Diversity In Living Organisms Class 9 Chapter Notes

Key points

• Classification means arranging organisms into groups based on similarities and differences; it makes the study of huge biodiversity easier.
• The main bases of classification are cell type, body organisation, mode of nutrition, reproduction, and evolutionary relationship.
• The five kingdoms proposed by R. H. Whittaker are Monera, Protista, Fungi, Plantae and Animalia.
• Correct taxonomic hierarchy: Kingdom → Phylum/Division → Class → Order → Family → Genus → Species.
• Monera are prokaryotic; all other kingdoms in this chapter are eukaryotic.
• Plants are classified mainly by body differentiation, presence of vascular tissue, seed formation and whether seeds are naked or enclosed in fruits.
• Animals are classified using body symmetry, body cavity, segmentation, notochord and level of organ-system development.
• Binomial nomenclature gives every organism a two-part scientific name: Genus + species, for example Homo sapiens.
• Vertebrates have a backbone and are grouped into Pisces, Amphibia, Reptilia, Aves and Mammalia.
• Exam answers must include examples; a feature without a correct example usually scores less in classification questions.

Must-know definitions

Biodiversity

The variety of living organisms found in a particular region or on Earth, including differences in form, structure, habitat and function.

Classification

The systematic arrangement of organisms into groups and subgroups on the basis of similarities and differences.

Taxonomy

The branch of biology that deals with identification, naming and classification of organisms.

Species

The basic unit of classification; a group of similar organisms that can interbreed among themselves to produce fertile offspring.

Binomial nomenclature

A two-word scientific naming system in which the first word is the genus and the second word is the species.

Prokaryotic cell

A cell without a well-defined nucleus and without membrane-bound cell organelles, as seen in bacteria.

Eukaryotic cell

A cell with a well-defined nucleus and membrane-bound organelles such as mitochondria.

Notochord

A flexible rod-like supporting structure present at some stage in chordates; it is an important feature for separating chordates from non-chordates.

Vascular tissue

Specialised conducting tissue, xylem and phloem, that transports water, minerals and food in plants.

Core concept: why classification is needed

Earth has millions of organisms, and they differ in size, structure, habitat, nutrition and reproduction. Studying each organism separately is impossible, so scientists use classification to group organisms with common features. The most basic difference is cell structure: organisms may be prokaryotic or eukaryotic. Next, we check whether the organism is unicellular or multicellular, whether cells form tissues and organs, and how the organism obtains food: autotrophic plants make food, while heterotrophic organisms depend on others. Classification also reflects evolutionary relationships: organisms with more shared characters are considered more closely related. For diagrams, draw a top-down tree: Living organisms → Five kingdoms → plant divisions/animal phyla → smaller groups. This tree format is often easier to remember than paragraph notes and helps in 3-mark comparison questions.

Five kingdoms at a glance

How to classify an unknown organism in exams

1. Step 1: Check cell structure — If there is no true nucleus, place it in Monera. If a true nucleus is present, continue with the next features.
2. Step 2: Check cellular organisation — Unicellular eukaryotes are usually Protista, while multicellular organisms may be fungi, plants or animals.
3. Step 3: Check nutrition — Autotrophic organisms with chlorophyll are placed in Plantae. Absorptive heterotrophs with a cell wall are fungi. Ingestive heterotrophs without a cell wall are animals.
4. Step 4: If it is a plant, check vascular tissue and seeds — No differentiated body points to Thallophyta; no vascular tissue points to Bryophyta; vascular tissue without seeds points to Pteridophyta; seeds lead to Gymnosperms or Angiosperms.
5. Step 5: If it is an animal, check body plan — Look for symmetry, body cavity, segmentation and notochord. Presence of backbone places it under Vertebrata.

Plant kingdom revision table

Animal groups: high-yield differences

Vertebrate classes: must remember

• Pisces: aquatic, streamlined body, gills, fins, two-chambered heart; examples: rohu, shark.
• Amphibia: live both in water and on land, moist skin, three-chambered heart; examples: frog, toad.
• Reptilia: dry scaly skin, lungs, lay eggs with tough covering; examples: lizard, snake, turtle.
• Aves: feathers, forelimbs modified into wings, beak, warm-blooded; examples: pigeon, crow.
• Mammalia: mammary glands, hair on skin, mostly give birth to young ones; examples: human, whale, bat.
• Memory chain for vertebrates: Fish → Frog → Lizard → Bird → Mammal shows increasing complexity in school-level classification.

Mini-examples for quick application

• {"title":"Example 1: Classify mushroom","bodyMarkdown":"Mushroom is eukaryotic, non-green, heterotrophic and absorbs food from decaying matter. Therefore, it belongs to Kingdom Fungi."}
• {"title":"Example 2: Mango plant in classification","bodyMarkdown":"Mango has roots, stem, leaves, vascular tissue, flowers and seeds enclosed in fruits. Therefore, it belongs to Plantae → Angiosperms."}
• {"title":"Example 3: Earthworm vs Ascaris","bodyMarkdown":"Earthworm has a segmented body, so it is Annelida. Ascaris is cylindrical and unsegmented, so it is Nematoda."}

Exam tip: common traps and marking cues

For 2-mark and 3-mark questions, do not write only examples; include the basis of classification. For example, in a question on gymnosperms and angiosperms, mention whether seeds are naked or enclosed in fruits. In animal phyla, the most repeated traps are: Porifera are animals, Nematoda are not segmented, Annelida are segmented, Arthropoda have jointed legs, and Echinodermata are marine. In scientific names, write the Genus first with capital letter and the species second with small letter, for example Homo sapiens. If asked for hierarchy, do not skip levels: Kingdom → Phylum/Division → Class → Order → Family → Genus → Species.

Quick revision checks

• Q: Which kingdom includes prokaryotic organisms? A: Monera.
• Q: What is the basic unit of classification? A: Species.
• Q: Why are bryophytes called amphibians of the plant kingdom? A: They live on land but require water for reproduction.
• Q: Name the phylum with jointed legs and chitinous exoskeleton. A: Arthropoda.

Frequently Asked Questions