Myofibrils are . a) the basic contractile units of skeletal muscle tissue
b) the contractile proteins located within a muscle cell
c) the boundaries of individual sarcomeres
d) specialized contractile organelles found in muscle cells
e) none of the listed responses is correct.

Option B

Explanation:

Myofibrils are very fine contractile fibers which extends in parallel to the columns along the length of the striated muscles fibres.

They are made of thick and thin myofilaments because of which the muscles appear striped.

The thick filaments in the muscles are composed of actin along with two other muscle protein known as tropomyosin and troponin. They help in contraction of muscles.

while the heads of the phospholipid structure attract water, the tails are hydrophobic. the model shows how the hydrophilic section folds around the fluid molecules to bring them into the cell so they don’t need to pass through the hydrophobic tails.