Question

Consider the following statements.
I. Kingdom Protista forms a link between monerans and other organisms like plants, animals, and fungi.
II. Protists reproduce asexually and sexually by a process involving cell fusion and zygote formation.
III. Being eukaryotes, the protist cell body contains a well-defined nucleus and other membrane-bound organelles.
Which of the statements given above are correct?
A. I and II
B. I and III
C. II and III
D. I, II and III

Answer 1

Hint: The five-kingdom system was proposed in 1969 by Whittaker. It includes Monera, Protista, Fungi, Plantae, and Animalia. The Monera and Protista include unicellular and organisms with simple cellular colonies.

Complete Answer:
- Monerans consist of unicellular organisms with a prokaryotic cell organization i.e. a true nuclear membrane is not present.
- They are present everywhere: in hot or thermal springs, in the deep ocean floor, in ice-cold conditions, in deserts, and also inside the body of plants and animals. They can be aerobic or anaerobic.
- Reproduction is mostly asexual by binary fission. A few also reproduce by sexual reproduction that is by conjugation, transformation, and transduction.
- A protist consists of eukaryotic organisms that are not an animal, plant, or fungus. Some protists may be more closely related to animals, plants, or fungi than they are to other protists. The protists include the eukaryotic forms that are considered to be the first eukaryotes evolved. Hence, it is considered as the connecting link between kingdom monera, and plants, animals, and fungi.
- Protists vary a lot in their organization. They can be single-celled, syncytial, or multicellular. (even though protists may show multicellularity, they are never multi-tissued.) They can be filamentous, may exist in colonies or coenobia. Not all protists are microscopic. Some are large species, for example, among the brown algal some protists forms may reach a length of 60 metres or more. Mode of nutrition can be autotrophic or heterotrophic.
- Reproduction in Protists is generally asexual under favorable environmental conditions, but under stressful conditions such as starvation or heat shock, they reproduce sexually. They reproduce sexually by a process involving cell fusion and zygote formation.
Protists consist of eukaryotes and they are characterized by the presence of a well-defined nucleus and membrane-bound cell organelles.

Hence, I, II, and III are correct. The correct option is D.

Note: The main criteria of the five-kingdom classification were cell structure, body organization, mode of nutrition, reproduction, and phylogenetic relationships. The monerans show the most extensive metabolic diversity. Protists include all the single-celled eukaryotes such as Chrysophytes, Dinoflagellates, Euglenoids, Slime-moulds, and Protozoans.