Passive transport
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The correct answer and explanation is :
Passive Transport is a biological process in which substances move across a cell membrane without the use of energy from the cell. This movement occurs due to concentration gradients, where molecules move from an area of higher concentration to an area of lower concentration. Because it doesn’t require cellular energy (ATP), passive transport is considered an energy-efficient way for cells to maintain homeostasis.
Types of Passive Transport
- Diffusion: This is the most common form of passive transport. It involves the movement of molecules from an area of high concentration to an area of low concentration until equilibrium is reached. For example, oxygen and carbon dioxide diffuse across the cell membrane, allowing cells to exchange gases in the lungs and tissues.
- Facilitated Diffusion: This process also involves the movement of substances from high to low concentration but requires the assistance of membrane proteins. These proteins, known as channel or carrier proteins, help large or charged molecules (like glucose or ions) pass through the cell membrane, which would otherwise be impermeable to them.
- Osmosis: This is a specific type of facilitated diffusion involving water molecules. Osmosis occurs when water moves across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. For example, when plant roots absorb water from the soil, they rely on osmosis to take in the water.
Key Points about Passive Transport
- No Energy Required: Passive transport does not use energy in the form of ATP. This makes it a cost-effective way for cells to regulate their internal environment.
- Direction of Movement: Molecules move along a concentration gradient (from high to low concentration).
- Types of Molecules: Small, nonpolar molecules (such as oxygen and carbon dioxide) move easily through the lipid bilayer by diffusion. Larger or polar molecules (like glucose and ions) require facilitated diffusion via proteins.
In summary, passive transport is a vital and energy-efficient mechanism that helps cells maintain balance by moving substances in and out as needed. The key processes—diffusion, facilitated diffusion, and osmosis—are essential for many physiological functions in the body, including nutrient uptake, waste removal, and the regulation of water balance.