The protist that reproduces both by binary fission and conjugation is

The correct option is Paramecium.

Detailed Explanation:
Paramecium is a genus of unicellular ciliated protists that exhibits both asexual and sexual modes of reproduction depending on environmental conditions:

1. Binary Fission (Asexual Reproduction):
Under favorable environmental conditions, Paramecium reproduces asexually by transverse binary fission. During this process, the micronucleus divides mitotically, the macronucleus divides amitotically, and the cell constricts transversely to divide the cytoplasm equally, resulting in two genetically identical daughter cells.

2. Conjugation (Sexual Reproduction):
Under unfavorable conditions (such as starvation or extreme temperatures), Paramecium undergoes conjugation, which is a form of sexual reproduction. Two individuals of compatible mating types align side-by-side and form a protoplasmic bridge. They exchange haploid micronuclear material, which leads to genetic recombination and rejuvenation of the species. Following conjugation, the cells separate and divide to produce new individuals.

Analysis of Other Options:
• Amoeba: Reproduces asexually via binary fission and multiple fission (during unfavorable conditions). It does not undergo conjugation.
• Euglena: Reproduces asexually by longitudinal binary fission. Sexual reproduction is not well-documented or typical for this organism, and it does not undergo conjugation.
• Monocystis: A protozoan parasite that reproduces by syngamy (fusion of gametes) and sporogony, but not by binary fission and conjugation.