Which component is responsible for initially stimulating a muscle contraction?
proteins
electrochemical signals
plasma membranes
striations

Option B, electrochemical signals

Explanation:

The first process that initiates the muscle contraction is the binding of calcium ion with troponin protein. After this chemical interaction, the active binding sites of actin gets exposed. After this myosin binds to the actin sites thereby forming a high-energy  head bridge and releasing the pi. Mysosin now goes to a lower energy state by undergoing conformational change. This causes power stroke and actin filament is pulled towards the M-line. Later on the muscle contracts by shortening  sarcomere.

This entire process is an electrochemical process. hence option B is correct.

water is a polar molecule. a chemical bond is a force of attraction between atoms or ions. bonds form when atoms share or transfer valence electrons. atoms form chemical bonds to achieve a full outer energy level, which is the most stable arrangement of electrons. so, false

explanation:

in h2o molecule, two water molecules are bonded by a hydrogen bond but the bond between two h - o bonds within a water molecule are covalent. the greater the electronegativity difference, the more ionic the bond is. bonds that are partly ionic are called polar covalent bonds. nonpolar covalent bonds, with equal sharing of the bond electrons, arise when the electronegativities of the two atoms are equal.