NCERT Class 9 Science Chapter 7 DIVERSITY IN LIVING ORGANISMS Notes

7.1 What is the Basis of What is the Basis of Classification?

Hierarchy of Characteristics for Classification

1. Cell Structure:

Eukaryotic vs. Prokaryotic:
Eukaryotic cells have membrane-bound organelles, including a nucleus.
Organisms lacking a clearly demarcated nucleus and organelles would exhibit different biochemical pathways, influencing cell design.
Nucleated cells possess the capacity for multicellularity and specialized functions, a fundamental trait for classification.

2. Cellular Organization:

Singular vs. Grouped Cells:
Organisms with cells forming indivisible groups exhibit division of labor.
Differentiation of cell functions leads to distinct body designs, evident in organisms like Amoeba and worms.

3. Mode of Nutrition:

Autotrophs vs. Heterotrophs:
Ability to produce own food (photosynthesis) or depend on external food sources necessitates different body designs.

4. Plant Characteristics:

Photosynthesis and Body Organization:
Level of body organization in plants varies based on photosynthetic capability.
Design features related to photosynthesis and nutrient acquisition are key for plant classification.

5. Animal Characteristics:

Development and Specialized Organs:
Individual body development and specialized organs for diverse functions are pivotal in animal classification.
Features like having a skeleton serve as sub-grouping criteria within the broader animal classification.

7.2 Classification and Evolution

Evolution and Classification

1. Evolutionary Perspective:

Evolution refers to the accumulation of changes in body design over time, enhancing an organism's survival capabilities.
Introduced by Charles Darwin in "The Origin of Species" (1859), evolution underscores the dynamic nature of life forms.

2. Primitive vs. Advanced Organisms:

Some groups exhibit ancient body designs that have undergone minimal change over time, termed 'primitive' or 'lower' organisms.
Conversely, other groups possess more recently acquired body designs, termed 'advanced' or 'higher' organisms.
While labels like 'primitive' and 'advanced' are used, they don't accurately reflect differences; instead, organisms are better described as 'older' or 'younger' based on the antiquity of their body designs.

3. Complexity and Evolutionary Time:

Older organisms are often simpler in design, while younger organisms tend to be more complex.
Complexity in design may increase over evolutionary time, suggesting a trend toward greater intricacy in newer organisms.

Biodiversity and Environmental Context:

1. Definition and Significance:

Biodiversity encompasses the variety of life forms within a particular region, influenced by interactions and adaptations to environmental factors.
A stable community of diverse species arises from interactions among different life forms, contributing to ecosystem stability.

2. Human Impact and Biodiversity Loss:

Human activities have disrupted the balance of diverse communities, leading to biodiversity loss.
Land use changes, pollution, and habitat destruction contribute to the decline of various species and ecosystems.

3. Global Distribution and Megadiversity:

Warm and humid tropical regions, particularly between the tropics of Cancer and Capricorn, host high biodiversity, termed megadiversity regions.
Countries like Brazil, Colombia, and Australia concentrate a significant portion of global biodiversity.

7.3 The Hierarchy of Classification- The Hierarchy of Classification- The Hierarchy of Classification Groups

Classification of Living Organisms

Five Kingdom Classification (Whittaker, 1959):

1.Monera:

Includes prokaryotic organisms without a nucleus.
Divided into Archaebacteria (Archaea) and Eubacteria (Bacteria) by Woese.
Diverse in habitat, ranging from extreme environments to common habitats.

2. Protista:

Eukaryotic organisms with diverse cell structures.
Single-celled or multicellular, often exhibiting characteristics of plants, animals, or fungi.
Found in aquatic environments, including freshwater and marine habitats.

3. Fungi:

Eukaryotic organisms with cell walls made of chitin.
Heterotrophic, primarily decomposers, but also includes parasites and symbionts.
Important for nutrient recycling and ecosystem functioning.

4. Plantae:

Multicellular eukaryotic organisms with cellulose cell walls.
Autotrophic, capable of photosynthesis to produce energy.
Varied in size and habitat, ranging from microscopic algae to towering trees.

5. Animalia:

Multicellular eukaryotic organisms without cell walls.
Heterotrophic, relying on external food sources for energy.
Exhibits diverse body plans, behaviors, and ecological roles.

Hierarchical Classification Scheme:

Kingdom: Broadest category encompassing all organisms.
Phylum (Animals) / Division (Plants): Grouping based on major body plans and structural similarities.
Class: Further subdivision based on shared characteristics and evolutionary relationships.
Order: Organisms grouped by similarities in anatomy, physiology, and behavior.
Family: Similar genera grouped together based on common ancestry.
Genus: Group of closely related species sharing a common ancestor.
Species: Basic unit of classification; includes organisms capable of interbreeding and producing viable offspring.

Species Concept:

Organisms within the same species are similar enough to interbreed and produce fertile offspring.
Species boundaries are fluid and subject to interpretation, especially in organisms with complex reproductive behaviors.
Evolutionary and genetic studies provide insights into species relationships and diversification processes.

7.4 Plantae

1. Thallophyta:

Characteristics:

Lack well-differentiated body design.
Predominantly aquatic.
Examples include Spirogyra, Ulothrix, Cladophora, and Chara.

