AP Biology : Understanding the Cell Membrane

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #82 : Cellular Biology

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

Possible Answers:

lose water, shrink in size and likely die

gain water, grow in size and likely burst

Cannot be determined without knowing the type of solute in the surrounding solution

not change in size

Correct answer:

gain water, grow in size and likely burst

Explanation:

The cell will take in water and most likely burst, killing the cell. When a cell is placed in a solution hypotonic to it, water will flow from the hypotonic surroundings into the hypertonic cell. This causes the cell to grow with water intake until it bursts like a water balloon.   

Example Question #83 : Cellular Biology

Passive transport that relies on transport proteins to allow molecules to pass through the cell membrane is called __________.

Possible Answers:

facilitated diffusion

osmosis

pumping

active transport

Correct answer:

facilitated diffusion

Explanation:

Facilitated diffusion is the type of passive transport that relies on transport proteins embedded in the cell membrane. No energy is used in this transport since the molecules follow their concentration gradients so it is not active transport. Osmosis refers to passive movement of water only.   

Example Question #84 : Cellular Biology

The function of the sodium-potassium pump is an example of __________.

Possible Answers:

osmosis

passive transport

facilitated diffusion

active transport

Correct answer:

active transport

Explanation:

Sodium-potassium pumps are an example of membrane proteins that undergo active transport. They function by using ATP for energy to pump potassium and sodium against their respective concentration gradients. Specifically, two molecules of sodium is pumped out of the cell for every three molecules of potassium pumped into the cell. The sodium-potassium pump is of monumental importance to all animals that use it, and it is often the target of lethal injection since even slightly altering its function is always fatal. Passive transport does not use energy. Both facilitated diffusion and osmosis are examples of passive transport.  

Example Question #151 : Ap Biology

Which of the following are types of endocytosis?

Possible Answers:

receptor-mediated endocytosis

phagocytosis

pinocytosis

All of these

Correct answer:

All of these

Explanation:

Endocytosis is the process by which the cell takes in macromolecules by creating new vesicles from the cell's plasma membrane. Phagocytosis, pinocytosis, and receptor-mediated endocytosis are all different types of endocytosis.  

Example Question #152 : Ap Biology

In facilitated diffusion, what occurs in the cell?

Possible Answers:

Molecules, such as glucose move from an area of lower concentration to an area of higher concentration.

Protein pumps use energy to pump molecules, such as glucose across the cell membrane.

Osmosis occurs.

Molecules, such as glucose, move through protein channels from an area of higher concentration to lower concentration.

Correct answer:

Molecules, such as glucose, move through protein channels from an area of higher concentration to lower concentration.

Explanation:

In facilitated diffusion, molecules, such as glucose move through protein channels from an area of higher concentration to an area of lower concentration.  It is not active transport, using energy. Movement of molecules through the cell membrane without use of a protein is known as simple diffusion; osmosis is a type of simple diffusion.

Example Question #153 : Ap Biology

What occurs during endocytosis?

Possible Answers:

The cell takes in material from outside the cell by enveloping the meterial and ingesting it.

The cell uses protein pumps to ingest substances.

Osmosis occurs and water moves outside the cell.

The cell secretes substances outside the cell.

Correct answer:

The cell takes in material from outside the cell by enveloping the meterial and ingesting it.

Explanation:

Endocytosis occurs when the cell engulfs an external substance and takes it into the cell by the infolding of the cell membrane.  Exocytosis occurs when the cell secretes a substance outside the cell.

Example Question #154 : Ap Biology

Glycoproteins, often found on the external side of the cell membrane for signalling purposes, are made of protein and __________.

Possible Answers:

Lipids

Carbohydrates

Proteins

RNA

Correct answer:

Carbohydrates

Explanation:

The glycolipids on the outside of the cell are made of proteins and carbohydrates.  Proteins result from translation from DNA to RNA, and they are modified in the Golgi apparatus to form glycoproteins.  "Glyco" refers to sugars, which are carbohydrates.  Lipids are fat molecules that are not often used in cell signaling, but rather as stored energy sources.

Example Question #155 : Ap Biology

What occurs during exocytosis?

Possible Answers:

The cell receptor is activated and substances move into the cell.

Water and salts are stored in the sarcoplasmic reticulum.

Foreign substances are engulfed by cells of the immune system.

The membrane of the vacuole fuses with the cell membrane, forcing the contents out of the cell.

Correct answer:

The membrane of the vacuole fuses with the cell membrane, forcing the contents out of the cell.

Explanation:

In exocytosis the membrane of a vacuole surrounding some material fuses with the cell membrane, forcing the contents out of the cell wall.  The substance is secreted out of the cell.  The process by which foreign matter is engulfed by immune cells is phagocytosis. Water and salts are stored in the sarcoplasmic reticulum in certain cell types (muscle) but this is not exocytosis, which involves the removal/expulsion of substances from the cell into the extracellular environment.

Example Question #156 : Ap Biology

The cell membrane regulates the passage of materials into and out of the cell. Much of the material transported across the cell membrane is via membrane-bound protein molecules, but this can be accomplished through various mechanisms.

When a substance is transported across the cell membrane across the concentrations gradient (from an area of low concentration to an area of high concentration), this is referred to as __________.

Possible Answers:

osmosis

co-transport

passive transport

diffusion

active transport

Correct answer:

active transport

Explanation:

In order for a material to be transported across the cell membrane, against its concentration gradient, energy is required. For example, the sodium-potassium pump hydrolyzes one molecule of ATP to pump 3 sodium ions out of the cell and 2 potassium ions into the cell. Since the potassium levels are much higher inside the cell than outside, energy is required. This is known as active transport.

Example Question #157 : Ap Biology

What molecules are used in eukaryotic membranes to strengthen them against osmotic stress?

Possible Answers:

Phospholipids

Polysaccharides

Sterols

Peripheral membrane proteins

Integral membrane proteins

Correct answer:

Sterols

Explanation:

In eukaryotes, sterol molecules are used to strengthen the plasma membrane. These molecules are able to pack very close together forming tight strucutres. 

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