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یکشنبه 28 اسفند 1390 05:39 ب.ظ
In the past, classification systems were typically produced by an individual botanist or by a small group. The result was a large number of systems (see List of systems of plant taxonomy). Different systems and their updates were generally favoured in different countries. Examples are the Engler system in continental Europe, the Bentham & Hooker system in Britain (particularly influential because it was used by Kew), theTakhtajan system in the former Soviet Union and countries within its sphere of influence and the Cronquist system in the United States.
Before the availability of genetic evidence, the classification of angiosperms (also known as flowering plants, Angiospermae, Anthophyta or Magnoliophyta) was based on their morphology (particularly of their flower) and biochemistry (the kinds of chemical compounds in the plant).
After the 1980's, detailed genetic evidence analysed by phylogenetic methods became available and while confirmed or clarified some relationships in existing classification systems, it radically changed others. This genetic evidence created a rapid increase in knowledge that led to many proposed changes; stability was "rudely shattered". This posed problems for all users of classification systems (including encyclopaedists).
In the late 1990s, an informal group of researchers from major institutions worldwide came together under the title of the 'Angiosperm Phylogeny Group' or APG. Their intention was to provide a widely accepted and more stable point of reference for angiosperm classification. Their first attempt at a new system was published in 1998 (the APG system). As of 2010, two revisions have been published, in 2003 (APG II) and in 2009 (APG III), each superseding the previous system. Eight researchers have been listed as authors to the three papers, and a further 33 as contributors (see Members of the APG below).
A classification presents a view at a particular point in time, based on a particular state of research. Independent researchers, including members of the APG, continue to publish their own views on areas of angiosperm taxonomy. Classifications change, however inconvenient this is to users. However, the APG publications are increasingly regarded as an authoritative point of reference and the following are some examples of the influence of the APG system:
- A significant number of major herbaria, including Kew, are changing the order of their collections in accordance with APG.
- The influential World Checklist of Selected Plant Families (also from Kew) is being updated to the APG III system.
- In the USA, a recent photographic survey of the plants of the USA and Canada is organized according to the APG II system.
- In the UK, the latest edition of the standard flora of the British Isles (by Stace) is based on the APG III system. The previous edition was based on the Cronquist system.
Peter F. Stevens, one of the authors of all three of the APG papers, maintains a web site, APweb, hosted by the Missouri Botanical Garden, which has been regularly updated since 2001, and is a useful source for the latest research in angiosperm phylogeny which follows the APG approach.
The principles of the APG's approach to classification were set out in the first paper of 1998, and have remained unchanged in subsequent revisions. Briefly, these are:
- The Linnean system of orders and families should be retained. "The family is central in flowering plant systematics." An ordinal classification of families is proposed as a "reference tool of broad utility". Orders are considered to be of particular value in teaching and in studying family relationships.
- Groups should be monophyletic (i.e. consist of all descendants of a common ancestor). The main reason why existing systems are rejected is because they do not have this property, they are not phylogenetic.
- A broad approach is taken to defining the limits of groups such as orders and families. Thus of orders, it is said that a limited number of larger orders will be more useful. Families containing only a single genus and orders containing only a single family are avoided where this is possible without violating the over-riding requirement for monophyly.
- Above or parallel to the level of orders and families, the term clades is used more freely. (Some clades have later been given formal names in a paper associated with the 2009 revision of the APG system.) The authors say that it is "not possible, nor is it desirable" to name all clades in a phylogenetic tree; however, systematists need to agree on names for some clades, particularly orders and families, to facilitate communication and discussion.
The initial 1998 paper by the APG made angiosperms the first large group of organisms to be systematically re-classified primarily on the basis of genetic characteristics. The paper explains the authors' view that there is a need for a classification system for angiosperms at the level of families, orders and above, but that existing classifications are "outdated". The main reason why existing systems are rejected is because they are not phylogenetic, i.e. are not based on strictly monophyletic groups (i.e. groups which consist of all descendants of a common ancestor). An ordinal classification of flowering plant families is proposed as a "reference tool of broad utility". The broad approach adopted to defining the limits of orders resulted in the recognition of 40 orders, compared to, for example, 232 in Takhtajan's 1997 classification.
Other features of the proposed classification include:
- Formal, scientific names are not used above the level of order, named clades being used instead. Thus eudicots and monocots are not given a formal rank on the grounds that "it is not yet clear at which level they should be recognized".
