The structure that allows the exchange of gases and nutrients between the mother and fetus is the: MCQ with Answer and Explanation

Explanation:
The 10% law of energy transfer, which states that only about 10% of the energy from one trophic level is transferred to the next, was proposed by Raymond Lindeman in 1942. This law explains why food chains typically have only 3-4 trophic levels; there is simply not enough energy available to support higher levels.

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.

Explanation:
Pancreatic lipase is the major enzyme for fat digestion, secreted by the exocrine pancreas into the duodenum. It hydrolyzes triglycerides into monoglycerides and free fatty acids, aided by bile salts that emulsify fats. Gastric lipase (stomach) plays a minor role. Liver produces bile but not lipase. Salivary glands produce salivary amylase.