DNA replication is said to be semi-conservative because: MCQ with Answer and Explanation

Explanation:
Cyanobacteria (blue-green algae) are prokaryotes, possessing a nucleoid region but no true nucleus or membrane-bound organelles. Amoeba, yeast (fungus), and Paramecium are eukaryotes. Cyanobacteria perform oxygenic photosynthesis and some fix nitrogen, having chlorophyll a and phycobilins. They are classified under Kingdom Monera. Examples: Nostoc, Anabaena.

Explanation:
Mature human RBCs have a lifespan of approximately 120 days, after which they are phagocytosed by macrophages in the spleen and liver. They lack nuclei and organelles, thus cannot repair themselves. New RBCs are produced in the bone marrow at a rate of about 2 million per second. Erythropoietin stimulates RBC production.

Explanation:
The Sinoatrial (SA) node, located in the right atrium, is the natural pacemaker because its cells are autorhythmic; they can spontaneously generate action potentials without external neural input. Crucially, the SA node has the highest intrinsic rate of depolarization (about 70-80 beats per minute) compared to other autorhythmic tissues like the AV node or Purkinje fibers. Therefore, it sets the pace for the entire heart, overriding slower pacemakers.