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Structure of HIV
1. HIV belongs to the group of viruses called retroviruses.
2. It is spherical in shape and it measures about 100 to 140 nanometer. 3. It contains the genetic material double stranded RNA surrounded by a protein envelope. 4. HIV causes AIDS in man.
Structure of bacterium
1. There is no well defined nucleus, but the genetic material DNA is condensed in the central region of the cell. Hence it is a prokaryote. 2. It possesses cell wall which lies adjacent and external to the plasma membrane. 3. Ribosome exists in groups called polyribosome or polysomes. Each ribosomes consists of a large and a small subunit. 4. A long thin flagellum is seen. It is useful for locomotion.
Structure of a chloroplast
1. The chloroplast is the photosynthetic organelle of green plants and it is surrounded by outer and inner membrane. 2. Within the inner membrane there is a liquid matrix called stoma which contains circular DNA, ribosome and enzymes for photosynthesis. 3. Since the chloroplast has ribosome and DNA, it is known as semiautonomous organelle. 4. In the stroma, there is an extensive system of double membranous structures called thylokoids arranged in patches called grana. The grana are disc shaped.
Structure of a mitochondrion
1. The mitochondria are rod shaped and bounded by outer and inner membranes. 2. The inner membrane has numerous infoldings called cristea which are present in mitochondrial matrix. 3. The liquid mitochondrial matrix contains circular DNA, ribosome, lipids, proteins, and enzymes to catalyst the reactions of Krebs cycle. 4. Since the mitochondria have DNA and ribosomes, they are called as semiautonomous organelle.
Mitosis - metaphase
1. Nuclear membranes disappear and the spindle fibers appear at opposite poles in the cytoplasm 2. The chromosomes orient themselves in the equator of the spindle...