Biology lesson "plant cell structure". potato stick
The BBC Future columnist decided to find out more about the most popular root vegetable in many countries and about the properties that make one or another variety of it optimal for cooking some dishes and completely unsuitable for others ... Boiled, baked, fried or mashed - no matter how you cook potatoes, spoil it is, generally speaking, difficult.
There is something in the satiety of well-baked potatoes, in the crunch of potato chips, in the creamy tenderness of mashed potatoes, something that resonates with warmth not only in our taste buds, but also in the heart.
(According to the best mashed potatoes recipe I know, by the way, pre-melted butter should be added to boiled potatoes gradually and until it stops being absorbed.)
This is such a familiar food product for us that when preparing it, we often do not take into account the difference even between species that look different from each other.
Meanwhile, not every potato is suitable for frying in a deep fryer, and only certain varieties are good in a salad. At school lessons in home economics, they usually do not teach to distinguish potatoes by variety, and it all seems to us “on the same face”.
However, anyone who has tried the same variety both fried and boiled for salad knows perfectly well that there is no equality in the world of root vegetables either.
Varieties differ in their chemical composition and, accordingly, technological properties. So if you want to succeed in a potato dish, it is very important to choose tubers with the right characteristics.
To the deep fryer, for example, some types should not be allowed in any way. I recently witnessed this personally in my kitchen, and the alarm signals from the smoke detector dispelled my last doubts about the professional suitability of the kind of potato from which I tried in vain to make chips.
There are hundreds of different varieties of potatoes, and, according to nutritionists and breeders, tubers with a yellowish, brown, purple or red skin can be quite different from each other not only in appearance, but also in their chemical composition.
The main difference is in the percentage of starch, and according to this criterion, potatoes are divided into two main categories.
The first type - starchy (or mealy) - includes potatoes with high content starch (on average, about 22% of the mass of the tuber, according to the results of a study by Diana McComber, which is cited in her work by nutritionist Guy Crosby).
It is dry and flaky; upon heat treatment, it acquires a granular texture.
Craving crispy fried potatoes? Then try not to use the so-called waxy potato - with it you will not get the desired result. The exemplary representative of the starchy potato (at least in the USA) is the Russet variety, which has a reddish skin. It is ideal for frying. Its low water content means that when the chips come into contact with boiling oil, most of water boils away before a crust forms on the surface, and the remaining amount of moisture is just enough to ensure that the inside of each piece is thoroughly steamed.
The numerous starch molecules in the Russet potato help to brown the edges of the cut slices, and because the flesh is quite dense, the chips are not in danger of being undercooked due to the oil that has penetrated deep inside.
Starchy potatoes are also suitable for mashing and baking.
Comparing the two types of cooked potatoes under a microscope, the researchers found interesting differences.
But woe to the cook who boils potatoes with a high starch content for salad - having absorbed water, it will quickly fall apart.
In a salad, it is better to put potatoes of wax varieties, which have a thin skin and watery pulp. It contains only about 16% starch, and when cooked, the tubers retain the integrity of the tissue.
Many of the varieties belonging to this category, by the way, have beautiful names, often formed from female names: "Charlotte", "Anya", "Kara" ...
Comparing starchy and waxy types of cooked potatoes under a microscope, the researchers found interesting differences between the two.
Unlike wax varieties, floury starch molecules tend to suck moisture from neighboring tissue areas.
That is why starchy varieties are perceived by us as dry and crumbly, and we recognize waxy ones by their wateriness.
Under a microscope, you can see that the cells that make up the tissue of starchy potatoes break up into small groups, like crumbs, when cooked. shortbread biscuits, and the tuber loses its structural unity. Waxy potatoes, on the contrary, keep their shape perfectly. This is explained by the fact that in boiled mealy potatoes, the breakdown of starch grains contained in the cells begins at lower temperatures than in wax potatoes (the difference is almost 12C).
As a result, in the first type, intercellular bonds are weakened faster, and cell walls are destroyed at earlier stages of the heat cooking process.
Not every type of potato is also suitable for beloved by many mashed potatoes.
These properties of potatoes are important to consider when choosing a variety that matches a particular culinary task. However, this knowledge may be needed not only at home in the kitchen.
Raymond Wheeler's article, Potatoes for Human Life Support in Space, talks about experiments to grow potatoes in zero gravity.
For manned interplanetary flights, the ability to grow edible fruits will be key, and for decades, experiments have been conducted to find out how potatoes and other crops behave in growth chambers under different external conditions. Varieties that are classified as starchy types are being tested , and to wax, and, apparently, chefs will not be able to get rid of the problem of choice even in space.
However, those astrochefs who fly to Jupiter will be rewarded - according to some scientists, chips cooked in the gravity of this planet have the perfect crunchiness.
But we have other laws of attraction on Earth. And then the Chinese government unexpectedly announced that the potato will now become a staple in the Chinese diet, along with rice and wheat.
Until now, potatoes in China have been used mainly as a seasoning for rice, and not as a full-fledged side dish.
In Chinese cuisine, finely chopped tubers are usually marinated in vinegar and then fried with hot pepper Chile. Another popular cooking method is to stew with the addition of soy sauce and anise.
However, the promised status of the main product does not mean at all that with its acquisition, the potato will take a more prominent position on the Chinese table. It is unlikely that baked "Russet" will replace traditional rice.
