5.2: Lab 5 Procedures
- Page ID
- 159717
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)PROCEDURE 1: OSMOSIS IN POTATO CELLS
In this part, we get to test osmosis in real cells by putting pieces of potato in solutions with different concentrations of salt. We are going to measure and weigh potato slices before and after they go into different solutions to see whether there is a change.
Equipment we’ll need:
- Three pieces of potato
- Three test tubes, one each with 10% salt solution, 0.9% salt solution, or DI water
- Ruler and electronic scale
- Use a cork borer to make three potato tissue cores. Cut each core to a length of 4cm.
- On a paper towel, use a pen to write 10%, 0.9%, and DI water spaced apart. Put a potato core under each label to make sure we keep track of which is which.
- Weigh each core and record its starting mass in Table 3 on the Answer Sheet (make sure the electronic scale is tared to 0.0g first).
- Place the 10% core in the test tube with the 10% salt solution, the 0.9% core in the test tube with the 0.9% salt solution, and the DI water core in the test tube filled with DI water.
- Keep the potatoes fully submerged for at least one hour.
- Now that we’re familiar with the experimental setup, let’s make predictions before seeing the results. Answer the questions on the Answer Sheet.
- After at least an hour, remove the potato cores and gently dry them on a paper towel.
- Weigh each core and record its final mass in Table 3 (make sure the scale is tared first).
- Answer the remaining questions about this experiment on the Answer Sheet.
Clean up/Disposal
- Throw away the used potato pieces in the trash.
- Pour any remaining liquids down the drain.
- Scrub off the grease pencil lines and any other markings. Remove any tape labels.
- Rinse test tubes and beakers. Place on the towel to dry.
PROCEDURE 2: DIFFUSION AND OSMOSIS ACROSS A MEMBRANE
A dialysis bag is a semipermeable plastic bag. While the plastic is chemically different from a phospholipid bilayer, it can act as a decent representation of a cell’s membrane. Thus, the dialysis bag will simulate a cell in this experiment. Our job is to determine which substances (glucose, starch, iodine, and water) the dialysis bag is permeable to. Recall from our experiments last week that the iodine solution (IKI) is a chemical indicator that turns black or dark blue in the presence of starch.
Equipment we’ll need:
- 1 dialysis tubing bag
- 100mL beaker and 250mL beaker
- DI water, iodine solution (IKI), 5% glucose solution, and 1% starch solution
- 2 pieces of string
- Paper towel
- Electronic scale
- Benedict’s reagent, a test tube, and a hotplate
- Fill the 250mL beaker with about 150mL of tap water. Place the beaker onto the hotplate and turn the hotplate on to about level 6 to create a hot water bath that is close to boiling. Keep an eye on this and turn down the heat/refill with more water as needed.
- Fill the 100mL beaker with 50mL of DI water.
- Add about 2mL of iodine solution (the pipette cap in the iodine bottles is about 1mL) to the DI water and gently swirl to mix. The beaker should be a light amber/golden color.
- Obtain one pre-soaked dialysis bag and cut two pieces of string. Fold over the end of the dialysis bag and use one of the strings to tie a tight knot over the fold to close off that end.
- Open the other end of the dialysis bag and fill the bag with 15mL of the starch and glucose solution.
- Fold over the other end of the dialysis bag and use the other string to tie a tight knot across the top of the dialysis bag.
- We should now have a dialysis bag filled with starch and glucose solution sealed on both ends with string. Check for leaking and re-tie if necessary.
- Use DI water to rinse off the outside of the dialysis bag over the sink. We want to make sure there is no starch or glucose on the outside of the bag.
- Use a paper towel to dry the dialysis bag.
- Place the dialysis bag on the electronic scale to measure its mass in grams. Record the initial mass on the Answer Sheet.
- Now that we’re familiar with the experimental setup, let’s make predictions before seeing the results. Answer the design questions on the Answer Sheet.
- Set the dialysis bag into the beaker with iodine solution. Let it sit for at least 30 minutes.
- After 30 minutes or more, remove the dialysis bag from the beaker and pat it dry with paper towels.
- Once again, place the dialysis bag on the electronic scale to measure its mass. Record the final mass on the Answer Sheet.
- Record the color of the beaker solution and the solution inside the bag in Table 2 on the Answer Sheet.
- Use a ruler to mark a 1cm line and 2cm line with a grease pen on the test tube.
- Pour the solution in the 100mL beaker into the test tube up to the 1cm line.
- Pour Benedict’s solution into the test tube up to the 2cm line.
- Place the test tube into the hot water bath for 5 minutes. Record the color in Table 2 on the Answer Sheet.
- Complete Table 2 and answer the follow-up questions in the Answer Sheet.
Clean up/Disposal
- Throw away the used dialysis bags in the trash.
- Pour liquids into the hazardous waste container by the sink.
- Scrub off the grease pencil lines and any other markings. Remove any tape labels.
- Rinse test tubes and beakers. Place on the towel to dry.
PROCEDURE 3: DIFFUSION IN DIFFERENT CONDITIONS
We are going to test the rate of diffusion through agar, a semisolid jelly-like substance, in different conditions. The agar is semipermeable, allowing some substances to diffuse through it. There are several things that affect the rate of diffusion, including temperature, density of the medium, size of the molecules, and amount of molecules. For example, we have two dyes available for today’s lab with very different molecular mass: potassium permanganate (KMnO4) is 158.03 g/mol and methylene blue is 319.85 g/mol. Our job for this experiment is to find out exactly how one of those factors affects diffusion.
Equipment we’ll need:
- Two plates with agar per group
- Plastic straw
- Dye (such as potassium permanganate, KMnO4)
- Work through the questions on the Answer Sheet to set up this experiment. Each group will choose their own independent variable to test.
- Obtain 2 agar filled petri dishes. Using a straw, poke and remove one hole in the center of each petri dish.
- Into the hole, add _____ drops of dye(s), such as potassium permanganate (KMnO4).
- Place the dish in the group’s specific condition.
- Allow diffusion to happen for _____ minutes.
- Record the results in the Answer Sheet.
Clean up/Disposal
- Throw away the used agar plates into the white and green bucket.
- Return used straws to the beaker.