Living organisms share certain distinctive features that differentiate them from non-living entities. These characteristics are:
Definition: Increase in mass and number of cells.
Details:
Growth in living organisms occurs due to cell division (intrinsic growth).
In unicellular organisms, growth and reproduction are synonymous as cell division increases both size and number.
In multicellular organisms, growth involves cell division, differentiation, and organ formation.
Non-living objects (e.g., mountains, crystals) may grow extrinsically (by accumulation), but this is not true growth.
Example: A seed grows into a plant; a human baby grows into an adult.
Definition: The process by which organisms produce offspring.
Details:
Reproduction can be sexual (involving gametes) or asexual (e.g., budding, fission).
Essential for species survival, though not all organisms reproduce (e.g., sterile hybrids like mules).
Unicellular organisms reproduce by cell division (e.g., binary fission in Amoeba).
Fungi, algae, and plants may reproduce asexually via spores or fragmentation.
Example: Bacteria divide by binary fission; plants propagate through cuttings.
Definition: The sum of all chemical reactions occurring in a living organism.
Details:
Includes anabolism (building up, e.g., photosynthesis) and catabolism (breaking down, e.g., respiration).
Metabolism is absent in non-living things, making it a defining feature of life.
Occurs in all living cells, from unicellular bacteria to complex humans.
Example: Glucose breakdown during cellular respiration to produce energy.
Definition: The presence of a definite cellular structure.
Details:
All living organisms are made of cells (unicellular or multicellular).
Cells contain organelles that perform specific functions (e.g., nucleus for genetic material, mitochondria for energy).
Example: Prokaryotic cells (bacteria) and eukaryotic cells (plants, animals).
Definition: The ability to respond to environmental stimuli.
Details:
Includes awareness and response to external factors like light, temperature, or touch.
Plants show responses (e.g., phototropism—growth toward light).
Animals exhibit complex behaviors due to nervous systems.
Example: Mimosa pudica (touch-me-not plant) folds leaves when touched; humans respond to pain.
Biodiversity: The variety of life forms on Earth, including plants, animals, microorganisms, and their ecosystems.
Details:
Earth hosts millions of species (estimated 1.7–100 million, with ~1.7 million identified).
Biodiversity varies across regions (e.g., tropical forests have higher diversity than deserts).
Studied through taxonomy, which involves identification, nomenclature, and classification.
Example: India, a megadiverse country, has diverse flora (e.g., orchids) and fauna (e.g., tigers).
Taxonomy: The science of identifying, naming, and classifying organisms.
Systematics: The study of evolutionary relationships among organisms.
Details:
Taxonomy includes:
Identification: Determining if an organism belongs to a known group.
Nomenclature: Naming organisms using standardized rules.
Classification: Grouping organisms based on shared characteristics.
Systematics considers evolutionary history and phylogenetic relationships.
Organisms are grouped into a hierarchy of categories called taxa.
Levels of Hierarchy (in descending order):
Kingdom → Phylum (or Division in plants) → Class → Order → Family → Genus → Species.
Example:
Human: Kingdom: Animalia, Phylum: Chordata, Class: Mammalia, Order: Primates, Family: Hominidae, Genus: Homo, Species: sapiens.
Mango: Kingdom: Plantae, Division: Angiospermae, Class: Dicotyledonae, Order: Sapindales, Family: Anacardiaceae, Genus: Mangifera, Species: indica.
Definition: A system of naming organisms with two names—genus and species.
Rules (by Carolus Linnaeus):
Genus name is capitalized; species name is lowercase.
Names are italicized (or underlined when handwritten).
Names are usually Latin or Latinized.
Example: Panthera leo (lion), Homo sapiens (human).
Tools and techniques used to study and classify organisms:
Herbarium: A collection of preserved plant specimens, dried and mounted on sheets.
Drawing Instructions for Herbarium Sheet:
Draw a rectangular sheet (A4 size, ~29 cm × 21 cm).
Place a dried plant specimen (e.g., a leaf or flower) in the center.
Add a label in the bottom-right corner (5 cm × 3 cm) with details: scientific name, family, date of collection, location, and collector’s name.
Show mounting tape or glue dots at corners to secure the specimen.
Label parts: “Herbarium Sheet,” “Specimen,” and “Label.”
Botanical Gardens: Collections of living plants for study and conservation.
Example: Indian Botanical Garden, Howrah.
Museums: Collections of preserved animal specimens (e.g., skeletons, stuffed animals).
Zoological Parks: Places where animals are kept in protected environments for study.
Key: A tool to identify organisms based on contrasting characters (e.g., dichotomous key).
Example: A key to differentiate insects based on wings (present/absent).
Monograph: Detailed study of a single taxon.
Flora, Fauna, Manuals: Books describing plants (flora), animals (fauna), or both in a region.
Description: A pyramid showing the taxonomic hierarchy from Kingdom (broadest) to Species (most specific).
Drawing Instructions:
Draw a tall triangle divided into 7 horizontal sections (like a layered cake).
Label each section from top to bottom: Kingdom, Phylum/Division, Class, Order, Family, Genus, Species.
On the right side, write an example (e.g., for humans: Animalia, Chordata, Mammalia, Primates, Hominidae, Homo, sapiens).
Add arrows pointing downward to show the hierarchy (broad to specific).
Title the diagram: “Taxonomic Hierarchy.”
Significance: Illustrates how organisms are organized from general to specific categories.
Here are key questions frequently asked in Class 11 CBSE exams (based on NCERT):
Define growth and metabolism. How do they differ in living and non-living things? (3 marks)
Answer: Growth is the increase in mass/number of cells (intrinsic in living; extrinsic in non-living). Metabolism is the sum of chemical reactions in living organisms (absent in non-living).
Explain binomial nomenclature with its rules and two examples. (5 marks)
Answer: Binomial nomenclature is a two-name system (genus + species). Rules: genus capitalized, species lowercase, italicized, Latinized. Examples: Homo sapiens, Mangifera indica.
What is taxonomic hierarchy? List the levels with an example for a plant and an animal. (5 marks)
Answer: Taxonomic hierarchy is the arrangement of organisms into taxa. Levels: Kingdom, Phylum/Division, Class, Order, Family, Genus, Species. Example: Human (Animalia, Chordata, Mammalia, Primates, Hominidae, Homo, sapiens); Mango (Plantae, Angiospermae, Dicotyledonae, Sapindales, Anacardiaceae, Mangifera, indica).
Differentiate between herbarium and botanical garden. (3 marks)
Answer: Herbarium: dried, preserved plant specimens on sheets for reference. Botanical garden: living plant collections for study and conservation.
What are taxonomic aids? Name any four and explain their role. (5 marks)
Answer: Taxonomic aids help study/classify organisms. Examples: Herbarium (preserved plants), Zoological Parks (live animals), Museums (preserved animals), Keys (identification tools).
Why is biodiversity important? Give an example of a biodiversity-rich region in India. (3 marks)
Answer: Biodiversity supports ecosystems, resources, and scientific study. Example: Western Ghats.
What is consciousness in living organisms? Give one example for a plant and an animal. (2 marks)
Answer: Consciousness is the ability to respond to stimuli. Example: Plant—phototropism in sunflowers; Animal—reflex action in humans.
Living vs Non-Living: Growth, reproduction, metabolism, cellular organization, and consciousness are unique to living organisms.
Biodiversity: Essential for ecological balance and human survival.
Taxonomy: Organizes life forms systematically for study.
Binomial Nomenclature: Universal naming system for clarity and consistency.
Taxonomic Aids: Practical tools for identification and classification.
