CHAPTER 3: CELL STRUCTURE AND FUNCTION
Original Practice Questions with Detailed Rationales 2026
1. The basic unit of structure and function in the human body is the:
a. Tissue
b. Organ
c. Cell
d. Molecule
ANSWER: C
Rationale:
a. Tissue - Incorrect. Tissues are groups of similar cells that work together to perform a specific function.
They are a higher level of organization than cells.
b. Organ - Incorrect. Organs are structures composed of two or more tissue types that work together to
perform specific functions. They are at a higher organizational level than cells.
c. Cell - Correct. The cell is the basic unit of structure and function in the human body. All living
organisms are composed of cells, and cells carry out all life processes.
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d. Molecule - Incorrect. Molecules are chemical structures composed of atoms. While molecules are
essential for cellular function, they are not living units and cannot carry out all life processes
independently.
2. Which of the following is NOT one of the three main parts of a cell?
a. Cell membrane
b. Cytoplasm
c. Nucleus
d. Ribosome
ANSWER: D
Rationale:
a. Cell membrane - Incorrect. The cell membrane (plasma membrane) is one of the three main parts of a
cell. It forms the outer boundary and regulates what enters and exits the cell.
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b. Cytoplasm - Incorrect. Cytoplasm is one of the three main parts of a cell. It is the fluid and organelles
between the cell membrane and nucleus.
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c. Nucleus - Incorrect. The nucleus is one of the three main parts of a cell. It contains genetic material
and controls cellular activities.
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d. Ribosome - Correct. Ribosomes are organelles within the cytoplasm, not one of the three main
structural divisions of the cell. They are components within the cytoplasmic region.
3. The cell membrane is primarily composed of:
a. Proteins and carbohydrates
b. Phospholipids and proteins
c. Carbohydrates and nucleic acids
d. Cholesterol and carbohydrates
ANSWER: B
Rationale:
a. Proteins and carbohydrates - Incorrect. While proteins are a major component, carbohydrates are
present in smaller amounts as glycoproteins and glycolipids on the outer surface.
b. Phospholipids and proteins - Correct. The cell membrane is primarily composed of a phospholipid
bilayer with embedded proteins. This is known as the fluid mosaic model. Phospholipids form the basic
structure, while proteins perform various functions such as transport and cell recognition.
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c. Carbohydrates and nucleic acids - Incorrect. Nucleic acids are found in the nucleus and cytoplasm, not
as structural components of the cell membrane.
d. Cholesterol and carbohydrates - Incorrect. While cholesterol is present in the membrane (especially in
animal cells) to maintain fluidity, it is not a primary structural component compared to phospholipids.
4. Which organelle is known as the "powerhouse" of the cell?
a. Ribosome
b. Endoplasmic reticulum
c. Mitochondria
d. Golgi apparatus
ANSWER: C
, Rationale:
a. Ribosome - Incorrect. Ribosomes are the sites of protein synthesis, not energy production.
b. Endoplasmic reticulum - Incorrect. The endoplasmic reticulum is involved in protein and lipid
synthesis and transport, not energy production.
c. Mitochondria - Correct. Mitochondria are known as the "powerhouse" of the cell because they
produce ATP (adenosine triphosphate) through cellular respiration, which provides energy for cellular
activities.
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d. Golgi apparatus - Incorrect. The Golgi apparatus modifies, sorts, and packages proteins for secretion
or delivery to other organelles.
5. The process by which water moves across a selectively permeable membrane from an area of higher
water concentration to an area of lower water concentration is called:
a. Diffusion
b. Active transport
c. Osmosis
d. Filtration
ANSWER: C
Rationale:
a. Diffusion - Incorrect. Diffusion is the movement of particles (solutes) from an area of higher
concentration to an area of lower concentration, not specifically water.
b. Active transport - Incorrect. Active transport requires energy (ATP) to move substances against their
concentration gradient, from low to high concentration.
c. Osmosis - Correct. Osmosis is the specific type of diffusion involving water molecules moving across a
selectively permeable membrane from an area of higher water concentration (lower solute
concentration) to an area of lower water concentration (higher solute concentration).
glencoe.mheducation.com
d. Filtration - Incorrect. Filtration is the movement of water and solutes through a membrane due to
hydrostatic pressure, not concentration gradients.
