Section 29 1 Review Plant Cells And Tissues Answer Key Pdf
Pamula Harrison
Dehydration: In this step, the aim is to remove water from the selected tissues to solidify them and facilitate the cutting of thin sections of slides, more thinly for use in light microscopes and thick for the electron microscope. Water is removed from the tissues through the dehydration method through ethanol (Shostak, 2013). The process is repeated through a hydrophobic clearing substance such as xylene to remove the alcohol and paraffin wax and the infiltrated agent. Resins are used to enhance cutting of thin sections of the tissues (Titford, 2009).
Later, newer techniques were devised to enhance the study of cell structure in detail using various laboratory chemicals to preserve tissues in their natural form before staining (Titford & Bowman, 2012). Joseph Von Gerlach was viewed as the pioneer of microscopical staining in 1858 when he used ammoniacal carmine successfully to stain cerebellum cells (Costa, Brito, Gomes, & Caliari, 2010).
In the wake of the nineteenth century, many medical centers hired physicians, pathologists and surgeons to handle surgical issues (Titford & Bowman, 2012). It is this crop of pathologists who devised intraoperative staining techniques for frozen tissues sections by adapting a special staining technique in histopathology. It is during this time that the paraffin infiltration staining technique was devised (Shostak, 2013). Owing to this achievement, the non-malignant and the malignant tumors were studied, and a bacterium was identified as the causal organism of the disease in the nineteenth century (Godwin, 2011).
The Gram staining method was named after a Danish inventor Hans Christian Gram, who invented it as an approach to differentiating bacteria species in 1875 (Musumeci, 2014). Gram devised the technique of staining for the purpose of distinguishing the type of bacterium infection and also as a way of making the bacteria visible on selected and stained lung tissues during examination (Shostak, 2013). Although this technique was found unsuitable for certain bacterium organisms, it is still used today and competes fairly with modern molecular techniques of histology (Rudijanto, 2007). However, Gram technique is infallibly limited in the application on matters of environmental microbiology (Titford, 2009). That aside, Gram techniques had had success when performed on biopsy of infected parts and produced results quickly especially when there is a significant difference in prognosis and treatment. The method is often used in modern histology especially in paraffin fixatives for tissue sectioning (Titford & Bowman, 2012). In a recent case in Kuwait, the Gram staining technique was particularly effective in the diagnosis of Gonorrhea giving 99.4% effective results (Iyiola & Avwioro, 2011). The method is still used today especially with paraffin sections and has been modified to suit different substances.
This study was done in order to compare different staining methods and assess their effectiveness. The specific aim was to assess if the newly developed staining methods, the Helicobacter pylori silver stain HpSS methods and the modified McMullen's methods in the identification of H pylori organism. The method involved selecting tissue sections of gastric biopsies of 63 patients diagnosed with dyspepsia. The section tissues were stained using the four staining methods. In all the 63 cases, 30 sections tested positive for Helicobacter pylori while 30 tested negative for all cases of pylori infection while the remaining were tested using a combination of five histological tests (Anderson, 2011). The results indicated that, the interobserver stain method was the best for antibodies at 98%, followed by Giemsa at 87%, then the HpSS at 85%. At gold standard level, it was found that the Giemsa stain method was the best followed by McMullen's method (Rotimi, Cairns, Gray, Moayyedi, & Dixon, 2000). The study conclusions were that in all cases of staining, the H pylori infection was revealed; however, the modified Giemsa stain was the most effective for its sensitivity, ease of use, reproducibility and cost-effectiveness.
The aim was to investigate the difference in capacity among different stains: Hematoxylin and Eosin, toluidine blue Stain, neuron-specific enolase (NSE) immunostaining and the S 100 protein. These stains were applied to assess the presence of neurons and mast cells in acute appendices Specimens were collected from clinically acute appendices categorized as histologically positive and negative. In the study all the 50 appendix specimens sections were subjected to Hematoxylin and Eosin, toluidine blue Stain, neuron-specific enolase (NSE) immunostaining and the S 100 protein. Hematoxylin and Eosin were applied as a routine stain for general study of the tissues while Toluidine blue stain was applied to enhance the easier study of mast cells. In addition, neuron-specific enolase (NSE) immunostaining was used as a marker and as well as the S 100 protein.
