Final answer:
Active transport is the cellular process that moves substances against their concentration gradient using energy from ATP, while osmosis is the passive diffusion of water across a semi-permeable membrane from higher to lower water concentration. Active transport is crucial for maintaining concentrations of ions essential for cell functions.
Step-by-step explanation:
The process of water diffusion against its concentration gradient, specifically mentioned in the question, is a phenomenon known as active transport. This cellular process involves movement of substances through carrier proteins or pumps in the cell membrane. Unlike passive diffusion where substances move along their concentration gradient, active transport requires energy to move substances from an area of lower concentration to an area of higher concentration. Osmosis, however, is a special case of diffusion where water moves from a region of high water concentration (or low solute concentration) to a region of low water concentration (or high solute concentration), passing through a semi-permeable membrane. No energy input in the form of ATP is needed for osmosis as it is a passive transport process.
Cells use active transport to maintain necessary concentrations of ions and other substances vital for their function. This process is energy-dependent, utilizing ATP generated through cellular metabolism. It is fundamental for maintaining vital cellular conditions, such as the electrolyte balance across the membrane in red blood cells, which maintains the balance between sodium and potassium ions crucial for cellular operation. Active transport mechanisms are essential for the survival of cells and can be affected negatively by metabolic poisons that disrupt ATP production.