That should be the cell membrane. The cell membrane acts as a filter in and out.
The answer for 21 I think is false
What do you need examples of?
Answer:
They fall from the clouds as ice crystals.
They form around particles in the atmosphere.
They form when water vapor is converted directly to ice crystals.
Explanation:
None, Electrons are not in the nucleus
<em>They</em><em> </em><em>are</em><em> </em><em>pres</em><em>ent</em><em> </em><em>in</em><em> </em><em>orbi</em><em>ts</em><em> </em><em>or</em><em> </em><em>ene</em><em>rgy</em><em> </em><em>shells</em><em>.</em><em> </em>