S10 C2 2 The Role of the Cell Membrane in Transport

Summary

Key Points

• —All matter is composed of particles that are constantly moving, with movement being least in solids and most in gases, and this movement can be influenced by adding or removing energy. 0:47
• —Particles of matter are attracted to each other, have spaces between them that vary by state, and these spaces can be occupied by particles of other substances. 1:02
• —Diffusion is the natural movement of particles from an area of high concentration to an area of low concentration until they are evenly distributed. 2:04
• —Cell membranes are selectively permeable, meaning they control which molecules can pass through, allowing small, non-charged molecules like water while blocking larger molecules or charged particles. 2:28
• —Osmosis is the specific movement of water across a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration, aiming to equalize concentrations. 3:12
• —A concentration gradient describes the difference in concentration of a substance across a space, and particles naturally move along this gradient from high to low concentration. 3:54
• —Solutions can be hypotonic (low solute concentration outside the cell, causing water to enter), hypertonic (high solute concentration outside the cell, causing water to leave), or isotonic (equal concentrations inside and outside the cell). 6:15
• —Passive transport, including diffusion and facilitated diffusion, moves substances across the membrane without requiring cellular energy, following the concentration gradient. 8:47
• —Active transport moves substances against their concentration gradient (from low to high concentration) and requires cellular energy, typically in the form of ATP. 9:10
• —Endocytosis and exocytosis are processes where cells use their membranes to engulf substances (endo) or expel them (exo) by forming vesicles. 9:39