Theme 1.
Definition of medical botany as science about plants, its connection with pharmacognosy. Anatomy of plant as a part of botany. Cell Theory. Structure of plant cell and its components, functions of its
Our need-driven uses of plants, along with our curiosity about our world, have spawned botany, the scientific study of plants. Today, botany is a thriving, exciting science that, directly or indirectly, deals with the largest part of our national and world economy.
But what exactly is a plant? Although you probably already have some notion as to what a plant is—a quiet, green organism that we eat, mow, and use for decoration and shade— it’s difficult to come up with a complete definition for the word plant. For example, not all plants are green and some plants consume animals. Botany is very importance of for pharmacy and medicine.
Plant cell structure
Plant cells are quite different from the cells of the other eukaryotic kingdoms’ organisms. Their distinctive features include:
- A large central vacuole (enclosed by a membrane, the tonoplast), which maintains the cell’s turgor and controls movement of molecules between the cytosol and sap.
- A cell wall composed of cellulose and protein, and in many cases lignin, and deposited by the protoplast on the outside of the cell membrane. This contrasts with the cell walls of fungi, which are made of chitin, and prokaryotes, which are made of peptidoglycan.
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- The plasmodesmata, linking pores in the cell wall that allow each plant cell to communicate with other adjacent cells. This is different from the network of hyphae used by fungi.
- Plastids, especially chloroplasts that contain chlorophyll, the pigment that gives plants their green color and allows them to perform photosynthesis.
- Plant groups without flagella (including conifers and flowering plants) also lack centrioles that are present in animal cells.
http://www.youtube.com/watch?v=uohe2V4yOzE
Cell membrane – the thin layer of protein and fat that surrounds the cell, but is inside the cell wall. The cell membrane is semipermeable, allowing some substances to pass into the cell and blocking others.
cell wall – a thick, rigid membrane that surrounds a plant cell. This layer of cellulose fiber gives the cell most of its support and structure. The cell wall also bonds with other cell walls to form the structure of the plant.
chlorophyll – chlorophyll is a molecule that can use light energy from sunlight to turn water and carbon dioxide gas into sugar and oxygen (this process is called photosynthesis). Chlorophyll is magnesium based and is usually green.
chloroplast – an elongated or disc-shaped organelle containing chlorophyll. Photosynthesis (in which energy from sunlight is converted into chemical energy – food) takes place in the chloroplasts.
cytoplasm – the jellylike material outside the cell nucleus in which the organelles are located.
Golgi body – (also called the golgi apparatus or golgi complex) a flattened, layered, sac-like organelle that looks like a stack of pancakes and is located near the nucleus. The golgi body packages proteins and carbohydrates into membrane-bound vesicles for “export” from the cell.
mitochondrion – spherical to rod-shaped organelles with a double membrane. The inner membrane is infolded many times, forming a series of projections (called cristae). The mitochondrion converts the energy stored in glucose into ATP (adenosine triphosphate) for the cell.
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nuclear membrane – the membrane that surrounds the nucleus.
nucleolus – an organelle within the nucleus – it is where ribosomal RNA is produced.
nucleus – spherical body containing many organelles, including the nucleolus. The nucleus controls many of the functions of the cell (by controlling protein synthesis) and contains DNA (in chromosomes). The nucleus is surrounded by the nuclear membrane
photosynthesis – a process in which plants convert sunlight, water, and carbon dioxide into food energy (sugars and starches), oxygen and water. Chlorophyll or closely-related pigments (substances that color the plant) are essential to the photosynthetic process.
ribosome – small organelles composed of RNA-rich cytoplasmic granules that are sites of protein synthesis.
rough endoplasmic reticulum – (rough ER) a vast system of interconnected, membranous, infolded and convoluted sacks that are located in the cell’s cytoplasm (the ER is continuous with the outer nuclear membrane). Rough ER is covered with ribosomes that give it a rough appearance. Rough ER transport materials through the cell and produces proteins in sacks called cisternae (which are sent to the Golgi body, or inserted into the cell membrane).
