This figure illustrates 3 hypotheses of how a cancer stem cell may arise: (1) A stem cell undergoes a mutation, (2) A progenitor cell undergoes two or more mutations, or (3) A fully differentiated cell undergoes several mutations that drive it back to a stem-like state.
Answer:
Option (B).
Explanation:
Neurons or nerve cell are the basic structural and functional unit of the nervous system. Fibers are the thread like long projection of the nerve cells.
Neurons are classified into three fibers- Group A fibers, B fibers and C fibers. The group C fibers cannot capable of doing the saltatory conduction of the nerve impulse because they are unmyelinated.
Thus, the correct answer is option (B).
Gonads are sex organs that produce gametes. Male gonads are the testes, which produce sperm and male sex hormones. Female gonads are the ovaries, which produce eggs (ova) and female sex hormones.
Answer:
d. Smoking
Explanation:
Nicotine is a chemical found in many plants such as tobacco. It is one of the 4000 chemicals that tobacco presents and the main component that acts in the brain.
This chemical is absorbed through the skin and lining of the mucosa of the nose and mouth, or in the lungs by prior inhalation. Nicotine can quickly reach the bloodstream and brain and reach maximum levels. The action of smoking cigarettes causes nicotine to reach the brain in just 10 seconds after inhalation. Although the acute effects dissipate in a few minutes, they cause the need to continue the intake of the substance (addiction)
