It happens when the two groups become sufficiently different and the two can no longer interbreed. A known example of speciation is the London underground mosquito where it formed a new species within the existing genus. There are examples in micro-evolution but not in macro-evolution.
This statement is true.
When a hormone binds to a hormone receptor it activates cell enzymes that start a cell cascade. This means that this enzyme makes changes in the activity other proteins or alters the expression of specific genes that change the cells activity.
Hyrax of the order Hyracoidea
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As the saltier blood circulates through the body, it makes the fluid outside of our body cells saltier than the fluid inside the cells. The cells notice the change right away. That's because the extra salt outside acts like a magnet, pulling water out of the cells.
Explanation: