The process of separation of leaf, flower, or fruit from the plant body is called abscission. It is primarily controlled by: MCQ with Answer and Explanation

Explanation:
Veins, especially in limbs, have one-way valves that prevent the backflow of blood as it returns to the heart against gravity. Arteries have thick walls to withstand pressure and lack valves. Capillaries have no valves.

Explanation:
The pineal gland is a small, pinecone-shaped gland located in the epithalamus, near the center of the brain. In humans, it is not a true eye, but it is photosensitive; it receives information about the light-dark cycle from the retina via the suprachiasmatic nucleus and the sympathetic nervous system, and uses this to regulate the secretion of melatonin, thus controlling circadian rhythms. In some lower vertebrates (like certain reptiles, amphibians, and fish), the pineal complex includes a parietal eye (or 'third eye'), a light-sensitive organ on the top of the head that can literally detect light and shadows, helping with camouflage and predator detection.

Explanation:
While most arteries carry oxygenated blood, the pulmonary artery carries deoxygenated blood from the heart to the lungs. Veins possess valves along their length to ensure unidirectional blood flow back to the heart against gravity. Capillaries are composed of a single layer of endothelial cells (thin walls) to facilitate the exchange of gases and nutrients. Only statement 2 is universally correct.