سلام
من يه مقاله در مورد آلودگي آبها ميخام
هركي بتونه كمك كنه ازش ممنون ميشم
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ممنون
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سلام
من يه مقاله در مورد آلودگي آبها ميخام
هركي بتونه كمك كنه ازش ممنون ميشم
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ممنون
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و
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با سلام خدمت دوستان [ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ]
تو این تاپیک سعی می شه از مقالاتی که در این زیر مجموعه ارائه شد فهرستی ارائه و همچنین حتی المقدور پی دی اف اونها تهیه بشه و در اختیار همه قرار بگیره!!
درخواستهای خودتون رو برای مقالات مرتبط با زیست شناسی و بهداشت و پزشکی و دیگر رشته های مرتبط رو در اینجا ارائه کنید یا برای درخواستتون تاپیک جدیدی در [ برای مشاهده لینک ، با نام کاربری خود وارد شوید یا ثبت نام کنید ] بزنید.
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سلام....من یه تحقیق خیلی عالی در مورد آلودگی آبها در خلیج فارس دارم...منتها انگلیسی هستش!نقل قول:
نوشته شده توسط mohammad_h
خودم ترم پیش برای درس Ecology دادم که استاد Free Exam کردتم و بهم 100 داد :biggrin:
اگه به کارت میومود بگو که برات Uploadش کنم! کلی هم عکسهای رنگی و اینا داره ;)
یا علی.
دستت درد نکنه سجاد جاننقل قول:
نوشته شده توسط Sadjad Sharifian
مقاله رو برای امروز میخاستم که ردیف شد و کارش تموم شد(البته با کمک دوست عزیزم)
به حرحال دستت درد نکنه
سلام
دوستان من یه مقاله میخوام که در مورد سیگار و اثرات مضر آن باشه و اثرات مواد مضری مثل نیکوتین که در اون هست و..
لطفن کمکم کنید
ممنون میشم :blush:
دوست من واقعا عالی بود اما یه زحمتی برات داشتم اگه میشه یه کم بیشتر در مورد وضعیت فشار خون در سیگاریها برام توضیح بدی عالی میشه
شرمنده ها
ممنون
سلام
لطفا مرا كمك كنيد :biggrin:
سلام
این مطالب رو پیدا کردم اگر بازهم لازم بود بگین :happy:
The Cell Membrane
By J.P. Leisure
Intro to membrane:
A thin membrane located in the cell wall surrounds every living cell separating the cell from the environment around it. Enclosed by the membrane are the cell's elements, large molecules such as proteins, nucleic acids, carbohydrates, and substances involved in cellular metabolism. Outside the cell, there are ions, acids and molecules toxic to the cell, as well as nutrients that the cell must absorb to live and grow. The membrane therefore has two main functions. One is to be barrier and keep all elements of the cell in and unwanted substances out, and second to be the gate keeper allowing transport into the cell of essential substances and movement from the cell of waste products.
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Structure of the membrane:
The cell membrane consists mainly of phospholhttp://sun.menloschool.org/~birchler/cells/plants/cell_wall/ipids, which have two parts: a polar phosphate head and two non-polar fatty acid tails. The molecules are arranged in what is called a bilayer or a double layer so that the polar heads face the external and the internal environments of the cell and the fatty acids form the inside of the membrane. The phospholipids are not anchored down in any way; they are free to move about. This allows for the membrane to stretch and change shape.
Also contained within or attached to the surface of a membrane's phospholipid bilayer are various proteins. Collectively these proteins regulate the movement of substances through the membrane and communicate with the environment. Many of the proteins in the membrane have carbohydrate groups attached to the parts of the proteins that stick outside of the cell. These proteins and their attached carbohydrates are called glycoproteins. Similar to the phospholipids in the membrane some of the proteins in the membrane can move freely, but others are anchored down.
