In an isotonic contraction, the muscle a. rapidly resynthesizes creatine phosphate and atp b. does not change in length but increases tension c. never converts pyruvate to lactate d. changes in length and moves the "load"

Option D " changes in length and moves the "load"

Explanation:

What means ' isotonic contraction' ?

⇒ Isotonic contractions maintain constant tension in the muscle as the muscle changes length.

This means that option B "does not change in length but increases tension" doesn't apply. (This is isometric)

Option A says : " Rapidly resynthesizes creatine phosphate and ATP

Creatine phosphate breakdown is the most rapid method available to resynthesize ATP. The next fastest is glycolysis followed by aerobic metabolism in the tricarboxylic acid cycle (Krebs' cycle).

Option C says " never converts pyruvate to lactate".

Pyruvate is converted to lactate in anaerobic conditions, by the enzyme Lactate dehydrogenase. If pyruvate never gets converted to lactate it means this enzyme is missing.

Option D says :"Changes in length and moves the load. This is the definition of an isotonic contraction. So option D is correct !

a) carbon, hydrogen

b) carbon, hydrogen, oxygen, nitrogen

c) carbon, hydrogen, oxygen, nitrogen, phosphorus

d) sugar

e) amino acid

f) nucleotide