1- why dong you usually get sick from the exact same pathogen twice

1 answer:

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1: For example, rhinovirus has over 100 different serotypes. Now, the good news is that you can't get ill from the same virus serotype right after getting better, due to the fact that you'll have developed antibodies which help to protect your immune system for a little while.

2:Most children in the United States are now vaccinated against measles virus; before vaccination was widespread, most were naturally exposed to this virus and suffered from an acute, unpleasant, and potentially dangerous viral illness. Whether through vaccination or infection, children exposed to the virus acquire long-term protection from measles. The same is true of many other acute infectious diseases: this state of protection is a consequence of immunological memory.

The basis of immunological memory has been hard to explore experimentally. Although the phenomenon was first recorded by the ancient Greeks and has been exploited routinely in vaccination programs for over 200 years, it is just now becoming clear that memory reflects a persistent population of specialized memory cells that is independent of the continued persistence of the original antigen that induced them. This mechanism of maintaining memory is consistent with the finding that only individuals who were themselves previously exposed to a given infectious agent are immune, and that memory is not dependent on repeated exposure to infection as a result of contacts with other infected individuals. This was established by observations made on remote island populations, where a virus such as measles can cause an epidemic, infecting all people living on the island at that time, after which the virus disappears for many years. On reintroduction from outside the island, the virus does not affect the original population but causes disease in those people born since the first epidemic. This means that immunological memory need not be maintained by repeated exposure to infectious virus

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The Earth takes a year to orbit around the Sun. What about the Moon?

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Answer

C. The Moon orbits the Earth about once a month

Over billions of years the earth’s gravitational field has tidally locked the moon in orbit so that its rotation about its axis is the same as that of its orbit around the earth.

This process is still continuing as the earth transfers some of its angular momentum to the moon lifting it to a higher orbit by a couple of centimeters a year. As it rises, its takes a fraction longer to complete an orbit, and its rotational speed slows down slightly to match.

The eventual conclusion of this is that the earth also would become tidally locked to the moon, and they will both face each other permanently. But this is going to take that long that the sun will probably have destroyed both the earth and the moon in its red giant phase before this happens.

Hope this helps!\

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Which type of cell is more complex, prokaryotic or eukaryotic?

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It is accually prokaryotic

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Pleazz helpp.. why do you think holding your breath or breathing into a bag effects the pulse rate??

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Hemophilia A is an X-linked blood clotting disorder. A normal man and a woman with hemophilia A have a child with Turner Syndrom

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Answer: e.Woman; there is not enough information to tell if the nondisjunction happened in meiosis I or II.

Explanation: There is not enough information to tell if the nondisjunction happened in meiosis I or II. Nondisjunction can occur during meiosis I and meiosis II, resulting in abnormal chromosomes number of gametes. The important difference between nondisjunction in meiosis 1 and Ii is that during meiosis 1, homologous chromosomes fail to separate while in meiosis II, sister chromatids fail to separate meaning it could have happened in meiosis I or II but we were not given.

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Approximately 90% of human cancer cells exhibit significant levels of telomerase. Does this mean that telomerase is an oncogene?

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No, telomerase is not an oncogene. It prevents the senescence that would occur due to shortened telomeres, but the cell proliferation might still be mitogen-dependent.

Explanation

telomerase is not responsible for causing deregulation while oncogenes cause deregulation .

Telomeres length shorten after the cell division which stops them to divide again and cell die.

Telomerase prevents this decline in some kinds of cells, including stem cells, by lengthening telomeres, and the hope was that activating the enzyme could prevent senescence.

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