Which of the following chemicals opens us binding sites allowing muscle filaments to connect to each other? select one:
a. atp
b. glucose
c. sodium
d. calcium

The correct answer will be option-D.

Explanation:

Calcium plays an important role in muscle contraction as they are released from the sarcoplasmic reticulum after they receive electric impulse.

Calcium triggers the muscle contraction cycle as these calcium ions bind to the troponin-tropomyosin complex. This binding exposes the myosin-binding site on the actin on which high energy myosin binds and cross-bridge is formed.

This cross-bridge formation causes the contraction of the sarcomere and therefore muscle contracts.

Thus, option-D is the correct answer.

multiple allele inheritance is traits controlled by more than 2 alleles (ex: pigeons having 3 alleles of one gene govern their feather color).   so the answer is a.