Concept:Guard cells open by absorbing water, which makes them turgid and bends them apart.
Explanation:Guard cells are found around the stomatal pore in plant epidermis.
When water moves into guard cells, they swell and become turgid.
This causes the thin outer walls to bulge, opening the pore.
Water enters guard cells through the cell membrane from the surrounding epidermal cells.
This movement of water occurs from a region of higher water concentration to a region of lower water concentration across a selectively permeable membrane.
Since the movement of water is passive and along the concentration gradient, the process is osmosis.
Answer:A. osmosis