- A substantial number of taxa whose classification had traditionally been uncertain are given places, although there still remain 25 families of "uncertain position".
- Alternative classifications are provided for some groups, in which a number of families can either be regarded as separate or can be merged into a single larger family. For example, the Fumariaceae can either be treated as a separate family or as part of Papaveraceae.
A major outcome of the classification is the disappearance of the traditional division of the flowering plants into two groups, monocots and dicots. The monocots are recognized as a clade, but the dicots are not, with a number of former dicots being placed in separate groups basal to both monocots and the remaining dicots, the eudicots or 'true dicots'.
The second paper published by the APG presents an update to the original classification of 1998. The authors say that changes have been proposed only when there is "substantial new evidence" which supports them.
The proposed classification continues the tradition of seeking broad circumscriptions of taxa, for example trying to place small families containing only one genus in a larger group. The authors say that they have generally accepted the views of specialsts, although noting that specialists "nearly always favour splitting of groups" regarded as too varied in their morphology.
APG II continues and indeed extends the use of alternative 'bracketed' taxa allowing the choice of either a large family or a number of smaller ones. For example, the large Asparagaceae family includes 7 'bracketed' families which can either be considered as part of the Asparagaceae or as separate families.
Some of the main changes in APG II are:
- New orders are proposed, particularly to accommodate the 'basal clades' left as families in the first system.
- Many of the previously unplaced families are now located within the system.
- Several major families are re-structured.
In 2007, a paper was published giving a linear ordering of the families in APG II, suitable for ordering herbarium specimens, for example.
The third paper from the APG updates the system described in the 2003 paper. The broad outline of the system remains unchanged, but the number of previously unplaced families and genera is significantly reduced. This requires the recognition of both new orders and new families compared to the previous classification. The number of orders goes up from 45 to 59; only 10 families are not placed in an order and only two of these (Apodanthaceae and Cynomoriaceae) are left entirely outside the classification. The authors say that they have tried to leave long-recognized families unchanged, while merging families with few genera. They "hope the classification [...] will not need much further change."
A major change is that the paper discontinues the use of 'bracketed' families in favour of larger, more inclusive families. As a result, the APG III system contains only 415 families, rather than the 457 of APG II. For example, the agave family (Agavaceae) and the hyacinth family (Hyacinthaceae) are no longer regarded as distinct from the broader asparagus family (Asparagaceae). The authors say that alternative circumscriptions, as in APG I and II, are likely to cause confusion and that major herbaria which are re-arranging their collections in accordance with the APG approach have all agreed to use the more inclusive families.
In the same volume of the journal, two related papers were published. One gives a linear ordering of the families in APG III; as with the linear ordering published for APG II, this is intended for ordering herbarium specimens, for example. The other paper gives, for the first time, a classification of the families in APG III which uses formal taxonomic ranks; previously only informal clade names were used above the ordinal level.
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چهارشنبه 24 اسفند 1390 11:00 ق.ظ
صمیمانه ترین شادباشها را از من پذایرا باشید
در سال نو، 365 روز سلامتی، شادی، پیروزی، مهر و دوستی
و عشق را برای شما آرزومندم.
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شنبه 27 اسفند 1390 10:55 ق.ظ
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سه شنبه 23 اسفند 1390 04:30 ب.ظ
Types of Fungi
Basidiomycetes and Ascomycetes
|Fungi with sporophores (fruiting bodies) large enough to be readily visible will usually belong to one of two main groups. The Basidiomycetes or the Ascomycetes. The main difference between these two groups is in the way in which they produce their microscopic spores.|
In the Basidiomycetes, the spores are produced externally, on the end of specialised cells calledbasidia.
In Ascomycetes, spores are produced internally, inside a sac called an ascus.
Asci and basidia are both microscopic structures.
Fungi with spores produced externally, on specialised cells called basidia.
Typically, there are 4 spores per basidium, although this varies from 1 to many, depending on the species.
|Fungi with spores produced inside a sac called an ascus.|
Each ascus usually contains 8 spores (sometimes 4, depending on the species).
