In plant cells, turgidity refers to the rigidity or stiffness of the cell due to the pressure exerted by the cell contents against the cell wall. This turgidity is responsible for maintaining the structure and shape of the plant cell. The correct answer is option 4, which states that vacuoles full of cell sap provide turgidity and rigidity in plant cells.

Vacuoles are membrane-bound sacs found in plant cells that store various substances, including water, enzymes, and ions. The main substance that contributes to turgidity is the cell sap, which is a watery solution containing sugars, salts, and other dissolved substances. When the vacuoles are filled with cell sap, it creates hydrostatic pressure, exerting force on the cell wall and making the cell rigid.

Options 1, 2, and 3 (Ribosomes, Mitochondria, and Golgi apparatus) are incorrect. Ribosomes are involved in protein synthesis, mitochondria produce energy in the form of ATP, and the Golgi apparatus modifies, sorts, and packages proteins. While these organelles play crucial roles in the cell, they are not directly responsible for providing turgidity and rigidity in plant cells.

Therefore, the correct answer is option