According to whatsonweibo.com observers, which covers the main trends of Chinese media, including social media, China’s culinary life will most likely include not whole potato dishes, but potato flour products, such as noodles and buns.
If so, then Chinese consumers will not have to rack their brains over choosing the right variety of potatoes, the choice will be made for them by the manufacturer.
Municipal budgetary educational institution
secondary school No. 8 in Poronaysk
RESEARCH
POTATO STICK
Performed: ,
Head: biology teacher
Poronaysk, 2013
Page
INTRODUCTION
There is practically no place on Earth where bacteria are found. They even live in the ice of Antarctica and in hot springs. Especially a lot of them in the soil. 1 gram of soil can contain hundreds of millions of bacteria. Most bacteria die at a temperature of +65–100 °C, but the spores of some of them tolerate heating up to +140 °C and cooling down to -253 °C.
Bacteria are relatively simple microscopic organisms. They are usually unicellular. Bacteria do not have a nucleus separated from the cytoplasm by a membrane. Such organisms are called prokaryotes. Bacterial cells are much smaller than plant or animal cells. On average, it is 0.5–5 microns. E. coli, for example, has a cell length of 1 to 6 microns. The largest of the bacteria reach a size of 750 microns, i.e. 0.75 mm. The smallest of them have sizes from 0.1 to 0.25 microns.
Bacteria was first seen through an optical microscope and described in the 17th century by Anthony van Leeuwenhoek. In the middle of the XIX century. Louis Pasteur discovered the pathogenic properties of bacteria, and also associated them with many economic important processes(e.g. food spoilage). Medical microbiology was developed in the writings of Robert Koch. In 1905 he was awarded Nobel Prize for tuberculosis research. Bacteriology is the study of bacteria.
Objective: Using the description of growing a microbiological culture of potato sticks, obtain and observe the potato stick bacterium.
Tasks:
1. Find a description of the method of growing a culture of potato sticks (search on the Internet).
2. Prepare equipment and materials for laboratory work.
3. Conduct observation of potato bacterium.
Methods of work: search, experimental.
I. KINGDOM OF BACTERIA
1. Characteristics of the structure of a bacterial cell
Bacterial cells are extremely small. Therefore, the study of their structure began only with the invention of the electron microscope. Traditionally, there is a division of bacteria according to the shape of the cell.
There are spherical cocci (for example, streptococci, staphylococci), rod-shaped bacilli (for example, Escherichia coli), vibrios curved in the form of a comma (for example, vibrio cholerae), spiral-shaped spirilli. Very often, bacteria form clusters in the form of long curved chains, groups and films.
Some bacteria have flagella - up to 1000. Among the bacteria there are mobile and immobile forms. Motile bacteria move by flagella or gliding. Many aquatic bacteria can sink or float, changing their density by releasing gas bubbles.
Bacteria actively move in the direction determined by certain stimuli. This phenomenon is called taxis. Most bacteria are colorless. Some are purple or green.
Bacterial cells are surrounded by a dense membrane, thanks to which they retain a constant shape. The composition and structure of the cell walls of bacteria differ significantly from those of plants and animals.
Outside, the shell can also be covered with a mucous capsule. I repeat once again that bacteria do not have a formed nucleus, and the hereditary material is distributed in the cytoplasm.
Picture 1 . The structure of a bacterial cell
2. bacterium potato stick
Soil microbe - spore-forming potato stick - is widely distributed in nature.
This microbe often causes potato (it is also called "viscous") bread disease. First, it enters the grain (during its ripening and threshing), and then into flour. Potato stick spores are heat-resistant, they do not die even when baking bread, therefore, in the future, under favorable conditions, they begin to show their viability. The optimal conditions for the reproduction of potato sticks are: an environment close to neutral (pH about 7.0), a temperature of 35-40 ° C, a slightly increased humidity of the bread. And here's what's interesting - potato disease is not observed in rye bread, since its acidity is much higher than that of wheat. Wheat bread "gets sick" only in the hot season, if it is stored in stuffy, poorly ventilated rooms, stacked hot in bulk or in high stacks. The development of the disease is also facilitated by the increased humidity of wheat bread with low acidity.
What is the manifestation of a "viscous" disease? In the crumb of bread or other moist flour products (biscuit cake, gingerbread), changes occur after a while. At the break of the loaf begins to feel weak bad smell, which quickly intensifies and becomes similar to the smell of valerian or overripe melon. The crumb darkens, it becomes soft, then fibrousness appears in it, and, finally, it turns into a sticky, viscous dirty brown mass with a sharp bad smell reminiscent of the smell of rotting fruit. This bread is not suitable for consumption.
II. GROWING A POTATO STICK CULTURE
1. Method for growing a culture of potato sticks
Potato stick develops on potatoes. To obtain it, you should take an unpeeled potato, cut into small cubes, place in a small bowl, pour water to the top and heat to 80 ° C. To infect the prepared nutrient medium with spores of potato sticks, you need to lower a small lump of soil into it, then put it in warm place for 3 days. During this time, the potato stick multiplies in large numbers, its size reaches 15 microns.
2. Culture Observation Potato Stick
Laboratory work "Preparing a nutrient medium and growing a potato stick culture"
Equipment:
Flasks (2 pcs.)
Hot water.
Cold water.
Potato tuber, soil
Knife, spatula.