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smooth endoplasmic reticulum – (smooth ER) a vast system of interconnected, membranous, infolded and convoluted tubes that are located in the cell’s cytoplasm (the ER is continuous with the outer nuclear membrane). The space within the ER is called the ER lumen. Smooth ER transport materials through the cell. It contains enzymes and produces and digests lipids (fats) and membrane proteins; smooth ER buds off from rough ER, moving the newly-made proteins and lipids to the Golgi body and membranes
thylakoid disk – thylakoid disks are disk-shaped membrane structures in chloroplasts that contain chlorophyll. Chloroplasts are made up of stacks of thylakoid disks; a stack of thylakoid disks is called a granum. Photosynthesis (the production of ATP molecules from sunlight) takes place on thylakoid disks.
vacuole – a large, membrane-bound space within a plant cell that is filled with fluid. Most plant cells have a single vacuole that takes up much of the cell. It helps maintain the shape of the cell.
Plasmolysis. When a freshwater (or terrestrial) plant is placed in sea water, its cells quickly lose turgor and the plant wilts.
This is because sea water is hypertonic to the cytoplasm. As water diffuses from the cytoplasm into the sea water, the cells shrink – drawing their plasma membrane away from the cell wall.
The photomicrograph shows plasmolyzed cells in the freshwater plant Elodea which has been placed in sea water. Note how the cell walls now show clearly.
Plant Cell Structure
Plants are unique among the eukaryotes, organisms whose cells have membrane-enclosed nuclei and organelles, because they can manufacture their own food. Chlorophyll, which gives plants their green color, enables them to use sunlight to convert water and carbon dioxide into sugars and carbohydrates, chemicals the cell uses for fuel.
Like the fungi, another kingdom of eukaryotes, plant cells have retained the protective cell wall structure of their prokaryotic ancestors. The basic plant cell shares a similar construction motif with the typical eukaryote cell, but does not have centrioles, lysosomes, intermediate filaments, cilia, or flagella, as does the animal cell. Plant cells do, however, have a number of other specialized structures, including a rigid cell wall, central vacuole, plasmodesmata, and chloroplasts. Although plants (and their typical cells) are non-motile, some species produce gametes that do exhibit flagella and are, therefore, able to move about.
Plants can be broadly categorized into two basic types: vascular and nonvascular. Vascular plants are considered to be more advanced thaonvascular plants because they have evolved specialized tissues, namely xylem, which is involved in structural support and water conduction, and phloem, which functions in food conduction. Consequently, they also possess roots, stems, and leaves, representing a higher form of organization that is characteristically absent in plants lacking vascular tissues. The nonvascular plants, members of the division Bryophyta, are usually no more than an inch or two in height because they do not have adequate support, which is provided by vascular tissues to other plants, to grow bigger. They also are more dependent on the environment that surrounds them to maintain appropriate amounts of moisture and, therefore, tend to inhabit damp, shady areas.
It is estimated that there are at least 260,000 species of plants in the world today. They range in size and complexity from small, nonvascular mosses to giant sequoia trees, the largest living organisms, growing as tall as 330 feet (100 meters). Only a tiny percentage of those species are directly used by people for food, shelter, fiber, and medicine. Nonetheless, plants are the basis for the Earth’s ecosystem and food web, and without them complex animal life forms (such as humans) could never have evolved. Indeed, all living organisms are dependent either directly or indirectly on the energy produced by photosynthesis, and the byproduct of this process, oxygen, is essential to animals. Plants also reduce the amount of carbon dioxide present in the atmosphere, hinder soil erosion, and influence water levels and quality.
Plants exhibit life cycles that involve alternating generations of diploid forms, which contain paired chromosome sets in their cell nuclei, and haploid forms, which only possess a single set. Generally these two forms of a plant are very dissimilar in appearance. In higher plants, the diploid generation, the members of which are known as sporophytes due to their ability to produce spores, is usually dominant and more recognizable than the haploid gametophyte generation. In Bryophytes, however, the gametophyte form is dominant and physiologically necessary to the sporophyte form.
Animals are required to consume protein in order to obtaiitrogen, but plants are able to utilize inorganic forms of the element and, therefore, do not need an outside source of protein. Plants do, however, usually require significant amounts of water, which is needed for the photosynthetic process, to maintain cell structure and facilitate growth, and as a means of bringing nutrients to plant cells. The amount of nutrients needed by plant species varies significantly, but nine elements are generally considered to be necessary in relatively large amounts. Termed macroelements, these nutrients include calcium, carbon, hydrogen, magnesium, nitrogen, oxygen, phosphorus, potassium, and sulfur. Seven microelements, which are required by plants in smaller quantities, have also been identified: boron, chlorine, copper, iron, manganese, molybdenum, and zinc.
