Cell structure and membrane transport sample question 1

Cytokinesis, which depends on a contractile ring that pinches the cell in two

MCAT · Biological and Biochemical Foundations · Biology

Cell structure and membrane transport

Cell structure and membrane transport is part of Biology in the MCAT Biological and Biochemical Foundations section. The questions below are written in the style of the real test, each with the answer and a worked explanation.

Question types you will see here include identify the transport mode, osmosis and tonicity, na+/K+ pump and ion gradients and saturable versus linear uptake.

Common traps: calling any protein-mediated transport 'active'; missing that a symporter's energy is the Na+ gradient, not ATP at the carrier; reading the gradient direction backwards.

Sample questions

Question 1
A cultured fibroblast is treated with a drug that depolymerizes actin filaments but leaves microtubules intact. Which process is most directly impaired?
- A.
  Separation of the sister chromatids toward the opposite spindle poles at anaphase
- B.
  Transport of vesicles along the length of a long cell extension
- C.
  Cytokinesis, which depends on a contractile ring that pinches the cell in two
- D.
  Beating of cilia on the apical surface of the cell
Answer: C. Cytokinesis, which depends on a contractile ring that pinches the cell in two
The cleavage furrow is produced by a ring of actin filaments and myosin II that tightens beneath the plasma membrane, so without actin the cytoplasm cannot divide and binucleate cells form. Chromosome movement, long-range vesicle transport by kinesin and dynein, and ciliary beating all depend on microtubules, which the drug leaves intact.

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