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diffusion osmosis active transport
A LevelBiology~4 min read
Overview
This lesson explores the fundamental mechanisms by which substances move across cell membranes: diffusion, osmosis, and active transport. Understanding these processes is crucial for comprehending how cells maintain homeostasis, absorb nutrients, and excrete waste products.
1. Diffusion: Passive Movement Down a Gradient
Diffusion is a passive process, meaning it does not require metabolic energy from the cell. It is driven by the random motion of particles. Substances move from an area where they are in **high concentration** to an area where they are in **low concentration**, effectively moving 'down' their concen...
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Key Concepts
- Diffusion: The net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient.
- Osmosis: The net movement of water molecules across a partially permeable membrane from a region of higher water potential to a region of lower water potential.
- Active Transport: The movement of substances across a cell membrane against their concentration gradient, requiring energy (ATP).
- Partially Permeable Membrane: A membrane that allows certain molecules or ions to pass through it by diffusion or osmosis.
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Exam Tips
- →Clearly distinguish between passive (diffusion, facilitated diffusion, osmosis) and active transport, focusing on the requirement for energy and movement relative to the concentration gradient.
- →For osmosis questions, always refer to 'water potential' and 'partially permeable membrane'. Avoid using terms like 'concentration of water' or 'strong/weak solution' without also linking to water potential.
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