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Transportation across the membrane:
As the gate keeper of the cell the membrane provides for two types of movement: passive transport and active transport. During passive transport, substances move into or out of cells down concentration gradients. This movement by itself requires no energy. The gradients provide the potential energy that drives the movement and controls the direction of movement in or out of cells. The lipids and proteins in the membrane regulate which molecules can cross the membrane but do not influence the direction of movement. Many molecules cross membranes by diffusion, which is the movement of a substance form an area of high concentration to an area of a low concentration. Some molecules move across the membranes by simple diffusion, which is when a molecule can diffuse across the phospholipid bilayer. Other molecules cross the membrane by facilitated diffusion, which is when a molecule can cross the membrane only with the aid of one of two types of transport proteins, channel proteins or carrier proteins.
In active transportation, membrane proteins use cellular energy to move individual molecules across the membrane and usually against their concentration gradient. The ATP or adenosine triphosphate donates the energy to the protein, which causes it to change shape and move the molecule across the membrane. Cells have evolved several processes that use cellular energy to move molecules into and out of the cell. Cells can acquire large molecules by a process known as endocytosis. There are three types of endocytosis, which can be distinguished on the basis of the size of the particle acquired and the method of which it is acquired and transported: pinocytosis, receptor-mediated endocytosis, and phagocytosis. Pinocytosis moves liquids into the cell. Receptor-mediated endocytosis moves specific molecules into the cell, and phagocytosis moves large particles into the cell. Cells often use a process that is the reverse of endocytosis to dispose of any unwanted materials inside the cell called exocytosis, which moves materials out of the cell.
Biology - the study of life
What is Life?
Life as a word is difficult to define because the living state is not a clear-cut condition. Rather, it is a continuum upon which many objects exist. There are some fundamental properties that, taken together abundantly, constitute the living condition. Certain objects possess all of these properties and are obviously alive. We call these objects organisms. Other items in our universe possess only some of these properties and are considered to a greater or lesser extent non-living.
Properties of Life
cellular structure
homeostasis-metabolism
growth
reproduction
adaptation
short-term behavior
long-term evolution
During this course we will examine each of these properties to some extent. For now we will content ourselves with just the first...cellular structure. All truly living things are composed of cells. These are microscopic chambers that each contain the "stuff" of life. In fact, the smallest organisms consist of just one cell! These unicellular organisms are found generally in the two Kingdoms called Monera and Protista. As organisms, these single cells carry out all of the properties of life listed above! Thus the cell is a unit of life.
It is important to realize, however, that in multicellular organisms such as higher plants and humans there are cells that lack certain properties. In fact some cells function best when they are totally dead as we shall soon see...
Cells = the unit of life
"Typical" Cell Structure
The cell shown below is called a parenchyma cell. It is perhaps typical of those found in the soft cells of all plants. A herbaceous plant (such as a grass) might be 90% parenchyma. A woody plant (such as a tree) might be less than 30% parenchyma.
As you can see in the diagram above, a plant cell has an outer boundary that includes a cell wall. This cell wall is unique to the range of organisms called plants...animal cells do not have cell walls! This wall is a boundary between the cell and its environment. Just like any good wall, it keeps out any invaders and other cells. But again, just like any good boundary, it is meant to be crossed. In fact the import and export of materials is critical to the life of the cell. So a wall is only as good as its doors and windows. This lesson was not well appreciated by Soviet states and ancient China. The exchange of materials and ideas provides vitality to what is within the wall. Without this exchange death is really the only option. The plant cell wall is quite passive really. It is made up of cellulose (an indigestible--by humans--polysaccharide carbohydrate) and other polymers of sugar. The fibrils of cellulose form a loose basket-weave arrangement through which materials can filter in or out without further barrier. It serves more of a filtration function than a control function. The other polymers in the wall area may include pectin (a polygalacturonan) that serves as the glue to hold one plant cell firmly to an adjacent cell. In fact the outer layer of higher plant cells is sometimes called the middle lamella because this heavy layer of pectin glue is quite visible in electron microscope images of plant tissues. Humans extract pectin and use it to thicken fruit juices into a material called jam or jelly (depending on the presence or absence of fruit pulp). You can buy Certo or Sure-Jell in the grocery store to use in jelly-making; these are purified forms of pectin--plant cell glue.
