Question

cell membranes are an essential element of life because they create a barrier that facilitates the regulation of the internal environment of an organism. single-cell organisms like bacteria and some algae have been found in extreme environments. for example, some of these organisms have been found near scalding hot ocean vents and in acidic pools and streams in yellowstone national park. one particular algal species lives in the park in lemonade creek where the water has a ph of 2. why can these organisms maintain a neutral intracellular ph in such an acidic environment? select all that apply. protons (h*) diffuse from regions of high ph to regions of low ph so the algae are maintaining their ph by releasing protons into the acidic creek. cell membranes provide a barrier to the free passage of charged or large polar molecules because these molecules cannot interact with the hydrophobic tails of membrane lipids. ph is a measure of the concentration of water in solution, and water is polar, so it crosses the membrane slowly without a protein channel or pump. ph is a measure of the concentration of protons in solution, and protons are ions, so they cannot cross the cell membrane without a protein channel or pump.

Explanation:

• Option 1: Protons diffuse from low pH (high proton concentration) to high pH (low proton concentration), so this option is incorrect.
• Option 2: Cell membranes (phospholipid bilayers) have hydrophobic tails. Charged or large polar molecules (like protons) cannot freely pass through due to the hydrophobic nature of the tails. This helps in maintaining internal pH.
• Option 3: pH is a measure of proton (\(H^{+}\)) concentration (\(pH=-\log[H^{+}]\)), not water concentration. So this option is incorrect.
• Option 4: Since pH is related to proton concentration and protons (\(H^{+}\) ions) cannot cross the non - polar membrane interior (hydrophobic tails of phospholipids) without protein channels/pumps, this helps in maintaining internal pH.

Answer:

B. Cell membranes provide a barrier to the free passage of charged or large polar molecules because these molecules cannot interact with the hydrophobic tails of membrane lipids.
D. pH is a measure of the concentration of protons in solution, and protons are ions, so they cannot cross the cell membrane without a protein channel or pump.