AP Biology : Understanding the Cell Membrane

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #21 : Understanding The Cell Membrane

Dialysis tubing is representative of a semi-permeable membrane. Only water can diffuse into or out of the bag.

A clamped piece of dialysis tubing is filled with a solution, and placed in a beaker containing another solution. After a set amount of time, the tubing can be dried and weighed to monitor fluid intake or outtake.

Which of the following solution compositions would result in the highest net weight gain of the dialysis tubing?

Possible Answers:

Dialysis tubing: 85% sodium solution

Beaker: 50% sucrose solution

Dialysis tubing: 45% sodium solution

Beaker: 35% sodium solution

Dialysis tubing: pure water

Beaker: pure water

Dialysis tubing: 50% sucrose solution

Beaker: 50% sodium solution

Dialysis tubing: 50% sodium solution

Beaker: Pure water

Correct answer:

Dialysis tubing: 50% sodium solution

Beaker: Pure water

Explanation:

In order for the bag to gain weight, water needs to enter the tubing. The dialysis tubing must be placed in a hypotonic solution—a solution containing a higher percentage of water (lower concentration of ions) than the dialysis solution. This will cause water to enter the more concentrated solution within the dialysis tubing, in an attempt to reach equilibrium

Sodium ions and glucose are both monoatomic, so the composition of the solute is irrelevant. We simply need to find the greatest difference in concentration between the tubing and the beaker, in which the greater concentration is found in the beaker. Essentially, we want the maximum value of .

The greatest difference, in this case, occurs when a 50% sodium solution is present in the tubing and pure water is present in the beaker.

Example Question #22 : Understanding The Cell Membrane

Which of the following compounds will require a carrier protein in order to cross the cellular membrane?

Possible Answers:

A steroid hormone

Glucose

Water

Hydrogen gas

Correct answer:

Glucose

Explanation:

Cellular membranes are considered semipermeable, and allow certain substances to pass through without assistance from proteins. We typically follow the rule of thumb that substances that are small or nonpolar will be able to pass through the membrane. Water and hydrogen gas are both very small and can pass through the membrane relatively easily. Steroid hormones are large, but nonpolar, so they can pass through. Glucose is both large and polar, so it requires a carrier protein in order to cross.

Example Question #23 : Understanding The Cell Membrane

Which of the following is a function of the plasma membrane?

Possible Answers:

To establish metabolic and size parameters for the cell

To move oxygen, waste, and nutrients in and out of the cell

To enclose the nucleus 

To provide a surface upon which DNA replication can occur

Correct answer:

To move oxygen, waste, and nutrients in and out of the cell

Explanation:

The plasma membrane acts as a selective barrier and defines the boundaries of the cell. It allows for the passage of oxygen, nutrients, and wastes. The nucleus is enclosed by the nuclear envelope, not the plasma membrane.

Example Question #121 : Ap Biology

Which part of the cell separates the internal parts of the cell from the external environment?

Possible Answers:

Mitochondria

Cytoplasm

Endoplasmic reticulum

Nucleus

Plasma membrane

Correct answer:

Plasma membrane

Explanation:

The plasma membrane, also called cell membrane, is composed of a phospholipid bilayer that separates the outside of the cell from the inside of the cell. It is selectively permeable, and contains many proteins that facilitate the transduction of signals in and out of the cell, and allow for passage of specific substances. The nucleus, endoplasmic reticulum, nucleus, and mitochondria are membrane-bound organelles that exhist in the cytoplasm of eukaryotic cells.

Example Question #122 : Ap Biology

Which of the following cell parts in considered amphipathic?

Possible Answers:

Integral proteins

Nucleus

Peripheral proteins

Adhesion proteins

Ribosomes

Correct answer:

Integral proteins

Explanation:

Amphipathic molecules have both hydrophobic and hydrophilic regions (polar and non-polar). Phospholipids are amphipathic because they have a polar head and a non-polar tail. Since integral proteins are embedded within the phospholipid bilayer, the parts that are on either side of the plasma membrane are hydrophilic, and the parts that are in contact with the tails of the phospholipids are hydrophobic.

Example Question #123 : Ap Biology

Which statement is true regarding phospholipids?

Possible Answers:

Phospholipid tails are hydrophobic

Phospholipids are composed of three fatty acids attached to a glycerol 

Phospholipids maintain a positive charge, creating polarization

Phospholipids make up the cytosol of the cell

Phospholipids are synthesized on ribosomes

Correct answer:

Phospholipid tails are hydrophobic

Explanation:

Phospholipids are the major component of cell membranes (the lipid bilayer), composed of two fatty acid tails attached to a glycerol head. The third hydroxyl group that is joined to a phosphate gives the cell a negative charge. The heads are hydrophilic, or “water loving” and the tails are hydrophobic, or “water fearing.” The hydrophilic heads create a selectively permeable “gate” into and out of the cell. Between the hydrophilic heads are the hydrophobic tails. Thus, small, uncharged, lipophilic molecules can diffuse into and out of the cell.

