Question 1

Which of the following best explains why the movement of Ca$$^{2+}$$ ions from the cytosol into the endoplasmic reticulum (ER) requires ATP?

Accepted Answer

Because Ca$$^{2+} is $$moving against its concentration gradient, from low concentration in the cytosol to high concentration in the ER.

Question 2

A plant cell is exposed to high temperatures for several days. To maintain optimal membrane fluidity, which change is most likely to occur in the cell's membrane composition?

Accepted Answer

Increase the proportion of phospholipids with longer and more saturated fatty acid tails.

Question 3

After eating a very salty meal, what immediate effect does the increased sodium in your bloodstream have on water movement between your blood and body tissues?

Accepted Answer

Your blood becomes hypertonic, causing water to move from body tissues into the bloodstream.

Question 4

Which of the following best describes the difference between simple diffusion and facilitated diffusion across the plasma membrane?

Accepted Answer

Simple diffusion does not require membrane proteins, while facilitated diffusion requires specific transport proteins.

Question 5

Which of the following substances is most likely to cross the plasma membrane by simple diffusion?

Accepted Answer

O$$_2 ($$oxygen gas)

Question 6

Yeast cells often have a higher concentration of glucose inside the cell than outside. Which transport mechanism do they use to import glucose?

Accepted Answer

Active transport, because glucose is moved against its concentration gradient.

Question 7

Which of the following best describes selective permeability of the plasma membrane?

Accepted Answer

The membrane allows some substances to cross more easily than others.

Question 8

A cell is placed in a solution containing a high concentration of a non-permeable solute. What will happen to the cell?

Accepted Answer

Water will move out of the cell, causing it to shrink.

Question 9

Which of the following is a key function of receptor-mediated endocytosis?

Accepted Answer

It allows the cell to selectively take in specific molecules from the extracellular environment.

Question 10

Which of the following best describes the role of cholesterol in the plasma membrane at high temperatures?

Accepted Answer

Cholesterol decreases membrane fluidity by restricting the movement of phospholipids.

Question 11

A muscle cell needs to rapidly increase its cytosolic Ca$$^{2+}$$ concentration to trigger contraction. Which protein is responsible for this process?

Accepted Answer

A channel protein that allows Ca$$^{2+} to $$move from the endoplasmic reticulum to the cytosol without ATP.

Question 12

Which of the following statements about active transport is correct?

Accepted Answer

Active transport moves substances against their concentration gradient and requires energy, often in the form of ATP.

Question 13

A cell is placed in a hypotonic solution. What is the most likely outcome?

Accepted Answer

Water will enter the cell, causing it to swell.

Question 14

Which of the following best explains why ions such as Na$$^+$$ and K$$^+$$ cannot cross the plasma membrane by simple diffusion?

Accepted Answer

They are charged and hydrophilic, so they cannot pass through the hydrophobic core of the membrane.

Question 15

Which of the following scenarios best illustrates the concept of facilitated diffusion?

Accepted Answer

Glucose moves into a cell through a specific membrane protein, down its concentration gradient, without the use of ATP.

Question 16

A patient is given an intravenous solution that is hypertonic relative to their blood plasma. What is the most likely effect on their red blood cells?

Accepted Answer

The red blood cells will lose water and shrink (crenate).

Question 17

Which of the following best describes the function of the plasma membrane?

Accepted Answer

It acts as a selective barrier, regulating the movement of substances into and out of the cell.

Question 18

Which of the following changes would most likely increase the fluidity of a cell membrane at low temperatures?

Accepted Answer

Increasing the proportion of unsaturated fatty acids in the membrane lipids.

Question 19

Which of the following is an example of a substance that requires a transport protein to cross the plasma membrane?

Accepted Answer

Glucose

Question 20

A cell needs to import large quantities of cholesterol from its environment. Which process is most likely to be involved?

Accepted Answer

Receptor-mediated endocytosis

Membrane Structure, Transport, and Fluidity: Study Notes for General Biology

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