Which one of the following types of tissues will have contractile proteins?

The correct answer is B, Muscle tissue. Muscle cells are packed with the contractile proteins actin and myosin, whose filaments slide over each other to shorten the cell and produce movement. Inside each muscle fibre, thin actin filaments and thick myosin filaments are arranged side by side. When a nerve signal arrives, calcium ions are released, myosin heads grip the actin and pull it inward, and the whole fibre contracts, using energy from ATP. All three kinds of muscle, skeletal, smooth and cardiac, work this way, which is why muscle is the tissue of movement, from walking to the beating of the heart. Option A is wrong because nervous tissue is specialised to carry electrical impulses, not to contract. Option C is wrong because bone is a hard connective tissue whose matrix of collagen and calcium phosphate gives support; it does not shorten. Option D is wrong because blood is a fluid connective tissue that transports gases, food and wastes; its proteins, such as haemoglobin and antibodies, are not contractile. Exam tip: actin and myosin are the contractile proteins of muscle; the sliding filament theory explains contraction.