In skeletal muscle Catt is essential for the contraction process. For skeletal
muscle cells, what is the source of Cat+.?

The source of Calcium (Ca⁺⁺) for the skeletal muscle cells is the sarcoplasmic reticulum, the main store of intracellular Ca⁺⁺.

Explanation:

Calcium (Ca⁺⁺) is an ion that plays an important role in muscle contraction, a process that requires high cytoplasmic concentrations of this ion to promote myofibrillary activity.

The sarcoplasmic reticulum (SR) -equivalent to the endoplasmic smooth reticulum- is an organelle that regulates the contractile activity of skeletal muscle. The two terminal cisterns of the SR attach to the T-tube, forming a triad, which surrounds the myofibrilla.

Once the muscle cell receives the signal to contract, the Ca⁺⁺ channels are opened and allow Ca⁺⁺ to enter the cell, promoting the exit of this cation from the SR and increased its cytoplasmic levels. This stimulates muscle contraction.

only about ten percent of the energy at one trophic level is passed on to organisms at the next trophic level. the remainder of the energy is used in life processes or lost as heat.

protein makes up the building blocks of organs, muscles, skin, hormones and pretty much everything that matters in your body.

some choices are:

peanut butter

seeds

eggs

yogurt

meats

fish

so pretty much meat, dairy, nuts, and grains.