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
"All living phenomena are due to underlying interactions. 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: Just as the properties of cellular organelles are not in the molecules but arise from their interaction, life is an emergent property at a higher level of organization.
Self-Consciousness: All living organisms handle chemicals entering their bodies. All organisms are aware of their surroundings. However, only human beings are aware of themselves (Self-consciousness).
3. Twin Characters & Exceptions
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).
Modes of Asexual Reproduction:
Budding Yeast, Hydra
True Regeneration Planaria (flatworm)
Fragmentation Fungi, Filamentous Algae, Protonema
Spores Fungi
4. Biodiversity & Taxonomy
The Number: The number of species that are known and described ranges between 1.7 - 1.8 Million.
Taxonomy Process Order:
Characterisation
Identification
Classification
Nomenclature
Systematics: Derived from Latin word 'systema' meaning systematic arrangement. It includes identification, nomenclature, classification AND evolutionary relationships.