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.
How AIDS develops. 1  The immune system is gradually disrupted. HIV kills cells in the lymph nodes (small glands filled with immune cells that trap foreign organisms) and in other sites. 2  Virus levels in the blood and the lymph nodes increase because the immune system cannot keep up with the amount of virus constantly produced. HIV constantly changes itself, avoiding attack by the antibodies and immune cells that normally control infections.