Active Transport vs Diffusion
Active transport and diffusion are two types of the molecule and ion transport methods across the cell membranes. Transport can be either active or passive depending on the form of energy that requires for transporting substances. Water, oxygen, and carbon dioxides passively move across membranes, whereas glucose and ions like Na+, Ca2+ and K+ actively move across membranes. The transport of substances across cell membranes is extremely essential to sustain the cell life. The transport of ions and molecules across membrane depends on the permeability of the membrane, the type of solute, and transport mechanisms.
What is Active Transport?
Transporting substances across a cell membrane against a concentration gradient; that is from the side with the lower concentration to the side with the higher concentration, is known as active transport. The energy requirement for active transport is fulfilled directly or indirectly by ATP hydrolysis. The two types of active transport methods are primary active transport and secondary active transport. Carrier proteins of primary active transport can hydrolysis ATP in order to power the transport directly. Ions like Na+, Ca2+, and K+ are transported by this mechanism. In secondary active transport, the concentration gradients established by ion pumps are used as the energy source to transport substances like glucose, chloride, and bicarbonate ions across the membrane.
What is Diffusion?
Diffusion involves the movement of substances across the membrane with the help of concentration gradient; that is from a higher concentration to a lower concentration. Water and gases including oxygen and carbon dioxides are the main substances that move by diffusion. The two types of diffusion are simple diffusion and facilitated diffusion. The main difference between these two types is that the facilitated diffusion involves carrier protein molecules. Carrier protein molecules form the carrier complex with the transporting substance. Due to the higher solubility of carrier complex in the lipid bilayer of membranes, the rate of facilitated diffusion is much higher than that of simple diffusion.
What is the difference between Active Transport and Diffusion?
• In active transport, substances move against a concentration gradient; thus, ATP energy is required for active transport, but in diffusion, substances move passively along a concentration gradient and it does not involve ATP energy.
• Two types of diffusion are simple diffusion and facilitated diffusion, whereas two types of active transport are primary and secondary active transport.
• In diffusion, both lipids and proteins are involved as membrane components responsible for transport whereas, in active transport, the membrane components involved are only proteins.
• In simple diffusion, transported substances do not bind to the cell membrane components whereas, in active diffusion, they do bind.
• Energy source of diffusion is the concentration gradient while that of active transport is either concentration gradient or ATP hydrolysis.
• Active transport is specific, whereas diffusion is non-specific.
• In active transport, saturation occurs at high concentrations of transported molecules whereas, in simple diffusion, saturation does not occur.