Smooth muscles depolarize as a result of a transmembrane current of Calcium ions. When an action potential depolarizes the muscle cell membrane, it also travels into the body of the cell via the t-tubules. Unlike skeletal muscle, smooth muscle is dependent in two sources of calcium in order to intiate contraction. These two sources are calcium sequestered in the S.R. of the smooth muscle cell.
Answer:
"Examine the list of all known species of birds and determine if any species cannot fly" would be the most reasonable answer.
Natural selection and speciation: 'Ecological speciation'. ... Natural selection is generally recognized as a central mechanism of evolutionary change within species. Thus, natural selection plays a major role in generating the array of phenotypic and genetic diversity observed in nature.
The answer is <span>d. homologous structures.
Homologous structures are </span><span>similar structures shared by different species. For example, the anatomy of joints in bones of birds and dinosaurs, support the idea that these two groups have a common ancestor. But since these two groups are different enough to be separated into different classes, it can be concluded that they evolved from the common ancestor.</span>
