In Paramecium, metabolic activities and growth is regulated by

The correct answer/option is: macronucleus

Step-by-step Explanation:

1. Paramecium is a unicellular ciliated protist that exhibits nuclear dimorphism. This means it contains two distinct types of nuclei: a large macronucleus and one or more small micronuclei.

2. Each type of nucleus has a specific function:
- Macronucleus: It is polyploid and contains multiple copies of the genome. It regulates all metabolic activities, vegetative growth, and daily cellular functions of the cell.
- Micronucleus: It is diploid and is primarily involved in genetic recombination and reproduction (such as conjugation), acting as the germline nucleus.

3. Since the question asks about the regulation of metabolic activities and growth, the organelle responsible is the macronucleus.