Grass Anatomy: Roots & Stems. A grass plant is composed of a root, a stem, leaves and a seed head. The root is fibrous, or composed of many small roots that move out in all directions.The stem, or culm, starts out a single section but develops nodes and internodes that segment it along its length.eaves & Seed-heads. Grass leaves emerge from nodes on the stem, with the newest growing on the opposite side from an older leaf below it. A single leaf is composed of a blade, sheath, ligule, auricle and collar.
HIV is the cause of the spectrum of disease known as HIV/AIDS. HIV is a retrovirus that primarily infects components of the human immune system such as CD4+ T cells, macrophages and dendritic cells. It directly and indirectly destroys CD4+ T cells.
What is AIDS? AIDS is not a virus but a set of symptoms (or syndrome) caused by the HIV virus. A person is said to have AIDS when their immune system is too weak to fight off infection, and they develop certain defining symptoms and illnesses. This is the last stage of HIV, when the infection is very advanced, and if left untreated will lead to death.