For micrograph pictures of basidia and spores click here (External site)
دیدگاه ها :
Within the Basidiomycetes, there are three main groups. These are separated by means of differences in the basidia and spores and how these are arranged on the fruiting body.
|Gill Fungi (Order Agaricales and Russulales)|
Boletes (Order Boletales)
Polypores, Chanterelles, Coral Fungi, Crust Fungi, Fan Fungiand Toothed Fungi (Order Aphyllophorales)
|Stinkhorns (Order Phallales)|
Puffballs and Earthstars
(Order Lycoperdales and Tulostomatales)
Earthballs (Order Sclerodermatales)
Bird's Nest Fungi (Order Nidulariales)
|Jelly Fungi (Order Tremellales)|
|The basidia develop in layers, called a hymenium, lining gills, tubes, teeth or folds on the fruiting bodies.|
Basidia are enclosed inside the fruiting body.
|Basidia in a hymenium or layer on the outer surface of the fruiting bodies.|
Asymmetrical spores, which are shot off simple basidia.
Symmetrical spores, not shot off the basidia.
The basidia are divided internally - there are various different forms.
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سه شنبه 23 اسفند 1390 04:24 ب.ظ
Types of Algae and How To Control Them
One of the most discussed topics on the web is how to get rid of algae. Algae will take over a tank when there is an imbalance of nutrients in the environment. It has been said before that algae control is nutrient control and that fact will become more obvious as you read on.
Many hobbyists see algae as an invasion. They are "like weeds", choking out the good plants and just generally messing up the tank environment. But nature cannot be blamed for what it does... it is what it is. Algae is a natural part of the water systems on this planet. Don't hate it because it happens to show up in a luxurious environment that you yourself have setup. At the very least, algae is pointing out some sort of imbalance in your aquarium setup that needs to be corrected.
Algae can help clean water and can be used as food for fry.
Before we get to the types, I would like to mention some benefits of algae. That's right, algae can serve a purpose! The main benefit of algae is that it helps clean the water in the tank. Green algae is just like the higher plants, in that it uses organic wastes in the water and produces oxygen. Another benefit of algae is that it can provide an alternative food source for omnivorous and herbivorous fish, especially small fry from egglayers who may sometimes survive on "green water".
Types Of Algae
Here is a list of the most common types of algae.
|Staghorn Algae||Description||What To Do|
|Staghorn algae looks like thick strands that may branch once or twice until it ends.|
The color is a blue-green-grey and the algae itself feels slimy to the touch.
Usually grows in high-light slow moving areas of the tank.
|Manually remove the threads with hand, or remove the leaf they are attached to.|
Lower light levels in tank.
Siamensis will eat this.
|Black Brush (Beard) Algae||Description||What To Do|
|Depending on extent of growth it could look like small tufts of black hairs, or a black carpet (as in the picture).|
The strands don't ever get very long, one centimeter is the usual size.
It usually forms on slow-growing plants such as Anubias, but it can also grow on gravel.
|This is one of the worst algaes to get rid of. It cannot be manually removed off a leaf or other surface, the entire leaf must be removed.|
Siamensis are one of the only known fish to eat this type of algae. If you have space it is highly recommended to get these fish as they really earn their keep.
|Green Spot Algae||Description||What To Do|
|Green Spot is just that, green spots on the glass or plant leaves.|
It usually doesn't grow in epidemic proportions (as in the picture!) and is more of an aesthetic problem than anything else.
Faster growing plants will not succumb to this type of algae, but slow growers like Anubias may.
|This algae can't be scraped off with a fingernail. You must use a razor on glass, or a scrubby pad meant for acrylic tanks if you want to take this off.|
Most rasping fish (otocinclus, plecos) cannot eat this algae as it is really fused onto the surface.
|Green Thread/Hair Algae||Description||What To Do|
|Image waiting||This algae can grow fairly quickly and within a few days take over a tank.|
It is usually in the form of long, wispy threads that can grow up to 20 centimeters.
|This algae can be removed manually, but it may grow back unless conditions are improved.|
Reduce light levels, and nutrient levels if necessary.
Some algae eating animals will go after this, Siamensis , Live bearers, and even most shrimp.
|Green Water Algae||Description||What To Do|
|A single-celled algae that floats in the water column.|
If it grows well enough it will soon turn the tank cloudy with green.
|This algae can't be manually removed except by a diatom filter.|
It cannot be eaten by fish except small fry and perhaps water fleas (daphnia).
The best way to get rid of this is nutrient control of the water column.
I have dedicated an entire article to this type of algae HERE.
|Blue Green Algae||Description||What To Do|
|This is actually not an algae, but a type of bacteria.|
It grows in thick slimy sheets, under rocks, over gravel, and can eventually cover everything in the tank.
