Reviewing Class 9 Science Notes and Exploration Chapter 12 Patterns in Life Diversity and Classification Class 9 Notes regularly helps in retaining important facts.
Class 9 Science Chapter 12 Patterns in Life Diversity and Classification Notes
Class 9 Science Exploration Chapter 12 Notes
Class 9 Science Chapter 12 Notes – Class 9 Patterns in Life Diversity and Classification
→ Biodiversity: It refers to the wide variety of living organisms found on Earth, from microscopic organisms to large plants and animals. It includes life in different habitats like forests, oceans, and mountains.
→ Biodiversity is essential for maintaining balance in nature. Every organism plays a role in keeping ecosystems stable and functioning properly.
→ Humans depend on biodiversity for food, shelter, medicines, and livelihoods. Farmers conserve different crop varieties to ensure better yield and survival.
→ Classification: Classification is the process of grouping organisms based on their similarities and differences, as well as their evolutionary relationships.
→ Need for Classification: Classification helps scientists understand how organisms are related, how they function, and how this knowledge can be used in conservation and sustainable practices.
→ Endemic species: Endemic species are organisms found only in a specific region. Examples: Nilgiritahr, Lion-tailed macaque, Indian variety of the pitcher plant-Nepenthes khasiczna, and Neelakurinji are found only in India.
→ Hotspots: Hotspots are regions rich in biodiversity but under threat. Examples: Western Ghats, Himalayas, North East India, Nicobar Islands.
→ Evolution: It is the gradual change in organisms leading to new species.
→ Evolution of Biodiversity: Biodiversity developed over millions of years through evolution. Small variations helped organisms survive better, and useful traits were passed to future generations, forming new species.
→ Criteria for Classification: Organisms are classified based on features like structure, nutrition, and cell type. These help in grouping organisms scientifically.
- External features: shape, size, body structure.
- Cell type: prokaryotic or eukaryotic.
- Organisation: unicellular or multicellular.
- Mode of nutrition: autotrophic or heterotrophic.
- Cell wall: presence or absence.
- Reproduction: asexual and/or sexual.
- Ecological role.
- Genetic similarity.
→ Biological Classification: It is the scientific system of grouping living organisms based on their similarities and differences in features such as external structure, internal organisation, and cellular structure.
→ Aristotle’s Classification: Around the 4th century BCE, Aristotle classified animals based on their habitat (land, water, air) and external features. This system had limitations as it relied only on visible characteristics.
→ Two-kingdom classification system: In the 18th century, scientists divided all living organisms into two kingdoms – Plantae and Animalia.
- Kingdom Plantae: Includes organisms that are non-motile (do not move) and can make their own food through photosynthesis.
- Kingdom Animalia: Includes organisms that move from place to place and depend on other organisms for food. This system created confusion for organisms like Amoeba, Paramecium and bacteria, as they did not fit clearly into either group.
→ Three-kingdom system (Protista added): To overcome the two-kingdom classification system limitation, a new kingdom Protista was introduced to include unicellular microscopic organisms such as Amoeba and Paramecium, which show both plant-like and animal-like features.
→ Four-kingdom system (Monera separated):
With the improvement of microscopes, scientists observed that bacteria do not have a true nucleus, unlike Amoeba. Therefore, bacteria were placed in a separate kingdom called Monera, leading to a four-kingdom classification system.
→ Five-kingdom classification system: This system includes Monera, Protista, Fungi, Plantae, and Aninialia, providing a more accurate way to classify living organisms.
→ Basis of Five Kingdom Classification:
- Cell type: prokaryotic or eukaryotic.
- Level of organisation: unicellular or multicellular.
- Cell structure: presence or absence of a cell wall.
- Mode of nutrition: autotrophic or heterotrophic.
→ Kingdom Monera: It includes unicellular prokaryotic organisms that lack a true nucleus and are found in all environments, including extreme ones.
→ It includes both useful and harmful organisms, with examples like Lactobacillus and Rhizobium being beneficial, while some members act as pathogens. Cyanobacteria in this kingdom produce oxygen, and some monerans also play an important role in decomposition and biogas production.
