<span>In order for individuals best suited for growth and reproduction in a particular environment to contribute disproportionately to the next generation natural selection must take place. Natural selection is one of the basic mechanism of evolution. This mechanism leads</span> to adaptations and adaptations contribute to survival and reproduction.
<span>It binds itself to the receptors present on the surface of the cell membrane, which activates the enzymes present inside cell. Then It passes through the cell membrane and attaches itself to a receptor protein present in the cytoplasm.
It passes on the signal to the secondary messengers inside the cell, which activate the receptors on the cell membrane.</span>
Active:requires the assistance of a carrier protein, also requires energy
Passive:does not require energy is also movement of ions and other atomic and other molecular substances.
