No, they don't have organs and organ system.
Cells form tissues, Tissues form organs, Organs forms organ system; Unicellular have their own one cell only. So, it can't possible that they have organs or organ system.
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B) A difference in pressure across a distance.
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Groups and periods are two ways of categorizing elements in the periodic table. Periods are horizontal rows (across) the periodic table, while groups are vertical columns (down) the table. Atomic number increases as you move down a group or across a period.
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The ozone layer absorbs a large portion of incoming UV radiation, which keeps ground-level ozone from forming. A higher percentage of UV radiation entering the troposphere would allow a greater amount of ozone to form in the troposphere. Ozone is a pollutant in the troposphere. By regulating the amount of UV radiation that enters the troposphere, the ozone layer also regulates the amount of ozone formation in the troposphere.
