26. The agents in which of the following procedures are intended to stabilize tissue structure by coagulating proteins and promoting cross-linking?
a) Clearing
b) Dehydration
c) Embedding
Correct answer: b) Dehydration
Explanation: Dehydration removes water from tissues and stabilizes their structure by allowing protein coagulation and cross-linking, which helps preserve morphology for histological processing.
27. Which of the following best describes the appearance of a unit membrane under a transmission electron microscope?
a) Junctional complex
b) Lipid bilayer
c) Pentalaminar structure
d) Porous structure
e) Trilaminar structure
Correct answer: e) Trilaminar structure
Explanation: The unit membrane appears as a trilaminar structure with two dark electron-dense layers (polar heads of phospholipids) and a lighter central layer (hydrophobic tails) under TEM.
28. The synthesis of all proteins appears to be initiated on which of the following cellular components?
a) Free polyribosome
b) Golgi complex
c) Nucleosomes
d) Ribophorin
e) RER
f) Signal recognition particles
Correct answer: a) Free polyribosome
Explanation: Protein synthesis is generally initiated on free polyribosomes, which may later attach to RER if the protein is destined for secretion or membrane insertion.
29. Which of the following pairs of functions is most closely associated with the Golgi complex?
a) Energy metabolism and glycogen synthesis
b) Energy metabolism and lipid metabolism
c) Glycogen synthesis and packaging of secretions
d) Glycosylation and sulfation of secretory products
e) Lipid metabolism and concentration
f) Phagocytosis and receptor recycling
g) Protein synthesis and packaging of secretory products
Correct answer: d) Glycosylation and sulfation of secretory products
Explanation: The Golgi complex modifies proteins and lipids post-translationally (glycosylation and sulfation) and packages them for secretion.
30. Which of the following descriptions best characterizes a phagosome?
a) Allows extracellular materials to enter cells without endocytosis
b) Contains densely packed, inactive hydrolytic enzymes
c) Contains aging organelles
d) Forms by budding from a lysosome
e) Is surrounded by a membrane derived from the Golgi complex
f) Provides amino acids for protein synthesis by fusing with the RER
g) Transports hormones and growth factors to the nucleus
Correct answer: b) Contains densely packed, inactive hydrolytic enzymes
Explanation: A phagosome is formed by engulfing material and fuses with lysosomes containing hydrolytic enzymes to degrade contents.
31. Which of the following is the location of Krebs cycle enzymes and mitochondrial DNA?
a) Cristae
b) F1 subunits
c) Inner mitochondrial membrane
d) Intracristal space
e) Matrix granules
f) Mitochondrial matrix
g) Outer mitochondrial membrane
Correct answer: f) Mitochondrial matrix
Explanation: The Krebs cycle occurs in the mitochondrial matrix, where enzymes and mitochondrial DNA are located.
32. Which of the following is the location of the electron-transport system?
a) Cristae
b) F1 subunits
c) Inner mitochondrial membrane
d) Intracristal space
e) Matrix granules
f) Mitochondrial matrix
g) Outer mitochondrial membrane
Correct answer: c) Inner mitochondrial membrane
Explanation: The electron transport chain resides in the inner mitochondrial membrane where oxidative phosphorylation occurs.
33. Which of the following is the site of core glycosylation of secretory proteins?
a) Golgi complex
b) Free polyribosomes
c) Mitochondria
d) RER
e) SER
Correct answer: d) RER
Explanation: Core glycosylation of proteins occurs in the rough endoplasmic reticulum where initial carbohydrate chains are added.
34. Which of the following is the site of steroid hormone synthesis?
a) Golgi complex
b) Free polyribosomes
c) Mitochondria
d) RER
e) SER
Correct answer: e) SER
Explanation: Smooth endoplasmic reticulum is the primary site for steroid hormone synthesis and lipid metabolism.
35. Which of the following is the site of actin and tubulin synthesis?
a) Centrioles
b) Free polyribosomes
c) Mitochondria
d) RER
e) SER
Correct answer: b) Free polyribosomes
Explanation: Actin and tubulin, cytoskeletal proteins, are synthesized on free polyribosomes in the cytoplasm.
36. Which of the following are important components of axonemes?
a) Centrioles
b) Basal bodies
c) Intermediate filaments
d) Microfilaments
e) Microtubules
Correct answer: e) Microtubules
Explanation: Axonemes, the core of cilia and flagella, are composed primarily of microtubules arranged in a 9+2 pattern.
37. Which of the following substances characteristically increases in abundance with increasing age in terminally differentiated cells such as neurons and muscle?
a) Cyclin
b) Desmin
c) Lipofuscin
d) Osmium
e) Phalloidin
f) Ribophorin
g) Urate oxidase
Correct answer: c) Lipofuscin
Explanation: Lipofuscin accumulates as “age pigment” in long-lived cells due to lysosomal degradation of cellular components.
