1.
Symplast
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The symplast of a plant is the inner side of the plasma membrane in which water and low-molecular-weight solutes can freely diffuse. The plasmodesmata allow the flow of small molecules such as sugars, amino acids. Larger molecules, including transcription factors and plant viruses, can also be transported through with the help of actin structures and this allows direct cytoplasm-to-cytoplasm flow of water and other nutrients along concentration gradients. In particular, symplastic flow is used in the systems to bring in nutrients from soil. It moves these solutes from epidermis cells through the cortex into the endodermis, once solutes reach the endodermal cells thorough apoplastic flow, they are forced into the symplastic pathway due to the presence of the Casparian strip. Once the solutes are passively filtered, they reach the pericycle. It is contrasted with the flow, which uses cell wall transport. The symplastic transport was first realized by Eduard Tangl in 1879, who discovered the plasmodesmata. In 1880, Hanstein coined the term symplast, the contrasting terms apoplast and symplast were used together in 1930 by Münch. Apoplast Plant sap Polar auxin transport, a type of cell-to-cell transport Protoplast Tonoplast
2.
Cell wall
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A cell wall is a structural layer surrounding some types of cells, situated outside the cell membrane. It can be tough, flexible, and sometimes rigid and it provides the cell with both structural support and protection, and also acts as a filtering mechanism. Cell walls are present in most prokaryotes, in algae, plants and fungi, a major function is to act as pressure vessels, preventing over-expansion of the cell when water enters. The composition of cell walls varies between species and may depend on type and developmental stage. The primary cell wall of plants is composed of the polysaccharides cellulose, hemicellulose. Often, other such as lignin, suberin or cutin are anchored to or embedded in plant cell walls. Algae possess walls made of glycoproteins and polysaccharides such as carrageenan, in bacteria, the cell wall is composed of peptidoglycan. The cell walls of archaea have various compositions, and may be formed of glycoprotein S-layers, pseudopeptidoglycan, Fungi possess cell walls made of the glucosamine polymer chitin. Unusually, diatoms have a wall composed of biogenic silica. A plant cell wall was first observed and named by Robert Hooke in 1665, in 1804, Karl Rudolphi and J. H. F. Link proved that cells had independent cell walls, before, it had been thought that cells shared walls and that fluid passed between them this way. The mode of formation of the wall was controversial in the 19th century. Hugo von Mohl advocated the idea that the wall grows by apposition. Carl Nägeli believed that the growth of the wall in thickness, each theory was improved in the following decades, the apposition theory by Eduard Strasburger, and the intussusception theory by Julius Wiesner. In 1930, Ernst Münch coined the term apoplast in order to separate the living symplast from the dead plant region, Cell walls serve similar purposes in those organisms that possess them. They may give cells rigidity and strength, offering protection against mechanical stress, in multicellular organisms, they permit the organism to build and hold a definite shape. Cell walls also limit the entry of large molecules that may be toxic to the cell and they further permit the creation of stable osmotic environments by preventing osmotic lysis and helping to retain water. Their composition, properties, and form may change during the cell cycle, in most cells, the cell wall is flexible, meaning that it will bend rather than holding a fixed shape, but has considerable tensile strength
3.
Cell membrane
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The cell membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is permeable to ions and organic molecules and controls the movement of substances in. The basic function of the membrane is to protect the cell from its surroundings. It consists of the bilayer with embedded proteins. Cell membranes can be artificially reassembled, Some authors that did not believe that there was a functional permeable boundary at the surface of the cell preferred to use the term plasmalemma to the extern region of the cell. The cell membrane surrounds the cytoplasm of living cells, physically separating the components from the extracellular environment. The cell membrane also plays a role in anchoring the cytoskeleton to provide shape to the cell, fungi, bacteria, most archaea, and plants also have a cell wall, which provides a mechanical support to the cell and precludes the passage of larger molecules. The cell membrane is permeable and able to regulate what enters and exits the cell. The movement of substances across the membrane can be passive, occurring without the input of cellular energy, or active. The membrane also maintains the cell potential, the cell membrane thus works as a selective filter that allows only certain things to come inside or go outside the cell. The cell employs a number of mechanisms that involve biological membranes,1. Passive osmosis and diffusion, Some substances such as carbon dioxide and oxygen, can move across the membrane by diffusion. Because the membrane acts as a barrier for certain molecules and ions, such a concentration gradient across a semipermeable membrane sets up an osmotic flow for the water. Transmembrane protein channels and transporters, Nutrients, such as sugars or amino acids, must enter the cell, such molecules diffuse passively through protein channels such as aquaporins in facilitated diffusion or are pumped across the membrane by transmembrane transporters. Protein channel proteins, also called permeases, are quite specific, recognizing and transporting only a limited food group of chemical substances. Endocytosis, Endocytosis is the process in which cells absorb molecules by engulfing them, the plasma membrane creates a small deformation inward, called an invagination, in which the substance to be transported is captured. The deformation then pinches off from the membrane on the inside of the cell, Endocytosis is a pathway for internalizing solid particles, small molecules and ions, and macromolecules. Endocytosis requires energy and is thus a form of active transport and this is the process of exocytosis
4.