Thought to have evolved from the green algae, plants have been around since the early Paleozoic era, more than 500 million years ago. The earliest fossil evidence of land plants dates to the Ordovician Period (505 to 438 million years ago). By the Carboniferous Period, about 355 million years ago, most of the Earth was covered by forests of primitive vascular plants, such as lycopods (scale trees) and gymnosperms (pine trees, ginkgos). Angiosperms, the flowering plants, didn’t develop until the end of the Cretaceous Period, about 65 million years ago—just as the dinosaurs became extinct.
Protoplasm, Cytoplasm and Cytosol: The Cell’s Content
The “living” content of a cell, the protoplasm , is surrounded by a membrane called plasmamembrane or plasmalemma. The protoplasm is usually next to the cell wall, so that the plasmalemma can hardly be seen. To display it, the cells are transferred into a high salt or sugar solution. As a result the protoplasm shrinks and detaches itself from the wall. The process is reversible and is called plasmolysis. This behavior is due to the properties of the membrane and the plasma. It is reviewed in more detail elsewhere. A substance that causes plasmolysis is called plasmolyticum and – depending on its chemical composition (potassium ions or calcium ions, for example) – the protoplasm takes on different shapes. The plasmolyticum has accordingly an influence on the properties of the membrane. The properties of the plasmamembrane differ from that of the tonoplast. The tonoplast is the membrane that surrounds the vacuole. The difference is especially striking if cells with a colored vacuole content are used. Often the vacuole is criss-crossed by numerous plasma cords. The plasma cannot therefore not simply be viewed as a solution that is influenced by the rules of hydrodynamics alone. Rather, it contains viscous, structure-determining components, whose chemical, physicochemical and structural properties have only been recognized recently and in fragments.
Cytoplasm and Caryoplasm
The nucleus is a rather conspicuous part of nearly every living plant cell. Its structure separated from the rest of the cell by the nuclear envelope, a membrane system that consists of two discrete membranes as can be seen on electromicroscopic images. The nuclear content is called the caryoplasm while that of the rest of the cell is called cytoplasm. But these terms are only valid at certain stages of a cell’s life cycle. In the course of cell-division and mitosis, the nuclear envelope disintegrates and the nucleus is replaced by the chromosomes. It makes consequently no sense to speak of caryo– and cytoplasm during these stages.
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The nucleus of plant cells is usually of a round or elliptic appearance, sometimes it is also shaped like a spindle. One nucleus per cell is the rule, but cells with two or more nuclei are no rare exception. The cells of certain algae of the genus Chladophora have many nuclei, they are polyenergid. The nucleoli that can often be perceived after staining are substructures of the nucleus. They, too, disintegrate during cell division and mitosis and do not reshape before a new nucleus has been formed.
Plastids
Plastids are organelles that occur only in plants. Their most prominent members are the chloroplasts. Others plastids are the colored chromoplasts and the colorless leucoplasts as well as their proplastids. Proplastids are vestigial bodies that are generated during germ cell development due to degeneration of plastids, for example. They may differentiate into complete plastids during the development of the plant embryo. Their ripening into chloroplasts occurs usually only after light exposure.
Chloroplasts contain the green plant color chlorophyll. They are the places where photosynthesis takes place. Chloroplasts enable the plants to convert solar energy into chemical energy. Because of this process, plants are called primary producers. The existence of consumers, like most animals, depends on them. Chloroplasts occur in most cell types, but only in organs above ground. They can be especially well observed in tissues consisting of a single layer as in the leaflike structures of some mosses (Funaria hygrometrica or Mnium hornum) or in the water plant Vallisneria). Here they are rather large and of a lens-shaped appearance. During daytime, when the light is diffuse, they occur mainly at the upper and lower surface of the chloroplast. They appear to be round under top view. If exposed to strong light, they gather in parallel to the lateral sides of the cell which gives them an elleptic appearance upon top view
The Calvin Cycle
Recall now what EE Blackman observed in 1905: in certain situations, the rate
of photosynthesis is governed by temperature, indicating that the chemical
changes of photosynthesis are controlled by enzymes. Such reactions are the
so-called dark reactions of photosynthesis. Carbon is converted to carbo-
hydrate during the dark reactions.
