Do the following lab activity, "The Importance of Surface Area." The instructions for this lab are below, and this lab must be done in the Biology Learning Center. There are worksheets for this activity in your worksheet packet. When you have completed each step of the activity, take the results to the front desk inthe Biology Learning Center for lab points.

• Kit #12
• some latex-free gloves, you will find them in a large, clear plastic bin on the counter just above the drawer where you found kit #12; they come in three sizes (sm, med, lg)
• some paper towels from the sink area
• a baggie with pre-cut cubes of blue agar from the student refrigerator (be sure to just get ONE baggie!)

Thanks to Joe Stanek and Mike Tveten for originally designing this lab activity. It has been used here and modified with their permission. Joe Stanek published this experiment in The American Biology Teacher, a publication of the National Association of Biology Teachers. Mike teaches fulltime at the Northwest Campus of Pima and Joe is now happily retired.

The amount of surface area is an important physiological attribute at all levels of life, from organelles to organisms. So much happens at membranes—reactions, diffusion, absorption, secretion, transport, communication—that there is often an evolutionary trend to increase surface area as much as anatomically possible.

We can observe maximized surface area at the level of the organelle:

• The inner membrane of mitochondria has evolved with many folds to create a larger membrane where electron transport and oxidative phosphorylation can occur during cellular respiration.

• There are numerous thylakoids stacked in chloroplasts to create a larger membrane used in photosynthesis.

• The endoplasmic reticulum has evolved with many folds, providing a larger surface for attachment of ribosomes, which manufacture proteins.

We can observe maximized surface area at the cellular level:

• The microvilli of epithelial cells in the digestive tract have evolved to increase the absorption of nutrients.

We can observe maximized surface area at the tissue level:

• The loop of Henle in the vertebrate kidney has evolved to be long enough to increase the filtering capabilities of the kidney.

We can observe maximized surface area at the organ level:

• The intestinal lining of vertebrates has evolved with numerous villi that extend into the intestine for optimal absorption of nutrients.

• The lungs of vertebrates have evolved with numerous alveoli that allow for optimal diffusion of gases.

We can observe maximized surface area at the organ system level:

• In fish, the gills have evolved with a large surface area in order to allow for optimal gas exchange.

• Flatworms have evolved with a large surface area for diffusion of gases directly through the skin, as well as a large surface area of their digestive tract.

• Vertebrate digestive tracts are extremely long, but folded into a small area, in order to allow for optimal digestion and absorption of nutrients.

Is it possible that surface area also determines the maximum size of a cell?

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