https://www.khanacademy.org/science/ap-biology/chemistry-of-life/structure-of-water-and-hydrogen-bonding/v/water-as-a-solvent 2024-05-06T19:22:43.24334365Z Water as a solvent Water, due to its polarity, acts as a fantastic solvent, especially for polar substances and ions. This is because the positive and negative ends of water molecules are attracted to ions, allowing them to dissolve. This property is crucial for chemical interactions within cells. However, non-polar substances like hydrocarbons do not dissolve well in water and are termed hydrophobic. Sal Khan video https://cdn.kastatic.org/googleusercontent/h9UjzS82yETbQX39PdB2dOKjImlZPvzu91WtQUjgGEKEOcDPnXkTfkomm8hk0rjftAQHAiMv4VLmFBQTsLoW8GRx Water as a solvent Water, due to its polarity, acts as a fantastic solvent, especially for polar substances and ions. This is because the positive and negative ends of water molecules are attracted to ions, allowing them to dissolve. This property is crucial for chemical interactions within cells. However, non-polar substances like hydrocarbons do not dissolve well in water and are termed hydrophobic. https://cdn.kastatic.org/ka-youtube-converted/lCvBp73ZJ-A.mp4/lCvBp73ZJ-A.mp4 552 Diffusion and osmosis https://www.khanacademy.org/science/ap-biology/chemistry-of-life/structure-of-water-and-hydrogen-bonding/v/importance-of-water-for-life 2025-08-23T06:00:52.132252272Z Importance of water for life Discussion of the properties of water that make it essential to life as we know it: polarity, "universal" solvent, high heat capacity, high heat of vaporization, cohesion, adhesion and lower density when frozen. video https://cdn.kastatic.org/googleusercontent/2FOaIjyqdCGbemYQMl19OchAdpjXARhI8BHGjRx-pyeNtANhkuzfNfJzXm2su9ghyGh66qPbZS2wFUx3A7MFS2yH Importance of water for life Discussion of the properties of water that make it essential to life as we know it: polarity, "universal" solvent, high heat capacity, high heat of vaporization, cohesion, adhesion and lower density when frozen. https://cdn.kastatic.org/ka-youtube-converted/fxlMABxU7zU.mp4/fxlMABxU7zU.mp4 532 Diffusion and osmosis https://www.khanacademy.org/science/biology/membranes-and-transport/diffusion-and-osmosis/v/diffusion-video 2023-09-14T11:22:40.102153098Z Diffusion - Introduction Diffusion occurs when particles move from an area of high concentration to low concentration, creating a concentration gradient. This natural, energy-free process occurs due to the random movement of particles, with a higher chance of particles moving from the high concentration side. Over time, this leads to an equilibrium state with equal concentrations on both sides. Sal Khan video https://cdn.kastatic.org/googleusercontent/RUQQq8sEkvIHMaAACUfO9mwKcYl24deX2nahzhdiPcW8Hu02regQ_phJzKBOoUg3VABgzF1J8ziAQfdkVITX558 Diffusion - Introduction Diffusion occurs when particles move from an area of high concentration to low concentration, creating a concentration gradient. This natural, energy-free process occurs due to the random movement of particles, with a higher chance of particles moving from the high concentration side. Over time, this leads to an equilibrium state with equal concentrations on both sides. https://cdn.kastatic.org/ka-youtube-converted/a_Y9wBQ610o.mp4/a_Y9wBQ610o.mp4 367 Diffusion and osmosis https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-and-osmoregulation/v/diffusion-and-osmosis 2023-04-04T21:01:09.417661961Z Diffusion and osmosis Diffusion refers to the movement of molecules from an area of high concentration to an area of lower concentration. Osmosis is a type of diffusion specifically for water molecules moving across a semi-permeable membrane. A concentration gradient is the difference in concentration of a substance between two areas, which drives diffusion or osmosis. Sal Khan video https://cdn.kastatic.org/googleusercontent/GAWZF4VBIdWVcjS-7wl2dscf4EwnEGvB8xTW_3plAmQZ7LtwQNjzEboBjQg3vYG4lDy6uKYj07N3Qq7-OcQQCTxktg Diffusion and osmosis Diffusion refers to the movement of molecules from an area of high concentration to an area of lower concentration. Osmosis is a type of diffusion specifically for water molecules moving across a semi-permeable membrane. A concentration gradient is the difference in concentration of a substance between two areas, which drives diffusion or osmosis. https://cdn.kastatic.org/ka-youtube-converted/aubZU0iWtgI.mp4/aubZU0iWtgI.mp4 1139 Diffusion and osmosis https://www.khanacademy.org/science/biology/membranes-and-transport/diffusion-and-osmosis/v/concentration-gradients 2024-05-06T19:22:43.24334365Z Concentration gradients Particles move