AP Biology : Understanding the Cell Membrane

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #71 : Understanding The Cell Membrane

 All of the following are known to be components of cell walls except which one?

Possible Answers:

chitin

cellulose

peptidoglycans

polysaccharides

actin

Correct answer:

actin

Explanation:

Actin is what makes up microfilaments. Chitin is indeed in cell walls of fungi. Cellulose is the main ingredient to plant cell walls and peptidoglycan are found in the cell walls of cyanobacteria and bacteria. Also, cellulose is made of polysaccharides, therefore, this is also an incorrect answer because it is a component of the cell wall.

Example Question #72 : Understanding The Cell Membrane

Which of the following best describes the fluid mosaic model of membranes? 

Possible Answers:

The membrane consists of a phospholipid bilayer with proteins of various lengths and sizes located on the exterior portions of the membrane.

The membrane consists of a phospholipid bilayer with proteins of uniform lengths and sizes located on the interior portions of the membrane.

The membrane consists of a phospholipid bilayer with proteins of various lengths and sizes located on the interior portions of the membrane.

The membrane contains a phospholipid bilayer with proteins of various lengths and sizes interspersed among the phospholipids. 

The membrane contains a phospholipid bilayer with proteins of uniform lengths and sizes interspersed among the phospholipids. 

Correct answer:

The membrane contains a phospholipid bilayer with proteins of various lengths and sizes interspersed among the phospholipids. 

Explanation:

The fluid mosaic model says that proteins can extend all the way through the phospholipid bilayer of the membrane. There are peripherial, integral, and transitional proteins. Therefore, these proteins are various sizes and lengths. 

Example Question #73 : Understanding The Cell Membrane

Which one of the following can be easily diffused across the cell membrane? 

Possible Answers:

water

chloride

sucrose

lipids

ions

Correct answer:

lipids

Explanation:

Lipids can diffuse freely across the cell membrane, because the cell membrane is made up of lipids. Ions will not be able to pass through the hydrophobic section of the membrane, because it is polar. Chloride is an ion. Water is polar and also won't be able to pass through the hydrophobic section of the membrane. Sucrose is too big to freely diffuse into the cell. 

Example Question #5 : Understanding Cytoplasmic Proteins

In regard to cellular membranes, what does it mean to be selectively permeable?

Possible Answers:

Polarization of the cell membrane allows for passive transport of all foreign molecules or ions

Polarization of the cell membrane allows for no entrance of foreign molecules or ions

Molecules and ions outside the cell are selected to enter the cell via active or passive transport through the phospholipid bilayer

Molecules and ions are always kept to the exterior of the phospholipid bilayer

Molecules and ions can pass freely through the phospholipid bilayer

Correct answer:

Molecules and ions outside the cell are selected to enter the cell via active or passive transport through the phospholipid bilayer

Explanation:

A cell must exchange molecules and ions with its surroundings.  This process is controlled by the selective permeability of the plasma membrane.  Passive transport requires no energy from the cell; molecules like water can diffuse into and out of the cell through the phospholipid bilayer freely by way of osmosis.  Other molecules and ions, like sodium, are actively transported across the phospholipid bilayer.  This requires ATP created by the cell.  Active transport moves solutes against their concentration gradients, which is why it requires energy. 

Example Question #71 : Understanding The Cell Membrane

Which of the following is NOT true of the cytoplasmic protein structures known as tonofibrils?

Possible Answers:

They converge at desmosomes and hemidesmosomes.

They are primarily found in endocrine tissues.

They are primarily made of kertain tonofilaments.

The protein filaggrin is thought to hold them together.

They are most typically anchored to the cytoskeleton.

Correct answer:

They are primarily found in endocrine tissues.

Explanation:

Tonofibrils are groups of keratin tonofilaments (intermediate filaments) most commonly found in the epithelial tissues, not endocrine tissues, and which play an important structural role in cell makeup.

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