The SA node, located in the right atrium, spontaneously generates electrical impulses, setting the heart rate. It is the natural pacemaker. The AV node delays the impulse before it reaches the ventricles.
Explanation:
Prokaryotic cells lack a true nucleus; their genetic material is located in a nucleoid region. They possess 70S ribosomes (50S+30S subunits), whereas eukaryotic cells have 80S ribosomes. Prokaryotes generally have a cell wall (except Mycoplasma) and circular DNA, not linear. Membrane-bound organelles like mitochondria, ER are absent. Examples: bacteria and blue-green algae. This distinction is fundamental in cell biology.
Explanation:
The pancreas functions as an exocrine gland (secreting digestive enzymes into the duodenum via the pancreatic duct) and an endocrine gland (secreting insulin, glucagon, somatostatin from the islets of Langerhans into the blood). Thyroid, pituitary, and adrenals are purely endocrine.
Explanation:
Phycoerythrin absorbs blue-green light, which penetrates deeper water, allowing red algae to photosynthesize at greater depths. Fucoxanthin is in brown algae, chlorophyll b green, carotenoids orange.
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