The arrangement goes from the outer protective layers to the inner contractile machinery. The whole muscle is enclosed by the epimysium. Inside, it’s organized into bundles called fascicles, each wrapped by the perimysium. Within those fascicles lie individual muscle fibers, each surrounded by the endomysium. The muscle fiber itself has its own membrane, the sarcolemma, just inside the endomysium. Inside the fiber, the long cylindrical elements are myofibrils, which contain the repeating units called sarcomeres—the basic contractile blocks. So the order from outside to inside is epimysium, fascicles with perimysium, individual muscle fibers with endomysium, sarcolemma, myofibrils, and then sarcomeres.

The inner lining of the heart chambers is the endocardium. This layer lines the interior surfaces of all four chambers and covers the heart valves, providing a smooth, frictionless surface for blood to flow over. The heart wall has three layers: the epicardium on the outside, the myocardium in the middle that contracts, and the endocardium on the inside that lines the chambers. The pericardium is the surrounding sac that encloses the heart but does not line the chambers. So endocardium is the correct layer that lines the chambers.

Amylase is the digestive enzyme that acts on starch, a carbohydrate. It speeds up the breaking of starch by hydrolyzing the bonds that hold its glucose units together, producing smaller sugars such as maltose and, ultimately, glucose. In humans, this starts in the mouth with salivary amylase and continues in the small intestine with pancreatic amylase, with final steps turning the products into glucose that the body can use for energy. So, the function described here—turning starch into glucose—is what amylase does. Other enzymes handle proteins, fats, and nucleic acids.

When a metal like potassium reacts with hydrogen gas, the product forms as an ionic compound. Potassium donates its one valence electron to hydrogen, producing K+ and H−. The strong electrostatic attraction between these oppositely charged ions binds the compound together, which is the essence of ionic bonding. Hydrogen bonds are intermolecular forces between separate molecules and aren’t the type of bond here. Covalent bonds involve sharing electrons between atoms, but in this case the electron transfer creates ions rather than a shared-electron pair. So the correct description is ionic bonding.