While observing cardiac muscle under the microscope for the first time, Jennifer noticed lines running perpendicular to the direction of the muscle. These lines are called

The right answer is intercalated discs.

Explanation:

If you observe cardiac muscles under a microscope, the first feature that appears is Intercalated discs. Cardiac muscles contains heart muscle cells which are called as cardiomyocytes which are linked by these discs to perform a single functional organ.

Intercalated discs helps in harmonizing the contraction of cardiac tissues.

the element that provides strength to the exoskeletons of clams and oysters is phosphorus.

this is so because calcium carbonate is the main component in the shells. calcium carbonate is strengthened by phosphorus.

explanation: