6 Osmosis Lab PDF

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Osmosis lab...

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Introduction Throughout the body there are several types of membranes that serve as barriers between fluid compartments (i.e. cell & interstitium). These compartments confine certain substances and processes to specific locations. One of these membranes are plasma membranes, that surrounds each cell and organelles. In addition to forming compartments, membranes must also allow some substances to pass while restricting the movement of others. The transport of various chemicals across these membranes is critical for maintaining homeostasis. The transport of substances across the membrane involves both physical processes (diffusion, osmosis) and biochemical processes (carrier mediated transport). In this lab, we will study some of the physical processes associated with transport of substances across membranes. A substance that enters into a solution or becomes dissolved in a liquid is called a solute and the liquid it is dissolved in is the solvent. Simple diffusion is the continual random movement of particles in a liquid or gas, and net diffusion occurs when there is measurable movement of particles from an area of greater concentration to lesser concentration. Movement will occur until there is uniform distribution of the diffusing substance. The rate of diffusion is directly proportional to the concentration gradient and the temperature, but inversely proportional to the size (molecular weight) of the solute and the distance traveled. Osmosis is the net diffusion of water across a selectively permeable membrane (also from high concentration to low concentration). Simple diffusion occurs across plasma membranes if there is a concentration difference across the membrane, and if the membrane is permeable to the solute in question. Osmosis can occur across all cell membranes, with potentially devastating results. Cells and multicellular organisms have evolved several mechanisms to prevent the damaging effects of osmosis: cell shrinking or swelling. Cell shrinking is called crenation, and cell swelling can lead to lysis. More on osmosis…..If a membrane is permeable to the solvent (water) and not the solute, water will diffuse from the region where there is more water (less solute) to less water (more solute). Since water is small, it also travels down its concentration gradient (from high to low). Some students like to think of it as, “solutes suck!” (but do not use this term on exams). Cells have a semipermeable membrane (water can passively cross, solutes cannot). Since cells are filled with solutes that cannot cross the membrane, they are osmotically active and can “suck in” water. To deal with this problem, animal cells can pump NaCl across their membranes to decrease the amount of osmosis. In this lab you will analyze weight data of cells placed in solutions of unknown concentrations. After evaluating the data, you will determine the concentration of the solution and its ’ tonicity (the concentration of a solution compared to another solution). Solutions will be isotonic (concentration is equal on both sides of the membrane), hypotonic (solute concentration is lower than cell), or hypertonic (solute concentration is higher than cell).

Objectives 1. Understand the concepts of osmosis and tonicity 2. Observe the effects of placing a cell (dialysis tubing) in isotonic, hypotonic, hypertonic solutions 3. Recognizing the conditions and significance of crenated and lysed red blood cells

Experimental Design 1. Each beaker (A, B, & C) is filled with an unknown solution (one beaker is filled with pure water, another with a 15% sucrose solution, and another with 30% sucrose) 2. The cell (1, 2, & 3) in each beaker are all filled with the same solution, but you don’t know what the solution is (it can be either pure water, 15% sucrose solution, or 30% sucrose) 3. Procedures for data collection: - Cells were weighed before they were placed into the beaker (time 0) - Every 15 minutes, the cells were removed from their beaker, blotted dried, and weighed. After being weighed, the cell was returned to their beaker

Procedures 1. After reviewing the experimental design, interpret the data below 2. You will need to determine whether the cell lost weight, gained weight, or had no significant weight loss 3. Then, you will need to determine which solution (pure water, 15% sucrose, or 30% sucrose) was in the cell and which was in beakers A, B, and C. 4. Data set 1: Make sure you understand how to analyze the data below, you will asked to do the same type of problem on your lab exam. External environment Beaker A Beaker B Beaker C

Weight of cells over time 23.9 24.2 24.2 24.1 24.1 22.9 21.6 20.2 18.85 18.1 24.4 22.0 19.9 17.5 16.1

Weight analysis (of cells)

Based on the data above, state the solution type (water, 15%, or 30%) for the cell and the beaker. Then state the tonicity of the beaker (hypotonic, hypertonic, isotonic) Beaker A Solution (cell) _____________

Beaker B Solution (cell) _____________

Beaker C Solution (cell) _____________

Solution (beaker) __________

Solution (beaker) __________

Solution (beaker) __________

Tonicity (beaker) ___________

Tonicity (beaker) ___________

Tonicity (beaker) ___________

Additional Questions 1. Red blood cells _____________________ in a hypertonic solution. A 0.10M NaCl solution is _____________________ (isotonic/hypotonic/hypertonic) relative to a 0.10 M glucose solution. 2. Picture a beaker filled with a 300 mOsm (isotonic) solution. Name two ways you could make the solution in that beaker hypertonic

3. Before the invention of refrigerators, people preserved meat by salting it. How does this work?

4. Want more data analysis practice? Analyze data set #2: External environment Beaker H Beaker I Beaker J

Weight of cells over time 21.1 22.8 23.9 24.8 27.6 27.6 27.5 27.4 24.9 24.3 23.2 22.3

Weight analysis (of cells) 25.6 27.3 21.6

Based on the data above, state the solution type (water, 15%, or 30%) for the cell and the beaker. Then state the tonicity of the beaker (hypotonic, hypertonic, isotonic) Beaker H Solution (cell) _____________

Beaker I Solution (cell) _____________

Beaker J Solution (cell) _____________

Solution (beaker) __________

Solution (beaker) __________

Solution (beaker) __________

Tonicity (beaker) ___________

Tonicity (beaker) ___________

Tonicity (beaker) ___________...