Sometimes small portions grow between the gravel and the sides of the tank.
It has a "musty" odor.
|This stuff can be removed manually, but it may grow back unless conditions are improved.|
Excess waste and poor water quality is usually the fault.
There's no fish that will eat this stuff.
I have had good luck manually removing as much as I could from the tank, and dosing with Mardel Lab's Maracyn for 3-4 days.
How to Control Them
Mentioned above are the types of algaes, and short descriptions on what to do about them. I labelled this section How to Control Them because there really isn't a way to completely eradicate algae from your tanks. Algae exists everywhere. It can travel as spores through the air, it can come in on anything put in the tank (nets, hoses, fish, snails, live plants, etc.) There are various general ways to try and control all forms of algae, and I will go over them here.
Algae control is
The main underlying method to controlling algae is a restriction of one or more things the algae needs to survive. What this boils down to is controlling the nutrients. Although not technically a nutrient, I will throw natural and man-made light into the mix, as this is another factor which can be controlled. As I've said before in other articles, figuring out which nutrients are out of control in your tank requires the use of a test kit. Without the use of a test kit, you will just face frustrating weeks and maybe months of "guessing games" with your tank. It could also be more expensive in the long run if you start buying products to help with one thing in particular, when really you should just be focusing on something entirely different.
It is also rare for an algae problem to go away within days. It may take weeks to completely control a particular kind of algae in your tank. So it is important that you understand which nutrients are the problem, and stick with the methods to help restrict them until the algae is no longer a problem.
This element is one of the building blocks of life on Earth, and is necessary in order for most things to survive (including fish and plants.) The problem of nitrogen is when it builds in excess of what the ecosystem can handle. Plants (and algae) can use nitrogen in three common forms: Ammonia, Nitrite, and Nitrate. If any of these forms are elevated, then algae can take hold. Restrict nitrogen by feeding less, keeping a lighter fish load, and doing more water changes.
This is probably the most common cause of algae in most tanks. Sometimes it is exposure to sunlight which will cause algae, so try to restrict sunlight from hitting your fishtank. In planted tanks where more artificial light is used, it is common to have some algae breakouts if the plants are not established or there are not enough plants. If this is the case, then increase the number of fast growing plants you have, and include some floating plants to help starve the algae.
This element builds up in a tank from excess fish waste. Overfeeding and heavy fishload increase this element which can contribute to algae. Sometimes well-water can have phosphate from agricultural runoff. There are products to remove phosphate from the water column through the filter, and I have found these to work well.
دیدگاه ها :
If you happen to have a planted tank and use fertilizer meant for aquatic plants, then overdosing can lead to algae problems. Add more plants, or ease off on the fertilizer dosage and try to find a balance.
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سه شنبه 23 اسفند 1390 04:11 ب.ظ
Classification of Algae-based on Habitat
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According to their habitat algae are classified into seven groups.
These are aquatic, free floating or completely submerged algae.
Terestial algae are called Edaphic algae. They live upon or inside the surface of earth. Edaphic algae are classified into two types,
· Saprophytes E.g. Mesotaemium, Botryduium
· Crypyophytes E.g. Nostoc, Anabaena
These are aerial forms of algae. They are found upon trunks of trees, walls, fencing wire, rocks and animals. Aerial algae are classified into four types. They are,
· Epiphyllophytes E.g. Trentepohlia
سه شنبه 23 اسفند 1390 04:13 ب.ظ
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سه شنبه 23 اسفند 1390 04:10 ب.ظ
Classification of Algae-based on Chlorophyll Content
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Though all algae contain chlorophyll, the major divisions can for the most part be distinguished on the basis of their predominant apparent color, due to other photosynthetic pigments that mask the chlorophyll green.
The main branches/lines of algae are:
The three most prominent lines of algae are the Brown Algae (Chromista), the red algae, and theGreen algae of which some of the most complex forms are founds among the green algae. This lineage (green algae) eventually led to the higher land plants. The point where these non-algal plants begin and algae stop is usually taken to be the presence of reproductive organs with protective cell layers, a characteristic not found in the other alga groups.
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سه شنبه 23 اسفند 1390 04:03 ب.ظ
Classification of Algae
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The classification of algae into taxonomic groups is based upon the same rules that are used for the classification of land plants, but the organization of groups of algae above the order level has changed substantially since 1960. Research using electron microscopes has demonstrated differences in features, such as the flagellar apparatus, cell division process, and organelle structure and function, that are important in the classification of algae. Similarities and differences among algal, fungal, and protozoan groups have led scientists to propose major taxonomic changes, and these changes are continuing.
