What is Living?
Key Characteristics of Living Organisms
- Growth: All living organisms exhibit growth. In multicellular organisms,
growth is defined by an increase in mass and number of cells. Plants grow
continuously throughout life due to meristematic tissues, while in animals,
growth is limited to certain stages. However, non-living things can also grow,
like crystals, but their growth is extrinsic and not due to internal metabolism.
- Reproduction: This is a defining feature of living organisms. Organisms
reproduce to maintain their species. While humans and animals reproduce
sexually, simpler organisms like bacteria and fungi reproduce asexually.
Interestingly, mules, worker bees, and sterile hybrids don’t reproduce but are
still considered living. - Metabolism: Metabolic reactions are the hallmark of life. All the chemical
reactions taking place in the body — whether anabolic (building up) or
catabolic (breaking down) — are part of metabolism. Even isolated enzymes
in a lab exhibit metabolic reactions, but only cells are living because they
regulate these processes. - Cellular Organization: The cell is the fundamental unit of life. Whether
it’s a single-celled bacterium or a complex multicellular organism like a
human, cellular organization is crucial for sustaining life. - Consciousness: The ability to respond to external stimuli is another
feature of living organisms. Whether it’s plants responding to light
(phototropism) or animals reacting to sounds, consciousness is the definitive
property of living beings. Humans possess the highest level of self-
awareness. - Self-Regulation and Homeostasis: Living organisms maintain internal
conditions (like temperature and pH) irrespective of external environment,
showcasing self-regulation—a quality absent in non-living entities.
Biodiversity
Biodiversity refers to the variety and variability of life on Earth. It includes everything
from microorganisms to whales and from desert cacti to rainforest orchids. It is what
makes our planet unique and habitable.
Levels of Biodiversity
- Genetic Diversity: This refers to the variation of genes within species. For
instance, the genetic variation among different rice varieties or dog breeds
shows genetic diversity. - Species Diversity: It refers to the variety of species within a region. For
example, the Western Ghats in India are rich in species diversity. - Ecosystem Diversity: This includes various ecosystems such as forests,
grasslands, deserts, and wetlands. Each ecosystem harbours unique life
forms adapted to specific conditions.
Importance of Biodiversity
Ecological Stability: Diverse ecosystems are more resilient and
productive. They maintain ecological balance and support life.
Economic Value: Biodiversity provides food, medicine, and raw materials.
Nearly 25% of modern medicines are derived from tropical plants.
Cultural and Aesthetic Value: Nature and its diversity enrich our lives
and cultures.
Threats to Biodiversity
Habitat Destruction: Deforestation and urbanization lead to the loss of
habitat and species.
Pollution: Air, water, and soil pollution drastically affect biodiversity.
Climate Change: Rising temperatures and altered rainfall patterns affect
sensitive species.
Overexploitation: Overfishing and hunting endanger many species.
India’s Biodiversity
India is one of the 17 mega-diverse countries in the world. It hosts:
Over 45,000 species of plants
Nearly 90,000 species of animals
Hotspots like the Himalayas, Western Ghats, and Indo-Burma region
Need for Classification
Imagine walking into a library with no organization — books thrown around randomly.
That’s what the biological world would look like without classification. Classification
brings order to the chaotic diversity of life.
Why is Classification Needed?
- Ease of Study: Helps biologists identify, study, and understand organisms.
- Predictive Value: If you know characteristics of a group, you can infer
traits of unknown species within that group. - Communication: A universal classification system enables scientists from
different regions to communicate effectively.
Historical Evolution
Aristotle: One of the earliest attempts at classification. He divided
organisms into animals and plants, and further by habitat (air, water, land).
Linnaeus: The “Father of Taxonomy” introduced a formal system with
hierarchical categories and binomial nomenclature.
Modern Systems: Now include evolutionary relationships, genetic and
biochemical data.
Types of Classification
Artificial Classification: Based on one or two characteristics (e.g., flower
colour)
Natural Classification: Considers multiple characteristics like
morphology and anatomy
Phylogenetic Classification: Based on evolutionary relationships and
genetic data
Taxonomy and Systematics
Many students use taxonomy and systematics interchangeably, but they are not
exactly the same. Let’s understand how these two branches of biology are
connected yet distinct.
Taxonomy
Derived from Greek words ‘taxis’ (arrangement) and ‘nomos’ (law), taxonomy
involves:
Identification: Recognizing an organism as different from others
Classification: Grouping organisms based on similarities
Nomenclature: Naming organisms according to standard rules
Systematics
Systematics is a broader field that includes taxonomy but also studies:
Evolutionary relationships between organisms
Phylogeny: The evolutionary history and lineage of species
Modern Tools in Taxonomy
- Morphology: Study of form and structure
- Embryology: Developmental stages
- Cytology: Cell structure
- Molecular Biology: DNA and protein analysis
- Ecology: Habitat and interactions.
Previous Year NEET Questions (Up to 2024)
- Which of the following is not a defining feature of living organisms?
A. Growth
B. Reproduction
C. Cellular organization
D. Consciousness
Answer: A. Growth
(NEET 2021) - Binomial nomenclature was given by:
A. Aristotle
B. Darwin
C. Linnaeus
D. Whittaker
Answer: C. Linnaeus
(NEET 2019) - Which of the following includes all three levels of biodiversity?
A. Species, genetic, and biochemical
B. Genetic, species, and ecosystem
C. Genetic, population, and community
D. Species, ecosystem, and biome
Answer: B. Genetic, species, and ecosystem
(NEET 2020) - Which is the correct sequence of taxonomic categories?
A. Class → Order → Family → Genus
B. Order → Class → Family → Genus
C. Class → Family → Order → Genus
D. Family → Class → Order → Genus
Answer: A. Class → Order → Family → Genus
(NEET 2022)
