can be seen with the most modern microscopes.

Do you know that…

Light microscopes with two lenses were invented in the 16th century. In the 17th century Dutchman Antonie van Leeuwenhoek designed a more advanced microscope, providing magnification up to 270 times, and in the 20th century. An electron microscope was invented, magnifying images tens and hundreds of thousands of times.

§ 7. Cell structure

1. Why is the microscope you are working with called a light microscope?

2. What are the smallest grains that make up fruits and other plant organs called?

You can get acquainted with the structure of a cell using the example of a plant cell by examining a preparation of onion scale skin under a microscope. The sequence of drug preparation is shown in Figure 18.

The microslide shows elongated cells, tightly adjacent to one another (Fig. 19). Each cell has a dense shell With at times, which can only be distinguished at high magnification. The composition of plant cell walls includes a special substance - cellulose, giving them strength (Fig. 20).

Rice. 18. Preparation of onion skin scale preparation

Rice. 19. Cellular structure of onion skin

Under the cell membrane there is a thin film - membrane. It is easily permeable to some substances and impermeable to others. The semi-permeability of the membrane remains as long as the cell is alive. Thus, the membrane maintains the integrity of the cell, gives it shape, and the membrane regulates the flow of substances from the environment into the cell and from the cell into its environment.

Inside there is a colorless viscous substance - cytoplasm(from the Greek words “kitos” - vessel and “plasma” - formation). When strongly heated and frozen, it is destroyed, and then the cell dies.

Rice. 20. Structure of a plant cell

In the cytoplasm there is a small dense core, 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 vital 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 “vacuum” - empty), limited by a membrane. They're filled cell sap– water with sugars and other organic and inorganic substances dissolved in it. By 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 coloring substances ( pigments), giving blue, purple, crimson color to petals and other parts of plants, as well as autumn leaves.

Preparation and examination of a preparation of onion scale skin under a microscope

1. Consider in Figure 18 the sequence of preparing the onion skin preparation.

2. Prepare the slide by wiping it thoroughly with gauze.

3. Use a pipette to place 1–2 drops of water onto the slide.

Using a dissecting needle, carefully remove small piece transparent skin from the inner surface of the onion scales. Place a piece of peel in a drop of water and straighten it with the tip of a needle.

5. Cover the peel with a cover slip as shown in the picture.

6. Examine the prepared preparation at low magnification. Note which parts of the cell you see.

7. Stain the preparation with iodine solution. To do this, place a drop of iodine solution on a glass slide. Use filter paper on the other side to pull off excess solution.

8. Examine the colored preparation. What changes have occurred?

9. Examine the specimen at high magnification. Find on it a dark stripe surrounding the cell - the membrane; underneath it is a golden substance - the cytoplasm (it can occupy the entire cell or be located near the walls). The nucleus is clearly visible in the cytoplasm. Find the vacuole with cell sap (it differs from the cytoplasm in color).

10. Sketch 2-3 cells of onion skin. Label the membrane, cytoplasm, nucleus, vacuole with cell sap.

In the cytoplasm of a plant cell there are 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 the skin cells of onion scales, for example, plastids are colorless.

The color of certain parts of them depends on the color of plastids and on the coloring substances contained in the cell sap of various plants. Thus, the green color of leaves is determined by plastids called chloroplasts(from the Greek words “chloros” - greenish and “plastos” - fashioned, created) (Fig. 21). Chloroplasts contain green pigment chlorophyll(from the Greek words “chloros” - greenish and “phyllon” - 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, place it in a drop of water on a glass slide and cover with a coverslip.

2. Examine the preparation under a microscope. Find chloroplasts in the cells.

3. Draw the structure of an Elodea leaf cell.

Rice. 22. Shapes of plant cells

The color, shape and size of cells in different plant organs are very diverse (Fig. 22).

The number of vacuoles, plastids in cells, 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.

ENVIRONMENT, CYTOPLASMA, NUCLEUS, NUCLEOLUS, VACUOLES, Plastids, CHLOROPLASTS, PIGMENTS, CHLOROPHYLL

Questions

1. How to prepare onion skin preparation?

2. What structure does a cell have?

3. Where is the cell sap and what does it contain?

4. What color can coloring substances found in cell sap and plastids give to different parts of plants?

Tasks

Prepare cell preparations of tomato, rowan, and rose hip fruits. To do this, transfer a particle of pulp into a drop of water on a glass slide with a needle. Use the tip of a needle to separate the pulp into cells and cover with a coverslip. Compare the cells of the fruit pulp with the skin cells of the onion scales. Note the color of the plastids.

Sketch what you see. What are the similarities and differences between onion skin cells and fruit cells?

