Five Kingdom Classification — ICSE Class 9 Biology Important Questions

Answer: (b) R.H. Whittaker.

R.H. Whittaker proposed the five-kingdom classification in 1969, dividing living things into Monera, Protista, Fungi, Plantae and Animalia.

Answer: (c) Monera.

Bacteria are prokaryotic and unicellular, lacking a true membrane-bound nucleus, so they belong to Kingdom Monera.

Answer: (b) Protista.

Protists are eukaryotic and mostly unicellular; Amoeba, Paramecium and Euglena all have a true nucleus and are grouped here.

Answer: (b) Fungi.

A chitinous cell wall, absence of chlorophyll and saprophytic (absorptive) nutrition are the defining features of Kingdom Fungi. Plants have cellulose walls and chlorophyll; animals lack cell walls.

Answer: (a) Because fungi lack chlorophyll and are heterotrophic (unlike autotrophic green plants), Whittaker placed them in a separate kingdom, Fungi. R correctly explains A.

1. Monera — bacteria (e.g. Bacillus).
2. Protista — Amoeba.
3. Fungi — Rhizopus (bread mould) / mushroom.
4. Plantae — mango tree / fern.
5. Animalia — earthworm / human being.

1. Members of Kingdom Monera are prokaryotic — their cells have no true (membrane-bound) nucleus and no membrane-bound organelles such as mitochondria or plastids. All the other four kingdoms are eukaryotic.

2. Their genetic material (DNA) lies free in the cytoplasm as a single circular strand (nucleoid), not enclosed in a nuclear membrane.

All living organisms are divided by Whittaker into five kingdoms:

• Monera — prokaryotic, unicellular (bacteria, blue-green algae).
• Protista — eukaryotic, unicellular (Amoeba, Paramecium, Euglena).
• Fungi — eukaryotic, mostly multicellular, heterotrophic with chitin walls (Rhizopus, yeast, mushroom).
• Plantae — eukaryotic, multicellular autotrophs with cellulose walls and chlorophyll (mosses, ferns, flowering plants).
• Animalia — eukaryotic, multicellular heterotrophs without cell walls (worms, insects, fish, mammals).

The main basis of the division is cell type, cellular organisation and mode of nutrition.

Whittaker used three main criteria:

1. Cell structure (complexity of cell): whether the organism is prokaryotic (no true nucleus, e.g. Monera) or eukaryotic (true nucleus, all other kingdoms).

2. Grade of organisation (body complexity): whether the organism is unicellular (a single cell carries out all functions, e.g. Protista, most Monera) or multicellular with division of labour (e.g. Fungi, Plantae, Animalia).

3. Mode of nutrition: whether the organism is autotrophic (makes its own food by photosynthesis, e.g. Plantae) or heterotrophic — either by absorption (Fungi) or by ingestion (Animalia).

Using these together, every organism can be placed in one of the five kingdoms.

Euglena is a unicellular freshwater organism that shows a mixture of characters:

Plant-like features: It contains chloroplasts with chlorophyll and can carry out photosynthesis in sunlight, making its own food (autotrophic).

Animal-like features: It has no cell wall (only a flexible pellicle), it moves actively using a whip-like flagellum, has a sensitive eyespot, and in the dark it feeds on ready-made food from the surroundings (heterotrophic).

Because it cannot be neatly called a plant or an animal, but is a single-celled eukaryote, Euglena is placed in Kingdom Protista. This organism is a good example of why the older two-kingdom (plant/animal) system failed and why Whittaker created Protista for such eukaryotic unicellular forms.

Kingdom Monera

• Prokaryotic — cells have no true nucleus or membrane-bound organelles.
• Mostly unicellular and microscopic; may have a rigid cell wall.
• Nutrition may be autotrophic or heterotrophic (saprophytic/parasitic).
• Reproduce mainly by binary fission.
• Examples: bacteria (Bacillus), blue-green algae (Nostoc, Anabaena).

Kingdom Fungi

• Eukaryotic, mostly multicellular (yeast is unicellular); body is a network of thread-like hyphae (mycelium).
• Cell wall made of chitin; no chlorophyll.
• Heterotrophic — feed as saprophytes on dead matter or as parasites; store food as glycogen.
• Reproduce by spores.
• Examples: Rhizopus (bread mould), mushroom, yeast, Penicillium.

Kingdom Animalia

• Eukaryotic, multicellular with tissues and organs and division of labour.
• Cells have no cell wall and no chlorophyll.
• Heterotrophic by ingestion (holozoic); food stored as glycogen or fat.
• Most show movement and have a nervous system for quick response.
• Examples: earthworm, housefly, frog, human being.

Thus these three kingdoms differ chiefly in cell type, presence of a cell wall, and mode of nutrition.

Drawbacks of the two-kingdom system

Earlier all organisms were put into just two kingdoms, Plantae and Animalia. This caused several problems:

1. It ignored the difference between prokaryotes and eukaryotes. Bacteria (prokaryotic) were grouped with green plants (eukaryotic) merely because both have cell walls, though their cells are fundamentally different.

2. It ignored unicellular vs multicellular organisation. Single-celled organisms like Amoeba and Paramecium were forced into the animal kingdom along with complex multicellular animals.

3. It could not place mixed or intermediate forms. Euglena has both chlorophyll (plant-like) and movement without a cell wall (animal-like), so it fitted neither kingdom properly.

4. It wrongly grouped fungi with plants. Fungi have cell walls but lack chlorophyll and are heterotrophic, so they are quite unlike green plants.

How the five-kingdom system solves these

Whittaker used cell type, cellular organisation and mode of nutrition together:

• Monera was created for all prokaryotes (bacteria, blue-green algae), separating them from eukaryotes.
• Protista was created for eukaryotic unicellular organisms (Amoeba, Euglena, Paramecium), giving intermediate forms a proper place.
• Fungi was made a separate kingdom for non-green, chitin-walled, heterotrophic organisms.
• Plantae now holds only multicellular autotrophs, and Animalia only multicellular heterotrophs without cell walls.

Thus the five-kingdom system reflects real differences in cell structure and nutrition and removes the confusion of the old two-kingdom scheme.

(i) Kingdoms:

• P (mushroom) — Kingdom Fungi.
• Q (Paramecium) — Kingdom Protista.
• R (fern) — Kingdom Plantae.
• S (bacteria) — Kingdom Monera.

(ii) The prokaryotic specimen is S (bacteria), as bacteria have no true membrane-bound nucleus.

(iii) The mushroom (P) is placed in Fungi rather than Plantae because it lacks chlorophyll and is heterotrophic (saprophytic), with a cell wall made of chitin instead of cellulose; it cannot make its own food.

(iv) The fern (R) is autotrophic — it makes its own food by photosynthesis using chlorophyll.