Question 1

The plasma membranes of some plant cells use transport proteins to move protons out of the cell against their concentration gradient. This is an example of:

Accepted Answer

Moving protons against their concentration gradient requires energy input, which is provided by ATP in active transport. Therefore, the plasma membranes of some plant cells using transport proteins to move protons out of the cell against their concentration gradient is an example of active transport.

Question 2

Which one of the following molecules would MOST likely require a transport protein to cross the plasma membrane of a red blood cell?

Accepted Answer

The molecules listed are represented in a coded format, but based on the context of the question, option D likely represents a complex, large, or polar molecule. Transport proteins are typically required for the movement of large, polar, or charged molecules across the plasma membrane, as these cannot easily pass through the lipid bilayer. Options A, B, and C, by contrast, likely represent smaller or less complex molecules (such as gases or simple molecules) that can diffuse directly through the membrane without assistance.

Question 3

The beaker in the illustration below contains two solutions of salt with different concentrations (measured by molarity, M). The two solutions are separated by a membrane that is permeable to both salt and water.

Which of the following will occur in this container?

Accepted Answer

The answer of The beaker in the illustration below contains...

Question 4

A beaker contains two solutions of salt dissolved in water. The two solutions have different concentrations (measured by molarity, M) and are separated by a membrane that is permeable to both salt and water.  Which of the following statements is TRUE?

Accepted Answer

The answer of A beaker contains two solutions of salt...

Question 5

Which of the following represents the order that molecules cross a synthetic membrane composed of phospholipids but not proteins, from most easily (freely permeable) to least easily (not permeable)?

Accepted Answer

Small, nonpolar molecules like O2 cross phospholipid membranes most easily, followed by small, uncharged polar molecules like water. Larger, uncharged polar molecules like glucose cross less easily, and ions like Na+ are generally not permeable without specific transport proteins.

Question 6

A researcher is using a modified version of FRAP. She has devised a technique that allows her to label all the peripheral membrane proteins with a fluorescent tag, and has bleached a specific area of the cell membrane. After 24 hours, she notices that fluorescence has returned to the bleached area. What can she deduce from this experiment?

Accepted Answer

The return of fluorescence to the bleached area indicates that labeled peripheral membrane proteins can move freely within the cell membrane, suggesting that they are not permanently associated with the membrane. This finding does not necessarily imply that peripheral membrane proteins are located only on the cell membrane or are similar to integral membrane proteins.

Question 7

Explain why the plasma membrane is permeable to some substances, while others require a channel, or carrier, protein to cross the membrane.

Accepted Answer

The answer of Explain why the plasma membrane is permeable...

Question 8

Imagine a cell that has a membrane composed mostly of lipids with saturated fatty acid tails, and that this membrane also has low cholesterol content. What are the characteristics of this cell membrane?

Accepted Answer

Saturated fatty acid tails in the lipids make the membrane less fluid because they can pack closely together, and low cholesterol content also decreases membrane fluidity, especially at lower temperatures. Cholesterol acts as a fluidity buffer, making membranes more fluid at low temperatures and less fluid at high temperatures. Therefore, none of the provided options accurately describe the characteristics of a membrane composed mostly of lipids with saturated fatty acid tails and low cholesterol content.

Question 9

The electrical component of an electrochemical gradient is due to:

Accepted Answer

The electrical component of an electrochemical gradient is due to a greater concentration of positive charges on the side of the membrane with the highest concentration of protons. This creates a positive charge imbalance across the membrane, which can drive the movement of charged particles such as ions. Therefore, the best choice is E - a greater concentration of positive charges on the side of the membrane with the highest concentration of protons.

Question 10

Suppose you are studying the transport of a certain polar molecule across the plasma membrane of cells in culture. Over a period of time, you measure the concentration of a polar molecule inside and outside of the cells. You find that the concentration of the molecule is lower in the cell but is gradually increasing. You also measure the ATP concentration inside the cell and find that it is not changing. Which of the following is probably responsible for the transport of this polar substance into the cell?

Accepted Answer

Since the concentration of the polar molecule is gradually increasing, it is likely that it is moving from an area of higher concentration (outside the cell) to an area of lower concentration (inside the cell) through a process that doesn't require energy. This suggests that the molecule is moving via facilitated diffusion, which uses carrier proteins to move polar or charged molecules across the membrane down their concentration gradient. The fact that ATP concentration inside the cell is not changing suggests that the process is not using energy.

Question 11

Which of the following is responsible, in part, for keeping the cytoplasm of red blood cells isotonic with the blood plasma, and thereby preventing either lysis or shrinking of the cells?