Do you know that…

The existence of cells was discovered by the Englishman Robert Hooke in 1665. Examining a thin section of cork (cork oak bark) through a microscope he constructed, he counted up to 125 million pores, or cells, in one square inch (2.5 cm) (Fig. 23). R. Hooke discovered the same cells in the core of elderberry and the stems of various plants. He called them cells. Thus began the study of the cellular structure of plants, but it was not easy. The cell nucleus was discovered only in 1831, and the cytoplasm in 1846.

Rice. 23. R. Hooke’s microscope and the view of a section of cork oak bark obtained with its help

Quests for the curious

You can prepare the “historical” preparation yourself. To do this, place a thin section of a light-colored cork in alcohol. After a few minutes, start adding water drop by drop to remove air from the cells - “cells”, which darkens the drug. Then examine the section under a microscope. You will see the same thing as R. Hooke in the 17th century.

§ 8. Chemical composition cells

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 are composed of the same chemical elements, which are also included in the composition of objects of inanimate nature. But the distribution of these elements in cells is extremely uneven. Thus, about 98% of the mass of any cell is made up of 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 a cell's mass is made up of 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 with each other to form inorganic And organic substances (see table).

Inorganic substances of the cell- This 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 mass of the cell 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 for the synthesis of organic molecules (proteins, nucleic acids, etc.). With a lack of minerals, the critical processes cell life.

Organic matter are found in all living organisms. These 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 life. Carbohydrates are part of cell membranes, giving them strength. Storage substances in cells - starch and sugars - are also classified as carbohydrates.

Proteins play a vital role in cell life. They are part of various cellular structures, regulate vital processes and can also be stored in cells.

Fats are deposited in cells. When fats are broken down, the energy needed by living organisms is also released.

Nucleic acids play a leading role in preserving hereditary information and transmitting it to descendants.

A 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 chemical elements are most abundant in a cell?

2. What role does water play in the cell?

3. What substances are classified as organic?

4. What is the importance of organic substances 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 the cells of an elodea leaf, under a microscope, you 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 cytoplasmic movement

You can observe the movement of the cytoplasm by preparing micropreparations of leaves of Elodea, Vallisneria, root hairs of watercolor, hairs of staminate filaments of Tradescantia virginiana.

1. Using the knowledge and skills acquired in previous lessons, prepare microslides.

2. Examine them under a microscope and note the movement of the cytoplasm.

3. Draw the cells, using arrows to show the direction of movement of the cytoplasm.

The movement of the cytoplasm promotes the movement of nutrients and air within 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 located nearby. Threads of cytoplasm connect neighboring cells, passing through pores in the cell membranes (Fig. 24).

Between the membranes of neighboring cells there is a special intercellular substance. If the intercellular substance is destroyed, the cells separate. This happens when potato tubers 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 in some places 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, eat, grow and reproduce. Substances necessary for the functioning 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 a cell divides. Cells of some parts of plants are capable of division, due to which their number increases. As a result of cell division and growth, plants grow.

Cell division is preceded by division of its nucleus (Fig. 25). Before cell division, the nucleus enlarges and bodies, usually cylindrical – chromosomes(from the Greek words “chroma” - color and “soma” - body). They transmit hereditary characteristics from cell to cell.

As a result of a complex process, each chromosome seems to copy itself. Two identical parts are formed. During division, parts of the chromosome move 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 contents are 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. An old cell usually has one large vacuole, so the cytoplasm in which the nucleus is located is adjacent to the cell membrane, while young cells contain many small vacuoles (Fig. 26). Young cells, unlike old ones, are able to divide.

INTERCELLULARS. INTERCELLULAR SUBSTANCE. CYTOPLASM MOVEMENT. CHROMOSOMES

Questions

1. How can you observe the movement of the cytoplasm?

2. What is the significance 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 occur?

7. What explains the growth of plant organs?

8. In what part of the cell are the chromosomes located?

9. What role do chromosomes play?

10. How does a young cell differ from an old one?

Think

Why do cells have a constant number of chromosomes?

A task 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 approximately 50 million cells of different types. In flowering plants there are about 80 various types cells.

In all organisms belonging to the same species, the number of chromosomes in cells is the same: in the house fly - 12, in Drosophila - 8, in corn - 20, in strawberries - 56, in crayfish - 116, in humans - 46, in chimpanzees , cockroach and pepper - 48. As you can see, the number of chromosomes does not depend on the level of organization.

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Even with the naked eye, or even better under a magnifying glass, you can see that the pulp of a ripe watermelon, tomato, or apple consists of very small grains or grains. These are cells - the smallest “building blocks” that make up the bodies of all living organisms.

What are we doing? Let's make a temporary microslide of a tomato fruit.

Wipe the slide and cover glass with a napkin. Use a pipette to place a drop of water on the glass slide (1).