Division-level classification, as with kingdom-level classification, is tenuous for algae. For example, some phycologists place the classes Bacillariophyceae, Phaeophyceae, and Xanthophyceae in the division Chromophyta, whereas others place each class in separate divisions: Bacillariophyta, Phaeophyta, and Xanthophyta. Yet, almost all phycologists agree on the definition of the respective classes Bacillariophyceae, Phaeophyceae, and Xanthophyceae.
The classes are distinguished by the structure of flagellate cells (e.g., scales, angle of flagellar insertion, microtubular roots, and striated roots), the nuclear division process (mitosis), the cytoplasmic division process (cytokinesis), and the cell covering. Many scientists combine the Micromonadophyceae with the Pleurastrophyceae, naming the combined group the Prasinophyceae. “Phylum” and “division” represent the same level of organization; the former is the zoological term, the latter is the botanical term
Properties of Major Algal Taxonomic Groups
Flagellation &Cell structure
± -carotene rarely fucoxanthin,.
1 apical flagellum in male gametes:
cell in two halves with elaborate
1,2,4 to many,
equal, apical or
a, c ,
1 or 2 unequal, apical flagella, in some, cell surface covered by characteristic scales.
(blue green algae)
2 lateral flagella
2 lateral, 1 trailing,1 girdling flagellum, in most, there
is a longitudinal
furrow and angular plates.
(red algae )
a, rarely d
± β carotene
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دوشنبه 8 اسفند 1390 12:51 ب.ظ
|Sixteen chemical elements are known to be important to a plant's growth and survival. The sixteen chemical elements are divided into two main groups: non-mineral andmineral. |
|The Non-Mineral Nutrients are hydrogen (H), oxygen (O), & carbon (C).|
These nutrients are found in the air and water.
In a process calledphotosynthesis, plants use energy from the sun to change carbon dioxide (CO2 - carbon and oxygen) and water(H2O- hydrogen and oxygen) into starches and sugars. These starches and sugars are the plant's food.
Photosynthesismeans "making things with light".
|Since plants get carbon, hydrogen, and oxygen from the air and water, there is little farmers and gardeners can do to control how much of these nutrients a plant can use.|
|The 13 mineral nutrients, which come from the soil, are dissolved in water and absorbed through a plant's roots. There are not always enough of these nutrients in the soil for a plant to grow healthy. This is why many farmers and gardeners use fertilizers to add the nutrients to the soil. |
The mineral nutrients are divided into two groups:
macronutrients and micronutrients.
Macronutrients can be broken into two more groups: Micronutrients
primary and secondary nutrients.
The primary nutrients are nitrogen (N), phosphorus (P), andpotassium (K). These major nutrients usually are lacking from the soil first because plants use large amounts for their growth and survival.
The secondary nutrients are calcium (Ca), magnesium (Mg), andsulfur (S). There are usually enough of these nutrients in the soil so fertilization is not always needed. Also, large amounts of Calcium and Magnesium are added when lime is applied to acidic soils. Sulfur is usually found in sufficient amounts from the slow decomposition of soil organic matter, an important reason for not throwing out grass clippings and leaves.
Micronutrients are those elements essential for plant growth which are needed in only very small (micro) quantities . These elements are sometimes called minor elements or trace elements, but use of the term micronutrient is encouraged by the American Society of Agronomy and the Soil Science Society of America. The micronutrients are boron (B), copper (Cu), iron(Fe), chloride (Cl), manganese (Mn), molybdenum (Mo) and zinc(Zn). Recycling organic matter such as grass clippings and tree leaves is an excellent way of providing micronutrients (as well as macronutrients) to growing plants.
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|In general, most plants grow by absorbing nutrients from the soil. Their ability to do this depends on the nature of the soil. Depending on its location, a soil contains some combination of sand, silt, clay, and organic matter. The makeup of a soil (soil texture) and its acidity (pH) determine the extent to which nutrients are available to plants.|
Soil Texture (the amount of sand, silt, clay, and organic matter in the soil)
Soil texture affects how well nutrients and water are retained in the soil. Clays and organic soils hold nutrients and water much better than sandy soils. As water drains from sandy soils, it often carries nutrients along with it. This condition is called leaching. When nutrients leach into the soil, they are not available for plants to use.