38. Which of the following are composed primarily of actin or actin-like proteins?
a) Basal bodies
b) Cilia
c) Cytochalasins
d) Intermediate filaments
e) Microfilaments
f) Microtubules
g) Molecular motors
Correct answer: e) Microfilaments
Explanation: Microfilaments are primarily composed of actin filaments and play roles in cell shape, motility, and intracellular transport.
39. In rat hepatocytes, the crystalline nucleoid (dense core) of peroxisomes is believed to be composed of which of the following substances?
a) Acid phosphatase
b) Catalase
c) L-amino acid oxidase
d) Divalent cations
e) Hydrogen peroxide
f) Lipofuscin
g) Urate oxidase
Correct answer: c) L-amino acid oxidase
Explanation: Peroxisome dense cores often contain crystallized L-amino acid oxidase involved in oxidative metabolism.
40. Which of the following is true of the smooth muscles of the iris?
a) Constrict the pupil in response to epinephrine
b) Are incapable of graded contractions
c) Are poorly innervated
d) Are of ectodermal origin
e) Release tension on the zonule when they contract
Correct answer: e) Release tension on the zonule when they contract
Explanation: Iris smooth muscles (ciliary muscles) adjust lens tension to control focus; they are capable of graded contraction.
41. Which of the following structures is likely to contain the most vasa vasorum in its tunica media?
a) Aorta
b) Arteriole
c) Blood capillary
d) Medium-sized artery
e) Thoracic duct
f) Vena cava
g) Venule
Correct answer: a) Aorta
Explanation: The aorta, a large vessel, has a thick tunica media requiring vasa vasorum for nutrient supply.
42. Which of the following structures contains the most elastin in its tunica media?
a) Aorta
b) Arteriole
c) Blood capillary
d) Medium-sized artery
e) Thoracic duct
f) Vena cava
g) Venule
Correct answer: a) Aorta
Explanation: The aorta contains abundant elastin to allow elastic recoil during systole and diastole.
43. Which of the following is true of the ventricles?
a) Are located at the base of the heart
b) Their myocardial cells contain abundant granules
c) Receive blood directly from the vena cava and the pulmonary veins
d) Their walls contain the right and left bundle branches
e) Contain more abundant elastic fibers than do the atria
Correct answer: d) Their walls contain the right and left bundle branches
Explanation: Purkinje fibers run within the ventricular walls, forming the conduction system branches.
44. Which of the following is true of blood capillaries?
a) Carry lymphocytes
b) Are blind-ended tubes
c) Contain valves
d) Characteristically lack occluding junctions between their lining cells
e) Are lined by cells derived from endoderm
Correct answer: b) Are blind-ended tubes
Explanation: Capillaries are the smallest blood vessels and form a network starting and ending blindly.
45. The sensory nerve fibers of arteries enter through the adventitia. Those that penetrate the farthest into the wall may extend into which of the following layers?
a) External elastic lamina
b) Lumen
c) Tunica adventitia
d) Tunica intima
e) Tunica media
Correct answer: e) Tunica media
Explanation: Sensory fibers (baroreceptors) extend into the tunica media to detect stretch in arterial walls.
46. How are electrical impulses passed from Purkinje fibers to ventricular cardiac muscle fibers?
a) Chemical synapses
b) Diffusion through the endomysium
c) Gap junctions
d) Saltatory conduction
e) Tight junctions (membrane fusion)
Correct answer: c) Gap junctions
Explanation: Purkinje fibers connect to cardiac muscle cells via gap junctions, allowing direct ionic conduction.
47. Which of the following is the approximate life span of an erythrocyte in the circulation?
a) 8 days
b) 20 days
c) 5 weeks
d) 4 months
e) 1 year
Correct answer: d) 4 months
Explanation: Human RBCs survive approximately 120 days in circulation before being phagocytosed in the spleen.
48. Which of the following is true of the darker staining central region of platelets?
a) Contains the marginal bundle of microtubules
b) Contains the platelet nucleus
c) Contains the platelet granules
d) Is termed the hyalomere
e) Is termed the central pallor
Correct answer: c) Contains the platelet granules
Explanation: The darker central region (granulomere) contains dense granules responsible for platelet functions.
49. Which of the following is the biochemical constituent of the erythrocyte cell surface that is primarily responsible for determining blood type (e.g., A, B, O; M, N)?
a) Carbohydrate
b) Lipid
c) Nucleic acid
d) Protein
Correct answer: a) Carbohydrate
Explanation: Blood group antigens are carbohydrate moieties attached to lipids or proteins on the erythrocyte membrane.
50. Which of the following is true of null cells?
a) Comprise 80% of circulating lymphocytes
b) Are terminally differentiated B lymphocytes
c) Are terminally differentiated T lymphocytes
d) Are neither T nor B lymphocytes
e) Are inactive helper cells
f) Are phagocytic
g) Have segmented nuclei
Correct answer: d) Are neither T nor B lymphocytes
Explanation: Null cells are lymphocytes that lack surface markers for T or B cells and include natural killer (NK) cells.