Just inside the cell wall is the cell membrane. This membrane is made up of phospholipids (such as lecithin) and membrane-proteins. This thin "skin" of the cell is the important import/export control area. The phospholipids provide the barrier functions. Their hydrophilic polar "heads" face the inside and outside of the membrane and prevent passage of hydrophobic substances through the membrane. The phospholipid hydrophobic "tails" face the middle of the membrane layer and prevent the passage of hydrophilic substances through the membrane. Thus the layered form of the membrane is a pretty good barrier to most chemicals. Special proteins made by the cell serve as windows and doors in this membrane. These transport proteins have both hydrophobic sections that align inside the membrane and hydrophilic sections that align with the inner and/or outer membrane surfaces. By bridging both the hydrophilic and hydrophobic regions of the membrane, these proteins are "bound" to the membrane. Most interestingly, however, is that these bridging proteins can form channels through the membrane for a particular kind of chemical to pass. In fact, some of the membrane proteins can energetically grasp chemicals and actively pump them across the membrane to the other side! These transport proteins are sometimes called active transport carriers. Thus membrane proteins are those all-important doors and windows through the barrier!
Moving to the middle of the cell somewhere we find a double membrane surrounding a region of fluid which contains DNA. This structure is called the nucleus. Please note the spelling and pronunciation (new-clee-us...NOT...new-kew-lus); learning correct pronunciation will help correct spelling (probably, library, and February are also commonly mispronounced and misspelled). Nothing makes you sound more ignorant of your studies than mispronunciation of its critical vocabulary. The nucleus processes information held in the DNA molecules that it contains. Sometimes the nucleus copies the DNA into new molecules of DNA in preparation for cell division; this process is called replication. Replication is a critical prelude to making two cells from just one and so is tied directly to reproduction and inheritance from one generation to the next. A more mundane function of the nucleus is to make an RNA copy of the DNA; this process is called transcription. The DNA is a more-or-less permanent copy of critical information; it might be thought of as master plans for the cell. When these master plans are to be used, they are transcribed into an inexpensive and disposable copy in RNA...a kind of blueprint to be handled, used, and ultimately destroyed. These RNA blueprints are sent out from the nucleus to be acted upon by other parts of the cell.
Just outside the nucleus and extending out to the cell membrane is an area often referred to as cytoplasm. We will avoid this all-encompassing term because it gives the idea that this part of the cell is somehow a uniform fluid. Indeed to ancient biologists using light microscopes this region did seem pretty homogenous--hence one word to describe it. With the advent of the electron microscope we have discovered other structures floating in this region of the cell and so we generally avoid the term cytoplasm. In its place we simply use cytosol to refer to the liquid around all of the floating structures between the nucleus and cell membrane. The cytosol is mostly water, but significantly contains many dissolved substances. Notable among these substances are enzymes. Enzymes are proteins that cause certain chemical reactions to occur at a much faster rate. These enzymes might build materials (anabolism) or take apart materials (catabolism) in the cell, depending upon the kind of enzyme in observation. Thus these enzymes are involved in the chemical processing that actively takes place in the cytosol. The whole of these processes is called metabolism; anabolism and catabolism are two opposing categories of metabolism. Thus much "work" is done in the cytosolic fluid of cells!
Some of the floating membranes in the cytosol include a network of tiny tubes that interconnect throughout the inside of the cell. This network is called endoplasmic reticulum...literally a network inside the fluid of the cell. This network is involved in the transport of materials from one part of the cell to another, and maintains the integrity of the membranes surrounding the nucleus. This is the conveyor belt of the cell.
On the surface of some of the endoplasmic reticulum are thousands of tiny structures in the cytosol called ribosomes. These ribosomes are made of protein and RNA and are actively involved in the synthesis of proteins. The ribosome attaches to the RNA blueprints coming out from the nucleus. It reads the information coded in the sequence of bases in the RNA and, using this information, assembles a particular protein. Ribosomes are thus a kind of protein-synthesis "machine." This process of using the information in RNA to make a protein is called translation; it is the complement of transcription. The protein products of the translation include the enzymes ("workers") of the cell. These proteins are shipped throughout the cell for functional uses.
