Correct choice is (d) It provides protection and surface area
Explanation: The microcarrier beads are used to increase the number of adherent cells per flask and are either dextran or glass based, they come in a range of densities and sizes. The beads are buoyant and therefore can be used with spinner culture flasks. The surface area available for cell growth on these beads is huge. It is a support matrix allowing for the growth of adherent cells in bioreactors.