An ideal soil contains equivalent portions of sand, silt, clay, and organic matter. Soils across North Carolina vary in their texture and nutrient content, which makes some soils more productive than others. Sometimes, the nutrients that plants need occur naturally in the soil. Othertimes, they must be added to the soil as lime or fertilizer.
Soil pH (a measure of the acidity or alkalinity of the soil)
Soil pH is one of the most important soil properties that affects the availability of nutrients. It is a good idea to have your soil tested. If you do, you will get a report that explains how much lime and fertilizer your crop needs.
Lime can be added to the soil to make it less sour (acid) and also supplies calcium and magnesium for plants to use. Lime also raises the pH to the desired range of 6.0 to 6.5.
- Macronutrients tend to be less available in soils with low pH.
- Micronutrients tend to be less available in soils with high pH.
In this pH range, nutrients are more readily available to plants, and microbial populations in the soil increase. Microbes convert nitrogen and sulfur to forms that plants can use. Lime also enhances the physical properties of the soil that promote water and air movement.
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- Nitrogen is a part of all living cells and is a necessary part of all proteins, enzymes and metabolic processes involved in the synthesis and transfer of energy.
- Nitrogen is a part of chlorophyll, the green pigment of the plant that is responsible for photosynthesis.
- Helps plants with rapid growth, increasing seed and fruit production and improving the quality of leaf and forage crops.
- Nitrogen often comes from fertilizer application and from the air (legumes get their N from the atmosphere, water or rainfall contributes very little nitrogen)
- Like nitrogen, phosphorus (P) is an essential part of the process of photosynthesis.
- Involved in the formation of all oils, sugars, starches, etc.
- Helps with the transformation of solar energy into chemical energy; proper plant maturation; withstanding stress.
- Effects rapid growth.
- Encourages blooming and root growth.
- Phosphorus often comes from fertilizer, bone meal, and superphosphate.
- Potassium is absorbed by plants in larger amounts than any other mineral element except nitrogen and, in some cases, calcium.
- Helps in the building of protein, photosynthesis, fruit quality and reduction of diseases.
- Potassium is supplied to plants by soil minerals, organic materials, and fertilizer.
- Calcium, an essential part of plant cell wall structure, provides for normal transport and retention of other elements as well as strength in the plant. It is also thought to counteract the effect of alkali salts and organic acids within a plant.
- Sources of calcium are dolomitic lime, gypsum, and superphosphate.
- Magnesium is part of the chlorophyll in all green plants and essential for photosynthesis. It also helps activate many plant enzymes needed for growth.
- Soil minerals, organic material, fertilizers, and dolomitic limestone are sources of magnesium for plants.
- Essential plant food for production of protein.
- Promotes activity and development of enzymes and vitamins.
- Helps in chlorophyll formation.
- Improves root growth and seed production.
- Helps with vigorous plant growth and resistance to cold.
- Sulfur may be supplied to the soil from rainwater. It is also added in some fertilizers as an impurity, especially the lower grade fertilizers. The use of gypsum also increases soil sulfur levels.
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دیدگاه ها :
- Helps in the use of nutrients and regulates other nutrients.
- Aids production of sugar and carbohydrates.
- Essential for seed and fruit development.
- Sources of boron are organic matter and borax
- Important for reproductive growth.
- Aids in root metabolism and helps in the utilization of proteins.
- Aids plant metabolism.
- Chloride is found in the soil.
|Iron (Fe) |
- Essential for formation of chlorophyll.
- Sources of iron are the soil, iron sulfate, iron chelate.
|Manganese (Mn) |
- Functions with enzyme systems involved in breakdown of carbohydrates, and nitrogen metabolism.
- Soil is a source of manganese.
|Molybdenum (Mo) |
- Helps in the use of nitrogen
- Soil is a source of molybdenum.
|Zinc (Zn) |
- Essential for the transformation of carbohydrates.
- Regulates consumption of sugars.
- Part of the enzyme systems which regulate plant growth.
- Sources of zinc are soil, zinc oxide, zinc sulfate, zinc chelate.
