The human immunodeficiency virus (HIV) that causes the disease known as aids selectively infects helper T cells (CD4+).
This retrovirus also infects macrophages and dendritic cells. When CD4+ T cell numbers decrease below a critical level (due to the killing of this cells with different mechanisms), cell-mediated immunity is lost. As a result, the body becomes progressively more susceptible to infections, leading to the development of AIDS.
<span> HIV can be transmitted only via body fluids like blood, semen, pre-seminal fluid, rectal fluids, vaginal fluids, and breast milk, which means that people usually get or transmit HIV through sexual behaviours and use of the needle. For HIV infection, these fluids must come in direct contact with a mucous membrane or damaged tissue. Another way is to be directly injected into the bloodstream (from a needle for example).</span>
This structure is held together by weak forces between the amino acid molecules in the chain. High temperatures will break these forces. The enzyme, including its active site, will change shape and the substrate no longer fit. The rate of reaction will be affected, or the reaction will stop.
There are choices for this question namely:
<span>movement of oocytes </span>
<span>movement of sperm if present </span>
<span>expelling of the fetus at delivery </span>
<span>all of the above
</span>
The correct answer is "all of the above". The smooth muscle layers in the female reproductive tract facilitates the movement of oocytes from the ampulla of the fallopian tube to the uterus. If sperm is present, the contraction of smooth muscle in the uterus will propel the sperm towards the fallopian tubes where it can fertilize the ovum. At delivery, uterine contractions (along with an adequate pelvis) facilitate the delivery of the fetus; without which the labor will be dysfunctional or prolonged and this is called dystocia.
Answer:
<u>Antigenic drift</u> refers to the slow accumulation of genetic changes to an influenza virus over time.
Explanation:
Antigenic drift is defined as the mechanism by which viruses undergo variation. This mechanism involves the slow accumulation of mutations in the viral genes, that are responsible for coding the antibody binding sites. This leads to the formation of a new strain of virus, which can't be inhibited by the old antibodies. Due to this, the virus can easily spread the disease.
The antigenic drift occurs in the influenza A virus and also the influenza B viruses.
Therefore, <u>Antigenic drift refers to the slow accumulation of genetic changes to an influenza virus over time.</u>