Description of work:
We grew bacteria called potato bacillus. To begin with, we took two flasks, then cut the potatoes. Then we placed several pieces of unpeeled potatoes into the flasks. We poured into one flask - hot water and put it in a warm room, and poured cold water into another flask and put it in a cold room. One day later we poured in some soil. Then, two days later, the water in two flasks became a little cloudy and mold with foam appeared on the surface of the water.
Preparation of micropreparations potato stick
Equipment:
1. Slides, coverslips, pipette, napkin, glass.
2. Cleaned the coverslips.
3. From the flask where the culture was located, the solution with microorganisms was poured into a glass.
4. A drop of culture was placed on a glass slide and covered with a coverslip.
5. Examined micropreparations under a microscope. Made microphotographs on Altami school USB microscope.
font-size:12.0pt;line-height:115%;font-family:" times new roman font-weight:normal>Pattern 2 . Micrograph of potato stick culture (methyl orange). 400 times magnification
Figure 3 . Micrograph of a potato stick (litmus)
CONCLUSION
Thus, the purpose of the work has been successfully achieved. To grow a potato stick culture, you need: potatoes, soil, two flasks, hot and cold water, knife, teapot. To study bacteria you need microscopes better than an electron microscope.
To prevent the development of potato disease of wheat bread, it is necessary to create unfavourable conditions for the development of potato sticks. Much depends on compliance technological process in the production of bread and its proper storage. But buyers need to remember a few rules:
1. Buy bread and bakery products only in stores where the conditions for storing these products are created (ventilated warehouses, trading floors with air conditioning, specially equipped shelves or showcases for the sale of rolls and loaves).
2. Calculate the volume of bought bread only for the next meal, or at least for a period not exceeding a twelve-hour period of time.
3. Store bakery products in fabric ("breathable") bags, and if the air temperature in the apartment is more than 20º C, then in the refrigerator.
4. In the hot season, switch to wholemeal bread, which is less susceptible to potato disease.
LIST OF USED LITERATURE
1. Sokolov, animals, first volume [Text] / . – M.: Enlightenment, 1984. – 463 p.
2. Gilyarov, dictionary of a young biologist [Text] / . - M.: Pedagogy, 1896. - 352 p.
3. Wikipedia [Electronic resource] /
Stanislav Yablokov, Yaroslavsky State University them. P. G. Demidova
For two years now I have been observing the microworld at home, and for a year I have been filming it with a camera. During this time, I saw with my own eyes how blood cells look, scales falling from the wings of butterflies, how the heart of a snail beats. Of course, a lot could be learned from textbooks, video lectures and thematic sites. But at the same time there would be no feeling of presence, proximity to what is not visible to the naked eye. That these are not just words from a book, but personal experience. An experience that is available to everyone today.
Onion peel. Magnification 1000×. Stained with iodine. The photo shows the cell nucleus.
Onion peel. Magnification 1000×. Stained with azure-eosin. In the photograph, a nucleolus is visible in the nucleus.
Potato. Blue spots are grains of starch. Magnification 100×. Stained with iodine.
Film on the back of a cockroach. Magnification 400×.
Plum peel. Magnification 1000×.
Bibionid bug wing. Magnification 400×.
The wing of a hawthorn butterfly. Magnification 100×.
Scales from the wings of a moth. Magnification 400×.
Chloroplasts in grass cells. Magnification 1000×.
Baby snail. Magnification 40×.
Clover leaf. Magnification 100×. Some cells contain a dark red pigment.
Strawberry leaf. Magnification 40×.
Chloroplasts in algal cells. Magnification 1000×.
Blood smear. Stained with azure-eosin according to Romanovsky. Magnification 1000×. In the photo: eosinophil on the background of erythrocytes.
Blood smear. Stained with azure-eosin according to Romanovsky. Magnification 1000×. In the photo: on the left - a monocyte, on the right - a lymphocyte.
What to buy
The theater begins with a hanger, and microphotography with the purchase of equipment, and above all, a microscope. One of its main characteristics is the set of available magnifications, which are determined by the product of the magnifications of the eyepiece and the objective.
Not every biological specimen is good for viewing at high magnification. This is due to the fact that the greater the magnification of the optical system, the smaller the depth of field. Consequently, the image of uneven surfaces of the drug will be partially blurred. Therefore, it is important to have a set of objectives and eyepieces that allows you to observe with a magnification from 10-20 to 900-1000×. Sometimes it is justified to achieve a magnification of 1500x (15x eyepiece and 100x objective). A larger magnification is meaningless, since the wave nature of light does not allow you to see finer details.
The next important point is the type of eyepiece. With how many eyes do you want to view the image? Usually, monocular, binocular and trinocular varieties are distinguished. In the case of a monocular, you will have to squint, tiring the eye during prolonged observation. Look into the binocular with both eyes (it should not be confused with a stereo microscope, which gives a three-dimensional image). For photo and video filming of micro-objects, you will need a “third eye” - a nozzle for installing equipment. Many manufacturers produce special cameras for their microscope models, but you can also use a regular camera by purchasing an adapter for it.
