AP Biology : Understanding the Cell Membrane

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #41 : Understanding The Cell Membrane

Which of the following terms best describes a phospholipid that has both a hydrophilic region and a hydrophobic region?

Possible Answers:

Complex molecule

Amphipathic molecule

Dualistic molecule

Ionic molecule

Correct answer:

Amphipathic molecule

Explanation:

An amphipathic molecule is one that has both hydrophilic and hydrophobic regions. In the case of phospholipids, the tail is hydrophobic and the head is hydrophilic. 

Example Question #42 : Understanding The Cell Membrane

Which of the following best describes solutions of equal solute concentrations?

Possible Answers:

Hypertonic

Hypotonic

Isotonic

None of these

Correct answer:

Isotonic

Explanation:

Isotonic is the correct term to describe solutions with equal solute concentrations. The root word "iso" means same; therefore, isotonic solutions have the same concentration of solute. A hypotonic solution will have less solute in it. A hypertonic solution will have a higher concentration of solute between the two solutions.

Example Question #43 : Understanding The Cell Membrane

Which of the following is not an example of endocytosis?

Possible Answers:

Receptor-mediated endocytosis

Pinocytosis

Exocytosis

Phagocytosis

Correct answer:

Exocytosis

Explanation:

Endocytosis is the process by which the cell takes in macromolecules by forming vesicles from the plasma membrane to carry the molecules into the cell. Exocytosis, on the other hand, is the opposite. This is the process by which cells use vesicles to secrete substances from the cell. Phagocytosis, pinocytosis, and receptor-mediated endocytosis are all types of endocytosis.  

Example Question #44 : Understanding The Cell Membrane

A scientist is given two solutions, solution A and solution B. Solution A has a higher number of total solutes, but solution B has a greater variety solutes. In comparison to solution A, solution B is __________.

Possible Answers:

hypotonic

hypertonic

acidic

isotonic

Correct answer:

hypotonic

Explanation:

Solution B is hypotonic to solution A. Solution B is hypotonic because it has an overall lower number of solutes in it even though it has more types of solutes in it. Diversity of the solutes does not not matter when comparing concentrations of solutions, only the overall number of solutes matters. Tonicity can be thought of as relative concentration. Remember that a solution cannot simply be hypertonic or hypotonic; its concentration must be compared to that of another solution.

Example Question #45 : Understanding The Cell Membrane

A scientist is given two solutions, solution A and solution B. Solution A has the same number of total solutes, but solution B has a greater variety solutes. In comparison to solution A, solution B is __________.

Possible Answers:

hypotonic

isotonic

basic

hypertonic

Correct answer:

isotonic

Explanation:

Solution A is isotonic to solution B. This means that both solutions are equal in terms of concentration. Even though solution B has a greater variety of solutes in it, both solutions have the same overall concentration, and thus tonicity. When deciding whether a solution is hypertonic, hypotonic, or isotonic to another solution only consider the overall number of solutes in the solutions not the types of solutes.  

Example Question #46 : Understanding The Cell Membrane

If an animal cell is placed in a solution that is hypertonic to the cell, the cell will __________.

Possible Answers:

gain water and expand

Cannot be determined without knowing the type of animal cell

not change in size

lose water and shrink

Correct answer:

lose water and shrink

Explanation:

The cell will lose water, shrink, and most likely die. When a cell is placed in a solution that is hypertonic to it, water will flow from the hypotonic inside of the cell to the hypertonic environment outside the cell. This causes the cell to shrink from water lost and die. Remember that water follows solutes.

Example Question #47 : Understanding The Cell Membrane

What is the term that describes when a cell expends energy to pump molecules across its membrane against their concentration gradients?

Possible Answers:

Facilitated diffusion

Active transport

Osmosis

Passive transport

Correct answer:

Active transport

Explanation:

Active transport occurs when the cell uses energy to pump molecules into and out of the cell against their concentration gradients. Passive transport occurs when molecules into and out of the cell down their concentration gradients and so no energy is used. Facilitated diffusion involves a protein carrier or channel facilitating the diffusion of a molecule across the plasma membrane, down its concentration gradient. Osmosis is the diffusion of water.  

Example Question #48 : Understanding The Cell Membrane

The process by which the cell secretes large macromolecules by the fusion of vesicles containing the macromolecules to the plasma membrane is called __________.

Possible Answers:

pinocytosis

exocytosis

endocytosis

phagocytosis

Correct answer:

exocytosis

Explanation:

Exocytosis is the process by which the cell secretes macromolecules. In this process a transport vesicle from the Golgi apparatus moves to and fuses with the plasma membrane by rearranging the lipid molecules of the two membranes. This in turn pushes the contents of the vesicle outside of the cell. Pinocytosis and phagocytosis are both types of endocytosis.  

Example Question #49 : Understanding The Cell Membrane

A scientist is given two solutions, solution A and solution B. Solution A has a higher number of total solutes, but solution B has a greater variety of solutes. In comparison to solution B , solution A is __________.

Possible Answers:

hypotonic

diluted

hypertonic

isotonic

Correct answer:

hypertonic

Explanation:

Solution A is hypertonic to solution B. Solution A is hypertonic because it has an overall higher number of solutes in it even though B has more types of solutes in it. Diversity of the solutes does not matter when comparing concentrations of solutions, only the overall number of solutes matters. Tonicity can be thought of as relative concentration. Remember that a solution cannot simply be hypertonic or hypotonic; its concentration must be compared to that of another solution.

Example Question #81 : Cellular Biology

A scientist is given two solutions, separated by a semi-permeable membrane that allows for the passage of water but not solutes. Solution A only has one type of solute and has a higher overall concentration than solution B. Solution B has three different types of solutes in it. The net movement of water is towards __________.

Possible Answers:

solution B

Cannot be determined without knowing the types of solutes involved

There will be no net flow of water

solution A

Correct answer:

solution A

Explanation:

Water will move towards the side the containing solution A. Solution A has a higher concentration of solutes so it is hypertonic to solution B and water will always move from a hypotonic solution towards a hypertonic solution even if the hypotonic solution has more types of solutes in it. The types of solutes is irrelevant for this case, only concentration of solutes matters. Remember: water follows solutes.

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