Answer:
① There are many test methods: many kinds of NMR test methods, including one-dimensional and two-dimensional, have been widely used in structural analysis and material identification; quantitative analysis is no longer limited to 1H NMR experiment, and quantitative analysis of heteronuclear and even two-dimensional NMR appears frequently;
② There are many calibration targets: most compounds have multiple sets of NMR lines, which can be used as calibration targets for quantitative analysis theoretically, which undoubtedly provides convenience for the processing of test data;
③ There are many types of quantitative information: in the literature reports, not only the integral area or intensity of the resonance spectral line is used as the data parameter of NMR quantitative analysis, but also the change value of chemical displacement under specific conditions can be used as the parameter of content determination;
④ There are many reference modes: nuclear magnetic resonance obtains the data information of quantitative analysis through direct comparison of signals. In the experiment, multiple modes such as internal standard, external standard, solvent calibration and physical calibration can be used to provide reference signals. In the determination of relative content, the mode of sample self-standard can also be used.
In a word, NMR is a mature analytical and testing method with distinct technical characteristics, multiple means, flexible methods and rich information, which has a strong competitiveness in drug analysis and identification.
Explanation:
http://www.creative-biostructure.com/nmr-services_28.htm
72 chromatids were present in the present in the primary oocyte during prophase 1 of meiosis.
The primary oocyte contains 72 chromatids during prophase 1 of meiosis as the mature ovum has 18 chromosomes.
The primary oocyte contains 72 chromatids , that means it contains 144 chromosomes. During the first meiotic division, it produces one secondary oocyte and one polar body.
The secondary oocyte has 72 chromatids, which again undergoes second meiotic division and produces mature ovum and second polar body . The mature ovum contains contains 36 chromatids which means it has 18 chromosomes.
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Answer:
Wind.
Explanation:
Gymnosperms are also known as naked plants as their ovules are in the unfertilized state and their seeds do not bear fruits. Gymnosperms are known as seed plants.
Gymnosperms pollen grains are transferred from the pollen cone to the ovule. Their pollen are generally transferred by winds as they are lighter and resistant to water. Sometimes, insects are also responsible for the transfer of pollen grains.
Thus, the correct answer is option (b).
