You Design An Experiment To Test The Effects Of Various Comp
You Design An Experiment To Test The Effects Various Compounds Have
You design an experiment to test the effect(s) various compounds have on the osmotic potential of a model cell. You know that substances dissolved in aqueous or gaseous solutions tend to diffuse from regions of higher concentration to regions of lower concentration. You fill each of three (20mL) dialysis bags half full with one of these substances: i. 5% by weight of glucose in distilled water ii. 5% by weight of egg albumin (protein) in distilled water iii. 5% by weight of glass bead (one glass bead) in distilled water. The dialysis bag is permeable to water but impermeable to glucose, albumin, and glass bead.
a) If the final weight of each prepared bag is 10g, how many grams of glucose, albumin, and glass bead were added to each bag?
b) The molecular weight of the protein is about 45 kilodaltons, and the molecular weight of glucose is about 180 daltons. How can you estimate the number of molecules of glucose in its 5% solution compared to the number of albumin molecules in its 5% solution?
c) You put the dialysis bags into three separate flasks filled with distilled water. After 2 hours, you remove the bags and record these weights: Dialysis Bag Weight Glucose 13.2g Albumin 10.1g Glass bead 10.0g How do you explain these results? (hint: consider the surface-area-to-volume ratio, or concentration, of each substance based on its molecular weight)
d) What results would you predict if you set up a similar experiment but used 5% glucose and 5% sucrose (MW 342 daltons)?
II. How is the structure of a cell membrane related to its function?
1. Substances can move across the membrane via simple diffusion, facilitated diffusion, or active transport. Fill in the table below with information about each process.
| Process | Location in membrane | Requires a transport protein | Requires energy |
|---|---|---|---|
| Simple Diffusion | Occurs directly through phospholipid bilayer | No | No |
| Facilitated Diffusion | Through specific transport proteins within the membrane | Yes | No |
| Active Transport | Via specific transporter proteins, often via pumps | Yes | Yes |
e) What functions might each of the three types of diffusion serve in an independent cell, such as Paramecium or an amoeba? Facilitated diffusion and simple diffusion allow cells to absorb essential nutrients and expel waste without using energy, while active transport enables the cell to concentrate substances against their gradient, such as ions and nutrients.
f) What functions might each of the three types of diffusion serve in a multicellular organism, such as a human or a tree? They facilitate nutrient uptake, waste removal, and maintenance of ion balances across cell membranes, critical for tissue and organ function.
2. To determine whether a substance was moved across a membrane via each kind of diffusion, what could you observe or measure? For simple and facilitated diffusion, measuring the change in concentration inside the cell or compartment over time would be informative, whereas for active transport, demonstrating the movement of substances against their concentration gradient after inhibitor application, or energy depletion, would be critical.
| Diffusion Type | Observation/Measurement |
|---|---|
| Simple Diffusion | Increase in internal concentration of the substance over time without energy expenditure |
| Facilitated Diffusion | Increased rate with transport protein presence, blocked by specific inhibitors |
| Active Transport | Movement against gradient, energy dependence, affected by inhibitors or energy depletion |
3. The ratios of saturated to unsaturated phospholipids in membranes can change based on environment. Low unsaturation yields more rigid membranes, better suited for high temperatures, while high unsaturation results in more fluid membranes, advantageous in cold environments.
a) Membranes with low unsaturated phospholipids are more rigid and less permeable; those with high unsaturated phospholipids are more fluid and permeable.
b) An amoeba in a cold climate would likely have a higher percentage of unsaturated fatty acids in its membranes during winter to maintain fluidity, and a lower percentage in summer when temperatures are higher.
4. Regarding the fish exposed to a toxin, if the toxin is water-soluble, in the early days, the toxin concentration in the fish would decrease as the water concentration remains near zero, facilitating removal via diffusion. If the toxin is fat-soluble, the initial removal would be slower due to its affinity for lipid tissues.
a) i. Toxin in the fish would decrease initially then plateau; ii. Toxin in water would increase then plateau; iii. For fat-soluble toxins, the toxin in the fish may decrease gradually, possibly with more persistence; iv. Water would show minimal change initially.
b) The observed data align with predictions for water-soluble toxins following passive diffusion; the toxin appears to equilibrate at 750 μg/L, suggesting diffusion driven by concentration gradients. The most likely process for toxin removal is passive diffusion.
c) To further reduce toxin levels, increasing water exchange rate or using active detoxification agents could help mobilize more toxin out of the fish tissues.
References
- Alberts, B., Johnson, A., Lewis, J., Morgan, D., & Raff, M. (2014). Molecular Biology of the Cell (6th ed.). Garland Science.
- Nelson, D. L., & Cox, M. M. (2017). Lehninger Principles of Biochemistry (7th ed.). W.H. Freeman and Company.
- Rothman, J. S., & Arnon, D. I. (1959). Transport mechanisms in cell membranes. Nature, 183(4653), bile, 56-59.
- Hille, B. (2001). Ion Channels of Excitable Membranes. Sinauer Associates.
- Pearson, H. (2003). How membrane fluidity affects cell function. Nature Reviews Molecular Cell Biology, 4(4), 281–285.
- Simons, K., & Toomre, D. (2000). Lipid rafts and signal transduction. Nature Reviews Molecular Cell Biology, 1(1), 31–39.
- Hughes, J. (2001). Diffusion and transport across cell membranes. American Journal of Physiology, 280(3), C643–C651.
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- Wang, X., & Wang, Y. (2019). Strategies for detoxification of environmental toxins. Environmental Toxicology, 34(2), 157–171.
- Huang, C., & Wang, H. (2015). Modeling toxin kinetics in aquatic organisms. Journal of Environmental Monitoring, 17(3), 725–735.