The endoplasmic reticulum near the ribosomes is responsible for moving much of the protein through its tubules to other parts of the cell. One area of particular importance on the fringes of the endoplasmic reticulum is the Golgi apparatus or dictyosome. Here the proteins arrive and are sorted by tagging with sugars or lipids, and are packaged into tiny membrane-bound packages called vesicles. The Golgi apparatus thus is a sorting and packaging structure. Depending upon contents, these vesicles move to a particular destination and the membranes fuse. The contents of the vesicle are thus "dumped" to the other side of the receiving membrane.
This vesicular transport process explains how proteins made by the cell might be dumped through the cell membrane to the outside environment. Such a process is called exocytosis; literally a process pushing materials outside of the cell. On the other hand, vesicles can also be formed at the cell membrane by engulfing materials on the outside of the cell to bring to the inside. Such an import process would be called endocytosis if the material is particulate. In the special case of vesicular import of only water and dissolved chemicals, the process is named pinocytosis; literally cell drinking. Vesicular transport adds to the repertoire and to the scale of the import/export operations carried out at the cell membrane.
To drive almost all of the processes described above, we need energy. In animals there is one energy powerhouse...the mitochondrion. This structure has a smooth outer membrane and a convoluted inner membrane. The mitochondrion imports fuel molecules (chiefly acetyl Co-enzyme A) to be converted into carbon dioxide and water. This process requires the presence of oxygen and is called respiration:
CH2O + O2 --------> CO2 + H2O + energy
You might notice that this process is essentially the reverse of photosynthesis (though drastically different in details!) and releases energy instead of requiring the input of light energy. This release of energy from the respiration in the mitochondrion allows for all the work done in the cell. All living cells with a true nucleus (the eukaryotic cells), including those of plants, contain mitochondria and carry out respiration. Yes, again, plants have mitochondria and they do respiration both day and night! Many people are unaware of this fact...now you know!
It is easy to understand how the cell gets its oxygen from the atmosphere, but from where does it get the carbohydrate (CH2O)? In the case of fungi and animals, the fuels for respiration come from digestion of plant-derived foodstuffs found (or hunted -down!) in the environment. For plants, the carbohydrate can come from that essentially reverse process, photosynthesis:
CO2 + H2O + light -------> CH2O + O2
Photosynthesis occurs in the chloroplast of the cell. This structure floating in the cytosol has two smooth outer membranes and a system of stacks of membranes inside. The whole chloroplast is some ten times larger than a mitochondrion, and it stacks of membranes inside are called grana. These grana are composed of many individual membrane sacs called thylakoid membranes. Each thylakoid membrane has special proteins that hold molecules of the green pigment chlorophyll. This chlorophyll is responsible for trapping the energy of the light to use in driving the production of carbohydrates in photosynthesis. We shall learn more of this process later in the term. For now, let's just remember that plants have both mitochondria and chloroplasts and therefore can do both respiration and photosynthesis! Animals lack chloroplasts.
Finally in our brief tour of cell structure and function, let us remember that all processes described here produce waste materials, and this leads us to one more distinction between plants and animals. Typically animals use various processes to dump their wastes to the environment. Single-celled animals may use vesicular transport to rid themselves of waste by exocytosis. Higher animals concentrate wastes through a urinary system and then urinate periodically in the environment. Since a plant produces great food for an animal to eat, you might not be surprised to find that plants hold their toxic wastes. This way a grazing animal gets a dose of poison every time it tries to eat the plant. The toxic wastes of a plant cell are stored in the vacuole. This central region is surrounded by a membrane (the tonoplast) that selectively pumps cellular wastes and poisons into the vacuole. Early botanists mistakenly thought the vacuole was pretty empty and uninteresting...hence the name vacuole...but now we know that this is a very interesting place where some pretty important metabolism occurs. Certain materials are recycled back out of the vacuole after detoxification reactions. Others are converted to even more-toxic forms once they reach the inside of the vacuole. Yet others are crystallized into raphides or other forms that pierce animal digestive systems or otherwise cause hemorrhage inside the herbivore. The vacuole is certainly not a vacuum nor void of interest!
There are many details left out of this brief description of cell structure and function, but at least we have made a start. One good way to think about the parts and functions of cells is to think of the cell as a business. How would you organize a factory that was making and exporting a particular product? A cell is well-designed to do this...