from high to low concentration areas, a process called diffusion. Each particle type has its own unique concentration gradient. This movement isn't planned, but happens randomly. Over time, particles spread evenly, balancing the probability of movement in all directions. This is a key concept in biology and chemistry. Sal Khan video https://cdn.kastatic.org/googleusercontent/14ZOkfLsVJcGGwxDhULnTET5ouiXWWLFjGUsQFHIyEtgJlhh4h37JCZA-F7nx8FFthSrOWOkYVz-7GxBDEa1ivls Concentration gradients Particles move from high to low concentration areas, a process called diffusion. Each particle type has its own unique concentration gradient. This movement isn't planned, but happens randomly. Over time, particles spread evenly, balancing the probability of movement in all directions. This is a key concept in biology and chemistry. https://cdn.kastatic.org/ka-youtube-converted/CNP-dCQ-Cmg.mp4/CNP-dCQ-Cmg.mp4 184 Diffusion and osmosis https://www.khanacademy.org/science/health-and-medicine/respiratory-system/gas-exchange-jv/v/fick-s-law-of-diffusion 2022-11-16T04:22:43.7414897Z Fick's law of diffusion Fick's law describes the movement of particles over time. There are a few strategies for maximizing particle movement, such as minimizing the distance the particles have to travel, using smaller molecules, increasing pressure, and increasing surface area. Fick's law can be expressed as an equation, but it is sometimes written in different forms. Rishi Desai video https://cdn.kastatic.org/googleusercontent/jXMeri5abeXOgMXe5sM-d76cYOCRXkriLvxFIl5u0BBUeqDmA9ppiIuaCIjN9QLMwzK8bbIHA-BgfDBXPmREQSI Fick's law of diffusion Fick's law describes the movement of particles over time. There are a few strategies for maximizing particle movement, such as minimizing the distance the particles have to travel, using smaller molecules, increasing pressure, and increasing surface area. Fick's law can be expressed as an equation, but it is sometimes written in different forms. https://cdn.kastatic.org/ka-youtube-converted/Cg4KlmI_acs.mp4/Cg4KlmI_acs.mp4 742 Diffusion and osmosis https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/cell-size/v/surface-area-to-volume-ratio-of-cells 2023-08-07T17:09:37.131449861Z Surface area to volume ratio of cells In order to stay alive, cells exchange resources, waste, and energy with their environments. This exchange happens across the cell membrane. As the volume of a cell increases, the ratio of surface area to volume decreases, making these exchanges less efficient. Some cells have folds in their membranes, which increase their surface area to volume ratio. video https://cdn.kastatic.org/googleusercontent/B3WhmjCm6ekkjB8rhEg9RK_cbF_lpQZfy26_0am0C0AXY4hV_3BUxzsFrDYrf9ae82CyBj9CUfMOVCkehxAGWA2k Surface area to volume ratio of cells In order to stay alive, cells exchange resources, waste, and energy with their environments. This exchange happens across the cell membrane. As the volume of a cell increases, the ratio of surface area to volume decreases, making these exchanges less efficient. Some cells have folds in their membranes, which increase their surface area to volume ratio. https://cdn.kastatic.org/ka-youtube-converted/uu9eHX6Tu8Q.mp4/uu9eHX6Tu8Q.mp4 312 Diffusion and osmosis https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-and-osmoregulation/v/osmosis 2024-05-06T19:22:43.24334365Z Osmosis Osmosis is a process where water molecules move from an area of low solute concentration to high solute concentration through a semipermeable membrane. This movement can be influenced by factors like solute size and charge. Understanding osmosis helps us grasp how cells maintain balance and control their internal environment. Sal Khan video https://cdn.kastatic.org/googleusercontent/5zu_ewQLVv3K9YYdURQ6En-3UA3eyDo-0dRBO5hg88GHbmgIfSeBEKAUNuEPQOBPiPQxNK0Y36qXLMUFn9hiRNSl Osmosis Osmosis is a process where water molecules move from an area of low solute concentration to high solute concentration through a semipermeable membrane. This movement can be influenced by factors like solute size and charge. Understanding osmosis helps us grasp how cells maintain balance and control their internal environment. https://cdn.kastatic.org/ka-youtube-converted/rCNlG_j_gSM.mp4/rCNlG_j_gSM.mp4 484 Diffusion and osmosis https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-and-osmoregulation/v/water-potential-example 2022-09-15T00:01:10.079780252Z Water potential example Example calculating the water potential of potato squares based on placing them in various concentrations of sucrose solutions. video