→ Kingdom Protista: It includes unicellular eukaryotic organisms that may or may not have a cell wall. These organisms are mostly found in water or moist environments and are microscopic in nature. Some protists are autotrophic, while others are heterotrophic. They play an important role in aquatic food chains, as some produce oxygen while others serve as food for small organisms. They also help in decomposition and nutrient cycling.
→ Kingdom Fungi: Kingdom Fungi consists of mostly multicellular heterotrophic organisms that have chitin cell walls, although some, like yeast, is unicellular. They are saprophytes that feed on dead and decaying matter and play a key role in decomposing organic waste and recycling nutrients.
→ Some fungi are symbiotic, while others are parasitic and cause diseases. Examples include Yeast, Aspergillus, Penicillium, and mushrooms. Fungi reproduce both sexually and asexually, commonly through spores, and grow best in warm and moist conditions.
→ Kingdom Plantae: It includes multicellular, autotrophic eukaryotic organisms that perform photosynthesis. Their cells have a rigid cell wall made of cellulose that provide strength and protection. These organisms prepare their own food through photosynthesis, act as primary producers in ecosystems, and play a vital role in oxygen production and food chains.
→ They are classified into five major groups: Thallophyta, Bryophyta, Pteridophyta, Gymnosperms, and Angiosperms.
→ Thallophyta (Algae)-Primitive plants:
Thallophyta includes simple and primitive plants with an undifferentiated body called a thallus, lacking true roots, stems, or leaves. They are mostly found in aquatic or moist habitats, absorb nutrients directly from their surroundings, and an example is Spirogyra.
→ Bryophyta – Amphibians of Plant Kingdom:
Bryophyta includes small, non-vascular plants that are found in damp and shady places and require water for reproduction, which is why they are called the “amphibians of the plant kingdom.” They show the first adaptation towards land and have simple root-like structures called rhizoids instead of true roots. Their body is slightly differentiated into stem-like and leaf-like parts, and examples include moss and Marchantia.
→ Pteridophyta – First Vascular Plants:
Pteridophyta includes seedless vascular plants that have true roots, stems, and leaves, along with vascular tissues such as xylem for water transport and phloem for food transport. They are more advanced and show adaptation towards land life, but still require water for reproduction and do not produce seeds. An example of pteridophytes is a fern.
→ Gymnosperms — Naked Seed Plants:
Gymnosperms are seed-producing plants with naked seeds that are not enclosed in fruits and are found in cones. They do not require water for fertilisation and are well adapted to dry and cold conditions. Their needle-like leaves help reduce water loss, and examples include pines and cycads.
→ Angiosperms – Flowering Plants: Angiosperms are the most advanced and diverse group of plants that produce flowers and fruits, with their seeds enclosed inside fruits. Flowers help in reproduction while fruits assist in seed dispersal, making them highly successful and widespread across almost all habitats on Earth. They are divided into monocots and dicots.
→ Kingdom Animalia: Kingdom Animalia includes multicellular, heterotrophic eukaryotic organisms that lack a cell wall and depend on other organisms for food. Most animals show locomotion, quick response to stimuli, and coordinated behaviour, which help them find food, escape predators, and interact with their environment.
→ Basis of Classification in Animals: The basis of classification in animals is the presence or absence of a notochord, which is a flexible rod- like structure that provides support to the body.
→ Animals without a notochord are called non-chordates (invertebrates), while animals with a notochord are called chordates. Chordates are further divided into protochordates and vertebrates.
→ Invertebrates- Animals without a notochord:
Invertebrates (non-chordates) are animals that do not have a notochord. They show a wide range of body complexity, from simple to highly advanced forms, and represent gradual evolution in body organisation.
→ Porifera – Simplest Animals: Porifera (pore bearers) are the simplest multicellular animals that lack true tissues and organs and have a body with pores through which water flows, bringing food and oxygen. They are mostly aquatic and sessile (fixed), and water flow helps in nutrition and respiration. Examples include sponges, and they cannot survive on land due to their dependence on water.