Example Question #124 : Ap Biology

Which of these correctly describes the fluid mosaic model and the part of the cell to which it applies?

Possible Answers:

The fluid mosaic model states that cells are arranged in a mosaic-like pattern within a given region; this applies to the organism as a whole.

The fluid mosaic model states that organelles are fluid and scattered throughout the cytosol of the cell; this applies to the cytosol.

The fluid mosaic model states that the cytosol is fluid, like a mosaic and allows organelles to move throughout the cell; this applies to the cytosol.

The fluid mosaic model states that the phospholipid bilayer is composed of hydrocarbons that are fluid and give the cell flexibility; this applies to the cell membrane.

The fluid mosaic model states that lipids and proteins are embedded in the phospholipid bilayer in a mosaic-like pattern; this applies to the cell membrane.

Correct answer:

The fluid mosaic model states that lipids and proteins are embedded in the phospholipid bilayer in a mosaic-like pattern; this applies to the cell membrane.

Explanation:

The fluid mosaic model states that amphipathic proteins are embedded in the phospholipid bilayer. The cell membrane is a fluid mosaic of phospholipids and proteins. Phospholipids and proteins move laterally within the membrane. The unsaturated hydrocarbon tails of the phospholipids keep membranes fluid at lower temperatures and cholesterol helps them resist changes in fluidity in the face of temperature changes. Like a mosaic, integral proteins are embedded in the lipid bilayer while peripheral proteins are attached to the membrane surface. Glycoproteins and glycolipids are also embedded on the exterior side of the plasma membrane and interact with surface molecules of other cells. This membrane structure results in selective permeability of the cell membrane, allows for cell-cell adhesion, and cell signaling.

 

Example Question #125 : Ap Biology

A small molecule passes through the phospholipid bilayer without consuming ATP in the process. This is an example of which of the following?

Possible Answers:

Passive transport; no energy is required when a molecule moves down its concentration gradient

Active transport; no energy is required when a molecule passes through the cell membrane via exocytosis 

Active transport; no energy is required when a molecule moves down its concentration gradient

Passive transport; no energy is required when a molecule moves up its concentration gradient

Active transport; no energy is required when a molecule moves up its concentration gradient 

Correct answer:

Passive transport; no energy is required when a molecule moves down its concentration gradient

Explanation:

Passive transport occurs when a molecule or ion moves down its concentration gradient and therefore requires no energy. More specifically, in facilitated diffusion, a type of passive transport, a transport protein speeds the movement of water or a solute across a membrane and down its concentration gradient. Active transport, on the other hand, uses energy or ATP to move solutes against their concentration gradients.

Example Question #126 : Ap Biology

The most abundant lipids in biological membranes are __________.

Possible Answers:

sterols

phospholipids

fats

hydrolipids

Correct answer:

phospholipids

Explanation:

Phospholipids are the most abundant because their structure makes it possible for them to form membranes since they have hydrophilic and hydrophobic regions. In the phospholipid bilayer of a cell, the hydrophilic heads are exposed to the intracellular and extracellular compartments, which contain cytosol, and extracellular fluid, both of which are aqueous. The tails of the phospholipids are hydrophobic, and thus "hide" from the aqueous environments on either side of the cell membrane. This structure allows small, uncharged, and fat-soluble molecules to diffuse across the membrane. 

Example Question #127 : Ap Biology

Diabetes insipidus occurs when the body is unable to secrete antidiuretic hormone (ADH). ADH acts on the collecting tubule of the kidneys to allow for water reabsorption. The reabsorption of water will raise the blood’s volume and result in an increase in blood pressure.

Which of the following best describes how not having ADH will affect a person's blood pressure and blood osmolarity?

Possible Answers:

Without ADH the blood pressure will be low and the solute concentration will be hypo-osmotic

Without ADH the blood pressure will be high blood pressure and the solute concentration will be hypo-osmotic

None of these

Without ADH the blood pressure will be low and the solute concentration will be hyperosmotic

Without ADH the blood pressure will be high and the solute concentration will be hyperosmotic

Correct answer:

Without ADH the blood pressure will be low and the solute concentration will be hyperosmotic

Explanation:

When the blood pressure is low or when the body’s osmolarity is high, the posterior pituitary releases ADH. The reabsorption of water will increase the blood’s volume and result in an increase in blood pressure. With the reabsorption of water, the osmolarity is lowered. Recall that osmolarity is the amount of solutes (e.g. sodium, potassium, chloride, etc.) over the amount of solvent (e.g. water). When water is reabsorbed, the water’s volume increases; therefore, the osmolarity is decreased. Without ADH, blood pressure becomes low and without enough water the osmolarity of the blood increases—hyperosmolarity.

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