What to do. Using a dissecting needle, take a small piece of fruit pulp and place it in a drop of water on a glass slide. Mash the pulp with a dissecting needle until you obtain a paste (2).

Cover with a cover glass and remove excess water with filter paper (3).

What to do. Examine the temporary microslide with a magnifying glass.

What we are seeing. It is clearly visible that the pulp of the tomato fruit has a granular structure (4).

These are the cells of the pulp of the tomato fruit.

What we do: Examine the microslide under a microscope. Find individual cells and examine them at low magnification (10x6), and then (5) at high magnification (10x30).

What we are seeing. The color of the tomato fruit cell has changed.

A drop of water also changed its color.

Conclusion: The main parts of a plant cell are the cell membrane, the cytoplasm with plastids, the nucleus, and vacuoles. The presence of plastids in the cell is a characteristic feature of all representatives of the plant kingdom.

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. Construction of a magnifying glass and using it to examine the cellular structure of plants.

1. Examine a hand-held magnifying glass. What parts does it have? What is their purpose?

A hand magnifying glass 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 a distance at which the image of the object through the magnifying glass is most clear.

2. Examine with the naked eye the pulp of a semi-ripe tomato, watermelon, or apple. What is characteristic of their structure?

The pulp of the fruit is loose and consists of tiny grains. These are cells.

It is clearly visible that the pulp of the tomato fruit has a granular structure. The apple's pulp is slightly juicy, and the cells are small and tightly packed together. The pulp of a watermelon consists of many cells filled with juice, which are located either closer or further away.

3. Examine pieces of fruit pulp under a magnifying glass. Draw what you see in your notebook and sign the drawings. What shape do the fruit pulp cells have?

Even with the naked eye, or even better under a magnifying glass, you can see that the flesh of a ripe watermelon consists of very small grains, or grains. These are cells - the smallest “building blocks” that make up the bodies of all living organisms. Also, the pulp of a tomato fruit under a magnifying glass consists of cells similar to rounded grains.

Laboratory work No. 2. The structure of a microscope and methods of working with it.

1. Examine the microscope. Find the tube, eyepiece, lens, tripod with stage, mirror, screws. Find out what each part means. Determine how many times the microscope magnifies the image of the object.

Tube is a tube that contains the eyepieces of a microscope. An eyepiece is an element of the optical system facing the eye of the observer, a part of the microscope designed to view the image formed by the mirror. The lens is designed to construct an enlarged image with accurate reproduction of the shape and color of the object of study. A tripod holds the tube with an eyepiece and objective at a certain distance from the stage on which the material being examined is placed. The mirror, which is located under the object stage, serves to supply a beam of light under the object in question, i.e., it improves the illumination of the object. Microscope screws are mechanisms for adjusting the most effective 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. You should work with a microscope while sitting;

2. Inspect the microscope, wipe the lenses, eyepiece, mirror from dust with a soft cloth;

3. Place the microscope in front of you, slightly to the left, 2-3 cm from the edge of the table. Do not move it during operation;

4. Open the aperture completely;

5. Always start working with a microscope at low magnification;

6. Lower the lens to the working position, i.e. at a distance of 1 cm from the 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 illuminate the field of view as much as possible and evenly;

8. Place the microspecimen on the stage so that the object being studied is under the lens. Looking from the side, lower the lens using the macroscrew until the distance between the lower lens of the lens and the microspecimen becomes 4-5 mm;

9. Look into the eyepiece with one eye and rotate the coarse aiming screw towards yourself, smoothly raising the lens to a position at which the image of the object can be clearly seen. You cannot look into the eyepiece and lower the lens. The front lens may crush the cover glass and cause scratches;

10. Moving the specimen by hand, find the desired location and place it in the center of the microscope’s field of view;

11. After finishing work with high magnification, set the magnification to low, raise the lens, remove the specimen from the work table, wipe all parts of the microscope with a clean napkin, cover it with a plastic bag and put it in a cabinet.

3. Practice the sequence of actions when working 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. Use a mirror to shine light into the opening of the stage.

2. Place the prepared preparation on the stage and secure the slide with clamps.

3. Using the screw, smoothly lower the tube so that the lower edge of the lens is at a distance of 1-2 mm from the specimen.

4. Look into the eyepiece with one eye without closing or squinting the other. While looking through the eyepiece, use the screws to slowly lift the tube until a clear image of the object appears.

5. After use, put the microscope in its case.

Question 1. What magnifying devices do you know?

Hand magnifier and tripod magnifier, microscope.

Question 2. What is a magnifying glass and what magnification does it provide?

A magnifying glass is the simplest magnifying device. A hand magnifying glass consists of a handle and a magnifying glass, convex on both sides and inserted into a frame. It magnifies objects 2-20 times.

