The<em> cell membrane</em> controls the movement of substances in and out of cells and organelles. In this way, it is selectively permeable to ions and organic molecules.
Superficially, the connection between the cell cycle and cancer is obvious: cell cycle machinery controls cell proliferation, and cancer is a disease of inappropriate cell proliferation. Fundamentally, all cancers permit the existence of too many cells.
The main driver of a climate zone is the amount and directness of sunlight that reaches the Earth's surface. In the tropical regions, there is a fairly constant amount of sunlight throughout the year. The maximum sun angle is also higher above the horizon.
The present system of binomial nomenclature<span> identifies each species by a scientific name of </span>two<span> words, Latin in form and usually derived from Greek or Latin roots. The first name (capitalized) is the genus of the organism, the second (not capitalized) is its species.</span>
