Cell Structure and Organelles Practice Quiz (14 questions)

1. Which statement summarizes the three central claims of cell theory?

A. Cells are life's basic units, but some organisms are not cellular and cells can form spontaneously.

B. Cells arise from pre-existing cells, but they are not life's basic units and organisms need not contain them.

C. Living organisms consist of cells, cells are life's basic units, and cells come from pre-existing cells.

D. Living organisms consist of tissues, tissues are life's basic units, and cells arise spontaneously.

Answer: (C)

Explanation

Cell theory holds that organisms are composed of cells, cells are the basic unit of life, and new cells arise from existing cells. The spontaneous-formation claim is a misconception because cell theory identifies pre-existing cells as the origin of cells.

2. What structure allows the plasma membrane to regulate which substances cross it?

A. A selectively permeable phospholipid bilayer with embedded proteins.

B. A rigid carbohydrate wall with proteins attached to its outer surface.

C. A double protein sheet enclosing a central layer of carbohydrates.

D. A single layer of phospholipids with no proteins within the membrane.

Answer: (A)

Explanation

The plasma membrane is a selectively permeable phospholipid bilayer containing embedded proteins, a structure that supports regulated passage. A carbohydrate wall is a different cellular structure and does not describe the plasma membrane.

3. How do ribosomal subunits become functional ribosomes in a cell?

A. They assemble from rRNA and lipids in the nucleolus, then join together inside the nuclear envelope.

B. They form from rRNA and proteins in the nucleolus, exit to the cytoplasm, and assemble there.

C. They form from DNA and proteins in the nucleus, then combine with rRNA at the plasma membrane.

D. They assemble from rRNA and proteins in the cytoplasm, then enter the nucleolus as complete ribosomes.

Answer: (B)

Explanation

Ribosomal subunits form in the nucleolus from rRNA and proteins, then leave for the cytoplasm, where the two subunits assemble. The subunits do not first assemble into complete ribosomes inside the nucleolus.

4. Which description best characterizes the endoplasmic reticulum?

A. A stack of flattened sacs whose internal space is the Golgi matrix.

B. A network of membranous tubules and sacs whose internal space is the lumen or cisternal space.

C. A network of protein fibers and channels whose internal space is the cytosol.

D. A set of membrane-bound vesicles whose internal space is the cell sap.

Answer: (B)

Explanation

The endoplasmic reticulum consists of membranous tubules and sacs, with an internal compartment called the lumen or cisternal space. The Golgi is also membrane-based, but its stacked sacs are not the ER network described here.

5. A cell needs to detoxify a drug and store calcium ions; which organelle is especially suited to these tasks?

A. The Golgi apparatus, which detoxifies drugs and synthesizes lipids for the cell.

B. The rough endoplasmic reticulum, which specializes in assembling secreted proteins and storing calcium.

C. The lysosome, which metabolizes carbohydrates and stores calcium in its lumen.

D. The smooth endoplasmic reticulum, which also synthesizes lipids and metabolizes carbohydrates.

Answer: (D)

Explanation

The smooth ER performs drug detoxification and calcium storage, as well as lipid synthesis and carbohydrate metabolism. The rough ER is associated with ribosomes and protein production, rather than being the organelle identified for these smooth-ER functions.

6. A cell is preparing to secrete a protein made by ER-bound ribosomes; how does that protein leave the endoplasmic reticulum?

A. Inside a membrane-wrapped vesicle that buds from the ER.

B. Through a nuclear pore after moving from the ER into the nucleus.

C. As a free protein that passes directly through the ER membrane.

D. Inside a ribosome that detaches and carries the protein out of the ER.

Answer: (A)

Explanation

Secretory proteins made by ribosomes attached to the rough ER leave the ER inside membrane-wrapped vesicles. The protein is cargo in the vesicle; it does not leave as a free protein passing through the ER membrane.

7. What role do lysosomes play in the ongoing life of a cell?

A. They assemble ribosomal subunits for protein synthesis.

B. They form the selectively permeable boundary around the cell.

C. They provide the main route for proteins to exit the ER.

D. They help the cell continually renew itself.

Answer: (D)

Explanation

Lysosomes contribute to the cell's continual renewal. Ribosomal subunit formation takes place in the nucleolus, rather than being a lysosomal role.