Endoplasmic reticulum
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The endoplasmic reticulum is a type of organelle in eukaryotic cells that forms an interconnected network of flattened, membrane-enclosed sacs or tube-like structures known as cisternae. The membranes of the ER are continuous with the nuclear membrane. The endoplasmic reticulum occurs in most types of cells, including Giardia. There are two types of endoplasmic reticulum, rough and smooth, the outer face of the rough endoplasmic reticulum is studded with ribosomes that are the sites of protein synthesis. The rough endoplasmic reticulum is especially prominent in such as hepatocytes. The smooth endoplasmic reticulum lacks ribosomes and functions in lipid manufacture and metabolism, the production of steroid hormones, the smooth ER is especially abundant in mammalian liver and gonad cells. The lacy membranes of the endoplasmic reticulum were first seen in 1945 using electron microscopy, the lacy membranes of the endoplasmic reticulum were first seen in 1945 by Keith R. Porter, Albert Claude, Brody Meskers and Ernest F. Fullam, using electron microscopy. The word reticulum, which network, was applied to describe this fabric of membranes. The general structure of the reticulum is a network of membranes called cisternae. These sac-like structures are held together by the cytoskeleton, the phospholipid membrane encloses the cisternal space, which is continuous with the perinuclear space but separate from the cytosol. The functions of the reticulum can be summarized as the synthesis and export of proteins and membrane lipids. The quantity of both rough and smooth endoplasmic reticulum in a cell can slowly interchange from one type to the other, transformation can include embedding of new proteins in membrane as well as structural changes. Changes in protein content may occur without noticeable structural changes, the surface of the rough endoplasmic reticulum is studded with protein-manufacturing ribosomes giving it a rough appearance. The binding site of the ribosome on the endoplasmic reticulum is the translocon. However, the ribosomes are not a part of this organelles structure as they are constantly being bound. A ribosome only binds to the RER once a specific protein-nucleic acid complex forms in the cytosol and this special complex forms when a free ribosome begins translating the mRNA of a protein destined for the secretory pathway. The first 5-30 amino acids polymerized encode a signal peptide, a message that is recognized. Translation pauses and the complex binds to the RER translocon where translation continues with the nascent protein forming into the RER lumen and/or membrane
5.
Actin
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Actin is a family of globular multi-functional proteins that form microfilaments. It is found in all eukaryotic cells, where it may be present at a concentration of over 100 μM. Many of these processes are mediated by extensive and intimate interactions of actin with cellular membranes, in vertebrates, three main groups of actin isoforms, alpha, beta, and gamma have been identified. The alpha actins, found in tissues, are a major constituent of the contractile apparatus. The beta and gamma actins coexist in most cell types as components of the cytoskeleton and it is believed that the diverse range of structures formed by actin enabling it to fulfill such a large range of functions is regulated through the binding of tropomyosin along the filaments. Other enzymes or organelles such as cilia can be anchored to this scaffolding in order to control the deformation of the cell membrane. It can also produce movement either by itself or with the help of molecular motors, Actin therefore contributes to processes such as the intracellular transport of vesicles and organelles as well as muscular contraction and cellular migration. It therefore plays an important role in embryogenesis, the healing of wounds, the evolutionary origin of actin can be traced to prokaryotic cells, which have equivalent proteins. Actin homologs from prokaryotes and archaea polymerize into different helical or linear filaments consisting of one or multiple strands, however the in-strand contacts and nucleotide binding sites are preserved in prokaryotes and in archaea. Lastly, actin plays an important role in the control of gene expression, a large number of illnesses and diseases are caused by mutations in alleles of the genes that regulate the production of actin or of its associated proteins. The production of actin is also key to the process of infection by some pathogenic microorganisms, mutations in the different genes that regulate actin production in humans can cause muscular diseases, variations in the size and function of the heart as well as deafness. The make-up of the cytoskeleton is also related to the pathogenicity of bacteria and viruses. Actin was first observed experimentally in 1887 by W. D. Halliburton, in 1942, Straub developed a novel technique for extracting muscle protein that allowed him to isolate substantial amounts of relatively pure actin. Straubs method is essentially the same as used in laboratories today. Adding ATP to a mixture of both proteins causes a decrease in viscosity, the hostilities of World War II meant Szent-Gyorgyi and Straub were unable to publish the work in Western scientific journals. Actin therefore only became known in the West in 1945. Straub suggested that the transformation of ATP-bound actin to ADP-bound actin played a role in muscular contraction, in fact, this is true only in smooth muscle, and was not supported through experimentation until 2001. The amino acid sequencing of actin was completed by M. Elzinga, the crystal structure of G-actin was solved in 1990 by Kabsch and colleagues
6.