Observation at high magnifications requires good illumination due to the small aperture of the objectives. The light beam from the illuminator, converted in an optical device - a condenser, illuminates the preparation. Depending on the nature of the illumination, there are several methods of observation, the most common of which are the methods of light and dark fields. In the first, the simplest, familiar to many from school, the preparation is illuminated evenly from below. In this case, through the optically transparent parts of the preparation, light propagates into the lens, and in opaque parts it is absorbed and scattered. On a white background, a dark image is obtained, hence the name of the method. With a dark-field condenser, everything is different. The light beam coming out of it has the shape of a cone, the rays do not fall into the lens, but are scattered on an opaque preparation, including in the direction of the lens. As a result, a light object is visible on a dark background. This observation method is good for studying transparent low-contrast objects. Therefore, if you plan to expand the range of observation methods, you should choose microscope models that provide for the installation of additional equipment: a dark-field condenser, a dark-field diaphragm, phase contrast devices, polarizers, etc.
Optical systems are not ideal: the passage of light through them is associated with image distortions - aberrations. Therefore, they try to make lenses and eyepieces in such a way that these aberrations are eliminated as much as possible. All this affects their final cost. For reasons of price and quality, it makes sense to buy plan achromatic lenses for professional research. Strong objectives (for example, 100× magnification) have a numerical aperture greater than 1 when using immersion, high refractive oil, glycerol solution (for UV), or just water. Therefore, if, in addition to “dry” lenses, you also take immersion lenses, you should take care of the immersion liquid in advance. Its refractive index must necessarily correspond to a particular lens.
Sometimes you should pay attention to the design of the stage and handles to control it. It is worth choosing the type of illuminator, which can be either an ordinary incandescent lamp or an LED, which is brighter and heats up less. Microscopes also have individual characteristics. Each additional option is an addition to the price, so the choice of model and configuration is up to the consumer.
Today, they often buy inexpensive microscopes for children, monoculars with a small set of objectives and modest parameters. They can serve as a good starting point not only for the study of the microcosm, but also for familiarization with the basic principles of the microscope. After that, the child should already buy a more serious device.
How to watch
You can buy far from cheap sets of finished drugs, but then the feeling of personal participation in the study will not be so bright, and they will get bored sooner or later. Therefore, care should be taken both about the objects for observation, and about available means for drug preparation.
Observation in transmitted light assumes that the object under study is sufficiently thin. Even the peel of a berry or fruit is too thick, so sections are examined under microscopy. At home, they are made with ordinary razor blades. In order not to crush the peel, it is placed between pieces of cork or filled with paraffin. With some skill, you can achieve a slice thickness of several cell layers, and ideally, you should work with a monocellular layer of tissue - several layers of cells create a fuzzy, chaotic image.
The test preparation is placed on a glass slide and, if necessary, covered with a coverslip. You can buy glasses in a medical equipment store. If the preparation does not adhere well to the glass, it is fixed by slightly moistening with water, immersion oil or glycerin. Not every drug immediately opens its structure, sometimes it needs “help” by tinting its shaped elements: nuclei, cytoplasm, organelles. Good dyes are iodine and greenery. Iodine is a fairly versatile dye, it can be used to color wide range biological preparations.
When going out into nature, you should stock up on jars for collecting water from the nearest reservoir and small bags for leaves, dried insect residues, etc.
What to watch
The microscope has been purchased, the instruments have been purchased - it's time to start. And you should start with the most accessible - for example, onion peel. Thin in itself, tinted with iodine, it reveals clearly distinguishable cell nuclei in its structure. This experience, familiar from school, should be done first. Onion peel should be poured with iodine for 10-15 minutes, then rinsed under running water.
In addition, iodine can be used to color potatoes. The cut must be made as thin as possible. Literally 5-10 minutes of his stay in iodine will show layers of starch, which will turn blue.
The balconies often accumulate a large number of corpses of flying insects. Do not rush to get rid of them: they can serve as valuable material for research. As you can see from the photos, you will find that insects have hairs on their wings that protect them from getting wet. The high surface tension of water does not allow the drop to "fall" through the hairs and touch the wing.
If you have ever touched the wing of a butterfly or a moth, then you probably noticed that some kind of “dust” flies off it. The pictures clearly show that this is not dust, but scales from the wings. They have different shape and come off fairly easily.
In addition, using a microscope, you can study the structure of the limbs of insects and spiders, consider, for example, chitinous films on the back of a cockroach. And with proper magnification, make sure that such films consist of tightly fitting (possibly fused) scales.
Not less than interesting object for observation - the peel of berries and fruits. However, either its cellular structure may be indistinguishable, or its thickness will not allow for a clear image. One way or another, you have to make a lot of attempts before you succeed. good drug: iterate over different varieties grapes to find one with interestingly shaped skin colorants, or cut a few plum skins to get a monocellular layer. In any case, the reward for the work done will be worthy.
Grass, algae, leaves are even more accessible for research. But, despite the ubiquity, choosing and preparing a good drug from them can be difficult. The most interesting thing about greenery is, perhaps, chloroplasts. Therefore, the cut must be extremely thin.
Acceptable thickness is often green algae found in any open water. You can also find floating algae and microscopic aquatic life- fry of snails, daphnia, amoebas, cyclops and slippers. A small baby snail, optically transparent, allows you to see your own heartbeat.
self explorer
After studying simple and affordable preparations, you will want to complicate the technique of observation and expand the class of objects under study. This will require both special literature and specialized tools, which are different for each type of object, but still have some universality. For example, the Gram stain method, when different types bacteria begin to differ in color, it can be applied to other, non-bacterial cells. Close to it is the method of staining blood smears according to Romanovsky. On sale there is both a ready-made liquid dye and a powder consisting of its components - azure and eosin. They can be bought in specialized stores or ordered online. If you can’t get the dye, you can ask the laboratory assistant who does your blood test at the clinic for a glass with a stained smear.