8. Which human cells are identified as carrying out phagocytosis?

A. Macrophages, which are white blood cells.

B. Neurons, which transmit electrical signals.

C. Red blood cells, which transport oxygen.

D. Epithelial cells, which line body surfaces.

Answer: (A)

Explanation

Macrophages are white blood cells that carry out phagocytosis. Red blood cells are associated with oxygen transport, not the phagocytic role described here.

9. A cell has a high metabolic demand. Which statement best describes how its mitochondria are expected to compare with those in a less active cell?

A. It may contain fewer mitochondria, because mitochondria are characteristic mainly of animal cells.

B. It may contain more mitochondria, because mitochondria occur in plants but are absent from fungi and protists.

C. It may contain more mitochondria, and mitochondria occur in eukaryotes such as plants and animals.

D. It should contain the same number of mitochondria, because their abundance is unrelated to metabolic activity.

Answer: (C)

Explanation

Mitochondria occur across eukaryotic groups, and their number depends on the cell’s metabolic activity. The idea that their abundance is unrelated to activity conflicts with this relationship.

10. Which description correctly identifies the mitochondrial matrix?

A. The narrow compartment between the outer and inner membranes, containing enzymes and mitochondrial DNA.

B. The compartment enclosed by the inner membrane, containing enzymes, mitochondrial DNA, and ribosomes.

C. The outer compartment beyond the outer membrane, containing mitochondrial DNA and ribosomes.

D. The folded region of the inner membrane, containing ribosomes but no mitochondrial DNA.

Answer: (B)

Explanation

The matrix is enclosed by the inner mitochondrial membrane and contains enzymes, mitochondrial DNA, and ribosomes. The space between the two membranes is the intermembrane space, not the matrix.

11. Which arrangement correctly describes the internal organization of a chloroplast?

A. Flattened stroma sacs form stacks called grana, while the surrounding fluid is the thylakoid space.

B. Flattened thylakoid sacs form stacks called grana, while the surrounding fluid is the stroma.

C. Flattened thylakoid sacs form the stroma, while the surrounding stacks are called grana.

D. Flattened grana sacs form stacks called thylakoids, while the surrounding fluid is the intermembrane space.

Answer: (B)

Explanation

Thylakoids are flattened sacs, stacks of thylakoids are grana, and the fluid outside them is the stroma. The thylakoid space is not the fluid surrounding the thylakoids.

12. What do plasmodesmata do in many plant tissues?

A. They form openings in cell walls that connect a plant cell to the extracellular space.

B. They form channels between chloroplasts inside a single plant cell.

C. They pass through plasma membranes to connect adjacent animal cells.

D. They pass through cell walls to connect adjacent plant cells.

Answer: (D)

Explanation

Plasmodesmata are channels through perforations in many plant cell walls that connect neighboring cells. They are not connections between animal cells; both plant and animal cells have plasma membranes.

13. A microscopist observes a comparatively large, rectangular cell with a cell wall and plastids. Which classification best fits these features?

A. An animal cell, which is usually larger and more regular in shape than a plant cell.

B. A plant cell, which is comparatively smaller and lacks a cell wall and plastids.

C. An animal cell, which is comparatively smaller and contains a cell wall and plastids.

D. A plant cell, which is usually larger and more regular in shape than an animal cell.

Answer: (D)

Explanation

Plant cells are usually larger and square or rectangular, and they have a cell wall and plastids. Animal cells are comparatively smaller and lack both a cell wall and plastids.

14. Which set of features is most characteristic of an animal cell compared with a plant cell?

A. A side-positioned nucleus, one central vacuole, fewer mitochondria, rare lysosomes, and no centrosome.

B. A central nucleus, small numerous vacuoles, numerous mitochondria, lysosomes, and a centrosome.

C. A side-positioned nucleus, small numerous vacuoles, numerous mitochondria, lysosomes, and a centrosome.

D. A central nucleus, one large central vacuole, fewer mitochondria, rare lysosomes, and no centrosome.

Answer: (B)

Explanation

Animal cells usually have a central nucleus, small numerous vacuoles, numerous mitochondria, lysosomes, and a centrosome. A side-positioned nucleus and a large central vacuole are more characteristic of plant cells.