Plant cell
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Plant cells are eukaryotic cells that differ in several key aspects from the cells of other eukaryotic organisms. A cell wall composed of cellulose and hemicelluloses, pectin and in many cases lignin, is secreted by the protoplast on the outside of the cell membrane. This contrasts with the walls of fungi, which are made of chitin, and of bacteria. Other types of plastids are the amyloplasts, specialized for storage, elaioplasts specialized for fat storage. Parenchyma cells are living cells that have functions ranging from storage and support to photosynthesis, apart from the xylem and phloem in their vascular bundles, leaves are composed mainly of parenchyma cells. Parenchyma cells that contain many chloroplasts and are concerned primarily with photosynthesis are called chlorenchyma cells, others, such as the majority of the parenchyma cells in potato tubers and the seed cotyledons of legumes, have a storage function. Collenchyma cells – collenchyma cells are alive at maturity and have only a primary wall and these cells mature from meristem derivatives that initially resemble parenchyma, but differences quickly become apparent. Plastids do not develop, and the secretory apparatus proliferates to secrete additional primary wall, pectin and hemicellulose are the dominant constituents of collenchyma cell walls of dicotyledon angiosperms, which may contain as little as 20% of cellulose in Petasites. Collenchyma cells are quite elongated, and may divide transversely to give a septate appearance. The role of cell type is to support the plant in axes still growing in length. Stretchable support is a way to describe what collenchyma does. Parts of the strings in celery are collenchyma, Sclerenchyma cells – Sclerenchyma cells are hard and tough cells with a function in mechanical support. They are of two broad types – sclereids or stone cells and fibres, the cells develop an extensive secondary cell wall that is laid down on the inside of the primary cell wall. The secondary wall is impregnated with lignin, making it hard, thus, these cells cannot survive for long as they cannot exchange sufficient material to maintain active metabolism. Sclerenchyma cells are dead at functional maturity, and the cytoplasm is missing, leaving an empty central cavity. Functions for sclereid cells include discouraging herbivory, by damaging digestive passages in small insect larval stages, functions of fibres include provision of load-bearing support and tensile strength to the leaves and stems of herbaceous plants. The major classes of cells differentiate from undifferentiated meristematic cells to form the structures of roots, stems, leaves, flowers. Xylem cells are elongated cells with lignified secondary thickening of the cell walls, xylem cells are specialised for conduction of water, and first appeared in plants during their transition to land in the Silurian period more than 425 million years ago
7.
Algae
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Algae is an informal term for a large, diverse group of photosynthetic organisms which are not necessarily closely related, and is thus polyphyletic. Included organisms range from unicellular genera, such as Chlorella and the diatoms, to forms, such as the giant kelp. Most are aquatic and autotrophic and lack many of the cell and tissue types, such as stomata, xylem, and phloem. No definition of algae is generally accepted, one definition is that algae have chlorophyll as their primary photosynthetic pigment and lack a sterile covering of cells around their reproductive cells. Some authors exclude all prokaryotes thus do not consider cyanobacteria as algae, Algae constitute a polyphyletic group since they do not include a common ancestor, and although their plastids seem to have a single origin, from cyanobacteria, they were acquired in different ways. Green algae are examples of algae that have primary chloroplasts derived from endosymbiotic cyanobacteria, diatoms and brown algae are examples of algae with secondary chloroplasts derived from an endosymbiotic red alga. Algae exhibit a range of reproductive strategies, from simple asexual cell division to complex forms of sexual reproduction. Algae lack the various structures that characterize land plants, such as the phyllids of bryophytes, rhizoids in nonvascular plants, and the roots, leaves, and other organs found in tracheophytes. Most are phototrophic, although some are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or phagotrophy. Some other heterotrophic organisms, such as the apicomplexans, are derived from cells whose ancestors possessed plastids. Fossilized filamentous algae from the Vindhya basin have been dated back to 1.6 to 1.7 billion years ago, the singular alga is the Latin word for seaweed and retains that meaning in English. Although some speculate that it is related to Latin algēre, be cold, a more likely source is alliga, binding, entwining. The Ancient Greek word for seaweed was φῦκος, which could mean either the seaweed or a red dye derived from it, the Latinization, fūcus, meant primarily the cosmetic rouge. It could be any color, black, red, green, accordingly, the modern study of marine and freshwater algae is called either phycology or algology, depending on whether the Greek or Latin root is used. The name Fucus appears in a number of taxa, most algae contain chloroplasts that are similar in structure to cyanobacteria. Chloroplasts contain circular DNA like that in cyanobacteria and presumably represent reduced endosymbiotic cyanobacteria, however, the exact origin of the chloroplasts is different among separate lineages of algae, reflecting their acquisition during different endosymbiotic events. The table below describes the composition of the three groups of algae. Their lineage relationships are shown in the figure in the upper right, many of these groups contain some members that are no longer photosynthetic
8.
