What characteristic is not representative of a type IIb muscle fibre?

Correct Answer: B

Rationale: Type IIb (or IIx in humans) muscle fibers are fast-twitch, with high motor unit strength and fast contractile speed, suited for explosive efforts like sprinting, but they have low oxidative capacity, relying on anaerobic glycolysis, leading to rapid fatigue. High fatigue resistance, typical of slow-twitch (Type I) fibers with rich mitochondria and myoglobin, doesn't fit Type IIb's profile they tire quickly due to limited aerobic endurance. Low oxidative capacity aligns with their anaerobic nature, and strength and speed reflect their power. Fatigue resistance misaligns with their design, distinguishing them from endurance-focused fibers, key to understanding muscle fiber specialization.

Correct Answer: B

Rationale: The inferior oblique, an extraocular muscle, resides in the eye socket, originating near the orbit's front and inserting on the eyeball, elevating and abducting it. Abdominal muscles (e.g., obliques) flex the trunk. Anterior neck hosts muscles like sternocleidomastoid. Facial muscles (e.g., zygomaticus) move skin. The inferior oblique's orbital location and eye movement role distinguish it, essential for gaze, unlike trunk, neck, or facial functions.

Correct Answer: D

Rationale: Sartorius, a long, strap-like muscle, flexes, abducts, and laterally rotates the hip, then flexes the knee, enabling leg crossing. Gluteus maximus extends the hip. Piriformis rotates it. Gracilis adducts, not crossing fully. Sartorius' multi-joint action distinguishes it, critical for this coordinated motion.

Correct Answer: C

Rationale: Intestinal symptoms like diarrhea, vomiting, and abdominal pain stem from toxins disrupting gut function. Enterotoxins, produced by bacteria such as Escherichia coli or Staphylococcus aureus, target intestinal cells, increasing secretion or reducing absorption by altering ion channels or tight junctions, as seen in cholera. Cytotoxins cause broader cell damage, not specific to the gut. Neurotoxins affect nerves, not digestion directly. Leukocidins attack immune cells, not intestinal ones. Enterotoxins' specific action on gut epithelium, leading to fluid loss and characteristic symptoms, distinguishes them as the cause, critical for diagnosing gastrointestinal bacterial infections.

Correct Answer: A

Rationale: Cellular respiration encompasses the breakdown of glucose to produce ATP, involving glycolysis, the Krebs cycle, and the electron transport chain. Glycolysis includes anaerobic glucose splitting, yielding pyruvate, which feeds the Krebs cycle under aerobic conditions. The Krebs cycle generates electron carriers, fueling the electron transport chain for ATP synthesis. Anaerobic splitting is a subset when oxygen is absent. Cellular respiration's integration of these stages, converting food to energy, makes it the overarching process, central to cellular metabolism across organisms.