Question

What type of transport occurs when substances cross the plasma membrane without any input of energy from the cell?

Answer 1

passive transport

Passive transport occurs when substances cross the plasma membrane without any input of energy from the cell. No energy is needed because the substances are moving from an area where they have a higher concentration to an area where they have a lower concentration. Concentration refers to the number of particles of a substance per unit of volume. The more particles of a substance in a given volume, the higher the concentration. A substance always moves from an area where it is more concentrated to an area where it is less concentrated. Its a little like a ball rolling down a hill. It goes by itself without any input of extra energy.