Answer:
An embryo sac is said to form when the haploid megaspore nucleus divides. It possesses two haploid nuclei and six haploid cells which do not have cell walls.
Explanation:
Answer:
By providing the numbers in which methane is more powerful than carbon dioxide the author is appealing to the scientific facts to convince people that the greenhouse effect is destroying our planet, and that global warming is a reality that we must counter attack and treat as a priority.
Explanation:
For anyone with this question as a multiple choice question, itś D.
To know what happens here, you need to analyze the alleles.
If the father is color blind and the daughter is not, you can suppose that is a recessive allele.
You can tell she is a carrier only, and because we received one sexual allele from each parent. If they ask you about the gender, we can suppose a cross between Xx and XY being lower x the recessive allele (color-blind vision).
When you draw the Punnett square, you'll found the probabilities are XX, XY, Xx, and xY.
So, you have a 50% chance of having a boy and 25% chance of having a color-blind boy.
Answer:
The fewer number of T cells a person has, the more chances to be affected by an opportunistic infection. When the number of T cells reaches 200 cells/µl, the person is at risk of being infected by other infections.
Explanation:
The whole immune system of a person who is infected with HIV infection seems to be severely affected. When the person is not treated or the disease is in a very advanced stage, the depletion of the T- cells turns to be very sharped, especially CD4+ T cells. At this point, the immune system can not resist the attack of other microorganisms. The <em>lower is the number of CD4+ T Cells, the higher possibility the person has to be attacked by opportunistic infections. </em>
Classically, it has been suggested that opportunistic infections appear after the CD4 + T lymphocytes reach very low levels, such as 200 cells/µl. The number of circulating T cells can be used as an indicator and a measure of global "immune competence", and the previously mentioned amount of CD4 + T cells is an accepted universal reference used to predict the risk of having one of these opportunistic infections.