Continuing the topic of blood research, we should mention the Goryaev camera - a device for counting the number of blood cells and assessing their size. Methods for examining blood and other fluids using the Goryaev camera are described in special literature.
AT modern world, where a variety of technical means and devices are within walking distance, everyone decides for himself what to spend money on. It can be an expensive laptop or a TV with an exorbitant diagonal size. There are also those who take their eyes off the screens and direct it far into space, acquiring a telescope. Microscopy can become an interesting hobby, and for some even an art, a means of self-expression. Looking into the eyepiece of a microscope, one penetrates deep into that nature, of which we ourselves are a part.
"Science and Life" about microphotography:
Microscope "Analit" - 1987, No. 1.
Oshanin S. L. With a microscope at the pond. - 1988, No. 8.
Oshanin S. L. Invisible to the world a life. - 1989, No. 6.
Miloslavsky V. Yu. - 1998, No. 1.
Mologina N. . - 2007, No. 4.
Glossary for the article
Aperture- the effective opening of the optical system, determined by the dimensions of mirrors, lenses, diaphragms and other parts. The angle α between the extreme rays of a conical light beam is called the angular aperture. Numerical aperture A = n sin(α/2), where n is the refractive index of the medium in which the object of observation is located. The resolution of the device is proportional to A, the illumination of the image is A 2 . To increase the aperture, immersion is used.
Immersion- a transparent liquid with a refractive index n > 1. The preparation and the microscope objective are immersed in it, increasing its aperture and thereby increasing the resolution.
plan achromatic lens- A chromatic aberration corrected lens that produces a flat image across the entire field. Ordinary achromats and apochromats (aberrations corrected for two and three colors, respectively) give a curvilinear field that cannot be corrected.
Phase contrast- a method of microscopic research based on a change in the phase of a light wave that has passed through a transparent preparation. The oscillation phase is not visible with a simple eye, so special optics - a condenser and a lens - turn the phase difference into a negative or positive image.
Monocytes- one of the forms of white blood cells.
Chloroplasts- green organelles of plant cells responsible for photosynthesis.
Eosinophils- blood cells that play a protective role in allergic reactions.
MINISTRY OF EDUCATION, SCIENCE AND YOUTH
REPUBLIC OF CRIMEA
CRIMEAN REPUBLICAN NON-SCHOOL EDUCATIONAL INSTITUTION
"CENTER FOR ECOLOGICAL AND NATURALISTIC CREATIVITY
STUDENT YOUTH»
OPEN LABORATORY LESSON:
STUDYING THE STRUCTURE OF THE PLANT CELL
Developed by:
Kuznetsova Elena Yurievna, methodologist of the highest category,
head of the educational team
"Fundamentals of Biology", Ph.D.
Simferopol, 2014
Topic of the lesson: Examining the structure of a plant cell under a microscope
Target: to consolidate and deepen knowledge about the structural features of a plant cell.
Lesson type: laboratory lesson
Used forms and methods: conversation, testing, work with microscopic equipment.
Introduced concepts: cell wall, nucleus, vacuole, chlorophyll grains, starch grains, plasmolysis, deplasmolysis.
Materials and equipment: microscopes with accessories, water, 5% saline solution, juicy onion scales, wallisneria leaf, potatoes.
Lesson plan:
Knowledge update. Testing.
The structure of the microscope and work with microscopic equipment.
Method for the manufacture of temporary preparations. Preparation of the preparation of the epidermis of juicy onion scales, microscopy.
Setting up an experiment. The phenomena of plasmolysis and deplasmolysis.
Starch grains of potato pulp.
Chlorophyll grains of Vallisneria leaf.
Lesson progress:
1. Knowledge update. Testing.
Test tasks on the topic "Structure of a plant cell"
1 What organelles are absent in an animal cell:
a) mitochondria b) plastids c) ribosomes d) nucleus
2. In which organelles is primary starch formed:
3. In which organelles does oxidative phosphorylation occur:
a) mitochondria b) chloroplasts c) nucleus d) ribosomes
4. Which group of lipids forms the basis cell membranes:
a) neutral fats b) phospholipids c) waxes d) carotenoids
5. A plant cell, unlike an animal cell, has:
a) endoplasmic reticulum b) Golgi complex
c) vacuole with cell sap d) mitochondria
6. The granular endoplasmic reticulum differs from the agranular one by the presence of:
a) centrosomes b) lysosomes c) ribosomes d) peroxisomes
7. Mitochondria are called the energy stations of the cell. This name of organelles is associated with their function:
a) protein synthesis b) intracellular digestion
c) transport of gases, in particular oxygen d) ATP synthesis
8. The supply of cell nutrients is contained in:
a) nucleus b) chloroplasts c) nucleolus d) leukoplasts
9. In which of these organelles is photophosphorylation carried out:
The structure of the microscope and work with microscopic equipment.
The structure of the mechanical device of the microscope includes a tripod, an object table, an illumination system, a rack, a micrometric screw, a tube and a revolver.
