<span>Cross bridges are created when myosin heads bind to ATP. This phenomenon is basically muscle contraction at work. In order for myosin heads to be bound with ATP at the actin active site, it must be excited with Calcium.
Once myosin heads bind with ATP, it begins to slide and perform muscle contractions in the body, allowing a person to move.</span>
Cell Differentiation<span> and Tissue. Within multicellular organisms, tissues are organized communities of </span>cells<span>that </span>work together<span> to carry out a specific function. The exact role of a tissue in an organism depends on what types of </span>cells<span> it contains.</span>
The answer is A//////////
<span>Without variation, there is no difference between members of a population to be "selected for" in the first place. This is a basic tenet of natural selection. A new trait must arise in order to advance or decrease the fitness of the individual, and hence, its ability to pass on its genes.</span>
