Question

a student claims, the hydrophilic heads of the phospholipids are the main reason that large hydrophobic molecules, like certain large fats, cannot cross the cell membrane. evaluate this statement using the provided text.
the statement is correct; the hydrophilic heads are the initial barrier for all molecules
the statement is irrelevant; the nucleus is what ultimately controls entry/exit.
the statement is incorrect; the hydrophobic tails would be welcoming to the large fat molecule.
the statement is incorrect; the size of the molecule, not its polarity, is the likely reason it cannot cross.
the text describes several chemical barriers. why is the acidic environment of the stomach considered a particularly critical chemical barrier?
it is the only place in the body where enzymes are used to kill pathogens.
it prevents fungi like athletes foot from spreading to internal organs.
it is the primary way the body defends against viruses like the common cold.
it protects the entire gi tract by working to destroy pathogens that are ingested with food and water.

Explanation:

For the first question, the cell - membrane has a phospholipid bilayer with hydrophilic heads facing outward and hydrophobic tails in the middle. Hydrophobic tails would be more welcoming to large fat molecules, so the statement about hydrophilic heads being the main barrier for large hydrophobic molecules is incorrect. For the second question, the acidic environment of the stomach is a critical chemical barrier because it destroys pathogens ingested with food and water, protecting the entire gastrointestinal (GI) tract.

Answer:

1. C. The statement is incorrect; the hydrophobic tails would be welcoming to the large fat molecule.
2. D. It protects the entire GI tract by working to destroy pathogens that are ingested with food and water.