The object of study is placed on the subject table. A lighting device is located under the subject table; it includes a two-sided mirror. Collecting the rays coming from the light source, the concave mirror reflects them in the form of a beam of rays, which is directed to the object through a hole in the center of the table.
The optical system of a microscope consists of an eyepiece, an objective and a tube connecting them. Lenses are of two kinds: for small and large magnification of the image. If it is necessary to change the lens, they use a revolver - a concave round plate with lenses screwed into it. All optical system mobile: by raising it by rotating the rack counterclockwise or lowering it by rotating it clockwise, they find a position at which the object becomes visible to the observer.
The structure of the microscope:
1 - eyepiece; 2- revolver for changing lenses; 3 - lens;
4 - rack for rough pickup;
5 - micrometer screw for precise aiming; 6 - object table; 7 - mirror; 8 - condenser
3. Methodology for the manufacture of temporary preparations. Preparation of the preparation of the epidermis of juicy onion scales, microscopy.
Prepare a glass slide with a drop of water;
From the fleshy scales of the bulb, cut a small piece (about 1 cm 2) from the inner (concave) side with a scalpel, remove the transparent film (epidermis) with tweezers or a needle. Put in the prepared drop and apply a coverslip;
To study the structure of the cell at low and high magnification;
Draw one cell. Mark the cell wall, the parietal layer of the cytoplasm, the nucleus, the vacuole with cell sap.
The structure of a plant cell
Setting up an experiment. The phenomena of plasmolysis and deplasmolysis.
Prepare a new preparation from onion skins. Remove the specimen from the microscope stage, replace the water under the coverslip with 5% common salt (NaCl) solution. The coverslip can be left on: put a drop of the solution near it so that it merges with the water under the glass, and then attach a strip of filter paper on the opposite side. The solution will go under the coverslip and replace the water.
We placed the cell in a hypertonic solution, i.e. the concentration of the solution outside the cell exceeds the concentration of substances in the cell. At the same time, water leaves the vacuole, the volume of the vacuole decreases, the cytoplasm moves away from the membrane and contracts along with the vacuole. There is a phenomenon plasmolysis .
Depending on the degree of concentration of the solution taken, the speed of processing and the shape of the cell, the patterns of plasmolysis may be different.
If plasmolysis proceeds slowly in a weak solution, the contents of the cell most often first move away from the membrane at the ends of the cell (corner plasmolysis), may be affected large plots cells (concave plasmolysis). The contents of the cell can separate into one round drop (convex plasmolysis). When the cell is exposed to a stronger solution, plasmolysis proceeds faster, and there are pictures of convulsive plasmolysis, in which the contents remain connected to the membrane by numerous Hecht threads.
The phenomenon of plasmolysis
A - Plant cell:
1 - cell wall;
2 - vacuole;
3 - parietal layer of the cytoplasm;
4 - core.
B - D - Plasmolysis:
B - corner;
B - concave;
G - convex;
D - convulsive
5 - Hecht threads
During plasmolysis, the cell remains alive. Moreover, an indicator of cell viability can be its ability to plasmolysis. When the cell is returned to clean water comes deplasmolysis , at which the cell absorbs water again, the vacuole increases in volume, and the cytoplasm, pressing against the membrane, stretches it.
sketch different stages plasmolysis with appropriate designations.
Carry out the phenomenon of deplasmolysis by displacing the salt solution from under the coverslip with water and filter paper.
Starch grains of potato pulp
starch grains - the main type of reserve nutrients of a plant cell. They are formed only in plastids of living cells, in their stroma. Grains of assimilation (primary) starch are deposited in chloroplasts in the light, which are formed with an excess of photosynthesis products - sugars.
Prepare a preparation of starch grains from potato pulp. For this purpose, squeeze the juice of the pulp of a potato tuber onto a glass slide into a drop of water. Examine under a microscope, draw.
Starchy potato grains
Vallisneria leaf chlorophyll grains
Prepare a preparation from a Vallisneria leaf, placing rather large cells of the lower third of the leaf blade in the center of the field of view, not far from the midrib. Examine this area under high magnification, sketch the chloroplasts.
Chloroplasts in Vallisneria leaf cells
Lesson conclusions:
Identify the differences between plant and animal cells;
Establish patterns of osmotic phenomena in the cell.
Homework:
Solve the crossword Cell structure»
Crossword "Cell structure"
Horizontally: 2 . Liquid mobile contents of the cell. 5 . The main organelle of the cell. 8 . Component microscope. 10 . unit of a living organism. 12 . A simple magnifying device. 13 . A tube in a microscope with magnifying glasses inserted. 16 . Microscope maker. 18 . Physiological process inherent in a living cell. 19 . On which preparations are prepared. 22 . The area between cells with destroyed intercellular substance filled with air.
Vertically: 1 . Oculus ( lat.). 3 . Complicated optical instrument. 4 . A thin area in the cell membrane. 6 . The main structure of the nucleus. 7 . Cell cavity filled with cell sap. 9 . The part at the upper end of the microscope tube, consisting of a frame and two magnifying glasses. 11 . The part of the microscope to which the tube is attached. 14 . cell cover. 15 . Small bodies in the cytoplasm of a plant cell. 17 . Part of the bulb from which the drug is prepared. 20 . The part of the microscope located at the lower end of the tube. 21 . aquatic plant, in the leaf cells of which you can see the movement of the cytoplasm.
