Question

Why isn't energy required for the passenger molecule to be carried across the cell membrane by the carrier molecules?

Answer 1

Passenger molecules are transported across the cell membrane by carrier proteins via passive transport, which follows the concentration gradient and does not require cellular energy input.

Step-by-step explanation:

Energy is not required for the passenger molecule to be carried across the cell membrane by the carrier molecules because this process is a form of passive transport. In passive transport, substances move along their concentration gradient, which means they move from an area of higher concentration to an area of lower concentration without the need for energy input from the cell. Carrier proteins facilitate this transport process by binding to the molecules, undergoing a change in shape to carry them across the membrane, and releasing them on the other side, all without consuming cellular energy such as ATP.

However, it's important to distinguish this process from active transport, where substances are moved against their concentration gradient, from an area of low concentration to an area of high concentration, and this requires energy, typically in the form of ATP. These proteins are often referred to as "pumps" as they use energy to pump molecules across the cell membrane.

Answer 2

Energy is not required for the passenger molecule to be carried across the cell membrane by the carrier molecule simply because they are moving down a concentration gradient, that is to say movement is from an area of high concentration to an area of low concentration.

When particle move from areas of high concentration to areas of low concentration, they do not need energy. For example this is how the aroma of cooking spreads from the kitchen (higher concentration) to all the other rooms in the house.