Q. In which of the following organisms is the nuclear membrane absent?
Answer: Nostoc
Notes: Nostoc, also known as star jelly, troll’s butter, witch's butter, and witch's jelly, is a genus of cyanobacteria. Nostoc does not have a nuclear membrane. This is a characteristic of prokaryotic cells, which lack a nucleus. The genetic material in these cells is found in the cytoplasm, not enclosed within a nuclear membrane. On the contrary, Volvox, Agaricus, and Penicillium are all eukaryotic organisms, hence possess a nuclear membrane.