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Chloroplasts are the site of starch production and -storage. Starch can easily be detected with the aid of potassium iodide (LUGOL’s reagent). The starch-iodine complex is deeply blue-violet.
Starch production during photosynthesis can be made visible by placing a mask at a leaf that covers it partially while leaving some places exposed to sunlight. After one day of exposure, the leaf is first bleached to get rid of other pigments and afterwards treated with potassium iodide. An image is gained that is the exact replication of the mask and at the same time represents starch synthesis in the leaf. This experiment has first been done by J. v SACHS, probably the most outstanding plant physiologist of the 20th century. He thought that starch was the primary product of photosynthesis. This assumption proved wrong. It is well-known today that the first products of photosynthesis are monomeric sugars (glucose and others) and that only part of them is used for starch production.
The structures of the chloroplasts of higher cells resemble largely that of mosses. Their average diameter is 4 – 8 mm, an average cells contains 10 through 50. Their chlorophyll is unevenly distributed. At high resolutions chlorophyll-rich and chlorophyll-poor areas can be distinguished. This is due to the inner structure of the chloroplast: it is organized into grana (chlorophyll-rich) and stroma (chlorophyll-poor). Upon stimulation with short-waved light (blue or violet) the chlorophyll emits an intensive red autofluorescence that looks especially impressive in a fluorescence microscope. The differences between grana and stroma become very obvious. The uniformity of the chloroplasts of all higher plants points out that the optimal form has been found rather early in evolution and has not been changed since. This is different with algae. The chloroplasts of green algae (Chlorophyceens) are very varied in shape. Many species have just one chloroplast that covers nearly the whole space of the cell’s interior. It is screw-like in Spirogyra-species, star-shaped in Zygnema and Zygnemopsis and netlike in Oedogonium.
The disc-shaped chloroplast of Mougeotia can be viewed either from above or in profile depending on the amount of light used. Its rotation is a well-analyzed example of an induced chloroplast movement. The chloroplasts of many species of algae contain often well-visible pyrenoids, structures, that produce and structure starch.
Chromoplasts are red, orange or yellow plastids. The color is usually the result of yellow xantophyll and yellow to red carotinoids. Both compounds do also exist in chloroplasts, but are concealed by chlorophyll. Chlorophyll is broken down much faster than carotinoids as can be observed in the colored leaves in autumn. Fluid transitions between chromo- and chloroplasts exist, just as between chromo- and leucoplasts. Typical chromoplasts cause the orange color of the carrot, the red color of the ripe pimento and tomato as well as the color of numerous flowers. Carotinoids are not very water-soluble and do therefore often crystallize within the chromoplasts. Their crystals can be disc-shaped, needle-like, jagged or sickle-like.
In many cases, flower and leaf colors are caused by the colored content of the vacuole. The color of the vacuole and that of the plastids may lead to a mixed color. The leaves of the copper beech, where the vacuole’s content is red and that of the chloroplasts is green are a typical example. The plastids of the red and brown algae are traditionally counted among the chromoplasts although they contain chlorophyll. The green colour is concealed by the red phycoerythrin (Rhodophyceae) or the brown fucoxanthin (Phaeophyta).
Leucoplasts are common, colorless plastids. They develop from proplastids, but form no homogeneous group of their own. A part of them can differentiate into chloroplasts or chromoplasts at light exposure, while this is not due for others. The guard cells, for example, contain leucoplasts, that are permanently exposed to light without developing into chloroplasts. Leucoplasts do also occur within colorless leaves (variegated leaves) or plant parts. There exists a number of examples which show that they developed from chloroplasts that lost their ability to produce chlorophyll. There are even species, like Neottia, an orchid that cannot produce chlorophyll at all and are thus dependent on a parasitic or saprophytic lifestyle (saprophy is the feeding from dead organic material).
A second class of leucoplasts occurs within the non-green tissues of otherwise green plants. It is especially common within roots. Though these leucoplasts are capable to become green, they do usually not since they are not exposed to light. The leucoplasts of the calyptra (a calyptra is any hood or cap of cells protecting a plant part) contain starch and are therefore counted among the amyloplasts (starch-containing leucoplasts). They have, as is explained later, the function of statolithes, that have an important part in the perception of gravity (geotropism).
