Osmosis handout.docx

**[Osmosis]** What was your traditional definition of osmosis? The net movement of water by osmosis is determined by differences in water potential between two solutions connected by a partially-permeable membrane. Water potential is the tendency of water molecules in a system to move. It is de...

**[Osmosis]** What was your traditional definition of osmosis? The net movement of water by osmosis is determined by differences in water potential between two solutions connected by a partially-permeable membrane. Water potential is the tendency of water molecules in a system to move. It is denoted by the symbol **ψ** and is measured in kiloPascals (kPa). Pure water has the highest water potential and has a value of 0 kPa. Solutions have a lower water potential than pure water, and have a negative water potential. **Water molecules always move from a region of high water potential to a region of low (more negative) water potential.** Water moves from a high water potential to a low water potential across a selectively permeable membrane. Water potential is a negative value. The more negative, the lower the water potential. [What is (osmotic) solute potential?] The water potential of a solution is affected by the amount of solute it contains. The greater the amount of solute, the lower the water potential. This is because water molecules bind to the solute molecules, reducing the number of water molecules that are free to diffuse. The contribution that solutes make to the water potential of a solution is the osmotic (solute) potential (**π / Ψ~S~),** and is a negative [What is pressure potential?] The water potential of a solution is also affected by the pressure applied to it. The **greater** the pressure, the **higher** the water potential. This is called the turgor pressure (pressure potential) (**P / Ψ~P~**) and is always a positive value. In plant cells, the pressure potential is a result of the cell wall exerting pressure on the cytoplasm. Water potential is calculated using the following equation: -- -- Answer the following equations using the above equation. 1. In which direction will the water molecules move?  2. Will water molecules move in or out of the cell? Diagram Description automatically generated 3. What is the water potential of a cell that has a solute potential of -630 kPa and a pressure potential of 330 kPa?  **[How do plan cells react to osmosis]** +-----------------------+-----------------------+-----------------------+ | **Hypertonic** |  | **Hypotonic** | | | | | | | **Isotonic** | | +=======================+=======================+=======================+ | | | | +-----------------------+-----------------------+-----------------------+ **[How do animal cells react to osmosis?]** +-----------------------+-----------------------+-----------------------+ |  | **Isotonic** |  | | **Hypertonic** | | | | | | **Hypotonic** | +=======================+=======================+=======================+ | | | | +-----------------------+-----------------------+-----------------------+ **[Prep for CP5]** What factors could affect transport of materials through the cell membrane? [Temperature] Temperature can affect the fluidity of the plasma membrane. - Low temperature -- permeability is low, lipids less fluid, - High temperature -- permeability increased, lipids are more fluid, vibration of molecules increases, - Too high a temperature causes too much vibration and ruptures. [Beetroots] Beetroots are root vegetables that appear red because the vacuoles in their cells contain a water soluble red pigment called betalain. These pigment molecules are too large to pass through membranes......usually! [Colorimeter] A colorimeter is a device used to measure the amount of light passing through a solution, compared to the amount entering -- giving a value in either transmission or absorbance. We are going to be using **percentage transmission**. The filter is used to select the colour of light which the solute absorbs the most. Note that the colour of the absorbed light is the "opposite" of the colour of the specimen, so the blue-green filter is appropriate for the red betalain pigment colour from the beetroot. [Research] As part of the prep for CP5 you are asked to do some research in the practical. You are going to be researching -- "Find out why beetroots appear red, what causes the red pigment to escape from cells and why this happens?" You have a couple of pages to write about this so do not be afraid to get into some detail. The most important thing about research tasks is to use a number of different sources, different types of sources of information and to cite them all correctly. In Referencing it is important to follow the particular style you are given to not only the letter but the "," and the "." Just copy the style in full and with as much information as you can.