All Free Biology MCQs with Answers

791. Which type of muscle is involuntary and non striated?

• A. Smooth muscle
• B. Skeletal muscle
• C. Cardiac muscle
• D. Biceps muscle

Explanation: Smooth muscle lines the gut, blood vessels and airways, contracting slowly and without conscious control. Skeletal muscle is striated and voluntary, while cardiac muscle is striated but involuntary, covering every combination between the three types.

792. A skeletal muscle fibre differs from most body cells in being

• A. without a plasma membrane
• B. multinucleated
• C. without any cytoplasm
• D. prokaryotic

Explanation: Each fibre is a long cylinder formed by the fusion of many cells, so it carries a row of nuclei beneath its membrane. This giant structure allows thousands of myofibrils to contract as one unit.

793. The strong bands of tissue that connect bone to bone across a joint are called

• A. tendons
• B. muscle fibres
• C. ligaments
• D. cartilage discs

Explanation: Ligaments stabilise a joint by tying the bones together while still permitting movement. Tendons attach muscle to bone, so the question to ask is what the band connects: bone to bone means ligament every time.

794. Two muscles that produce opposite movements at the same joint are described as

• A. synergists
• B. flexors only
• C. rotators
• D. antagonists

Explanation: Antagonistic pairs such as biceps and triceps allow controlled movement in both directions because muscles can pull but never push. Synergists assist one another, which is the opposite relationship.

795. The thick filaments of the sarcomere are composed mainly of the protein

• A. myosin
• B. actin
• C. troponin
• D. tubulin

Explanation: Myosin molecules form the thick filament, their heads projecting to pull on actin during contraction. Actin makes the thin filament, troponin regulates it, and tubulin builds microtubules, so each protein has its own place in the sarcomere.

796. ATP is required during muscle contraction for

• A. storing glycogen in the muscle
• B. detaching myosin heads from actin and pumping calcium back after contraction
• C. synthesising haemoglobin
• D. nothing once contraction has begun

Explanation: Each myosin head needs a fresh ATP to release actin and re-cock, and the calcium pump needs ATP to restore relaxation. Without ATP the heads stay locked, which is exactly what causes rigor mortis.

797. The light band of the myofibril that contains actin but no myosin is the

• A. A band
• B. H zone
• C. I band
• D. Z line

Explanation: The I band holds only thin actin filaments and shortens during contraction, while the A band spans the whole length of the myosin. The Z line bisects each I band and marks the boundary of the sarcomere.

798. When a muscle fibre is stimulated, the calcium ions needed for contraction are released from the

• A. mitochondria
• B. Golgi apparatus
• C. nucleus
• D. sarcoplasmic reticulum

Explanation: The sarcoplasmic reticulum stores calcium and floods the fibre with it when an impulse arrives along the T tubules. Mitochondria supply the ATP for contraction but not the calcium that triggers it.

799. A single motor neuron together with all the muscle fibres it supplies is called

• A. a sarcomere
• B. a motor unit
• C. a reflex arc
• D. a myofibril

Explanation: All fibres of one motor unit contract together when the neuron fires, and fine muscles like those of the eye have tiny units for precise control. A sarcomere is a contractile segment inside a fibre, a different level of organisation.

800. The immediate reserve that regenerates ATP at the very start of vigorous muscle contraction is

• A. creatine phosphate
• B. glycogen only
• C. lactic acid
• D. haemoglobin

Explanation: Creatine phosphate donates its phosphate to ADP in a single step, replenishing ATP within seconds before glycogen breakdown catches up. Lactic acid is a product of anaerobic glycolysis, not a fuel reserve.