A tripod magnifying glass magnifies objects 10-25 times. Two magnifying glasses are inserted into its frame, mounted on a stand - a tripod. A stage 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 viewing tube, or tube, of this light microscope. At the upper end of the tube there 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, you can see an image of an object illuminated by this mirror.

Question 4. How to find out what magnification a microscope gives?

To find out how much the image is magnified when using a microscope, you need to multiply the number indicated on the eyepiece by the number indicated on the objective lens you are using. For example, if the eyepiece provides 10x magnification and the objective provides 20x magnification, then the total magnification is 10 x 20 = 200x.

Think

Why can't we study opaque objects using 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 stage and hit the lens system of the objective and eyepiece. And light does not pass through opaque objects, and therefore we will not see an image.

Tasks

Learn the rules of working with a microscope (see above).

Using additional sources of information, find out what details of the structure of living organisms can be seen with 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 been replaced by modern electron microscopes, which allow us to examine molecules and electrons. And an electron scanning 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.

Cellular structure of plant organisms students educational institutions studied in sixth grade. Biological laboratories equipped with observational equipment use an optical magnifying glass or microscopy. Cells of tomato pulp microscope are studied in practical classes and arouse genuine interest among schoolchildren, because it becomes possible, not in the pictures of a textbook, but to see with their own eyes the features of the microworld that are not visible to the naked eye with optics. The branch of biology that systematizes knowledge about the totality of flora is called botany. The subject of the description are also tomatoes, which are described in this article.

Tomato, according to modern classification, belongs to the dicotyledonous pynopetalous family of Solanaceae. A perennial herbaceous cultivated plant, widely used and grown in agriculture. They have a juicy fruit that is consumed by humans due to its high nutritional and taste qualities. From a botanical point of view, these are polyspermous berries, but in non-scientific activities, in everyday life, people often classify them as vegetables, which is considered erroneous by scientists. It is distinguished by a developed root system, a straight branching stem, and a multi-locular generative organ weighing from 50 to 800 grams or more. They are quite high in calories and healthy, increase the effectiveness of the immune system and promote the formation of hemoglobin. They contain proteins, starch, minerals, glucose and fructose, fatty and organic acids.

Preparation of a microslide for examination under a microscope.

The preparation must be microscoped using the bright field method in transmitted light. Fixation with alcohol or formaldehyde is not done; living cells are observed. The sample is prepared using the following method:

• Using metal tweezers, carefully remove the skin;
• Place a sheet of paper on the table, and on it a clean rectangular glass slide, in the center of which drop one drop of water with a pipette;
• Using a scalpel, cut off a small piece of flesh, spread it over the glass with a dissecting needle, and cover the top with a square cover slip. Due to the presence of liquid, glass surfaces will stick together.
• In some cases, tinting with a solution of iodine or brilliant green can be used to increase contrast;
• Viewing starts at the lowest magnification - a 4x objective and a 10x eyepiece are used, i.e. it turns out 40 times. This will ensure the maximum viewing angle, allow you to correctly center the microsample on the stage and quickly focus;
• Then increase the magnification to 100x and 400x. At larger zooms, use the fine focusing screw in 0.002 millimeter increments. This will eliminate image shake and improve clarity.

What organelles can be seen in tomato pulp cells under a microscope:

1. Granular cytoplasm - internal semi-liquid medium;
2. Limiting plasma membrane;
3. The nucleus, which contains genes, and the nucleolus;
4. Thin connecting threads - strands;
5. Single-membrane organelle vacuole responsible for secretion functions;
6. Crystallized chromoplasts of bright color. Their color is influenced by pigments - it ranges from reddish or orange to yellow;

Recommendations: educational models are suitable for examining tomatoes - for example, Biomed-1, Levenhuk Rainbow 2L, Micromed R-1-LED. At the same time, use the lower LED, mirror or halogen backlight.

1. Answer the question.

Why do I use magnifying devices?

• Answer: To study small objects.

Hand magnifier

2. Consider a hand-held magnifying glass. Write the names of its parts and the functions they perform.

3. Take pieces of tomato pulp (watermelon, apple). Examine them with the naked eye. What do you get out?

• Answer: Soft thin peel and seeds.

4. Examine the pieces with a magnifying glass. What do you see?

• Answer: Pulp cells.

5. Conclusion

• Answer: The magnifying glass is so strong that you can see cells that are not visible to the naked eye.

Light microscope

1) Examine the microscope. Find the main parts of the microscope. Using the textbook text and drawing, find out what their meaning is.

2) Familiarize yourself with the rules of working with a microscope. Learn to set the light, achieve good illumination of the field of view.

3) Check each other’s knowledge of the rules for using a microscope.

4) Determine how many times the microscope magnifies the image of the object. (300 times. Depends on the microscope)

5) Practice the sequence of actions when working with a microscope.