BIOL 251 Practice Exam: Cell Structure and Function
BIOL 251 Practice Exam: Cell Structure and
Function
Oct 28, 2026 · @mr.books
Instructions
This is an original, unofficial 50-question practice exam on cell structure and function for a
typical college-level Human Anatomy and Physiology I course. It is not an official BIOL 251
exam and does not reflect any institution's syllabus.
Choose the single best answer. Twenty-six questions are paired with one of eleven
original diagrams; in most the diagram is needed to answer, and in a few it supports a
description given in the text. Each answer is followed by a rationale that explains the
correct choice and why each other option fails, so cover the answers while you work.
Target mix: 10 foundational, 15 conceptual, 15 application and analysis, 10 advanced
integration or clinical questions.
Questions 1-17
Question 1. Which statement is a principle of the cell theory?
A. Cells arise spontaneously from nonliving organic matter when conditions are suitable.
B. Only plant and animal tissues are made of cells; microorganisms are not.
C. The cell is the basic structural and functional unit of living organisms, and all cells come
from pre-existing cells.
D. All human cells share the same structure because they contain the same organelles in
the same proportions.
Correct Answer: C. The cell is the basic structural and functional unit of living
organisms, and all cells come from pre-existing cells.
Rationale: The cell theory has three tenets: all organisms are composed of one or more
cells, the cell is the basic unit of structure and function, and new cells arise only from
division of existing cells. Option A describes spontaneous generation, which was
disproved by the work of Pasteur and others. Option B is wrong because bacteria,
protozoa, and fungi are also cellular. Option D is a common misconception: although
nearly all human cells carry the same DNA, they differ greatly in organelle content
Page 1 of 40
,BIOL 251 Practice Exam: Cell Structure and Function
and shape. A muscle cell is packed with mitochondria, while a mature red blood cell
has none. This relationship between structure and function is a central theme of the
course.
Question 2. Arrow 2 indicates a stack of flattened membranous sacs studded with small
dark dots. What is the main function of this organelle?
A. Sorting and packaging proteins into secretory vesicles
B. Detoxifying drugs and synthesizing steroid hormones
C. Producing most of the cell's ATP
D. Synthesizing proteins destined for secretion, the plasma membrane, or lysosomes
Correct Answer: D. Synthesizing proteins destined for secretion, the plasma
membrane, or lysosomes
Page 2 of 40
,BIOL 251 Practice Exam: Cell Structure and Function
Rationale: Arrow 2 marks the rough endoplasmic reticulum. The dots are ribosomes
attached to its cytosolic surface, and they feed newly made polypeptides into the ER
lumen, where folding begins. These proteins are then sent to the Golgi apparatus.
Option A describes the Golgi apparatus (arrow 3), which has no ribosomes. Option B
describes the smooth ER, which lacks ribosomes and appears tubular. Option C
describes mitochondria (arrow 4). The ribosome-studded surface is the key visual
clue that separates rough ER from every other membranous organelle.
Question 3. Arrow 4 indicates the interior of the bilayer. Why can sodium ions not diffuse
through this region unaided?
A. The region consists of nonpolar fatty acid tails, which exclude charged and polar
particles.
B. The region is filled with closed channel proteins that block all ions.
C. The region is made of hydrophilic phosphate heads that repel the water around the
ions.
D. The region is coated with carbohydrate chains that act as a physical filter.
Correct Answer: A. The region consists of nonpolar fatty acid tails, which exclude
charged and polar particles.
Page 3 of 40
, BIOL 251 Practice Exam: Cell Structure and Function
Rationale: Each phospholipid has a polar, hydrophilic head and two nonpolar,
hydrophobic fatty acid tails. In the bilayer the tails face each other, creating an oily
core. Ions such as Na+ are charged and surrounded by water molecules, so they
cannot enter this nonpolar environment without help from a channel or carrier.
Option B is incorrect because proteins occupy only a small part of the core region.
Option C describes the surface layers, not the interior, and phosphate heads do not
repel ions in a way that explains the barrier. Option D is incorrect because
carbohydrate chains are on the outer surface and function in recognition, not
filtering.
Question 4. Arrow 2 indicates small, flat molecules wedged between phospholipid tails.
What is their main role in the membrane?
A. They form channels that let fat-soluble molecules cross the bilayer.
B. They stabilize membrane fluidity by limiting tight packing of tails in the cold and
restraining excess movement when warm.
C. They bind extracellular ligands and activate intracellular signaling.
D. They are the main reason the membrane is permeable to glucose.
Correct Answer: B. They stabilize membrane fluidity by limiting tight packing of tails in
the cold and restraining excess movement when warm.