Starch
We got to know starch in the section above as a content of chloroplasts and leucoplasts (amyloplasts). It is produced by the polymerization of glucose residues, which again are products of photosynthesis. Since the plant is able to transport sugars from leaf to root or from leaf to seed and fruit, starch production can also take place in these organs. Different species produce starch grains of different shape. Since the shape of starch grains informs about their origin, they are helpful in the identification of seeds and other starch-containing plant parts. The following numbers show the variations in their diameters. Starch grains from potato tubers have a diameter of 70 – 100 µm, that of the endosperm of wheat 30 – 45 µm and that of corn endosperm 12 – 18 µm. Their shape reflects their development. The starch molecules are long-stretched and only sparsely branched. They are deposited within the plastids and their development begins at a so-called formation center from where it proceeds radially. Layer follows layer and the thickness of one layer is dependent on the average molecular length. A starch grain is therefore organized like a crystal (semi-crystalline). This can be shown very impressively with a polarization microscope. Within the moistened specimen can a layering be viewed that is dependent on the water content of the single molecular parts.
A. Model of a starch grain structure. The single lines symbolize starch molecules. They are arranged in a radial pattern. B. Layering of the starch grains. a. Formation center and layer borders, b. Diagram of the refraction conditions. The ordinate shows the refraction index. (according to A. FREY-WYSSLING, 1938)
The denser the molecular packaging, the less water is deposited. Layers with less water content refract light stronger than those with much water. After drying of the preparatioo layering can be perceived any more. Depending the central or peripheral placing of the formation center, starch grains with either concentric or eccentric layering develop. The starch grains of graminaceous plants (wheat, corn, etc.) are usually concentric, while those of the potato are always eccentric.
Sometimes plastids with two to three formation centres occur in graminaceous plants. This leads to the development of several starch grains. During growth common outer layers may be formed.
Compound starch grains are typical for oat, they are built from a large number of smaller grains.
Starch grains in bean seeds (Phaseolus vulgaris) are very big, their shape is round or oval, the spacing of the layers is very regular. Their centers can easily be hollowed out by addition of water displaying radial ruptures in microscopic images. In the sap of Euphorbia splendens dumb-bell shaped starch grains can be found.
Except for very few examples, plant cells are surrounded by a cellulose containing cell wall. It is flexible and distortable during growth, but loses its ability for distortion after growth has stopped, while a limited flexibility remains. Because of these changes, it is distinguished between primary and secondary cell walls. As we will see when talking about electron microscopic pictures of the cell wall, both forms differ mainly in the arrangement of their cellulose microfibrils. While they are unorganized within the amorphous matrix of the primary cell wall, they are organized into several ordered layers that are arranged one on top of the other at right angles in the secondary cell wall. The secondary cell walls of many cells, especially those of vascular tissues, are incrusted with strengthening material. Two important ones are: lignin, the ground substance of wood and
suberin, the ground substance of cork
Their details are reviewed here. In addition, secondary walls contain often phenolic oxidation products that lends them a dark color (red to black with various shades).
Starch is a polymer made by plants to store energy.You see, plants need energy to grow and grow and grow. |
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Here is a short section of starch, with only 4 glucose molecules. Starch can also have a lot of branches. Each branch is a short chain made from glucoses, and each branch can make more branches. Crazy, huh? |
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Another good thing about starch: Each little glucose likes to have water all around it. That can be really hard on the plant. In a starch polymer, the glucose units have other glucose units around them, and that works just as well as water. So, the plant doesn’t need so much water, and everybody’s happy!
Hey, what about us?!
We need glucose for energy, too. You eveeed energy to think! When you eat starchy food, special proteins called enzymes (which are also polymers, by the way) break starch down into glucose, so your body can burn it for energy. This starts happening right in your mouth! There’s an enzyme in your spit (yep, your spit!) that starts to cut up the starch. Check out this link to see how you can taste this enzyme working.
Foods that have a lot of starch include: grains (like rice and wheat), corn, and potatoes.
Our bodies can’t make starch – only plants make starch. We have two ways of storing excess glucose. I’m sure you know about this first way! If you eat a lot more starch than you need for energy, then your body can store it by turning it into fat. (That’s just one job that your liver does.)
