The answer is the first choice
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>
Answer:
The CNS, or central nervous system is comprised of neurons, the cell units that form it. These cells, in turn, are formed by their cell bodies, the dendrites on them and the terminal ends of the axons, which are like the connectors, or roadways, for neurons. When viewed on a microscope, brain tissue, particularly, looks stained with two different colors: grey, or pinkisk, for the grey matter, and whiter for the white matter, which are the axons. This is basically why the two are called grey matter and white matter of the CNS.
So one difference between these two matters is the color they display when viewed. The second is the parts of the neuron that form the two; while the white matter is formed from the neuronal axons, the grey matter is formed by the dendrites, cell bodies and axonal terminals. A third differentiation is that most synaptic activity takes place in the grey matter, while most conduction of information from the cell bodies is performed by the axons.
Answer:
pollen is important in fertilization because pollen carries male gamete and it helps in transportation of male gamete during fertilization in mainly gymnosperms and angiosperms.