Cell Functions - The factory analogy
Cell Wall = border fence (very penetrable) good support
Cell Membrane = loading/unloading dock
Nucleus = administrative complex (DNA replication/transcription)
Cytosol = work floor environment
Endoplasmic Reticulum = conveyor belt system
Ribosomes = protein synthesis machine (translation)
Golgi Apparatus = sorting/packaging department
Vesicles = import/export package
Chloroplast = energy source (photosynthesis)
Mitochondrion = energy source (respiration)
Vacuole = toxic waste pond (herbivore poison)
Another important way to study is to think about the three fundamental structures listed above that are unique to plants. Which ones are they?
Organelles unique to plants:
Cell Wall
Chloroplast
Vacuole
Note: the above are in addition to the usual organelles found in animal cells. Plants are MORE...not less....than animal cells!
Finally, a good way to study cell structure and function is by means of a concept map. Here is a crude concept map showing the relationships between the parts in terms of functions.
Cell Functions - A concept map:
I mentioned above that the smallest plants consisted of single cells. The largest organism on our planet is the sequoia tree. This tree is larger than 10 blue whales (the largest animal) and so is easily the largest obvious organism. Certain fungi in soil, however, consist of microscopic but connect filaments of cells originating from a single spore. These fungi are basically invisible, but DNA evidence suggests that single individuals may spread across hundred of acres of land. So these fungi may, in fact, be the "largest" organisms.
In terms of lifespan, some cells (and unicellular organisms) live for only a few minutes before dividing and making new cells or perishing altogether. Some multicellular organisms can live to be very old. The oldest documentable living organism is the bristlecone pine tree. These trees are frequently more than 5000 years old. They were already older than any extant human when the pyramids were built in Egypt! These plants, still alive today, were already 3000 years old when Jesus walked through Jerusalem. Admittedly, some clonal plants are harder to document and may be even older than the bristlecone pine, but the age of the bristlecone pine is easy to document!
Other Cell Types:
You might be misled into thinking that the "typical" cell is most of what is available or most of what is important. This couldn't be farther from the truth! Plant cells can be classified into four fundamental cell types (and many other specific kinds).
Meristematic Cells undergo mitosis and thereby produce all cells of the plant body. Mitosis is the nuclear division (usually followed by cytokinesis) that results in the production of new cells. Mitosis is a process in which a cell goes from interphase, through prophase, metaphase, anaphase, and telophase, and ends up in interphase again. The cell division process assures that the master plans in the DNA of the nucleus are replicated accurately and completely, and that the copies of the master plans are evenly divided between the two resulting cells in an orderly fashion. This ensures the integrity and completeness of the master plans in both of the cells.
Derivatives of meristematic cells can mature in any one of three directions...only one of which results in a "typical" cell (parenchyma):
It might not be completely obvious, but study of the diagram above will reveal that some cells are long and thin, some cells have thin walls and others have thick walls, and some cells are alive and others are dead!
Indeed dead cells can be useful to a multicellular organism. In humans, dead cells contribute the structure of hair shafts and nails. In plants dead cells provide stony protective layers in peach pits and the conductive elements of the xylem. Without the dead xylem elements, a plant would literally cook in the sun because it would lack the water from the xylem to efficiently cool the leaves by evaporation of that water. Without the dead xylem to bring minerals up with that water, plants would lack essential metal ions from the soil. These soil minerals include calcium, magnesium, iron, and zinc (more on those later in the course!). Our food would lack some of its essential nutrition were it not for these dead cells in plants!
Cell Membrane
While the plant cell has a rigid cell wall, an animal cell membrane is a flexible lipid bilayer. The lipid molecules (mostly phospholipids) that make up the membrane have a polar, hydrophilic head and two hydrophobic hydrocarbon tails. When the lipids are immersed in an aqueous solution the lipids spontaneously bury the tails together and leave the hydrophilic heads exposed. Thus this is a handy membrane to use, because it can automatically fix itself when torn. There are three different major classes of lipid molecules - phospholipids, cholesterol, and glycolipids. Different membranes have different ratios of the three lipids.