Accepted Answer

The sodium/potassium pump is responsible for maintaining the concentration gradient of sodium and potassium ions across the cell membrane, which helps to regulate the osmotic balance of the cell. This helps to keep the cytoplasm of red blood cells isotonic with the blood plasma, preventing lysis or shrinking of the cells. Facilitated diffusion (A) and sodium channels (B) are not directly involved in maintaining osmotic balance, and osmosis (D) is a passive process that can contribute to changes in cell volume but is not responsible for regulating osmotic balance.

Question 12

If cells had single-layer membranes like micelles, how would the structures of transmembrane proteins be affected?

Accepted Answer

If cells had single-layer membranes like micelles, transmembrane proteins would need to have a hydrophobic region in the cell interior and a hydrophilic region in the extracellular space to interact appropriately with the membrane's environment.

Question 13

Some plant cells take advantage of the high concentration of protons outside the cell to move solutes, such as sucrose, across the plasma membrane into the cell where the sucrose concentration is already relatively high. This type of transport is an example of:

Accepted Answer

This type of transport, where a solute is moved against its concentration gradient using the energy from a proton gradient, is called secondary active transport. It requires a carrier protein or co-transporter to facilitate the movement of the solute. Facilitated diffusion, osmosis, and passive transport do not involve the use of energy or proton gradients to move solutes against their concentration gradient.

Question 14

The beaker in the illustration below contains two solutions of salt with different concentrations (measured by molarity, M). The two solutions are separated by a membrane that is permeable to both salt and water.  Which of the following will occur in this container?

Accepted Answer

This is an example of osmosis, where water will move from an area of low solute concentration to an area of high solute concentration. In this case, Solution A has a higher concentration of salt (higher solute concentration) than Solution B, so water will move from Solution B to Solution A, resulting in a net diffusion of water from A to B. At the same time, the salt will diffuse from Solution A to Solution B down its concentration gradient. Therefore, there will be a net diffusion of salt from B to A.

Question 15

G protein-coupled receptors are transmembrane receptors involved in cell signaling. The amino acid sequence of these proteins reveals that the polypeptide chain of the protein has seven hydrophobic regions. Based on this information, what can you conclude about how the protein is associated with the cell membrane?

Accepted Answer

The seven hydrophobic regions in the amino acid sequence of G protein-coupled receptors suggest that these regions span the hydrophobic core of the cell membrane, indicating that the polypeptide chain likely spans the membrane seven times.

Question 16

Some drugs are now being delivered into cells through liposomes, in which the drug is surrounded by a phospholipid bilayer. Explain how the drugs enter the cell.

Accepted Answer

The answer of Some drugs are now being delivered into...

Question 17

The active maintenance of a constant internal environment is referred to as:

Accepted Answer

Homeostasis refers to the active maintenance of a constant internal environment, including factors such as body temperature, pH balance, and chemical composition of body fluids. Equilibrium, stability, symmetry, and balance may be related concepts but do not specifically refer to the active maintenance of internal conditions.

Question 18

Some drugs are now being delivered into cells through liposomes, in which the drug is surrounded by a phospholipid bilayer. How do the drugs enter into the cell?

Accepted Answer

The liposome, being made up of phospholipids, can fuse with the phospholipid bilayer of the target cell, allowing the drug to enter the cell. This process is called endocytosis. Option A is incorrect because the drug is protected by the liposome and does not destroy it. Option B is also incorrect because the liposome does not cut a hole in the cell membrane. Option D is incorrect because protein channels transport small molecules, not liposomes.

Question 19

Suppose you are studying the transport of a certain polar molecule across the plasma membrane of cells in culture. Over a period of time, you measure the concentration of a polar molecule inside and outside of the cells. You find that the concentration of the molecule is higher in the cell and is gradually increasing. You also measure the ATP concentration inside the cell and find that it is decreasing. Which of the following is probably responsible for the transport of this polar substance into the cell?

Accepted Answer

The answer of Suppose you are studying the transport of...

Question 20

Some diseases result from defective transport across the membrane. For example, cystic fibrosis results when a chloride ion transporter does not function. Which of the following is affected when this transporter does NOT function?

Accepted Answer

When the chloride ion transporter does not function in cystic fibrosis, the concentration gradient of chloride ions is disrupted as they cannot pass through the membrane. This, in turn, disrupts the electrical gradient of the cell as chloride ions play a crucial role in balancing the charge of other ions inside and outside of the cell. Therefore, both the chloride concentration gradient and the electrical gradient of the cell are affected.

Quiz 5: Organizing Principles: Lipids, Membranes, and Cell Compartments