Charophyceae
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Charophyceae is a class of charophyte green algae. Some botanists include Charophyceae and chlorophyte green algae in the plant kingdom, Charophyceae are a class within the Streptophyta. Current consensus treats Charophyceae as a class under division Charophyta, with Chlorophyta remaining a distinct division. # The thallus is erect with regular nodes and internodes, at each node there is a whorl of branches. The whole plant is calcified and Equisetum-like, the internodes of the main axis consist of a single elongated cell, in Chara the internodes are corticated covering the main axis. In other genera these are absent, where there is a single row of cortical cells the cortex is referred to as diplostichous, where there are two rows of cortical cells it is termed triplostichous. The intermodal cells elongate and do not divide they be come many times longer than broad
9.
Charales
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Charales is an order of freshwater green algae in the division Charophyta, class Charophyceae, commonly known as stoneworts. Linnaeus established the genus Chara in 1753, the Charales have large, macroscopic thalli growing up to 120 cm long, they are branched, multicellular, and use chlorophyll to photosynthesize. They may be called stoneworts, because the plants can become encrusted in lime after some time, the stem is actually a central stalk consisting of giant, multinucleated cells. They are unique in having a whorl of small branchlets at each node in the stipe, in these whorls it is possible to see the phenomenon of cytoplasmic streaming. In fact the streaming in Chara is the fastest recorded of any cell, Cytoplasmic streaming is caused by the microfilaments found inside the cell, as proven by the use of cytochalasin B to stop streaming. There are about 400 species worldwide, with 33 in Britain and Ireland according to Groves and Bullock-Webster), however Stewart, Characeae are the principal plant life of some of the volcanic crater lakes of Nicaragua, and can be found in excess of 20 meters depth in some circumstances. Introduced tilapia consumed all the Characeae in Lake Apoyo, ex A. Braun Chara curta Nolta wx Kütz. Chara denudata R. D. Wood Chara fragifera Durieu Chara intermedia Braun Chara mucosa J. Groves & Bullock-Webster Chara rudis Leonh, nitellopsis obtusa J. Groves Tolypella intricata Leonh. Var. globularis C. vulgaris var. papillata Wallr, ex A. Braun Nitella flexilis var. flexilis Nitella translucens C. A. Var. aspera C. aspera var. curta Braun ex Leonh, var. globularis C. vulgaris var. papillata Wallr. Ex A. Braun Nitella flexilis var. flexilis Nitella translucens C. A, var. glomerata R. D. Wood County LondonderryC. aspera Deth. Var. aspera C. vulgaris var. papillata Wallr, ex A. Braun C. globularis Thuill. Var. globularis C. globularis var. virgata R. D. Wood C. hispida L. C. hispida var. hispida C. vulgaris L. var. vulgaris C. vulgaris L. var. contraria J. A. Moore C. vulgaris var. papillata Wallr. Ex A. Braun Nitella flexilis var. flexilis Nitella translucens C. A and they can be pioneer colonizers or ephemerals. They are usually found in low to medium nutrient-rich water and tend to due to eutrophication. Some stoneworts can survive in brackish or maritime habitats and occur in saline lakes in Australia that have twice the salinity of seawater. As a result, the Charales have the most complex structure of all green algae, the possible sister group of the land plants are also known as brittleworts or skunkweed. These curious labels arise from the fragility of their lime-encrusted stems, many botanists propose that the stoneworts and their relatives be placed in a division, sub-kingdom, or even kingdom by themselves, often named Charophyta
