Question

What is the definition of simple diffusion?

Answer 1

Hint: Simple diffusion can be described as a process in which the movement of substances occurs via a semipermeable membrane or in a solution without any help from transport proteins.
The examples of simple diffusion can be bacteria delivering small nutrients, movement of water and oxygen into the cytoplasm.

Complete answer:
Diffusion can be described as the process of movement of molecules from a region of higher concentration to a region of lower concentration allowing the entry and exit of substances in and out of cells. It can be broadly classified into two main types: Simple diffusion and facilitated diffusion.
Simple diffusion can be defined as the process of movement of solutes along a concentration gradient in a solution or across a semipermeable membrane. This process neither transports proteins, protein channels nor membrane proteins. This process occurs without any expenditure of ATP energy. It doesn’t show transport saturation. The speed of simple diffusion is comparatively slower than facilitated diffusion. Simple diffusion takes place in a number of biological systems such as delivery of oxygen, water, and other small molecules to the cells of the body.
Unlike simple diffusion in cases where cell membranes require specialized membrane proteins in order to help transportation of substances across the membrane is known as facilitated diffusion. Facilitated diffusion is classified into the active and passive transport of solutes across the membrane.

Note:
Facilitated diffusion and active transport both the processes show transport saturation and require carrier proteins . Facilitated diffusion doesn’t require expenditure of ATP energy whereas on the other hand active transport requires expenditure of ATP energy. Unlike Facilitated diffusion, movement of solutes in active transport occurs from low concentration to high concentration.