Nucleus is the double membrane bound organelle present in eukaryotic cells. It is the site where DNA is present in these cells.
DNA replication is the process of formation of new DNA strands using the existing ones as a template. It occurs in the nucleus only.
DNA transcription is the process of formation of RNA using a DNA template strand. Since DNA is present in the nucleus only, DNA transcription also occurs in the nucleus.
Most of the carbon that's stored in plants - and in anything that eats them - is released back into the atmosphere by respiration when the organisms die and are eaten by microbes.
