The Living World - NEET Notes
1. Characteristics of Living Organisms
Living organisms exhibit the following fundamental characteristics:
1.1 Growth
Unicellular organisms: Growth occurs by an increase in cell size and
number.
Multicellular organisms: Growth occurs by cell division.
Non-living objects: Growth by external accumulation (e.g.,
mountains, crystals) is not considered biological growth.
1.2 Reproduction
Sexual reproduction: Involves the fusion of gametes (e.g., humans,
flowering plants).
Asexual reproduction: Without gamete fusion (e.g., binary fission in
Amoeba, fragmentation in Spirogyra).
Some organisms (e.g., mules, sterile worker bees) do not reproduce
but are still living.
1.3 Metabolism
Sum of all biochemical reactions occurring in an organism.
Anabolism (synthesis of complex molecules, e.g., photosynthesis) and
catabolism (breakdown of molecules, e.g., respiration).
Metabolism is a defining feature of living organisms.
1.4 Consciousness and Response to Stimuli
Ability to sense and respond to external and internal stimuli.
Includes phototropism in plants, reflex action in animals, and
homeostasis.
Consciousness is considered the defining property of living beings.
2. Diversity in the Living World
Around 1.7-1.8 million species identified.
Taxonomy helps in classification and identification.
Biodiversity: The variety of life forms in different habitats.
2.1 Need for Classification
Organizes living organisms systematically.
Helps in the study of relationships among organisms.
1. Characteristics of Living Organisms
Living organisms exhibit the following fundamental characteristics:
1.1 Growth
Unicellular organisms: Growth occurs by an increase in cell size and
number.
Multicellular organisms: Growth occurs by cell division.
Non-living objects: Growth by external accumulation (e.g.,
mountains, crystals) is not considered biological growth.
1.2 Reproduction
Sexual reproduction: Involves the fusion of gametes (e.g., humans,
flowering plants).
Asexual reproduction: Without gamete fusion (e.g., binary fission in
Amoeba, fragmentation in Spirogyra).
Some organisms (e.g., mules, sterile worker bees) do not reproduce
but are still living.
1.3 Metabolism
Sum of all biochemical reactions occurring in an organism.
Anabolism (synthesis of complex molecules, e.g., photosynthesis) and
catabolism (breakdown of molecules, e.g., respiration).
Metabolism is a defining feature of living organisms.
1.4 Consciousness and Response to Stimuli
Ability to sense and respond to external and internal stimuli.
Includes phototropism in plants, reflex action in animals, and
homeostasis.
Consciousness is considered the defining property of living beings.
2. Diversity in the Living World
Around 1.7-1.8 million species identified.
Taxonomy helps in classification and identification.
Biodiversity: The variety of life forms in different habitats.
2.1 Need for Classification
Organizes living organisms systematically.
Helps in the study of relationships among organisms.
