In biology, we distinguish between Characteristic Features (found in living things but may have exceptions) and Defining Properties (present in ALL living organisms without exception, absent in non-living).
❌ Not Defining
Growth: Mountains and sand mounds can grow (by accumulation).
Reproduction: Mules, sterile worker bees, and infertile human couples are living but cannot reproduce.
✅ Defining Properties
Metabolism: No non-living object exhibits metabolism.
Cellular Organization: The defining property of all life forms.
Consciousness: Response to external stimuli.
NCERT EXCERPT
2. Vital Text Highlights
"Properties of tissues are not present in the constituent cells but arise as a result of interactions among the constituent cells."
The Concept of Emergence: Life is an emergent property. Just as organelle properties arise from molecular interactions, tissue properties arise from cell interactions.
Self-Consciousness: All living organisms have consciousness (response to surroundings). However, only human beings are aware of themselves (Self-consciousness).
3. Twin Characters & Reproduction
Growth: Defined by increase in mass and increase in number of individuals.
Unicellular: Growth and Reproduction are Mutually Inclusive (same event).
Multicellular: Growth and Reproduction are Mutually Exclusive (different events).
Budding Yeast, Hydra
True Regeneration Planaria (flatworm)
Fragmentation Fungi, Algae, Protonema
Spores Fungi
4. Taxonomy & Nomenclature Rules
Biodiversity: 1.7 - 1.8 Million described species (Robert May estimates 7 million).
Binomial Nomenclature (Carolus Linnaeus):
Language: Latin (written in Italics).
Format: Genus (Capitalized) + species (small).
Author Citation: Abbreviated at the end (e.g., Mangifera indica Linn.).
🦁 Tautonyms Genus and species name are identical.
Accepted in Zoology (ICZN).
Ex: Gorilla gorilla, Naja naja. NOT accepted in Botany.
🥦 Trinomials Three word names (includes variety/sub-species).
Ex: Homo sapiens sapiens
Ex: Brassica oleracea var. botrytis (Cauliflower).
5. The Taxonomic Hierarchy
The Rule of Similarity: As we go HIGHER (Species → Kingdom), common characters DECREASE. As we go LOWER (Kingdom → Species), common characters INCREASE.