Cell Physiology lab

Outline of the day 1.Turn in your lab reports at the front –More than 10 minutes late = bad 2.Any questions on last week’s lab? 3.Quiz 4.Introduction to the lab 5.Lab! 6.Check out Get a stamp Make sure I mark you down for attendance

Quiz Ends 10 minutes after it’s started –Ends at: ____

Lab this week! Exploring cell physiology –How membranes work Using beets! –The affect of surface area to volume ratio on diffusion Using potatoes!

Cells Plasma membrane (lipid bilayer) Cell wall (only on plants, fungi, protists, and bacteria) Plant Animal Animal cell - ccasa by MesserWoland at Plant cell - PD by Mariana Ruiz - LadyofHats at

Membranes Membranes separate the cell from the outside –If the membranes break, the cell dies Cell diagram from Wellcome images N Credit Medical Art Service, Munich /, Wellcome Images Cell membrane diagram - public domain by LadyofHats Mariana Ruiz -

Today We want to look at how pH affects membranes –Does pH damage membranes? But we can’t actually see membranes under a microscope to see if they’ve been damaged!

That’s where beets come in! Beet cells are filled with a red pigment When beet cell membranes are damaged, they release the red pigment Images from: all cc licensed

Beets Photos from: both cc licensed; art by Marc Perkins Strong AcidNeutralStrong Base ? We’re going to put beet cores in different pH solutions –And observe what happens

How will we measure the color change? Spectrophotomers! –Machines that measure how much light is absorbed by (or transmitted through) a solution Missing image: Image showing light passing through a sample in a spec to demonstrate physics of what is going on. Missing image: Image of OCC’s specs.

Calibrating the spectrophotometer 1.Turn spec on, let it warm up (>10 minutes). 2.Select the wavelength you want to use. 3.With nothing in the meter, adjust the meter to read  using the infinity control knob (left knob / power switch). 4.Place a cuvette filled with the blank solution into the sample holder. The blank solution has only the solvent in it (water today). 5.Adjust the meter to read 0 absorbance (full scale) using the zero control knob (right knob). 6.Put your sample tube in the sample holder! (Repeat this procedure whenever you adjust the wavelength)

Surface area to volume ratio A factor that can affect the rate of diffusion into a substance Questions: –Which cube(s) have the highest surface area to volume ratio? –Which cube(s) will gain the most water? Cube diagrams by Marc Perkins

Addition to the potato section! Calculate the % weight change for each treatment –% weight change = (weight change) / (initial weight) * 100 Time (minutes) Initial Final Weight change % weight change

Before you leave Clean up your work area –Wash glassware and store upside down Show me your lab report so I can stamp it –Need to have all data fields filled in –Complete at home and then turn in at the beginning of next lab Remember that we’ll have a quiz at the beginning of the next class –6-7 questions on today’s lab –3-4 questions on the lab we’ll do next week

Calibrating the spectrophotometer 1.Turn spec on, let it warm up (>10 minutes). 2.Select the wavelength you want to use. 3.With nothing in the meter, adjust the meter to read  using the infinity control knob (left knob / power switch). 4.Place a cuvette filled with the blank solution into the sample holder. The blank solution has only the solvent in it (water today). 5.Adjust the meter to read 0 absorbance (full scale) using the zero control knob (right knob). 6.Put your sample tube in the sample holder! (Repeat this procedure whenever you adjust the wavelength)

Notes for the instructor: I’d add in an image of OCC’s specs to the presentation, as well as an image of how specs work. You could either break the calibration procedure up into multiple slides, illustrating them with images, or walk the students through the calibration on their specs with a single-page slide (being sure to have the students do everything on their specs as you explain it). I waffle between how I prefer to do it, though I do like being able to leave up a single-page version of the calibration proceedure during lab. I’d prefer to find better images of plant and animal cells, though the ones included are good enough for the purpose (to demonstrate that plant and animal cells are similar, but that plants have cell walls, which animals don’t).

License information This work is licensed under the Creative Commons Attribution- NonCommercial-ShareAlike 3.0 License. To view a copy of this license, visit sa/3.0/us/ or send a letter to Creative Commons, 171 Second Street, Suite 300, San Francisco, California, 94105, USA. The slides in this presentation were originally created by Marc C. Perkins ( You are free to use, modify, and distribute these slides according to the terms of the Creative Commons license (e.g., you must attribute the slides, no commercial uses are allowed, and future distributions must be licensed under a similar license). Attribution should be given to Marc C. Perkins (and any later editors), including a link back to Marc’s current website. This applies both while distributing the slides and during use of the slides; attribution during use can be satisfied by, for instance, placing small text on at least one of the slides that has been shown (see below for an example). Slides in this presentation based on those created by Marc C. Perkins.

History August 2007: Marc Perkins released first version. (If you modify these slides and redistribute them, add your information to the list)