Which of the following organisms has a nutritive process most similar to that of animals?

Correct Answer: D

Rationale: Animals are heterotrophs, obtaining nutrients by consuming organic matter. Bread mold, a fungus, also functions heterotrophically, secreting enzymes to break down external organic substrates like bread, absorbing the products. Seaweed, oak trees, and grass are autotrophs, using photosynthesis to synthesize food from sunlight. Bread mold's reliance on external digestion and absorption mirrors animal nutrition, unlike plants' self-production, making it the closest match in nutritive strategy, reflecting shared ecological roles as decomposers or consumers.

Correct Answer: A

Rationale: Somatic motor (efferent) neurons, part of the voluntary nervous system, release acetylcholine at neuromuscular junctions to initiate skeletal muscle contraction, driving movements like lifting. Sympathetic neurons regulate involuntary functions (e.g., heart rate), not skeletal muscle. Sensory neurons transmit stimuli to the CNS, not activating muscles. 'Muscle neuron' isn't a term neurons innervate, not reside in, muscle. Somatic motor neurons' direct, voluntary control distinguishes them, essential for skeletal muscle's deliberate action, unlike autonomic or sensory roles.

Correct Answer: B

Rationale: Contraction of many sarcomeres, via actin-myosin sliding, shortens the myofibril, a bundle of sarcomeres within a fiber, reducing overall muscle length. Thick filaments (myosin) don't shorten actin slides over them. Motor proteins (myosin) drive this, not shortening themselves. Sarcoplasmic reticulum releases Ca²⁺, not contracting. Myofibril shortening aggregates sarcomere action, distinguishing it, key to muscle movement.

Correct Answer: A

Rationale: Muscle fibres contain nested structures. Myosin, a protein molecule, forms thick myofilaments bundles of myosin within sarcomeres, the contractile units. Sarcomeres align in myofibrils, spanning the fibre. Myosin, at the molecular level (about 160 nm long), is smaller than myofilaments (micrometres), sarcomeres (2 micrometres), and myofibrils (cell-length). Its role as a building block for thicker structures marks it as the smallest, foundational to contraction mechanics, distinguishing it from larger assemblies in muscle hierarchy.

Correct Answer: C

Rationale: Smooth muscle lacks striations banded patterns from aligned sarcomeres unlike striated skeletal (multinucleate, voluntary) and cardiac (uninucleate, involuntary, branched) muscles. Involuntary control and single nuclei are shared with cardiac muscle, and branching is cardiac-specific. Smooth muscle's non-striated, spindle-shaped cells suit its role in visceral organs, distinguishing its microscopic appearance and function from the organized contractile bands of other types, key for histological identification.