Diversity in the Living World

Biology is the science of life forms and living processes. The living world constitutes an amazing diversity of living organisms. Early man deified some of the inanimate matter (wind, sea, fire etc.) and some among the animals and plants. The common feature of all such forms of inanimate and animate objects was the sense of awe or fear that they evoked.

1.1 Growth

Increase in mass and increase in number of individuals are twin characteristics of growth.

• Plants: Growth by cell division occurs continuously throughout their life span.
• Animals: Growth is seen only up to a certain age. However, cell division occurs in certain tissues to replace lost cells.
• Unicellular organisms: Grow by cell division. In vitro cultures allow us to count the number of cells under a microscope.
• Non-living objects: Mountains, boulders, and sand mounds also grow by accumulation of material on the surface (accetion).

1.2 Reproduction

Reproduction is the production of progeny possessing features more or less similar to those of parents.

• Asexual Reproduction:
  • Fungi: Multiply by millions of asexual spores.
  • Yeast & Hydra: Reproduce by budding.
  • Planaria (Flatworms): Show true regeneration (a fragmented organism regenerates the lost part of its body).
  • Fungi, Filamentous Algae, Protonema of Mosses: Multiply by fragmentation.
  • Bacteria, Unicellular Algae, Amoeba: Reproduction is synonymous with growth (increase in number of cells).

1.3 Metabolism

The sum total of all the chemical reactions occurring in our body is metabolism. All plants, animals, fungi and microbes exhibit metabolism.

• No non-living object exhibits metabolism.
• Metabolic reactions can be demonstrated outside the body in cell-free systems. An isolated metabolic reaction outside the body of an organism, performed in a test tube is neither living nor non-living.

1.4 Consciousness

The ability to sense their surroundings or environment and respond to these environmental stimuli which could be physical, chemical or biological is the most obvious and technically complicated feature of all living organisms.

• Plants respond to external factors like light, water, temperature, other organisms, pollutants, etc.
• Photoperiod affects reproduction in seasonal breeders, both plants and animals.
• All organisms handle chemicals entering their bodies.
• Human being is the only organism who is aware of himself, i.e., has self-consciousness.

2. Diversity in the Living World

The number of species that are known and described ranges between 1.7-1.8 million. This refers to biodiversity or the number and types of organisms present on earth.

2.1 Nomenclature

There is a need to standardize the naming of living organisms such that a particular organism is known by the same name all over the world. This process is called Nomenclature.

Nomenclature or naming is only possible when the organism is described correctly and we know to what organism the name is attached to. This is Identification.

2.2 Binomial Nomenclature

Proposed by Carolus Linnaeus. Each name has two components: the Generic name and the Specific epithet.

3. Taxonomic Categories

Classification is not a single step process but involves hierarchy of steps in which each step represents a rank or category. Since the category is a part of overall taxonomic arrangement, it is called the taxonomic category and all categories together constitute the taxonomic hierarchy.

Each category, referred to as a unit of classification, in fact represents a rank and is commonly termed as taxon (pl. taxa).

3.1 Detailed Hierarchy

Species

A group of individual organisms with fundamental similarities. One should be able to distinguish one species from the other closely related species based on the distinct morphological differences.

• Mangifera indica (Mango)
• Solanum tuberosum (Potato)
• Panthera leo (Lion)

Here, indica, tuberosum and leo represent specific epithets, while Mangifera, Solanum and Panthera represent genera.

Genus

Comprises a group of related species which has more characters in common in comparison to species of other genera.

• Potato and Brinjal belong to genus Solanum.
• Lion (Panthera leo), Leopard (P. pardus) and Tiger (P. tigris) belong to genus Panthera.
• Cats belong to genus Felis.

Family

Group of related genera with still less number of similarities as compared to genus and species. Families are characterised on the basis of both vegetative and reproductive features of plant species.

• Plants: Genera Solanum, Petunia and Datura are placed in family Solanaceae.
• Animals: Genus Panthera and genus Felis (cats) are placed in family Felidae. (Dogs are in Canidae).

Order

Assemblage of families which exhibit a few similar characters. The similar characters are less in number as compared to different genera included in a family.

• Plants: Families Convolvulaceae and Solanaceae are included in order Polymoniales mainly based on floral characters.
• Animals: Families Felidae and Canidae are included in order Carnivora.

Class

Includes related orders.

• Order Primata (monkey, gorilla, gibbon) and Order Carnivora (tiger, cat, dog) are placed in Class Mammalia.

Phylum (Animals) / Division (Plants)

• Classes comprising animals like fishes, amphibians, reptiles, birds along with mammals constitute the next higher category called Phylum (Chordata - presence of notochord and dorsal hollow neural system).
• For plants, classes with a few similar characters are assigned to a higher category called Division.

Kingdom

All animals belonging to various phyla are assigned to the Kingdom Animalia. All plants from various divisions belong to Kingdom Plantae.

4. Taxonomical Aids

Taxonomic studies establish and identify organisms which require intensive laboratory and field studies. The collection of actual specimens of plant and animal species is essential and is the prime source of taxonomic studies.

4.1 Herbarium

• Store house of collected plant specimens that are dried, pressed and preserved on sheets.
• Sheets are arranged according to a universally accepted system of classification.
• Herbarium Label: Carries information about date and place of collection, English, local and botanical names, family, collector’s name, etc.
• Herbaria serve as a Quick Referral System in taxonomical studies.

4.2 Botanical Gardens

• Specialized gardens having collections of living plants for reference.
• Plant species are grown for identification purposes and each plant is labeled indicating its Botanical/Scientific name and its Family.
• Famous Gardens:
  • Kew (England)
  • Indian Botanical Garden (Howrah, India)
  • National Botanical Research Institute (Lucknow, India)

4.3 Biological Museum

• Set up in educational institutes like schools and colleges.
• Collections of preserved plant and animal specimens for study and reference.
• Specimens are preserved in containers or jars in preservative solutions.
• Insects are preserved in insect boxes after collecting, killing and pinning.
• Larger animals like birds and mammals are usually stuffed and preserved.
• Museums often have collections of skeletons of animals too.

4.4 Zoological Parks (Zoos)

• Places where wild animals are kept in protected environments under human care.
• Enable us to learn about their food habits and behaviour.
• Conditions are provided as similar as possible to their natural habitats.

4.5 Key

• Taxonomical aid used for identification of plants and animals based on the similarities and dissimilarities.
• Based on the contrasting characters generally in a pair called couplet.
• It represents the choice made between two opposite options. This results in acceptance of only one and rejection of the other.
• Each statement in the key is called a lead.
• Separate taxonomic keys are required for each taxonomic category such as family, genus and species for identification purposes.
• Keys are generally analytical in nature.

4.6 Other Taxonomical Aids

Practice Important Points

• Systematics: Derived from Latin word 'systema' which means systematic arrangement of organisms. Linnaeus used Systema Naturae as the title of his publication.
• Order Polymoniales: Includes Convolvulaceae and Solanaceae.
• Family Anacardiaceae: Includes Mango.
• Family Poaceae: Includes Wheat.
• Family Hominidae: Includes Man.
• Family Muscidae: Includes Housefly.
• Order Sapindales: Mango.
• Order Poales: Wheat.
• Order Diptera: Housefly.
• Order Primata: Man.

High Order Thinking Questions
Diversity in Living World