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سه شنبه 2 اسفند 1390 04:27 ب.ظ
سیانوفیتها یا جلبکهای سبز _ آبیاین گروه از جلبکها ، ساختاری ساده داشته و به صورت تک سلولی ، کلنی و یا رشتهای بوده، غالبا در پوششی از ماده ژلاتینی قرار دارند. هسته در این جلبکها مشخص نبوده و به صورت گرانولهایی در داخل سیتوپلاسم پراکنده است. رنگیزههای این جلبکها ، شامل کلروفیل ، کاروتن ، فیکواریترین و فیکوسیانین هستند. مواد ذخیرهای در این جلبکها گلیکوژن یا نشاسته خاصی به نام فلوریدین است. نوستوک و اسیلاتوریا از گونههای معروف این گروه هستند.
اوگلنوفیتها یا جلبکهای تاژکداراین دسته از جلبکهای تک سلولی ، دارای تاژک غشایی ظریف بدون دیواره سلولزی هستند. در عدهای از جلبکهای تاژک دار. لکهای به رنگ قرمز ، به نام لکه چشمی در محلی نزدیک به تاژک قرار دارد. این لکه نسبت به نور حساس است. پیگمانهای رنگی به صورت کلروفیل و کاروتن بوده و اندوخته غذایی آنها ،گلوسیدی به نام پارامیلوم میباشد. جلبک اوگلنا بهترین نمونه از جلبکهای تاژکدار است.
کلروفیت یا جلبکهای سبزاین جلبکها دارای کلروپلاست و هسته مشخص هستند. در ساختار جدار آنها سلولز و پکتوز دیده میشود. بعضی از جلبکهای تک سلولی و عده زیادی رشته مانند هستند. جلبکهای سبز علاوه بر کلروفیل ، دارای کاروتن و گزانتوفیل هستند. مواد اندوختهای در این جلبکها ، نشاستهای است و با معرف ید ، آبی رنگ میشود. جلبک اسپیروژیر و شارا از این گروه هستند.
فائوفیتا یا جلبکهای قهوهایتقریبا همه جلبکهای قهوهای دریازی هستند. ساختمان رشتهای دارند و عموما نسبت به بیشتر جلبکهای دیگر ، سازمان پیچیدهتری دارند. در واقع امروزه جلبک قهوهای تک سلولی وجود ندارد. معروفترین این جلبکها ، فوکوس است که در امتداد بسیاری از سواحل دریاها ، یافت میشود. در این جلبکها ، رنگیزههای کلروفیل و فوکوگزانتین قهوهای وجود دارد. لامینارین ومانیتول از مواد ذخیرهای این جلبکها ، محسوب میشود.
رودوفیتا یا جلبکهای قرمزجلبکهای قرمز تقریبا همگی پرسلولی و دریازی هستند. این جلبکها ، علفهای دریایی موجود در آبهای استوایی را تشکیل میدهند. رنگیزه فیکواریتدین نقش کمکی مهمی را در فتوسنتز این جلبکها ، ایفا میکند. جلبکهای قرمز مشبکتر و ظریفتر از جلبکهای قهوهای سخت و ستبر هستند. از این جلبکها ، جنس گلیدیوم منبع ژله آگار است و از آن به عنوان محیط کشت میکروبها ، استفاده میشود.
جلبکها از نظر اقتصادی در تولید مواد پروتئینی اهمیت زیادی دارند، زیرا بطور مستقیم یا غیر مستقیم در زنجیره غذایی آبزیان ، بخصوص ماهیها و همچنین انسان قرار میگیرند. جلبکها با عمل فتوسنتز بر اکسیژن محیط افزوده، از این راه موجب تصفیه آبهای آلوده و فاضلابها میشوند. برخی از جلبکها ، قادرند ازت هوا را در خود ، تثبیت کنند. ازت جذب شده در آنها چه در زمان حیات و چه پس از مرگ بر حاصلخیزی زمین میافزاید. از پوسته سیلیسی دیاتومهها که نوعی از جلبکها هستند، در ساختن خمیردندان ، ساختار صافیها و جلوگیری از انفجار استفاده میشود.