https://cdn.kastatic.org/googleusercontent/vb71hP0K86EREaQatrJrB9f3dnQMykHy7uoR-Gzfoo-MNrGk4WirI4RuSV28Ai_9d2bSzA5-tbN2Vz8AqIV5zNlOew Water potential example Example calculating the water potential of potato squares based on placing them in various concentrations of sucrose solutions. https://cdn.kastatic.org/ka-youtube-converted/BsnJDe4Tl-4.mp4/BsnJDe4Tl-4.mp4 405 Diffusion and osmosis https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-and-osmoregulation/v/hypotonic-isotonic-and-hypertonic-solutions-tonicity 2023-09-14T11:22:40.102153098Z Hypotonic, isotonic, and hypertonic solutions (tonicity) Cells react differently in hypotonic, isotonic, and hypertonic solutions. In a hypotonic solution, water rushes into the cell causing it to expand or even burst. In an isotonic solution, there is no net flow of water, keeping the cell stable. In a hypertonic solution, water leaves the cell, causing it to shrivel. These reactions are due to the semipermeable nature of cell membranes and the concentration of solutes. Sal Khan video https://cdn.kastatic.org/googleusercontent/5T4Kl6aMA2bQE3_l4YOlLy_yyW_z5jFkn8pkFNylrj0XdYYE8qift3NyRvstZ1_Tp-p28YkBaMcTehT0LO17SHNB Hypotonic, isotonic, and hypertonic solutions (tonicity) Cells react differently in hypotonic, isotonic, and hypertonic solutions. In a hypotonic solution, water rushes into the cell causing it to expand or even burst. In an isotonic solution, there is no net flow of water, keeping the cell stable. In a hypertonic solution, water leaves the cell, causing it to shrivel. These reactions are due to the semipermeable nature of cell membranes and the concentration of solutes. https://cdn.kastatic.org/ka-youtube-converted/afWnU10ZNfg.mp4/afWnU10ZNfg.mp4 390 Diffusion and osmosis https://www.khanacademy.org/science/cambridge-o-level-biology-cie/x2a084a90105205d2:movement-into-and-out-of-cells/x2a084a90105205d2:new-lesson/v/hemodialysis 2023-06-08T11:07:19.872850684Z Hemodialysis Here we give a description of the process of dialysis as an artificial procedure of excretion. Khadijatul Qubra video https://cdn.kastatic.org/googleusercontent/ZCdwTudJg6e6n-P2gsaUborP4izvMsGo71pvEVlX9dNYWcLXcP7VHkWpn2grt4TUP1KoJLQP9NswyHBuBLSFTBw Hemodialysis Here we give a description of the process of dialysis as an artificial procedure of excretion. https://cdn.kastatic.org/ka-youtube-converted/q6mDn8GPGpI.mp4/q6mDn8GPGpI.mp4 378 Diffusion and osmosis https://www.khanacademy.org/science/ap-biology/chemistry-of-life/structure-of-water-and-hydrogen-bonding/a/hs-water-and-life-review 2025-08-23T06:00:52.132252272Z Lesson summary: Water and life Review key terms and the unique properties of water. article https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-and-osmoregulation/a/osmosis 2024-01-19T18:25:11.349624553Z Osmosis and tonicity Osmosis and tonicity. Hypertonic, isotonic, and hypotonic solutions and their effect on cells. article https://www.khanacademy.org/science/cambridge-o-level-biology-cie/x2a084a90105205d2:movement-into-and-out-of-cells/x2a084a90105205d2:new-lesson/e/osmosis 2023-12-03T23:39:25.543647125Z Osmosis and tonicity Test your knowledge on the process of osmosis! Ashley exercise https://www.khanacademy.org/science/cambridge-o-level-biology-cie/x2a084a90105205d2:movement-into-and-out-of-cells/x2a084a90105205d2:new-lesson/e/diffusion-and-osmosis 2022-08-23T00:49:21.470582385Z Diffusion, osmosis, and tonicity Test your knowledge on the processes of diffusion, osmosis, and tonicity! Ashley exercise https://www.khanacademy.org/science/cambridge-o-level-biology-cie/x2a084a90105205d2:movement-into-and-out-of-cells/x2a084a90105205d2:new-lesson/e/osmosis-and-diffusion 2026-04-21T09:50:34.424034119Z Osmosis and Diffusion Let's solve some questions! vibhor exercise https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-and-osmoregulation/e/mechanisms-of-transport--tonicity-and-osmoregulation-exercise 2023-08-07T17:09:37.131449861Z Mechanisms of transport: tonicity and osmoregulation Test your knowledge of mechanisms of transport: tonicity and osmoregulation! Ashley Mucha exercise https://www.khanacademy.org/science/cambridge-o-level-biology-cie/x2a084a90105205d2:movement-into-and-out-of-cells/x2a084a90105205d2:new-lesson/e/plasmolysis-and-imbibition 2025-11-30T11:50:38.943839903Z Plasmolysis and Imbibition This exercise helps students compare plasmolysis, osmosis, and imbibition by using short, realistic plant-cell scenarios. They identify how hypertonic vs. hypotonic solutions change turgor, how to recognize incipient vs. full plasmolysis, how deplasmolysis begins, and why tissues wilt or stiffen. Khan Academy exercise