The sinoatrial (SA) node is a specialized cluster of cells in the right atrium near the opening of the superior vena cava. It generates electrical impulses spontaneously, setting the pace of the heartbeat, hence called the pacemaker. The impulse spreads to the atrioventricular (AV) node, then to bundle of His and Purkinje fibers. Normal SA node firing rate is 60-100/min.
Consider statements about vitamins: 1. Vitamin B12 contains cobalt. 2. Vitamin K is essential for blood clotting. 3. Beriberi is caused by Vitamin C deficiency. Which are correct?
Explanation:
Vitamin B12 (cyanocobalamin) is a complex vitamin that contains the trace mineral cobalt. Vitamin K is essential for the synthesis of prothrombin and other clotting factors in the liver. Beriberi is caused by a deficiency of Vitamin B1 (thiamine), whereas Vitamin C deficiency causes scurvy. Thus, statements 1 and 2 are correct.
Explanation:
Prokaryotes lack a true nucleus and nuclear membrane; their genetic material is concentrated in a nucleoid region. They possess ribosomes (70S), a plasma membrane, and usually a cell wall. The absence of membrane-bound organelles is a defining feature distinguishing them from eukaryotes. Thus, the nuclear membrane is absent.
Explanation:
Apoptosis is a highly regulated and organized process of programmed cell death that occurs in multicellular organisms. It is crucial for development, maintaining tissue homeostasis, and eliminating damaged or infected cells. Unlike necrosis (accidental cell death), apoptosis does not cause inflammation and involves cell shrinkage and fragmentation.
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