Question

Which of the following organisms is not a eukaryote?
(a) Paramecium caudatum
(b) Escherichia coli
(c) Euglena viridis
(d) Amoeba proteus

Answer 1

Hint: A cell is broadly divided into prokaryotes and eukaryotes based on the presence or absence of a well- defined nucleus and cell organelles. One of the members of prokaryotes resides in the human colon in a symbiotic relationship.

Complete answer:
Bacteria are single- celled microscopic organisms that live in a variety of environments,i.e, hot water, or even ice. They are the simplest of organisms and constitute a large domain of prokaryotic microorganisms. Escherichia coli is a gram- negative rod- shaped bacteria symbiotically associated with the human colon. It is a prokaryote due to the absence of any well- defined nucleus. Instead, in the nucleoid, the genetic material lies freely in the cytoplasm associated with some proteins helping in its supercoiling.
- Kingdom Protista includes unicellular eukaryotes.
- Euglena viridis are unicellular protists. They are devoid of the cell walls. Instead, a protein- rich layer called ‘pellicle’ is present just beneath the cell membrane to make their body flexible. They are biflagellated with unequal sizes of flagella located at its anterior end. The presence of chloroplasts makes them photosynthetic. Chlorophyll a and b are the photosynthetic pigments found in Euglena viridis.
- Paramecium caudatum is a protozoan protist that develops a number of cilia during a part or for the whole of their life. These cilia help them to locomote in freshwater. It is a surface feeder with bacteria as its chief food. Their characteristic feature is the presence of two dissimilar nuclei- a large macronucleus and a smaller micronucleus. The osmoregulation is maintained by contractile vacuoles and radial canals.
- Amoeba proteus is a protozoan protist under the group of Rhizopoda or Sarcodina. They develop temporary cytoplasmic extensions known as pseudopodia as their locomotory apparatus. The body is surrounded by plasmalemma which renders it the flexibility to continuously change its forms. This unicellular and transparent eukaryote can be easily found in clean water habitats like a highly oxygenated lake.
bSo, the correct answer is ‘Escherichia coli.’

Note: In contrast to algae, Euglena viridis do not store starch. Instead, a glucose polymer ‘paramylon’ in the cytosol is their reserve food material. They exhibit a different kind of nutrition wherein, in sunlight, they act as photoautotrophic while in its absence, they become heterotrophic. This is the reason, their nutrition is considered mainly mixotrophic.