Henry Hadfield Owens yeah yeah come here thanks for sitting down as you know I'm calling everybody up to talk about grades for IB Biology as of right now taking a look you're doing pretty well seems like your formative grades are great you're doing all the work in class turning in all your homework that's awesome your sumita of grade though summative grade looks like it's dropping just a little bit those exam scores look like they're hurting you a little bit more you know then that formative grade so I think what you really need to do is you need to sit down you need to study uh you need to make sure you know the content right because you are so insanely smart and honestly you have so much potential and I really don't want to see you throw it all down the drain Carl are you practicing with the water again no no [Music] in this section we're going to talk a bit more about just how amazing water is as a molecule and how it is important for living systems and one of the main properties it has is being a solvent we covered some of this information in section a1.1 but to recap water is a polar molecule that has both negative and positive ends due to differences in the pull of electrons between the oxygen and hydrogen atoms these charges along with its bent structure allow it to do many important things in biological systems we call water the universal solvent because it can easily dissolve many substances within it in this case we would call water the solvent the particles dissolved in it the solute and we call the process of this happening or substances dissolving salvation polar molecules and charged atoms can easily dissolve in water because of its polarity water ends up surrounding these substances which could be an ion like sodium or chloride or a molecule like glucose based on charged attractions Andor the creation of hydrogen bonds if the substance is negatively charged the positive ends of the water molecule will be pulled towards it and vice versa if it is positively charged this is what it means and looks like for a substance to dissolve in water water molecules tend to stick together because of their hydrogen bonds but they can also freely move which means that those hydrogen bonds are constantly being broken and reformed as molecules shift when a solute is added and salvation takes place water molecules tend to have strong intermolecular attractions to some solutes more so than other water molecules which means they break some of those hydrogen bonds between each other and move to encapsulate the solute this shift and attractive forces cause water molecules to move to parts of a solution that have more Sol Ute available as they tend to be more attracted to the dissolved solute we can illustrate this concept by viewing different solutions both inside and outside of a cell let's say that our cell is in an aquous solution which contains water and also has an aquous cytoplasm within the membrane which contains water as all cells do as we have already learned about the cell membrane water can freely move in and out of the cell through the membrane via simple diffusion now let's say we have one solute call it Sugar that cannot move across the membrane and this is in a high concentration outside of the cell based on what we know about the attractive forces of water which way will the water naturally move the answer is it will move towards the higher concentration of solute because the water has a greater attractiveness towards the solute than two other water molecules so it will move out until enough water molecules have enclosed and encased those particles making as many connections as possible in the a1.1 video we we discussed how these water molecules will spread out and be even based on these concentration gradients and this explanation and the process of Salvation that we just went through describes one reason for why this occurs and why water will always spread out amongst solutes we have specific terms to describe solutions that have the ability to impact water movement and again water will always move from a low solute concentration to a high solute concentration if a solution has a comparatively low amount of solute we call it hypotonic and if it has a high amount of solute we call it hypertonic in this scenario like we saw with the cell the water will move out because the external solution is hypertonic but if we flip the solute concentration in this example the exterior solution is hypotonic which means water will move into the cell if both of the concentrations contain the same amount of solute we call the solution isotonic and water will move both in and out at the same rate with no net change in solvent concentration make sure you know the ins and outs of these three terms including being able to explain them in terms of solute concentration for the IB exam we covered this in detail on the last slide but I want to note here that the net movement of water is called osmosis and based on the solution a cell is in especially within our body the movement of water can be forced either into or out of a cell this happens because the cell membrane is permeable to water and selectively permeable to most solutes if different concentrations of solutes showing hypotonic or hypertonic Solutions are built on either side of the membrane osmosis will be forced and water will move no matter if it is beneficial or harmful to the cell the physics and force of this movement will take over and if solute concentrations are the same between the inside and outside of the cell water will continue to move both in and out at the same rate in which we refer to the solution as isotonic [Music] experiments have been done on both plant and animal cells to elicit water movement in terms of plants potatoes are great to use for osmosis experimentation your teacher may have you do an experiment like this in class and even open up the possibility for you to ask a unique question using these methods for the biology internal assessment water naturally mov moves into plant roots because the roots are hypertonic compared to the water in the adjacent soil but what happens if you take a plant like a piece of a potato and submerge its tissue into different solutions that contain different concentrations of the same solute we can see an illustrated setup here based on the solution you should see water moving into and out of the potato pieces at rates comparable to the concentrations of the solutions compared to the concentration within the potato so assuming the potato has an internal cell solute concentration equal to the middle experimental group this should not show a change in mass because the two solutions are isotonic at the highest concentration of experimental solution we should see water move out of the potato because the external solution is hypertonic which means the potato will lose water and therefore lose mass and the lowest concentration experimental solution should be hypotonic to the potato so water will move in and will gain Mass when compared to its original Mass before being placed in the solution when completing this experiment within your classroom make sure to calculate standard deviation and standard error to help analyze your data these two concepts will show up on the IB exam and within your internal assessment recall that plant cells have a cell membrane and a cell wall where animal cells only have a cell membrane for this reason these two different types of eukariotic cells handle different amounts of osmotic change in different ways plant cells cells are able to take in large amounts of water because they are stabilized and supported by their cell walls the water vacu of a plant cell being completely full puts this pressure on the cell which is called turer pressure which is a natural and beneficial pressure for the plant cell to have when all of the cells within a plant contain this high pressure the plant can stand upright which is important to compete for light for photosynthesis If plants do not receive water for an extended period of time they lose this pressure and start to bend over or Wilt so make sure to keep Watering your plants if you want them to survive and thrive animal cells on the other hand cannot withstand the same amount of pressure if they are placed in an extreme hypotonic solution and too much water moves in they will not be able to withstand this pressure and end up bursting and dying which on a large scale is not good for any single celled or multicellular organism if plant or animal cells are placed into extremely Hy hypertonic Solutions water will be forced out which will result in shrinking and crenation which is when abnormal notches on the surface of cells form due to water loss like we can see in this red blood cell the last example that you need to know of is in unicellular freshwater organisms like amoeba and parami these single celled organisms contain contractile vacul that collect excess water as it accumulates in the cell and pump it out this is used to regulate the water concentration compared to the salutes inside of the cell which help it maintain a homeostatic balance and control the movement of water and other substances across its membrane understanding water movement has many important applications for science including within the medical field when organs need to be transported from One hospital to another or when somebody needs intravenous fluids let's say that a patient needs to receive a heart transplant and they have a donor heart prepared at another hospital and it needs to be moved the heart is made out of living cardiac muscle tissue which needs to be maintained during the transport if you place it in a liquid or cold Icy slush consistency pseudo liquid that is hypotonic to the heart tissue it will force water to move in which could make the cells burst or if it is hypertonic it can force water to move out of the cells which can make them dehydrate and die the answer here is that the solution needs to be isotonic to the organ tissue to achieve this a solution called normal saline is created which contains the perfect amount of sodium chloride to be isotonic to the tissue water can then move both in and out at the same rate keeping the tissue alive and healthy during the transport the same is true if somebody needs intravenous fluids called IV for short if somebody is hooked up to an IV they are receiving solutes directly into their bloodstream for this reason the solute concentration of the IV solution is made to be equal to that of human blood this ensures that the intake of the fluid and nutrients does not alter the water balance of blood cells or adjacent tissues in any [Music] way [Music]