These pathologists devised intraoperative staining techniques for frozen tissues sections by adapting a special staining technique in histopathology (Loreto, Leonardi, Musumeci, Pannone, & Castorina, 2013). It is during this time that the paraffin infiltration staining technique was devised (Titford, 2009). While these changes have taken place, there are old stain procedures that are still in use today and many others have been replaced with new immunal or staining techniques.
The plant cell wall is an elaborate extracellular matrix that encloses each cell in a plant. It was the thick cell walls of cork, visible in a primitive microscope, that in 1663 enabled Robert Hooke to distinguish and name cells for the first time. The walls of neighboring plant cells, cemented together to form the intact plant (Figure 19-68), are generally thicker, stronger, and, most important of all, more rigid than the extracellular matrix produced by animal cells. In evolving relatively rigid walls, which can be up to many micrometers thick, early plant cells forfeited the ability to crawl about and adopted a sedentary life-style that has persisted in all present-day plants.
An important clue to the mechanism that dictates this orientation came from observations of the microtubules in plant cells. These are arranged in the cortical cytoplasm with the same orientation as the cellulose microfibrils that are currently being deposited in the cell wall in that region. These cortical microtubules form a cortical array close to the cytosolic face of the plasma membrane, held there by poorly characterized proteins (Figure 19-74). The congruent orientation of the cortical array of microtubules (lying just inside the plasma membrane) and cellulose microfibrils (lying just outside) is seen in many types and shapes of plant cells and is present during both primary and secondary cell-wall deposition, suggesting a causal relationship.
If the entire system of cortical microtubules is disassembled by treating a plant tissue with a microtubule-depolymerizing drug, the consequences for subsequent cellulose deposition are not as straightforward as might be expected. The drug treatment has no effect on the production of new cellulose microfibrils, and in some cases cells can continue to deposit new microfibrils in the preexisting orientation. Any developmental change in the microfibril pattern that would normally occur between successive lamellae, however, is invariably blocked. It seems that a preexisting orientation of microfibrils can be propagated even in the absence of microtubules, but any change in the deposition of cellulose microfibrils requires that intact microtubules be present to determine the new orientation.
Plant cells can change their direction of expansion by a sudden change in the orientation of their cortical array of microtubules. Because plant cells cannot move (being constrained by their walls), the entire morphology of a multicellular plant depends on the coordinated, highly patterned control of cortical microtubule orientations during plant development. It is not known how the organization of these microtubules is controlled, although it has been shown that they can reorient rapidly in response to extracellular stimuli, including low-molecular-weight plant growth regulators such as ethylene and gibberellic acid (see Figure 21-113).
Plant cells are surrounded by a tough extracellular matrix in the form of a cell wall, which is responsible for many of the unique features of a plant's life style. The cell wall is composed of a network of cellulose microfibrils and cross-linking glycans embedded in a highly cross-linked matrix of pectin polysaccharides. In secondary cell walls, lignin may be deposited. A cortical array of microtubules can determine the orientation of newly deposited cellulose microfibrils, which in turn determines directional cell expansion and therefore the final shape of the cell and, ultimately, of the plant as a whole.
Figure 1. The various differentiation pathways a plant cell can follow and the used terminology to describe them. Differentiation is generally associated with decreased, dedifferentiation with increased developmental potency. In a strict sense, dedifferentiation can take place only within the same developmental lineage and can be considered as the reversion of differentiation. Transdifferentiation is used to describe cell fate changes independent of developmental potency. However, in plant biology, transdifferentiation leading to increased developmental potency is often referred to as dedifferentiation, especially during callus formation. Callus formation is not a step back in the developmental lineage but rather the result of overproliferation/transdifferentiation of differentiated cells. Some or most of the cells of the heterogenous callus tissue can have increased developmental potency.
Why do plant cells look like little rectangles? Look at Figure 1 and notice how all the cells seem to stack on each other, with no spaces in between. Might this allow the cells to form structures that can grow upright?
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