→ Cnidaria: Cnidaria are animals with tissue-level of organisation and stinging cells, and they use tentacles for feeding and defence. They have a single opening that functions as both mouth and anus for food intake and waste removal. Examples include Hydra, jellyfish, and corals.
→ Platyhelminthes — Flatworms: Platyhelminthes are flat-bodied animals with bilateral symmetry, meaning their body can be divided into two halves. They are dorsoventrally flattened and show directional movement. Many are parasitic and have hooks and suckers for attachment.
→ Nematoda – Roundworms: Roundworms have elongated, cylindrical bodies that allow efficient movement in soil, water, or inside hosts. They show a more advanced body plan with two openings (mouth and anus) and organ-system level of organisation. Separate sexes are usually present, showing further development.
→ Annelida: Annelida are segmented worms with organ-system level of organisation and a true body cavity. Their body is divided into segments, which allows better movement and flexibility. They show efficient movement and have a well- developed nervous system. Examples include earthworms.
→ Arthropoda: This group includes insects, crabs, and spiders. They have jointed appendages and a hard external skeleton (exoskeleton) that provides protection, prevents water loss, and supports movement. Their segmented body parts are specialised for different functions, allowing them to survive in diverse environments.
→ Mollusca: Mollusca are soft-bodied animals, often protected by a hard shell in many species, and show organ-system level of organisation. Their body is divided into a head, a muscular foot, and a hump. Examples include snails, octopus, and squid.
→ Echinodermata – Spiny Skin Animals:
Echinodermata are marine animals with spiny skin and an internal skeleton made of calcium carbonate, and they lack a notochord. Examples include starfish and sea urchins.
→ Protochordates: Protochordates are primitive chordates that have a notochord in at least one stage of their life and show early features of chordates. They have a basic internal support structure, and an example is Amphioxus.
→ Vertebrates: Vertebrates are advanced animals with a backbone (vertebral column) that protects the spinal cord and supports the body. They have well-developed organ systems and show complex behaviour and coordination. Vertebrates are divided into fish, amphibians, reptiles, birds, and mammals based on habitat, reproduction, and body covering.
→ Adaptations as Outcomes of Structural Change: The diversity in animals is a result of structural changes over long periods of time. Different features help organisms survive in their environments, such as fins and gills in fish for aquatic life, feathers and hollow bones in birds for flight, fat storage in camels for desert survival, and thick fur in polar bears for cold regions. In mammals, the presence of mammary glands helps in nourishing and protecting the young ones, increasing their chances of survival.
→ Hierarchical Classification: Classification of organisms follows a step-by-step system from broader groups to more specific ones. As we move to lower levels, organisms share more similarities. The main levels are Kingdom → Phylum → Class → Order → Family → Genus → Species.
→ Binomial Nomenclature: Scientific naming, or binomial nomenclature, is a universal system introduced by Carolus Linnaeus to avoid confusion caused by different local names for the same organism. In this system, each organism is given a scientific name made of two parts: the genus and the species. For example, the tiger is named Panthera tigris, where Panthera is the genus and tigris is the species. A species includes organisms that can interbreed and produce offspring.
→ Rules for Writing Scientific Names: The scientific names are written following specific rules.
- Each name has two parts: genus and species.
- The genus name begins with a capital letter and is written first, followed by the species name, which is written in lowercase letters.
- When printed, the scientific name is written in italics and underlined when handwritten.
→ Fossils as Evidence: Fossils are preserved remains or traces of ancient organisms found in layers of rocks, sand, or mud. They provide evidence of how life has changed over time and act as natural records of past life. Older rock layers contain simpler organisms, while newer layers show more complex organisms. Fossils help scientists understand evolution and study past life forms.
→ Biodiversity Under Threat: Biodiversity is essential for maintaining ecological balance, but it is under threat due to human activities causing its rapid decline. Activities such as pollution, deforestation, overuse of resources, and climate change are harming biodiversity. The loss of one species can affect many others, leading to an imbalance in ecosystems and possible extinction.
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