Biodiversity: Class 9 Biology

Key points

Biodiversity means the variety of living things on Earth, at the level of genes, species and ecosystems. It is greatest in warm, wet regions such as tropical rainforests and coral reefs. It gives us food, medicines, fibres, timber, clean air and water, and it keeps ecosystems stable.

Classification is the arrangement of organisms into groups on the basis of similarities and differences. Taxonomy is the science of classification. Classification makes the study of millions of species easier, shows relationships and helps in naming and identifying organisms. Carolus Linnaeus is called the father of modern taxonomy.

The hierarchy of classification, from the largest group to the smallest:

• Kingdom
• Phylum (called division in plants)
• Class
• Order
• Family
• Genus
• Species

A species is a group of organisms that look alike and can breed with each other to produce fertile offspring. Members of a species share a common set of features. The species is the basic unit of classification.

Binomial nomenclature is the system of giving each organism a scientific name of two parts, introduced by Linnaeus. The first part is the genus and begins with a capital letter. The second is the species and begins with a small letter. The name is written in italics or underlined separately, for example Homo sapiens for humans, Panthera leo for the lion and Mangifera indica for the mango. The system gives one name that is used worldwide, which avoids the confusion of local names.

The five kingdoms (Whittaker's system):

• Monera: prokaryotes, with no true nucleus, mostly unicellular, for example bacteria and cyanobacteria.
• Protista: mostly unicellular eukaryotes, for example Amoeba, Paramecium, Euglena and algae such as Chlamydomonas.
• Fungi: eukaryotes with chitin in the cell wall, no chlorophyll, and absorptive nutrition, for example mushrooms, yeast and moulds.
• Plantae: multicellular eukaryotes with cellulose cell walls and chlorophyll, which make food by photosynthesis.
• Animalia: multicellular eukaryotes with no cell wall and no chlorophyll, which take in food and usually move.

Viruses are not placed in any kingdom because they are not made of cells. They have a core of nucleic acid (DNA or RNA) inside a protein coat, and they can reproduce only inside a living host cell.

Main groups of plants:

• Bryophytes (mosses and liverworts): small, no true roots or vascular tissue, need water for reproduction.
• Pteridophytes (ferns): have vascular tissue, true roots, stems and leaves, and reproduce by spores.
• Gymnosperms (pine, deodar): naked seeds in cones, no flowers or fruits.
• Angiosperms (flowering plants): seeds enclosed in fruits. They are divided into monocots, with one seed leaf and parallel leaf veins (wheat, maize), and dicots, with two seed leaves and net veined leaves (gram, mango).

Main groups of animals:

• Invertebrates (no backbone): sponges (Porifera), Cnidaria, flatworms, roundworms, annelids, arthropods and molluscs.
• Arthropods have jointed legs and an exoskeleton, and include insects (six legs), arachnids (eight legs), crustaceans and myriapods.
• Vertebrates (with a backbone): fishes, amphibians, reptiles, birds and mammals.
• Mammals have hair, mammary glands and give birth to live young (with a few exceptions).

Biodiversity is threatened by habitat destruction (deforestation, urban growth), overhunting, pollution, climate change, introduced species and the spread of disease. Species whose numbers fall very low are called endangered, and when none remain the species is extinct. The extinction of one species can affect others that depend on it.

Conservation is the protection and wise use of living resources. It includes national parks, wildlife sanctuaries and game reserves, protection of forests, laws against hunting, breeding of endangered animals in zoos, seed banks and public awareness. In Pakistan, protected species include the snow leopard, the markhor and the Indus river dolphin.

A useful conservation answer links a particular pressure to a practical response. Protecting a wetland can preserve feeding and breeding sites; a seed bank preserves selected plant material outside its natural habitat. Neither action alone solves every threat.

Study tip: Make a one page table of the five kingdoms with cell type, number of cells, nutrition and examples, as it is the most common long question. Learn the rank order with a memory sentence of your own. When you write a scientific name, always follow the genus and species rule exactly.

Definitions and flashcards

Say the meaning first, then open the card to check.

Short questions with model answers

These are the kind of questions asked for 2, 3 and 5 marks. Try each one before opening the answer.

Common mistakes

• Writing scientific names without capital letter for the genus, or with a capital for the species, or not italicising or underlining them.
• Listing the ranks of classification in the wrong order, or starting from species when asked for largest to smallest.
• Saying that fungi are plants. Fungi have chitin and no chlorophyll, so they form a separate kingdom.
• Calling viruses living cells or placing them in Monera.
• Confusing an endangered species with an extinct species.

Practise this chapter

Practice questions and timed test Printable worksheet