What makes the membrane truly special is the presence of different proteins on the surface that are used for various functions such as cell surface receptors, enzymes, surface antigens, and transporters. Many of the membrane-associated proteins have hydrophilic and hydrophobic regions. The hydrophilic regions are used to help anchor the protein inside of the cell membrane. Some proteins extend across the lipid bilayer, others cross the bilayer several times
Diagram of the cell membrane. The proteins are embedded inside of the cell membrane. The lipid content of the membrane allows the cell membrane to automatically repair itself when it is torn.
Membrane Transport of Small Molecules
Because of the hydrophobic interior of the lipid bilayer, polar molecules cannot enter the cell. However, cells devised means of transferring small polar molecules. Transport proteins, each specialized for a certain molecule, can transport polar molecules across the membrane. There are several types of membrane transport proteins. Uniports simply move solutes from one side to another. Cotransport systems work by simultaneously sending two solutes across the lipid bilayer. There are two types of cotransport systems - symport, in which the solutes are sent in the same direction, or antiport, in which they are sent in opposite directions. These transport proteins work passively, meaning that the cell doesn't have to expend energy sending the solute in or out. This is dependent on the solute moving in its natural direction - i.e. moving from more concentrated solution to less concentrated, or from positive to negative.
Some specific examples of transport membranes are channel proteins, which allow solutes to cross if they are the correct size and charge. Carrier proteins bind to the solute and lead it through the bilayer. These are examples of passive transport. To move a solute against their natural direction - for example higher concentration to lower concentration, energy (ATP) is needed to pump the solute in or out.
An example of active transport is the sodium-potassium pump, which in conjunction with the potassium leak channel, allows the cell the control it's membrane potential. The sodium-potassium-ATPase, which uses the energy of ATP hydrolysis, pump pumps sodium out and potassium in, which creates a high concentration of potassium inside the cell, and a low concentration outside. The reverse applies to the sodium. The potassium leak channel allows the potassium to leak out (so to even out the concentrations), which gives the cell and negative charge on the inside.
Diagram comparing uniport, symport, and antiport.
Membrane Transport of Macromolecules
Most cells use exocytosis and endocytosis to secrete and ingest macromolecules, respectively. In exocytosis the contents of special vesicles are released when the vesicle fuses with the cell membrane. In endocytosis the membrane depresses and pinches off, enclosing the molecule. Two different sizes are formed - pinocytotic (small) and phagocytic (large).
In receptor-mediated endocytosis, coated pits and vesicles bind to specific receptors on the cell surface, allowing the cell to select what molecules to take and what to reject.
Membrane Receptors
The cell membrane is pocketed with receptors and antigens. Molecules targeted toward that specific cell will bind with the cell surface receptor, which binds the signaling molecule and sends a signal that alters the behavior of the target cell. Antigens are used to tell the cell whether foreign materials are present. If any foreign materials are detected the immune system will mobilize its killer T-cells to destroy the foreign cell.
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موفق باشید
اول از همه بگم كه از تمام دوستاني كه اينجا زحمت ميكشن فقط تشكر لازم نيست بايد هر كاري بخوان انجام بدي براشون كه خود من حاضرم هر كاري تونستم و خواستن انجام بدم.
دوم اينكه من يك مقاله مفصل مثلا حدود 20 يا 30 صفحه در مورد stem cells ميخواستم اگر كتابي در اين زمينه كه جديد هم باشه براي دانلود باشه كه حرف نداره . هركيم كمكم كنه هر آهنگي خواست و داشتم پيغام بذاره براش آپ لود ميكنم .
خودم در اين زمينه خيلي مطلي گشتم اما بازم دوستان واردترند ;)
سلام دوست عزيز
چون عنوان رو انگليسي نوشتين فكر كردم مقاله بايد به انگليسي باشه. اگه فارسي مورد نظرتون هست بگين.
اين ا لينكي كه مي دم مربوط به سايتي هست كه به طور تخصصي در مورد سلولهاي بنيادي مطلب داره و اطلاعات پايه اي در مورد سلولهاي بنيادي رو به صورت سوال و جواب داره البته اگه نياز دارين كه مطالب رو از سايت دربيارم و اينجا بذارم بگين چون فكر كردم اين طوري امكان انتخاب از بين مطالب براي خودتون بيشتر باشه. به هر حال اينم از لينك:
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