Reproduction:

Naked embryos called spores.
Reproductive organs inconspicuous, termed 'cryptogamae.'

2. Bryophyta:

Characteristics:

Differentiated plant body forming stem and leaf-like structures.
Lack specialized tissue for water conduction.
Examples include moss (Funaria) and Marchantia.

Reproduction:

Naked embryos (spores).
Reproductive organs inconspicuous (cryptogamae).

3. Pteridophyta:

Characteristics:

Differentiated into roots, stem, and leaves.
Possess specialized tissue for water conduction.
Examples include Marsilea, ferns, and horse-tails.

Reproduction:

Naked embryos (spores).
Reproductive organs inconspicuous (cryptogamae).

4. Gymnosperms:

Characteristics:

Derived from Greek words 'gymno-' (naked) and 'sperma-' (seed).
Bear naked seeds.
Usually perennial, evergreen, and woody.
Examples include pines and deodar.

Reproduction:

Seeds produced directly on cones or similar structures.
No fruit covering the seeds.

5. Angiosperms:

Characteristics:

Derived from Greek words 'angio' (covered) and 'sperma-' (seed).
Seeds develop inside fruits.
Also called flowering plants.
Examples include all flowering plants.

Reproduction:

Seeds enclosed within fruits.
Plant embryos in seeds have cotyledons (seed leaves).
Further Classification:
Monocotyledonous (Monocots): Seeds with single cotyledon.
Dicotyledonous (Dicots): Seeds with two cotyledons.

7.5 Animalia

Classification of Animals

1. Porifera:

Characteristics:

Non-motile animals attached to solid support.
Numerous pores (holes) throughout the body.
Minimal body differentiation and tissue division.
Covered with a hard outer layer or skeleton.
Example: Sponges.

2. Coelenterata (Cnidaria):

Characteristics:

Water-dwelling animals.
Body with a cavity.
Body made of two layers of cells.
Some live in colonies (corals), others solitary (Hydra).
Examples: Jellyfish, sea anemones.

3. Platyhelminthes:

Characteristics:

Bilaterally symmetrical body.
Triploblastic with three layers of cells.
Flatworms with flattened dorsoventral body.
Lack true body cavity (coelom).
Examples: Planarians, liverflukes.

4. Nematoda:

Characteristics:

Bilaterally symmetrical cylindrical body.
Triploblastic with tissues but no real organs.
Presence of a pseudocoelom.
Often parasitic, causing various diseases.
Examples: Filarial worms, roundworms.

5. Annelida:

Characteristics:

Bilaterally symmetrical with true body cavity (coelom).
Segmented body with extensive organ differentiation.
Segments lined up from head to tail.
Found in diverse habitats including freshwater, marine water, and land.
Examples: Earthworms, leeches.

6. Arthropoda:

Characteristics:

Largest group of animals.
Bilaterally symmetrical and segmented.
Open circulatory system with blood-filled coelomic cavity.
Jointed legs.
Examples: Prawns, butterflies, spiders, crabs.

7. Mollusca:

Characteristics:

Bilateral symmetry with reduced coelomic cavity.
Limited segmentation.
Open circulatory system and kidney-like excretory organs.
Presence of a foot for movement.
Examples: Snails, mussels.

8. Echinodermata:

Characteristics:

Exclusively marine animals with spiny skin.
Triploblastic with a coelomic cavity.
Water-driven tube system for movement.
Hard calcium carbonate skeleton structures.
Examples: Starfish, sea urchins.

9. Protochordata:

Characteristics:

Bilaterally symmetrical, triploblastic, and coelomic.
Presence of a notochord, at least at some stages.
Notochord serves as a support structure.
Examples: Lancelets, tunicates.

10. Vertebrata:

Characteristics:

True vertebral column and internal skeleton.
Bilaterally symmetrical, triploblastic, and coelomic.
Presence of notochord, dorsal nerve cord, paired gill pouches.
Examples: Fish, amphibians, reptiles, birds, mammals.

Subdivisions of Vertebrates:

Pisces (Fish): Aquatic animals with scales, gills, and streamlined bodies.
Amphibia (Amphibians): Lack scales, possess mucus glands, and have a three-chambered heart.
Reptilia (Reptiles): Cold-blooded, scaled, breathe through lungs, and lay eggs.
Aves (Birds): Warm-blooded, feathered, lay eggs, and modified forelimbs for flight.
Mammalia (Mammals): Warm-blooded, produce live young ones, mammary glands for milk production.

7.6 Nomenclature Nomenclature

Carolus Linnaeus

Carolus Linnaeus is a Swedish botanist and physician who is also called the ‘Father of taxonomy‘.
He introduced the Binomial nomenclature and laid the ground rules which paved way for modern taxonomy.

Binomial Nomenclature

Binomial Nomenclature was introduced by Linnaeus as a method of naming organisms in taxonomy.
It consists of two parts.
The first part is the Genus name which is written in capital.
The second part is the species name, which is not capitalised.

NCERT Class 9 Science Chapter 7 DIVERSITY IN LIVING ORGANISMS Notes