BIO 251 LAB PRACTICAL EXAMINATION QUESTIONS AND
ANSWERS WITH RATIONALES/GRADED A+/2026 UPDATE/100%
CORRECT /INSTANT DOWNLOAD
Section 1: Microscopy & Laboratory Techniques (Questions 1-25)
1. Which part of the compound light microscope controls the amount of light reaching the
specimen?
A. Ocular lens
B. Objective lens
C. Iris diaphragm
D. Coarse adjustment knob
Answer: C
Rationale: The iris diaphragm (or condenser diaphragm) adjusts the amount of light passing
through the specimen. The ocular lens (A) magnifies the image for the eye. The objective lens (B)
provides primary magnification. The coarse adjustment knob (D) focuses the specimen.
2. When carrying a microscope, you should always hold it by which two parts?
A. Ocular lens and objective lens
B. Arm and base
C. Stage and light source
D. Coarse and fine adjustment knobs
Answer: B
Rationale: The arm and base provide stable, secure handling. Holding by the ocular (A) or stage
(C) may damage components or drop the microscope. Knobs (D) are not designed for carrying.
3. The total magnification when using a 10x ocular lens and a 100x oil immersion objective lens
is:
A. 110x
, B. 100x
C. 1,000x
D. 10,000x
Answer: C
Rationale: Total magnification = ocular magnification (10x) × objective magnification (100x) =
1,000x. 10 × 100 = 1,000.
4. Which objective lens requires the use of immersion oil to increase resolution?
A. 4x scanning lens
B. 10x low power lens
C. 40x high power lens
D. 100x oil immersion lens
Answer: D
Rationale: The 100x oil immersion lens requires oil to reduce light refraction and increase
resolution at high magnification. Lower power lenses (A, B, C) do not require oil.
5. Immersion oil has the same refractive index as glass. This prevents:
A. Light absorption by the specimen
B. Light scattering (refraction) at the air-glass interface
C. Damage to the objective lens
D. Staining of the specimen
Answer: B
Rationale: Immersion oil fills the gap between the slide and the lens, preventing light from
bending (refracting) as it passes through air, thereby increasing resolution and image clarity. It
does not prevent lens damage (C) or affect staining (D).
6. The coarse adjustment knob should only be used with which objective lens to avoid damaging
the slide or lens?
A. 100x oil immersion lens
B. 40x high power lens
C. 4x scanning lens
ANSWERS WITH RATIONALES/GRADED A+/2026 UPDATE/100%
CORRECT /INSTANT DOWNLOAD
Section 1: Microscopy & Laboratory Techniques (Questions 1-25)
1. Which part of the compound light microscope controls the amount of light reaching the
specimen?
A. Ocular lens
B. Objective lens
C. Iris diaphragm
D. Coarse adjustment knob
Answer: C
Rationale: The iris diaphragm (or condenser diaphragm) adjusts the amount of light passing
through the specimen. The ocular lens (A) magnifies the image for the eye. The objective lens (B)
provides primary magnification. The coarse adjustment knob (D) focuses the specimen.
2. When carrying a microscope, you should always hold it by which two parts?
A. Ocular lens and objective lens
B. Arm and base
C. Stage and light source
D. Coarse and fine adjustment knobs
Answer: B
Rationale: The arm and base provide stable, secure handling. Holding by the ocular (A) or stage
(C) may damage components or drop the microscope. Knobs (D) are not designed for carrying.
3. The total magnification when using a 10x ocular lens and a 100x oil immersion objective lens
is:
A. 110x
, B. 100x
C. 1,000x
D. 10,000x
Answer: C
Rationale: Total magnification = ocular magnification (10x) × objective magnification (100x) =
1,000x. 10 × 100 = 1,000.
4. Which objective lens requires the use of immersion oil to increase resolution?
A. 4x scanning lens
B. 10x low power lens
C. 40x high power lens
D. 100x oil immersion lens
Answer: D
Rationale: The 100x oil immersion lens requires oil to reduce light refraction and increase
resolution at high magnification. Lower power lenses (A, B, C) do not require oil.
5. Immersion oil has the same refractive index as glass. This prevents:
A. Light absorption by the specimen
B. Light scattering (refraction) at the air-glass interface
C. Damage to the objective lens
D. Staining of the specimen
Answer: B
Rationale: Immersion oil fills the gap between the slide and the lens, preventing light from
bending (refracting) as it passes through air, thereby increasing resolution and image clarity. It
does not prevent lens damage (C) or affect staining (D).
6. The coarse adjustment knob should only be used with which objective lens to avoid damaging
the slide or lens?
A. 100x oil immersion lens
B. 40x high power lens
C. 4x scanning lens
