🔋college physics i – introduction review

key term - Passive Transport

Definition

Passive transport is a mechanism by which molecules or ions move across a cell membrane without the expenditure of cellular energy. It relies on the random thermal motion of particles and the concentration gradient between the two sides of the membrane to facilitate the movement of substances.

5 Must Know Facts For Your Next Test

  1. Passive transport does not require the input of cellular energy, such as ATP, to drive the movement of substances across the cell membrane.
  2. The rate of passive transport is determined by the concentration gradient, the permeability of the membrane, and the size and charge of the molecules or ions being transported.
  3. Passive transport is important for the movement of essential nutrients, gases, and waste products in and out of cells, as well as for maintaining the proper balance of ions within the cell.
  4. Diffusion and osmosis are two common forms of passive transport, where substances move down their concentration gradients without the expenditure of energy.
  5. Facilitated diffusion is a type of passive transport that uses specialized carrier proteins to facilitate the movement of molecules or ions across the cell membrane, even when the concentration gradient is not favorable.

Review Questions

  • Explain how the concentration gradient drives the process of passive transport.
    • The concentration gradient, which is the difference in the concentration of a substance on either side of a membrane, is the driving force behind passive transport. Molecules or ions will naturally move from an area of higher concentration to an area of lower concentration, driven by the random thermal motion of the particles. This movement down the concentration gradient does not require the expenditure of cellular energy, as the concentration gradient provides the necessary 'push' for the substances to cross the membrane.
  • Describe the role of membrane permeability in passive transport.
    • The permeability of the cell membrane is a crucial factor in determining the rate of passive transport. The membrane's structure and composition, particularly the presence of specialized transport proteins, can influence how easily certain molecules or ions can cross the barrier. For example, the lipid bilayer of the cell membrane is permeable to small, uncharged molecules like oxygen and carbon dioxide, allowing them to diffuse freely. However, the membrane may be less permeable to larger or charged molecules, which may require facilitated diffusion or other passive transport mechanisms to cross.
  • Analyze the differences between diffusion, osmosis, and facilitated diffusion as forms of passive transport.
    • Diffusion, osmosis, and facilitated diffusion are all forms of passive transport, but they differ in the specific mechanisms involved. Diffusion is the movement of molecules or ions down their concentration gradient, driven solely by the random thermal motion of the particles. Osmosis is the movement of water molecules across a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration. Facilitated diffusion, on the other hand, uses specialized transport proteins to facilitate the movement of molecules or ions across the cell membrane, even when the concentration gradient is not favorable. While all three processes do not require the expenditure of cellular energy, they involve distinct mechanisms and have different implications for the movement of substances across the cell membrane.