All Free Biology MCQs with Answers

951. Tidal volume is approximately

• A. 500 mL
• B. 3000 mL
• C. 1200 mL
• D. 6000 mL

Explanation: Tidal volume (air in normal breath) is about 500 mL at rest in healthy adults.

952. The respiratory center is located in the

• A. Cerebrum
• B. Cerebellum
• C. Medulla oblongata
• D. Hypothalamus

Explanation: The respiratory center in the medulla oblongata controls breathing rate and depth.

953. Hemoglobin has highest affinity for O2 when

• A. pH is low
• B. CO2 is high
• C. pH is high
• D. Temperature is high

Explanation: Hemoglobin has highest O2 affinity at high pH, low CO2, and low temperature (in the lungs).

954. The chloride shift occurs to

• A. Maintain electrical neutrality
• B. Increase O2 transport
• C. Decrease CO2
• D. Activate enzymes

Explanation: As HCO3- leaves RBCs, Cl- enters to maintain electrical neutrality (chloride shift or Hamburger shift).

955. Asthma is characterized by

• A. Emphysema
• B. Bronchoconstriction and inflammation
• C. Lung cancer
• D. Pneumonia

Explanation: Asthma involves bronchoconstriction, airway inflammation, and excess mucus production, causing wheezing and dyspnea.

956. The sliding filament theory involves

• A. Actin and myosin
• B. Tropomyosin only
• C. Troponin only
• D. Collagen

Explanation: Muscle contraction involves sliding of actin (thin) filaments past myosin (thick) filaments.

957. The functional unit of skeletal muscle is

• A. Myofibril
• B. Sarcomere
• C. Muscle fiber
• D. Tendon

Explanation: The sarcomere (between two Z-lines) is the basic functional unit of muscle contraction.

958. Calcium binds to

• A. Actin
• B. Myosin
• C. Troponin
• D. Tropomyosin

Explanation: Ca2+ binds to troponin, causing tropomyosin to move and expose myosin-binding sites on actin.

959. ATP is required for muscle contraction for

• A. Only cross-bridge formation
• B. Only cross-bridge detachment
• C. Both formation and detachment
• D. Neither

Explanation: ATP is required for myosin head cocking (after power stroke) and detachment from actin.

960. Bone is composed of

• A. Only collagen
• B. Only calcium phosphate
• C. Collagen and calcium phosphate
• D. Cartilage only

Explanation: Bone contains organic collagen (flexibility) and inorganic calcium phosphate/hydroxyapatite (hardness).