Assertion (A): Epithelial tissues form protective layers. Reason (R): They are highly vascularized to transport nutrients. MCQ with Answer and Explanation

Explanation:
Platelets (thrombocytes) are small, anucleate cell fragments that adhere to the site of injury, release clotting factors, and aggregate to form a platelet plug, initiating the coagulation cascade. RBCs transport oxygen, WBCs defend against infection, and plasma proteins like albumin maintain osmotic balance. Clotting factors are also present in plasma, but platelets are the primary cellular component.

Explanation:
Robert Hooke, an English scientist, is credited with the discovery of cells in 1665. He observed a thin slice of dead cork tissue from an oak tree under a primitive compound microscope. He saw a honeycomb-like structure of small compartments, which he called 'cells' (from the Latin 'cella', meaning small room). He was actually observing the non-living cell walls of dead plant cells.

Explanation:
The vascular cambium is a thin layer of meristematic cells located between the primary xylem and primary phloem in the vascular bundles of dicot stems and roots, and in the secondary vascular tissue. It is a lateral meristem that divides periclinally (parallel to the surface). It produces secondary xylem (wood) cells towards the inside (center) of the stem or root, and secondary phloem (inner bark) cells towards the outside (periphery). Since it produces xylem much faster than phloem, the secondary xylem accumulates and forms the bulk of the wood.