The tissue (pulp) of potatoes, vegetables and fruits consists of thin-walled cells that grow approximately equally in all directions. This tissue is called parenchyma. The contents of individual cells is a semi-liquid mass - the cytoplasm, into which various cellular elements (organelles) are immersed - vacuoles, plastids, nuclei, starch grains, etc. (Fig. 9.2). All cell organelles are surrounded by membranes. Each cell is covered with a shell, which is the primary cell wall.
The shells of each two neighboring cells are fastened with the help of the middle plates, forming the backbone of the parenchymal tissue (Fig. 9.3).
Contact between the contents of the cells is carried out through plasmodesmata, which are thin cytoplasmic strands passing through the membranes.
The surface of individual specimens of vegetables and fruits is covered with an integumentary tissue - epidermis (fruits, ground vegetables) or periderm (potatoes, beets, turnips, etc.).
Since fresh vegetables contain a significant amount of water, all the structural elements of their parenchymal tissue are hydrated to one degree or another. Water as a solvent has an important effect on the mechanical properties of plant tissue. By hydrating to some extent hydrophilic compounds, it plasticizes the structure of the walls and middle plates. This provides a sufficiently high turgor pressure in the tissues.
Turgor is a state of tension arising from the pressure of the contents of the cells on their elastic membranes and the pressure of the membranes on the contents of the cells.
Turgor pressure can decrease, for example, when vegetables and fruits wither or dry out, or increase, which is observed when wilted vegetables are immersed in water. This property of vegetables and fruits can be taken into account in their culinary processing. So, potatoes and root crops with a weakened tour-mountain before mechanical cleaning it is recommended to soak for several hours to reduce processing time and reduce waste.
Rice. 9.2. The structure of a plant cell
Rice. 9.3. Plant tissue wall:
1 -- middle plate; 2 - plasmalemma.
Magnification x 45000 (according to J.-C. Roland, A. Seleshi, D. Seleshi)
The vacuole is the largest element located in the center of the cell. It is a kind of bubble filled with cell sap, and is the most hydrated element of the vegetable and fruit parenchyma cell (95 ... 98% water). The composition of the dry residue of cell sap includes, in one amount or another, almost all water-soluble nutrients.
The main mass of sugars contained in potatoes, vegetables and fruits in a free state, soluble pectin, organic acids, water-soluble vitamins and polyphenolic compounds is concentrated in vacuoles.
The cell sap contains approximately 60 ... 80% of minerals from their total amount in vegetables and fruits. Salts of monovalent metals (potassium, sodium, etc.) are almost completely concentrated in the cell sap. Salts of calcium, iron, copper, magnesium are contained in it somewhat less, since they are part of other tissue elements.
Cell sap contains both free amino acids and soluble proteins, which form solutions of relatively low concentration in vacuoles.
A thin layer of cytoplasm with other organelles occupies a near-wall position in the cell. The cytoplasm consists mainly of proteins, enzymes and a small amount of lipids (the ratio of proteins and lipids is 90:1). In the cytoplasm, as in vacuoles, they are in the form of a solution, but more concentrated (10%).
Plastids are organelles that are present only in plant cells. The most typical of these are chloroplasts, which contain chlorophyll. Under certain physiological conditions, plastids do not form chlorophyll; in these cases, they produce either proteins (proteoplasts) or lipids and pigments (chromoplasts), but most often such plastids perform reserve functions, and then starch (amyloplasts) accumulates in them, so plastids are colored and colorless. The latter are called leukoplasts.
The composition of chloroplasts, in addition to chlorophyll, includes proteins and lipids in a ratio of 40:30, as well as starch grains.
During the development of chromoplasts, large globules or crystals containing carotenoids, including carotenes, are formed. The presence of these pigments in green vegetables and some fruits (gooseberries, grapes, renklod plums, etc.) causes different shades of their green-yellow color. Carotenes give a yellow-orange color to carrots, turnips, etc. However, orange color does not always indicate their high content in fruits and vegetables; for example, the color of oranges, tangerines is due to another pigment - cryptoxanthin. At the same time, the relatively high content of carotene in green vegetables can be masked by chlorophyll.
Amyloplasts are filled mainly with large starch granules. It should be noted that in plant cells, all the starch grains contained in them are located in a space limited by the shell of amyloplasts or other plastids.
The cell nucleus contains chromatin (despiralized chromosomes), consisting of DNA and basic proteins (histones), and nucleoli rich in RNA.
Membranes are an active molecular complex capable of exchanging substances and energy.
The cytoplasm at the border with the cell wall is covered with a simple membrane called the plasmalemma. The outer edge of the plasmalemma can be seen when examining plant tissue preparations treated with a concentrated saline solution under a microscope. Due to the difference between the osmotic pressure inside the cell and outside it, water moves from the cell to environment, causing plasmolysis - separation of the cytoplasm from the cell membrane. Similarly, plasmolysis can be induced by treating sections of plant tissue with concentrated solutions of sugars or acids.
Cytoplasmic membranes regulate cell permeability by selectively retaining or passing molecules and ions of certain substances into and out of the cell.
The vacuole, like the cytoplasm, is also surrounded by a simple membrane called the tonoplast.