But what if glucose is needed RIGHT NOW? Like if you have to get up and run run run?!!! There’s no time to break down fat! You need glucose NOW!! How do our bodies store glucose so that it’s ready fast? Click here for the answer.
Starch is very similar to cellulose. But cellulose is a fiber that you can’t digest. The thing that makes these two polymers different is simply how the glucose molecules are put together in the polymer chain. Click here to learn more about how plants make starch, and how it differs from cellulose.
Starch has some uses other than food. It’s used in pressing clothes to keep them from wrinkling. It’s also used to make foam packing “peanuts”. This packing is better for the earth than Styrofoam packing. It dissolves in water, and it’s biodegradable (meaning that little critters can eat it!)
Inulin is used increasingly in foods because it has unusual nutritional characteristics. It ranges from completely bland to subtly sweet and can be used to replace sugar, fat, and flour. This is particularly advantageous because inulin contains a third to a quarter of the food energy of sugar or other carbohydrates and a sixth to a ninth of the food energy of fat. It also increases calcium absorption[1] and possibly magnesium absorption[2], while promoting intestinal bacteria. Nutritionally, it is considered a form of soluble fiber, and it is important to note that consuming large quantities (particularly for sensitive and/or unaccustomed individuals) can lead to gas and bloating. Inulin has a minimal impact on blood sugar, making it generally considered suitable for diabetics and potentially helpful in managing blood sugar-related illnesses.
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Uses and health benefits
Inulin is indigestible by the human enzymes ptyalin and amylase, which are adapted to digest starch. As a result, inulin passes through much of the digestive system intact. It is only in the colon that bacteria metabolise inulin, with the release of significant quantities of carbon dioxide and/or methane. Inulin-containing foods can be rather gassy, particularly for those unaccustomed to inulin, and these foods should be consumed in moderation at first. Most individuals can adapt to increased dietary fiber and most Americans consume only half the daily recommended value of dietary fiber. There are two types of dietary fiber, soluble and insoluble. Insoluble fiber increases the movement of materials through the digestive system and increases stool bulk; it is especially helpful for those suffering from constipation or stool irregularity. Soluble fiber dissolves in water to form a gelatinous material. It can help lower blood cholesterol and glucose levels. Inulin is considered a soluble fiber.
Because normal digestion does not break inulin down into monosaccharides, it does not elevate blood sugar levels and may therefore be helpful in the management of diabetes. Inulin is also an effective prebiotic, stimulating the growth of beneficial bacteria in the gut. Inulin passes through the stomach and duodenum undigested and is highly available to the gut bacterial flora. This contrasts with proprietary probiotic formulations based on Lactic acid bacteria (LAB) in which the bacteria have to survive very challenging conditions through the gastrointestinal tract before they are able to colonize the gut. Some traditional diets contain up to 20g per day of inulin or oligofructose. Many foods naturally high in inulin or oligofructose, such as chicory, garlic, and leek, have been seen as “stimulants of good health” for centuries.
Inulin is also used in medical tests to measure the total amount of extracellular volume and determine the function of the kidneys.
Literature
1. Botany / Randy Moore, W.Denis Clark, Kingsley R.Stern, Darrell Vodopich. – Dubuque, IA, Bogota, Boston, Buenos Aires, Caracas,Chicago, Guilford, CT, London, Madrid, Mexico City, Sydney, Toronto: Wm.C.Brown Publishers.- 1994.-P.44-81.
2. Kindsley R. Stern. Introductory plant biology-
3. Gulko R.M. Explanatory Dictionary of Medicinal Botany- Lviv: LSMU, 2003.-200 p.
4. Laboratory handbook on Pharmaceutical Botany (for students of “pharmacy“ specialty) / S.M. Marchyshyn, M.I. Shanayda, I.Z. Kernychna. – Ternopil: TSMU, 2012. – P.7-12.
5. Anatomy of plant сells, tissues, organs and their morphology / Methodical instructions for laboratory works in botany for students of pharmaceutical department / R. Gulko, O. Baran. – L’viv, 2005. – P. 17–25.
6. Botany / [Randy Moore, W.Denis Clark, Kingsley R.Stern, Darrell Vodopich]. –
Prepared by ass. prof. Shanayda M.I.
