Posterior end of Amoeba is characterized by

The correct option is Lack of food vacuoles.

To understand why this is correct, we can analyze the structural and functional specialization of the cytoplasm and organelles along the antero-posterior axis of a moving Amoeba proteus.

During locomotion, Amoeba exhibits a clear polarity:
1. Anterior End (Front): This is the advancing end of the organism where active pseudopodia (false feet) are formed. Phagocytosis (food capture) occurs primarily at the anterior region. Consequently, newly formed food vacuoles containing ingested prey are concentrated in the anterior and middle regions of the cell body.
2. Posterior End (Rear): This is the trailing end of the cell, often characterized by a wrinkled, sticky region known as the uroid. As the organism moves forward, cytoplasm flows away from the rear. The undigested waste materials are brought to the posterior surface for exocytosis (defecation). Since food vacuoles are transported, digested, and eventually expelled, the stable, actively digesting food vacuoles are typically absent at the extreme posterior tip just prior to or after waste elimination. Thus, the posterior end is characterized by a lack of active food vacuoles.

Let's also look at why the other options are incorrect:
- Amphid: Amphids are sensory organs found in nematodes (roundworms), not in unicellular amoebae.
- Uropygium: The uropygium is a biological term referring to the posterior part of a bird's body (where the tail feathers attach) or the tail-like structure in certain arachnids (like whip scorpions). It is not present in unicellular organisms.
- Plasmid: Plasmids are small, circular, double-stranded DNA molecules distinct from a cell's chromosomal DNA, commonly found in bacteria. They are not structural features characterizing the posterior end of an eukaryotic Amoeba.