The theory of 'use and disuse' was proposed by: MCQ with Answer and Explanation

Explanation:
Trypsinogen is an inactive proenzyme secreted by the pancreatic acinar cells. Upon entering the small intestine (duodenum), it is specifically activated into the active enzyme trypsin by the enzyme enterokinase (also known as enteropeptidase), which is secreted by the intestinal mucosa. Trypsin then activates other pancreatic proenzymes like chymotrypsinogen and procarboxypeptidase. Pepsinogen is activated by HCl.

Explanation:
The Munch hypothesis, or mass flow hypothesis, explains the movement of sugars (primarily sucrose) through the phloem. It proposes that sugars are actively loaded into the phloem at the source (e.g., leaves), which lowers the water potential and causes water to enter from the xylem by osmosis. This creates a high turgor pressure. At the sink (e.g., roots, fruits), sugars are unloaded, increasing water potential, and water leaves the phloem, creating a low turgor pressure. The bulk flow of sap is driven by this turgor pressure gradient from source to sink.

Explanation:
During the light reactions of photosynthesis, photolysis of water occurs at photosystem II, splitting water into protons, electrons, and molecular oxygen. The oxygen comes from water, not CO₂. This was demonstrated by using isotopically labeled oxygen (H₂O¹⁸). Glucose is formed in the Calvin cycle. Chlorophyll absorbs light but does not provide oxygen. The overall equation: 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O.