Page 4 of 40
BIOL 251 Practice Exam: Cell Structure and
Function
Oct 28, 2026 · @mr.books
Instructions
This is an original, unofficial 50-question practice exam on cell structure and function for a
typical college-level Human Anatomy and Physiology I course. It is not an official BIOL 251
exam and does not reflect any institution's syllabus.
Choose the single best answer. Twenty-six questions are paired with one of eleven
original diagrams; in most the diagram is needed to answer, and in a few it supports a
description given in the text. Each answer is followed by a rationale that explains the
correct choice and why each other option fails, so cover the answers while you work.
Target mix: 10 foundational, 15 conceptual, 15 application and analysis, 10 advanced
integration or clinical questions.
Questions 1-17
Question 1. Which statement is a principle of the cell theory?
A. Cells arise spontaneously from nonliving organic matter when conditions are suitable.
B. Only plant and animal tissues are made of cells; microorganisms are not.
C. The cell is the basic structural and functional unit of living organisms, and all cells come
from pre-existing cells.
D. All human cells share the same structure because they contain the same organelles in
the same proportions.
Correct Answer: C. The cell is the basic structural and functional unit of living
organisms, and all cells come from pre-existing cells.
Rationale: The cell theory has three tenets: all organisms are composed of one or more
cells, the cell is the basic unit of structure and function, and new cells arise only from
division of existing cells. Option A describes spontaneous generation, which was
disproved by the work of Pasteur and others. Option B is wrong because bacteria,
protozoa, and fungi are also cellular. Option D is a common misconception: although
nearly all human cells carry the same DNA, they differ greatly in organelle content
Page 1 of 40
,BIOL 251 Practice Exam: Cell Structure and Function
and shape. A muscle cell is packed with mitochondria, while a mature red blood cell
has none. This relationship between structure and function is a central theme of the
course.
Question 2. Arrow 2 indicates a stack of flattened membranous sacs studded with small
dark dots. What is the main function of this organelle?
A. Sorting and packaging proteins into secretory vesicles
B. Detoxifying drugs and synthesizing steroid hormones
C. Producing most of the cell's ATP
D. Synthesizing proteins destined for secretion, the plasma membrane, or lysosomes
Correct Answer: D. Synthesizing proteins destined for secretion, the plasma
membrane, or lysosomes
Page 2 of 40
,BIOL 251 Practice Exam: Cell Structure and Function
Rationale: Arrow 2 marks the rough endoplasmic reticulum. The dots are ribosomes
attached to its cytosolic surface, and they feed newly made polypeptides into the ER
lumen, where folding begins. These proteins are then sent to the Golgi apparatus.
Option A describes the Golgi apparatus (arrow 3), which has no ribosomes. Option B
describes the smooth ER, which lacks ribosomes and appears tubular. Option C
describes mitochondria (arrow 4). The ribosome-studded surface is the key visual
clue that separates rough ER from every other membranous organelle.
Question 3. Arrow 4 indicates the interior of the bilayer. Why can sodium ions not diffuse
through this region unaided?
A. The region consists of nonpolar fatty acid tails, which exclude charged and polar
particles.
B. The region is filled with closed channel proteins that block all ions.
C. The region is made of hydrophilic phosphate heads that repel the water around the
ions.
D. The region is coated with carbohydrate chains that act as a physical filter.
Correct Answer: A. The region consists of nonpolar fatty acid tails, which exclude
charged and polar particles.
Page 3 of 40
, BIOL 251 Practice Exam: Cell Structure and Function
Rationale: Each phospholipid has a polar, hydrophilic head and two nonpolar,
hydrophobic fatty acid tails. In the bilayer the tails face each other, creating an oily
core. Ions such as Na+ are charged and surrounded by water molecules, so they
cannot enter this nonpolar environment without help from a channel or carrier.
Option B is incorrect because proteins occupy only a small part of the core region.
Option C describes the surface layers, not the interior, and phosphate heads do not
repel ions in a way that explains the barrier. Option D is incorrect because
carbohydrate chains are on the outer surface and function in recognition, not
filtering.
Question 4. Arrow 2 indicates small, flat molecules wedged between phospholipid tails.
What is their main role in the membrane?
A. They form channels that let fat-soluble molecules cross the bilayer.
B. They stabilize membrane fluidity by limiting tight packing of tails in the cold and
restraining excess movement when warm.
C. They bind extracellular ligands and activate intracellular signaling.
D. They are the main reason the membrane is permeable to glucose.
Correct Answer: B. They stabilize membrane fluidity by limiting tight packing of tails in
the cold and restraining excess movement when warm.
Page 4 of 40