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سه شنبه 2 اسفند 1390 04:30 ب.ظ
عسکر اله قلی
سه شنبه 2 اسفند 1390 04:27 ب.ظ
|جلبکها گروهی از تالوفیتها (ریسه داران) دارای کلروفیل هستند. جلبکها اکثرا آبزی بوده و بطور شناور و یا چسبیده به کف یا تکیهگاه در آب قرار میگیرند. جلبکهای کوچک میکروسکوپی و شناور در آب را فیتوپلانکتون مینامند. دانش شناسایی جلبکها را جلبک شناسی (Phycology) میگویند.|
اطلاعات اولیهجلبکها گروه بزرگی از گیاهان هستند که از لحاظ شکل و اندازه ، تنوع وسیعی دارند. برای اولین بار ، لینه گیاه شناس ، در سال 1754 ، این گیاهان را با نامآلجی معرفی کرد. رومیها از واژه fucus ، چینیها از واژه tsao و مردم هاوایی از واژه limo برای معرفی این گیاهان استفاده میکردند. در تقسیمات جهانی گیاهی ، جلبکها 1800 جنس و 21000 گونه دارند. بیشتر جلبکها ، آبزی هستند. در جلبکها هر سلول دارای 1 تا 2 عدد کلروپلاست و بندرت دارای کروماتوفورهستند.در جلبکها ساختارهای تولید مثلی بطور کامل به هاگ یا گامت تبدیل میشوند. جلبکها یا یوکاریوت هستند، یا پروکاریوت. تولید مثل در جلبکها به دو طریق جنسی و غیر جنسی صورت میگیرد. جلبکها فاقد هر نوع منفذ یا روزنه هستند و ریزوئیدها در آنها در صورت وجود بسیار ساده است. اندامهای جنسی در جلبکها یا تک سلولی است یا پرسلولی. ذخیره غذایی در جلبکها ، نشاسته است و به صورت اتوتروف زندگی میکنند و دیواره سلولی در آنها از سلولز تشکیل شده است.
تفاوت بین جلبکها و قارچها
- جلبکها در زیستگاههای آبی ، در خاک ، در سطح گیاهان یا داخل آنها ، بر سطح یا داخل موجودات جانوری ، در سنگها یا برف و یخ دیده میشوند. قارچها عمدتا ساپروفیت یا پارازیت (انگل) هستند.
- جلبکها ترجیحا در نور زندگی میکنند و قارچها در جاهای تاریک یا مکانهای دارای نور کم زندگی میکنند.
- در جلبکها دیواره سلولی از سلولز تشکیل شده و در قارچها دیواره از کیتین ، سلولز قارچی و قندهای 5 کربنی ساخته شده است.
- در جلبکها ، پیکره تالوئیدی از سلولهای پارانشیمی حقیقی است. در قارچها پیکره از سلولهای پارانشیم کاذب ، ساخته شده است.
- در جلبکها پیگمانهای فتوسنتزی مانند کلروفیل و کاروتنها وجود دارند، در حالی که قارچها فاقد کلروفیل هستند.
- جلبکها اتوتروف هستند، در صورتیکه قارچها هتروتروف میباشند.
- ذخیره غذایی در جلبکها نشاسته و در قارچها به صورت گلیکوژن است.
سطوح طبقه بندی جلبکها (Algae Classification)چون شناسایی تمام جلبکها مشکل است، از این رو آنها را بر طبق صفات و مشخصات موروثی و خواص مورفولوژیکی و فیزیولوژیکی به صورت زیر دسته بندی میکنند:
- شاخه (Division) با علامت Phyta.
- زیر شاخه (Sub Division) با علامت Phytina.
- رده (Class) با علامت Phyceae.
- زیررده (Sub Class) با علامت Phycideae.
- راسته (Order) با علامت ales.
- زیر راسته (Sub Order) با علامت inales.
- تیره (Family) با علامت aceae.
- گونه (Species).
اساس طبقه بندی
- رنگیزهها: مقادیر مواد رنگی ، نوع مواد و ترکیب شیمیایی و انوع بازترکیبی آنها.
- شکل خارجی: اندازه ، شکل ، زواید و دیگر ساختمانها.
- شکل کروماتوفور یا کلروپلاست: آیا فنجانی ، ستارهای ، عدسی و ... هستند؟
- مواد ذخیرهای: نشاسته ، چربی و ... و ترکیب شیمیایی آنها.
- تاژکها: ساختمان ، نوع ، تعداد و موقعیت آناتومی و اتصال آن به سلول.
- دیواره سلولی: ساختمان ظریف دیواره و ساختار شیمیایی آن.
- هسته و کروموزومها: حضور یا عدم حضور یک هسته و شکل کروموزوم.
- دادههای اکولوژیک: توجه به زیستگاهها ، آیا ساکن آب شیرین هستند یا آب شور؟
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سه شنبه 2 اسفند 1390 04:29 ب.ظ