Main structural components membranes - proteins and polar lipids (phospholipids). There are various types of structure of the cytoplasmic membrane: three-layer (from two layers of protein with a biomolecular layer of lipids), granular (from particles whose diameter is about 100 10-10 m, or from smaller particles - subunits). At present, the membrane is considered as a liquid structure penetrated by proteins.
The surface of nuclei, plastids and other cytoplasmic structures is covered with a double membrane consisting of two rows of simple membranes separated by a perinuclear space. These membranes also prevent mixing of the contents of two neighboring organelles. Individual substances pass from one organelle to another only in strictly defined quantities necessary for the flow of physiological processes in tissues.
Cell walls in combination with the middle plates are called cell walls. Unlike membranes, they are characterized by complete permeability.
Cell walls make up 0.7 ... 5.0% of the fresh weight of vegetables and fruits. So, in vegetables of the fruit group, for example, in zucchini, their number does not exceed 0.7%. In leafy vegetables - white cabbage, lettuce, spinach - about 2%. Root crops differ in the highest content of cell walls - 2 ... 4%.
The composition of the cell walls mainly includes polysaccharides (80 ... 95%) - cellulose, hemicelluloses and protopectin, therefore they are often called cell wall carbohydrates. The composition of the cell membranes includes all of the above polysaccharides. It is believed that the middle plates consist mainly of acidic polysaccharides (protopectin), which play the role of an intercellular cementing substance, which is sometimes accompanied by protein compounds, and in the oldest tissues - lignin.
Tab.9.1. The content of extensin and hydroxyproline
in the cell walls of some plant foods(%)
In addition to carbohydrates, the cell walls contain nitrogenous substances, lignin, lipids, waxes, and minerals.
From nitrogenous substances in the cell walls of plant tissue, structural protein extensions - a polymer from the group of glycoproteins, the protein part of which is associated with carbohydrates - arabinose and galactose residues. Molecular mass the protein part of such macromolecules is 50,000, the extension has the form of a rigid rod, 50% consists of hydroxyproline. The cell wall contains several protein fractions that differ in the content of hydroxyproline.
Extensions in some respects resemble the protein collagen, which performs similar functions in animal tissues. The content of extensin and hydroxyproline in the cell walls of various vegetables and potatoes is not the same (Table 9.1). The cell walls of a potato consist of about 1/5 of extensin. In the cell walls of root crops, it is contained 2 times less than in the cell walls of potatoes; in the cell walls of melon, the content of extensin does not exceed 5%.
The ratio of carbohydrates and extensin in cell walls depends on the type of plant tissue. The cell walls of many plant foods are about 1/3 cellulose, 1/3 hemicellulose, and 1/3 pectin and protein. In the cell walls of tomatoes, there is another 1:1 ratio between carbohydrates and protein.
Lignin is a complex natural polymer that forms the cell walls of plants. It plays the role of an encrusting substance that holds together cellulose and hemicellulose fibers. It is covalently bound to hemicellulose polysaccharides (xplan), pectins and protein. The content of lignin in plant tissues depends on their type and degree of lignification. A significant amount of lignin is contained in the cell walls of beets, carrots, less accumulates in white cabbage.
Due to the fact that the softening of potatoes, vegetables and fruits, which occurs during their thermal cooking, is associated with the destruction of cell walls, it seems appropriate to consider the structure of the latter.
According to modern concepts, the cell wall is a highly specialized aggregate consisting of various polymers (cellulose, hemicelluloses, pectins, proteins, etc.), the structure of which is different plants encoded with the same degree of accuracy as the structure of protein molecules.
On fig. 9.4 shows a model of the structure of the primary cell wall.
The primary cell wall consists of fibers (microfibrils) of cellulose, which occupy less than 20% of the volume of the hydrated wall. Being parallel in the cell walls, cellulose fibers form micelles with the help of hydrogen bonds, which have a regular, almost crystalline packing. One micelle of cellulose can be separated from another by a distance equal to ten of its diameters. The space between cellulose micelles is filled with an amorphous basic substance (matrix) consisting of pectin substances, hemicelluloses (xyloglucan and arbinogalantan) and a structural protein associated with tetrasaccharides.
The primary cell wall is considered as a whole bag-like macromolecule, the components of which are closely interconnected. Numerous hydrogen bonds exist between cellulose micelles and xyloglucan. In turn, xyloglucan is covalently linked to the galactan side chains of pectin substances, and pectin substances through arabinogalactan are covalently linked to the structural protein.
Considering that the cell walls of many vegetables and fruits are characterized by a relatively high content of divalent cations, mainly Ca and Mg (0.5 ... 1.0%), chelate bonds in the form of salt bridges.
Rice. 9.4. The structure of the primary cell wall (according to Albersheim):
1 - cellulose microfibril: 2 - xyloglucan; 3 - main
rhamnogalacturonic chains of pectin substances; 4 - side
galactan chains of pectin substances; 5-structural protein
with arabinose tetrasaccharides; 6- arabinogalactan
The probability of formation of salt bridges and the degree of esterification of polygalacturonic acids are inversely related. Salt bridges contribute to the strengthening of cell walls and parenchymal tissue in general.
The integumentary tissues of potato tubers, root crops and other vegetables are characterized by a reduced nutritional value due to the concentration of fiber and hemicelluloses in them, therefore, when cooking potatoes and most vegetables, these tissues are removed.