6. Which organelle is responsible for protein synthesis?
a. Lysosome
b. Ribosome
c. Peroxisome
Original Practice Questions with Detailed Rationales 2026
1. The basic unit of structure and function in the human body is the:
a. Tissue
b. Organ
c. Cell
d. Molecule
ANSWER: C
Rationale:
a. Tissue - Incorrect. Tissues are groups of similar cells that work together to perform a specific function.
They are a higher level of organization than cells.
b. Organ - Incorrect. Organs are structures composed of two or more tissue types that work together to
perform specific functions. They are at a higher organizational level than cells.
c. Cell - Correct. The cell is the basic unit of structure and function in the human body. All living
organisms are composed of cells, and cells carry out all life processes.
quizlet.com
d. Molecule - Incorrect. Molecules are chemical structures composed of atoms. While molecules are
essential for cellular function, they are not living units and cannot carry out all life processes
independently.
2. Which of the following is NOT one of the three main parts of a cell?
a. Cell membrane
b. Cytoplasm
c. Nucleus
d. Ribosome
ANSWER: D
Rationale:
a. Cell membrane - Incorrect. The cell membrane (plasma membrane) is one of the three main parts of a
cell. It forms the outer boundary and regulates what enters and exits the cell.
,quizlet.com
b. Cytoplasm - Incorrect. Cytoplasm is one of the three main parts of a cell. It is the fluid and organelles
between the cell membrane and nucleus.
quizlet.com
c. Nucleus - Incorrect. The nucleus is one of the three main parts of a cell. It contains genetic material
and controls cellular activities.
quizlet.com
d. Ribosome - Correct. Ribosomes are organelles within the cytoplasm, not one of the three main
structural divisions of the cell. They are components within the cytoplasmic region.
3. The cell membrane is primarily composed of:
a. Proteins and carbohydrates
b. Phospholipids and proteins
c. Carbohydrates and nucleic acids
d. Cholesterol and carbohydrates
ANSWER: B
Rationale:
a. Proteins and carbohydrates - Incorrect. While proteins are a major component, carbohydrates are
present in smaller amounts as glycoproteins and glycolipids on the outer surface.
b. Phospholipids and proteins - Correct. The cell membrane is primarily composed of a phospholipid
bilayer with embedded proteins. This is known as the fluid mosaic model. Phospholipids form the basic
structure, while proteins perform various functions such as transport and cell recognition.
www.pearson.com
c. Carbohydrates and nucleic acids - Incorrect. Nucleic acids are found in the nucleus and cytoplasm, not
as structural components of the cell membrane.
d. Cholesterol and carbohydrates - Incorrect. While cholesterol is present in the membrane (especially in
animal cells) to maintain fluidity, it is not a primary structural component compared to phospholipids.
4. Which organelle is known as the "powerhouse" of the cell?
a. Ribosome
b. Endoplasmic reticulum
c. Mitochondria
d. Golgi apparatus
ANSWER: C
, Rationale:
a. Ribosome - Incorrect. Ribosomes are the sites of protein synthesis, not energy production.
b. Endoplasmic reticulum - Incorrect. The endoplasmic reticulum is involved in protein and lipid
synthesis and transport, not energy production.
c. Mitochondria - Correct. Mitochondria are known as the "powerhouse" of the cell because they
produce ATP (adenosine triphosphate) through cellular respiration, which provides energy for cellular
activities.
www.pearson.com
d. Golgi apparatus - Incorrect. The Golgi apparatus modifies, sorts, and packages proteins for secretion
or delivery to other organelles.
5. The process by which water moves across a selectively permeable membrane from an area of higher
water concentration to an area of lower water concentration is called:
a. Diffusion
b. Active transport
c. Osmosis
d. Filtration
ANSWER: C
Rationale:
a. Diffusion - Incorrect. Diffusion is the movement of particles (solutes) from an area of higher
concentration to an area of lower concentration, not specifically water.
b. Active transport - Incorrect. Active transport requires energy (ATP) to move substances against their
concentration gradient, from low to high concentration.
c. Osmosis - Correct. Osmosis is the specific type of diffusion involving water molecules moving across a
selectively permeable membrane from an area of higher water concentration (lower solute
concentration) to an area of lower water concentration (higher solute concentration).
glencoe.mheducation.com
d. Filtration - Incorrect. Filtration is the movement of water and solutes through a membrane due to
hydrostatic pressure, not concentration gradients.
6. Which organelle is responsible for protein synthesis?
a. Lysosome
b. Ribosome
c. Peroxisome
