One Y and one X chromosome.
A vaccine works by stimulating the immune system to produce antibodies without actually infecting someone with that disease. They trigger the immune system to produce its own antibodies as though the body has been infected with the disease. But a vaccine will not make someone immune to a disease, it will simply help the body be able fight the infection better.
One is to involve exercising curiosity in order to ask questions and seek answers about the universe.
Collenchyma and Parenchyma because they are cellulose containing cells.
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Since an animal only becomes more complex, and not simpler, an ancestor to all organisms would have to be the most simple and primitive organism.
