Questions: Which structure in a ciliate may contain up to 1000 copies of each chromosome?

The answer is the third one: the macronucleus.

Explanation for each option:

• The pellicle: This is a protective layer that covers the cell membrane of ciliates. It does not contain chromosomes, so it cannot have copies of them.

• The micronucleus: This is the smaller type of nucleus in ciliates, which contains the genetic material necessary for reproduction. It typically contains only one or two copies of each chromosome, not up to 1000.

• The macronucleus: This is the larger type of nucleus in ciliates, responsible for controlling non-reproductive cell functions. It can contain up to 1000 copies of each chromosome, as it is highly polyploid.

• The alveolus: This is a membrane-bound sac found in some protists, including ciliates, but it is not involved in storing chromosomes.

In summary, the macronucleus is the structure in a ciliate that may contain up to 1000 copies of each chromosome.