Patterns in Life: Diversity and Classification — Class 9 MCQs with Answers

Key concepts: Patterns in Life: Diversity and Classification (Class 9 Science)

Millions of species exist, so biologists group them by shared characteristics rather than studying each separately. This chapter builds the classification hierarchy, works through the five kingdoms and the major plant and animal divisions, and explains binomial nomenclature and the peculiar position of viruses.

Classification

Arranging organisms into groups based on shared characteristics. It makes the study of enormous diversity manageable and reveals evolutionary relationships.

Basis of classification

Groups are formed on fundamental characteristics — cell type, number of cells, mode of nutrition and body organisation — rather than superficial resemblance.

Taxonomic hierarchy

The ranked series Kingdom, Phylum (or Division), Class, Order, Family, Genus, Species. Moving down the ranks, similarity increases and numbers decrease.

Species

The basic unit of classification: a group of organisms so similar that they can interbreed and produce fertile offspring.

Binomial nomenclature

Carolus Linnaeus's two-word naming system: genus followed by species, as in Homo sapiens. It gives every organism one universally accepted name.

Rules of writing scientific names

The genus begins with a capital letter and the species with a small one; the name is italicised in print and underlined separately when handwritten.

Five-kingdom classification

Whittaker's scheme of Monera, Protista, Fungi, Plantae and Animalia, based on cell structure, body organisation and mode of nutrition.

Monera

Prokaryotes — organisms without a true nucleus or membrane-bound organelles, such as bacteria and blue-green algae. They may be autotrophic or heterotrophic.

Protista

Unicellular eukaryotes such as Amoeba, Paramecium and Euglena, often moving by cilia, flagella or pseudopodia.

Fungi

Eukaryotic, mostly multicellular heterotrophs that feed saprophytically on dead organic matter and have cell walls of chitin.

Plant divisions

Plantae is divided into Thallophyta, Bryophyta, Pteridophyta, Gymnosperms and Angiosperms, in order of increasing complexity of body and reproductive structure.

Bryophyta — the amphibians of the plant kingdom

Plants such as mosses that live on land but need water for the transfer of male gametes during reproduction, hence the nickname.

Angiosperms and gymnosperms

Angiosperms bear seeds enclosed inside a fruit, while gymnosperms bear naked seeds. Angiosperms are further split into monocots and dicots by seed leaf number.

Animal phyla

The major groups run Porifera, Coelenterata, Platyhelminthes, Nematoda, Annelida, Arthropoda, Mollusca, Echinodermata and Chordata, in broadly increasing complexity.

Arthropoda

The largest animal phylum, with jointed legs, an exoskeleton of chitin and an open circulatory system — insects, spiders and crustaceans.

Chordata

Animals with a notochord, a dorsal hollow nerve cord and paired gill pouches at some stage of life. Vertebrates are the familiar sub-group.

Vertebrate classes

Pisces, Amphibia, Reptilia, Aves and Mammalia, distinguished by features such as skin covering, respiratory organs, body temperature control and mode of reproduction.

Viruses

Non-cellular entities of nucleic acid within a protein coat. They are inert outside a host and reproduce only inside a living cell, so they sit outside the five-kingdom scheme.