Cell Biology Techniques Practice Quiz (11 questions)

1. What does microscopy resolution describe?

A. The degree to which an image is enlarged compared with the specimen

B. The range of specimen depths that appear in focus at one time

C. The amount of light collected from a specimen by the objective lens

D. The smallest distance at which two points can still be seen as separate

Answer: (D)

Explanation

Resolution is the minimum separation at which two points remain distinguishable as separate. Image enlargement describes magnification, not resolution.

2. A researcher observes a cell dividing and producing two new cells; which principle of cell theory does this illustrate?

A. Every living organism consists of at least one cell

B. Cells are visible to the unaided eye when they are dividing

C. Every cell arises through the division of another cell

D. The cell is the structural and functional unit of living organisms

Answer: (C)

Explanation

The third principle of cell theory states that every cell arises from the division of another cell. The idea that organisms consist of one or more cells is a different principle and does not describe the origin of new cells.

3. Why can an optical microscope show cells but not fine cytoplasmic details?

A. Its best resolution is about 200 nm, limiting the fine detail it can distinguish

B. Its eyepiece magnification is too low to display large organelles in a cell

C. Its focused light cannot pass through cells, so it reveals only their outer boundaries

D. Its maximum total magnification is about 200 nm, limiting how far it enlarges an image

Answer: (A)

Explanation

The optical microscope has a best resolution of about 200 nm, which is sufficient for cells and large organelles but not fine cytoplasmic details. The 200 nm figure describes resolution, not maximum magnification.

4. Which preparation approach allows cells to remain alive during bright-field observation?

A. Dehydrating the specimen through concentrated alcohol

B. Using routine fixation, sectioning, and staining

C. Applying a vital stain such as neutral red

D. Embedding the specimen in resin before cutting sections

Answer: (C)

Explanation

Vital stains such as neutral red can be used while keeping cells alive. Routine fixation, sectioning, and staining procedures generally kill cells.

5. What is the role of a fluorochrome in fluorescence microscopy?

A. It stains the entire specimen uniformly to reveal cell boundaries.

B. It emits visible light when excited by ultraviolet light.

C. It binds directly to the target molecule and blocks its activity.

D. It focuses ultraviolet light onto the specimen to improve resolution.

Answer: (B)

Explanation

A fluorochrome associated with a target-specific antibody emits visible light when ultraviolet light excites it, making the target molecule detectable. An antibody provides target-specific binding; the fluorochrome is the light-emitting component.

6. What practical resolution range is given for electron microscopes?

A. Approximately 0.5–1 nm

B. Approximately 200 nm

C. Approximately 0.1–0.2 nm

D. Approximately 5–10 nm

Answer: (A)

Explanation

The practical resolution is given as approximately 0.5–1 nm, while the theoretical resolution is finer, at 0.1–0.2 nm. The 5–10 nm range refers to the resolution of a scanning electron microscope.

7. What is the purpose of heavy-metal salts in positive staining for transmission electron microscopy?

A. To coat one side of a structure and reveal its surface relief

B. To surround the specimen and make its outline appear light

C. To remove biological material and leave a metal replica behind

D. To accumulate in cellular material and make those regions appear dark

Answer: (D)

Explanation

In positive staining, heavy-metal salts accumulate in regions rich in cellular material, where they scatter electrons and appear dark. Surrounding a specimen to create a light outline against a dark background is the function of negative staining.

8. During cryofracture, at what stage is the tissue frozen in liquid nitrogen at approximately $-196^\circ\text{C}$?

A. After the fracture faces are metal-shadowed

B. After a carbon layer is applied perpendicular to the metal shadowing

C. Before the tissue is fractured to expose internal planes

D. After the biological material is dissolved to leave a replica

Answer: (C)

Explanation

Freezing the tissue at approximately $-196^\circ\text{C}$ comes before fracturing, which can split membranes through their middle. Metal shadowing and carbon coating occur later, after fracture faces are prepared.

9. How do primary and secondary cell cultures differ in their origin?

A. A primary culture forms after cells become senescent, while a secondary culture forms before their first division.

B. A primary culture begins with cells taken directly from tissue, while a secondary culture is recultured from an earlier culture.

C. A primary culture begins with cells transferred from an earlier culture, while a secondary culture comes directly from tissue.

D. A primary culture contains genetically modified cells, while a secondary culture contains unmodified cells from tissue.

Answer: (B)

Explanation

A primary culture is established directly from a tissue sample, whereas a secondary culture is made by collecting and reculturing cells from an earlier culture. Transferring cells from an earlier culture describes the secondary culture, not the primary one.

10. Which stem cell potency category includes the ability to form embryonic annexes such as the placenta and umbilical cord?

A. Unipotency, which includes one specialized cell type and no embryonic annexes

B. Multipotency, which includes a limited range of related cell types

C. Pluripotency, which includes all organismal cell types but excludes embryonic annexes

D. Totipotency, which includes all organismal cell types and embryonic annexes

Answer: (D)

Explanation

Totipotent cells can produce all organismal cell types, including embryonic annexes such as the placenta and umbilical cord. Pluripotent cells can produce any cell type except those annexes.

11. Why do endoplasmic reticulum and Golgi membranes appear in the microsome fraction after cell homogenization?

A. Homogenization converts these membranes into intact organelles that sediment with mitochondria.

B. Homogenization releases membrane proteins that bind ribosomes in the final supernatant.

C. Homogenization fuses these membranes with nuclei, which sediment in the first pellet.

D. Homogenization fragments these membranes into small vesicles that sediment as microsomes.

Answer: (D)

Explanation

Breaking open cells fragments the endoplasmic reticulum and Golgi membranes into vesicles called microsomes, which collect in the third pellet. The first pellet contains nuclei and intact cells, rather than fused membrane structures.