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BOT2605 Assignment 02 Questions Answers, mark obtained = 97%
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By: shirl_naidoo • 3 year ago
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QUESTION 11.1) Silica Gel is used in chromatography as a stationary phase. Silica gel
chromatography separates molecules based on their relative attraction to silica
(greater for more polar molecules then for less polar molecules). Sephadex is often
used to separate molecules on the bases of their size. In column chromatography,
the stationary phase is most frequently composed of silica gel particles of 40–63 μm.
Different particle sizes are used for attaining a preferred separation of certain
molecular sizes. In this instance, due to silica gel's polarity, non-polar components
tend to elute before more polar ones, hence the name normal phase
chromatography. However, when hydrophobic groups such as C18 groups are
attached to the silica gel then polar components elute first and the method is referred
to as reverse phase chromatography. Silica gel is also applied to aluminum, glass, or
plastic sheets for thin layer chromatography.
Gel filtration chromatography separates proteins, peptides, and oligonucleotides
based on size. Molecules move through a bed of porous beads, diffusing into the
beads to greater or lesser degrees. Smaller molecules dispersed further into the
pores of the beads and therefore move through the bed more slowly, while larger
molecules enter less or not at all and thus move through the bed more quickly.
Molecular weight and three-dimensional shape contribute to the degree of retention.
Gel Filtration Chromatography may be used for analysis of molecular size, for
separations of components in a mixture, or for salt removal or buffer exchange from
a preparation of macromolecules.
1.2) Thin-layer chromatography is a “solid-liquid adsorption” chromatography. In this
method stationary phase is a solid adsorbent substance coated on glass plates. As
adsorbent material all solid substances used. in column chromatography (alumina,
silica gel, cellulose) can be utilized. In this method, the mobile phase travels upward
through the stationary phase The solvent travels up the thin plate soaked with the
solvent by means of capillary action. During this procedure, it also drives the mixture
priory dropped on the lower parts of the plate with a pipette upwards with different
, flow rates. Thus the separation of analytes is achieved. This upward travelling rate
depends on the polarity of the material, solid phase, and of the solvent. In cases
where molecules of the sample are colourless, florescence, radioactivity or a specific
chemical substance can be used to produce a visible coloured reactive product so as
to identify their positions on the chromatogram. Formation of a visible colour can be
observed under room light or UV light. The position of each molecule in the mixture
can be measured by calculating the ratio between the the distances travelled by the
molecule and the solvent. This measurement value is called relative mobility, and
expressed with a symbol Rf. Rf. value is used for qualitative description of the
molecules
1.3) Medicinal plants holds importance globally as a valuable source of herbal
medicines and products. In developing countries, up to 80% of the population is
dependent on herbal products and medicines for primary health care. As the global
population increases, there is an increase in the demand for medicinal plants, herbal
drugs and natural health care products. According to the International Union for
Conservation of Nature and the World Wildlife Fund, there are between 50,000 and
80,000 flowering plant species used for medicinal purposes worldwide. Among
these, about 15,000 species are threatened with extinction from overharvesting and
habitat destruction. Locals that live close to nature have a deep understanding for
medicinal plants and their properties, as they depend on medicinal plants for
survival. Although local people and traditional healers are aware of the dangers of
over havesting and destruction of plant habitats, knowledge regarding proper
havesting techniques can be shared and thought through local programs and proper
communication among local farmers/botanists and traditional healers. Important
conservation techniques include; proper collection of medicinal plants, and among
traditional healers – selective harvesting. Selective harvesting involves an
experienced healer “inyanga” that seeks the guidance of an ancestral spirit before
collecting a medical plant. The healer will then be advised through dreams and
prayers, he then combines knowledge of his own with that from spiritual advice and
decides on the best way to harvest (reference: Medicinal plants of SA).
Factors to take into account when harvesting medicinal plants include:
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