The correct answer is that "t<span>roponin holds the tropomyosin in place on the actin".
In excitation-contraction coupling, tropomyosin prevents the interaction between actin and myosin in resting muscles. In the event of excitation, there is release of calcium from the sarcoplasmic reticulum wherein the troponin will bind this calcium and will release tropomyosin and expose myosin enabling it to attach to actin and therefore facilitating muscle contraction.</span>
ATP<span> is responsible for cocking (pulling back) the myosin head, ready for another cycle. When it binds to the myosin head, it causes the cross bridge between actin and myosin to detach. </span>ATP<span> then provides the energy to pull the myosin back.</span>
Our genes can be affected by the environment and change the way our traits are displayed, called the phenotype. However, changes in phenotype have an underlying genotypic source. Epigenetics or epigenetic changes are changes in the way traits are expressed as an effect of the environment (i.e. food we ate, chemicals in the body, environmental stresses), without changes in the DNA. Simply put, in epigenetics, some parts of the DNA are turned on or off in response to environmental conditions.
<span><span>A plant that, when self-fertilized, only produces offspring with the same traits.</span></span>
