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Embryonic development
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The first movements of the foetus and appearance of hair on its head are usually observed during which month of pregnancy?After one month of pregnancy the heart of the embryo is formed.
By the end of the second month the foetus develops limbs and digits.
By the end of 12 weeks (first trimester) most of the major organ systems are formed.
The first movements of the foetus and the appearance of hair on the head are usually observed during the fifth month.
By the end of 24 weeks (second trimester) the body is covered with fine hair, the eyelids separate and eyelashes are formed.
Hence the answer is the fifth month. -
Which one of the following statements about morula in humans is correct?The morula is the solid ball of 8–16 blastomeres formed by cleavage of the zygote.
Cleavage divisions are rapid mitotic divisions without any growth phase in between; the zygote is simply partitioned into smaller and smaller cells, so the total amount of cytoplasm stays almost the same as in the zygote.
Before each division, however, the DNA is replicated, so every blastomere has a full diploid set.
A morula with 16 cells therefore contains about 16 times the DNA of the uncleaved zygote.
Hence the morula has almost equal quantity of cytoplasm as an uncleaved zygote but much more DNA.