What is osmosis?

Osmosis is specifically defined as the movement of water molecules across a selectively permeable membrane, typically toward a region of higher solute concentration (such as salt). This process occurs to balance solute concentrations on either side of the membrane. When there is a higher concentration of solutes (such as salt) on one side of the membrane, water will naturally move toward that side in an effort to dilute the solute, effectively balancing the concentrations.

This choice correctly identifies the fundamental concept of osmosis, which plays a crucial role in various biological functions, including maintaining cell turgor pressure and regulating fluid balance in organisms. Understanding this phenomenon is particularly important in the contexts of physiology and medicine, such as in managing conditions that involve fluid shifts within the body.

The other options describe different biological processes. For instance, diffusion of oxygen refers to gas exchange rather than osmosis, while the flow of nutrients in the bloodstream pertains to nutrient absorption rather than water movement. Likewise, the absorption of solids in the intestines involves different mechanisms, such as active transport and endocytosis, rather than osmosis specifically focused on water movement.