Question 1

Which polymer is primarily responsible for the tensile strength of the plant cell wall, and what is its structural composition?

Accepted Answer

Cellulose; linear polymer of β1,4-linked glucose units

Question 2

A mutation disrupts the function of cellulose synthase in a plant. Which of the following would most likely occur as a result?

Accepted Answer

Cell wall microfibrils would fail to form, reducing tensile strength.

Question 3

Which molecule acts as the substrate for cellulose synthase during cellulose biosynthesis?

Accepted Answer

UDP-glucose

Question 4

In the plant cell wall, which component forms a negatively charged, hydrophilic network that gives compressive strength to primary walls and mediates cell-cell adhesion?

Accepted Answer

Pectin

Question 5

Which of the following best describes the relationship between cortical microtubules and cellulose microfibril orientation in plant cells?

Accepted Answer

Cortical microtubules guide the orientation of newly deposited cellulose microfibrils.

Question 6

Which equation correctly represents the repeating unit of cellulose, a linear polymer of glucose?

Accepted Answer

$$\mathrm{(C_6H_{10}O_5$)}_n$$

Question 7

During the cell cycle, which phase is characterized by DNA replication?

Accepted Answer

S phase

Question 8

A flow cytometer is used to analyze DNA content in a population of cells. Which phase will show cells with approximately double the DNA content compared to G1 phase?

Accepted Answer

G2 and M phases

Question 9

Which protein complex is responsible for triggering essential processes of the cell cycle, and what is its regulation mechanism?

Accepted Answer

Cyclin-Cdk complex; regulated by cyclin binding and phosphorylation

Question 10

Which checkpoint in the cell cycle ensures that the environment is favorable and all DNA is replicated before entering mitosis?

Accepted Answer

G2/M transition

Question 11

What is the function of the retinoblastoma (Rb) protein in cell cycle control?

Accepted Answer

It prevents excessive cell growth by inhibiting cell cycle progression until the cell is ready to divide.

Question 12

Which event occurs when G1-Cdk and G1/S-Cdk phosphorylate the Rb protein?

Accepted Answer

E2F is released, activating expression of genes required for DNA replication.

Question 13

Which of the following statements about cyclin-dependent kinases (Cdks) is correct?

Accepted Answer

Cdk activity is regulated by binding to cyclins, whose concentrations oscillate during the cell cycle.

Question 14

A cell is exposed to a Cdk inhibitor protein (CKI). What is the most likely outcome?

Accepted Answer

Cdk activity will be suppressed, halting cell cycle progression.

Question 15

Which process ensures that DNA replication occurs only once per cell cycle?

Accepted Answer

Origin licensing by loading inactive DNA helicases, followed by S-Cdk activation

Question 16

Which of the following is a real-world application of understanding cell cycle checkpoints in medicine?

Accepted Answer

Developing cancer therapies that target defective checkpoint proteins

Question 17

If a plant cell wall lacked cross-linking glycans, which structural property would be most affected?

Accepted Answer

Robustness of the cell wall network

Question 18

Which phase of the cell cycle is associated with the highest concentration of M-cyclin?

Accepted Answer

M phase

Question 19

A yeast cell is observed to remain in G0 phase for an extended period. Which of the following is the most likely explanation?

Accepted Answer

The cell has differentiated to perform a specific function and lacks sufficient nutrients or growth factors.

Question 20

Which of the following best describes the function of lignin in the plant cell wall?

Accepted Answer

Forms a strong waterproof polymer that reinforces secondary walls

23: Plant Cell Walls and the Eukaryotic Cell Cycle: Structure, Function, and Regulation

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