Patterns in Life: Diversity and Classification — CBSE Class 9 Science Important Questions

Answer: (c) species.

Species is the smallest unit of classification — a group of organisms so similar that they can interbreed and produce fertile offspring.

Answer: (b) Monera.

Bacteria are unicellular organisms with prokaryotic cells (no true nucleus), so Whittaker placed them in kingdom Monera.

Answer: (c) species.

In binomial nomenclature the first word (Mangifera) is the genus and the second word (indica) is the species. The genus begins with a capital letter and the species with a small letter.

Answer: (b) They belong to the same order.

Family lies below order in the hierarchy (Order to Family to Genus). If two organisms share a family, they must also share every rank above it, including order, class, phylum and kingdom.

Answer: (a) Both A and R are true and R is the correct explanation of A.

Unlike green plants, fungi lack chlorophyll and obtain food from dead organic matter (saprophytic nutrition). This different mode of nutrition is exactly why Whittaker placed them in a separate kingdom, Fungi.

Biodiversity is the variety of living organisms (plants, animals and micro-organisms) found in a region or on the Earth.

We classify organisms because there is a vast variety of them; grouping by similarities and differences makes them easier to study and identify, shows how different groups are related, and lets us understand the whole living world through a few representative types.

1. The name has two parts — the genus (written first, beginning with a capital letter) and the species (written second, beginning with a small letter).

2. The scientific name is written in italics (or underlined separately when handwritten), e.g. Homo sapiens.

From the largest group to the smallest, the levels are: Kingdom, Phylum (Division in plants), Class, Order, Family, Genus, Species. As we go down, the number of organisms decreases but the similarities among them increase.

Whittaker's five kingdoms are Monera, Protista, Fungi, Plantae and Animalia.

The three main criteria used were:

1. Cell structure — whether the cells are prokaryotic (no true nucleus) or eukaryotic (with a true nucleus).
2. Body organisation — whether the organism is unicellular or multicellular.
3. Mode of nutrition — whether it is autotrophic (makes its own food) or heterotrophic (depends on others).

Although both are unicellular, they differ in the most fundamental feature — cell type.

A bacterium has a prokaryotic cell: it lacks a true, membrane-bound nucleus and membrane-bound organelles. Hence it is placed in kingdom Monera.

Amoeba has a eukaryotic cell: its genetic material is enclosed in a true nucleus and it has membrane-bound organelles. Hence it is placed in kingdom Protista.

Since the presence or absence of a true nucleus is a basic criterion of classification, the two are placed in different kingdoms.

Monera: prokaryotic (no true nucleus), unicellular; nutrition autotrophic or heterotrophic; cell wall may be present. Example: bacteria, blue-green algae.

Protista: eukaryotic, unicellular; some have organs of locomotion like cilia or flagella; autotrophic or heterotrophic. Example: Amoeba, Paramecium, Euglena.

Fungi: eukaryotic, mostly multicellular; cell wall of chitin; saprophytic or parasitic heterotrophs (no chlorophyll). Example: Rhizopus, mushroom, yeast.

Plantae: eukaryotic, multicellular; cell wall of cellulose; autotrophic (photosynthesis using chlorophyll). Example: mango tree, fern, moss.

Animalia: eukaryotic, multicellular; no cell wall; heterotrophic (holozoic) nutrition; most can move. Example: human, earthworm, fish.

(a) The hierarchy of classification is the arrangement of organisms into a series of groups placed one below another in a definite order — Kingdom, Phylum, Class, Order, Family, Genus, Species — each smaller group sharing more characters.

(b) Human classification:
Kingdom Animalia to Phylum Chordata to Class Mammalia to Order Primata to Family Hominidae to Genus Homo to Species sapiens. So the scientific name of humans is Homo sapiens.

(c) As we move up from species to kingdom, each group becomes larger and includes more and more diverse organisms, so the number of characters they all share becomes fewer. As we move down to species, the group is smaller and the members are more alike, so they share more common characters.

(i) Bacterium to Monera; mushroom to Fungi; moss to Plantae; earthworm to Animalia.

(ii) The bacterium is a prokaryote (it has no true, membrane-bound nucleus).

(iii) The mushroom is saprophytic — it is a heterotroph that absorbs food from dead and decaying organic matter.

(iv) The moss (Plantae) has a cell wall of cellulose and is autotrophic (makes its own food), whereas the earthworm (Animalia) has no cell wall and is heterotrophic.