What are the soluble proteins secreted by bacteria that enter host cells called?

Correct Answer: C

Rationale: Bacteria, particularly pathogenic ones, use secretion systems like type III to inject soluble proteins into host cells. These effector proteins manipulate host processes disrupting signaling, cytoskeletal structure, or immune responses to facilitate infection. Often part of virulence strategies in pathogens like Salmonella, they differ from receptors, which receive signals, and enzymes, which catalyze reactions, though some effectors have enzymatic activity. Antibodies are host-derived, not bacterial. Effector proteins' role in crossing host membranes and altering cellular function distinguishes them, reflecting their specialized purpose in bacterial pathogenesis and host-pathogen interactions.

Correct Answer: A

Rationale: Cellular respiration in animals breaks down glucose with oxygen to produce energy. This process glycolysis, Krebs cycle, and electron transport chain yields ATP, the cell's energy currency, powering functions like muscle movement. Oxygen is a reactant, not a product, while RNA and DNA are genetic molecules, not respiration outputs. ATP's role as the direct energy product, formed via oxidative phosphorylation, marks it as the primary outcome, essential for cellular work and distinguishing it from structural or input substances.

Correct Answer: D

Rationale: Acetylcholine (Ach), released by somatic motor neurons, excites skeletal muscle fibers by binding nicotinic receptors, opening Na⁺ channels to depolarize the sarcolemma, initiating contraction. GABA, inhibitory in the CNS, doesn't excite muscle. Na⁺ is an ion, not a neurotransmitter it enters post-Ach binding. Ca²⁺ triggers contraction internally, not as a neurotransmitter. Ach's excitatory role at the neuromuscular junction distinguishes it, key for signal transmission, unlike inhibitory, ionic, or intracellular agents.

Correct Answer: D

Rationale: Muscle names encode specific traits. Quadriceps femoris combines quadriceps, indicating four origins four distinct attachment points on the pelvis or femur with femoris, pinpointing its location on the thigh's femur bone. Action (e.g., extension) isn't specified, nor are insertion points (tibia via patella) or fibre direction (e.g., rectus). Location and origin count align with naming conventions, as seen in biceps or triceps, where number denotes origins and the second term locates it. This reflects skeletal muscle nomenclature's focus on anatomical anchors, distinguishing it from action-based or directional terms, crucial for identifying muscles in clinical and educational contexts.

Correct Answer: D

Rationale: Contraction begins with a neural signal. Calcium release from the sarcoplasmic reticulum into the cytoplasm is the first intracellular step, triggered by sarcolemma depolarization. This calcium binds troponin, exposing actin sites, followed by ATP binding and hydrolysis to drive myosin movement. ADP detachment occurs later in the cycle. Calcium's release initiates the cascade, distinct from subsequent biochemical steps, ensuring contraction aligns with nerve input, a critical sequence in muscle physiology.