While culturing some cells, you lower the temperature of the culture. What happens immediately to the membrane fluidity?

The correct answer is the membrane will become less fluid.

Membrane fluidity is termed as viscosity which is found on the lipid bilayer and is found in the synthetic lipid membrane and in cell membrane.

The fluidity of the membrane is being influenced by lipid packing. Viscosity of membrane is well known to affect the biomolecules which are found within the protein, the diffusion of proteins and in the rotation.

We can increase the membrane by heating it up. When lipids are heated up, they do acquire thermal energy.