The release of calcium ions initiates muscle contractions. ... The contraction of a striated muscle fiber occurs as the sarcomeres, linearly arranged within myofibrils, shorten as myosin heads pull on the actin filaments.
Substances are made of basic particles called atoms
Answer:
The majority of an atoms' mass comes from the protons and neutrons that make up its nucleus. Electrons are the least massive of an atom's constituent particles, with a mass of 9.11 x 10-31 kg and a size too small to be measured by current techniques.
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During active transport proteins powered by ATP move substances up a concentration gradient. During active transport, a protein pump uses energy, in the form of ATP, to move molecules from an area of low concentration to an area of high concentration. An example of active transport is the sodium-potassium pump, which moves sodium ions to the outside of the cell and potassium ions to the inside of the cell.