3. Compare and contrast active transport to passive transport of diffusion of molecules across the cell membrane. You may use a diagram and/or an analogy to help?
Active transport and passive transport are two mechanisms by which molecules can move across the cell membrane.
Passive transport, also known as diffusion, is a process in which molecules move from an area of higher concentration to an area of lower concentration. This movement occurs spontaneously and does not require the input of energy. There are three types of passive transport: simple diffusion, facilitated diffusion, and osmosis.
Simple diffusion occurs when small, nonpolar molecules, such as oxygen and carbon dioxide, move directly through the lipid bilayer of the cell membrane. They move down their concentration gradient, with no need for any specific transport proteins.
Facilitated diffusion, on the other hand, involves the movement of larger, charged molecules or ions. These molecules cannot easily pass through the lipid bilayer, so they require the presence of specific transport proteins called carrier proteins or channel proteins. These proteins act as tunnels or gates, allowing specific molecules to pass through. Facilitated diffusion also occurs down the concentration gradient and does not require energy input.
Osmosis is a special type of passive transport that specifically refers to the movement of water molecules. Water can move freely through the lipid bilayer, but it can also move through specialized channel proteins called aquaporins. Osmosis occurs when there is a difference in the concentration of solutes (such as ions or molecules) on either side of the membrane, causing water to move from an area of lower solute concentration to an area of higher solute concentration.
In contrast, active transport requires the input of energy, usually in the form of ATP. Active transport involves the movement of molecules against their concentration gradient, from an area of lower concentration to an area of higher concentration. This process is carried out by specific proteins called pumps, which use ATP to transport molecules across the cell membrane. Active transport is essential for maintaining concentration gradients in the cell, and it allows the cell to accumulate molecules or ions that are needed in higher concentrations inside the cell.
An analogy to understand the difference between active transport and passive transport is using a bicycle. Passive transport is like coasting downhill on a bicycle without pedaling. The bike moves with the help of gravity, without any energy input. This represents the movement of molecules down their concentration gradient in passive transport.
In contrast, active transport is like riding a bicycle uphill. It requires the input of energy in the form of pedaling to move the bike against gravity. Similarly, in active transport, molecules are moved against their concentration gradient and require the input of energy to be transported across the cell membrane.
Overall, the main differences between active transport and passive transport include the requirement of energy, the direction of movement (against or with the concentration gradient), and the involvement of specific transporter proteins.