The ER and bodies linked with it during ultracentrifugation are separated as a fraction known as

The correct option is Microsome.

Step-by-Step Explanation:

1. Understanding Ultracentrifugation and Cell Fractionation:
Cell fractionation is a laboratory technique used to separate cell organelles based on their size, shape, and density. In this process, cells are first homogenized (ruptured) to release their internal contents, forming a mixture called the homogenate. This homogenate is then subjected to sequential centrifugation at increasing speeds and durations (ultracentrifugation).

2. Behavior of the Endoplasmic Reticulum (ER) during Homogenization:
Unlike larger, robust organelles such as nuclei or mitochondria which can remain intact, the extensive membrane network of the Endoplasmic Reticulum (ER) is highly delicate. When the cells are disrupted during homogenization, the ER membranes break apart into smaller fragments. These membrane fragments spontaneously reseal to form small, spherical, closed vesicles.

3. Sedimentation of the ER Fraction:
When the homogenate undergoes differential centrifugation, the heavier components sediment first at lower speeds:
- Nuclei pellet at low speeds.
- Mitochondria, lysosomes, and peroxisomes pellet at medium speeds.
- At very high speeds (typically around 100,000 × g or higher in an ultracentrifuge), the small vesicles derived from the fragmented ER, along with their attached ribosomes (often referred to as the rough ER fragments) and other associated membrane bodies, sediment out of the supernatant. This specific pellet/fraction is called the microsome fraction.

4. Why other options are incorrect:
- Episome: A non-chromosomal DNA element (like a plasmid) found in some bacteria that can replicate independently or integrate into the host chromosome.
- Polysome: A cluster of multiple ribosomes translating a single mRNA molecule simultaneously.
- Quantasome: A granular particle found in the thylakoid membranes of chloroplasts that functions as a photosynthetic unit.

Therefore, the fragmented ER vesicles and associated structures isolated during high-speed ultracentrifugation are collectively and correctly known as microsomes.