Organisms and Population Class 12 Notes PDF Download - NCERT Chapter 11 NEET 2027

NEET Dropper here! Dropping complete Chapter 11 Notes for all NEET 2027 Aspirants 🔥 

### *NEET 2027: Chapter 11 Organisms and Populations - Expanded Notes*  

_Class 12 Biology | NCERT Line-by-Line + PYQ + Diagrams_  

### *1. Organism & Its Environment*  

- *Ecology*: Term by Ernst Haeckel. Study of interactions among organisms & with abiotic environment.  

- *Hierarchy*: Organism → Population → Community → Ecosystem → Biome → Biosphere.  

- *Major Abiotic Factors*:  

    1. *Temperature*: Most ecologically relevant. Affects enzyme kinetics. Avg temp on land: 0-50°C.  

    2. *Water*: Life originated in water. Desert = <10cm rainfall. Productivity of ocean limited by light.  

    3. *Light*: Photosynthesis, foraging, migration, reproduction. UV = harmful.  

    4. *Soil*: Weathering of rocks. pH, minerals, topography decide vegetation.  

- *NEET Gold*: Stenothermal/Eurythermal, Stenohaline/Euryhaline. _Asked 4 times in NEET_.  

### *2. Responses to Abiotic Factors*

**Response** **How** **Example** **NEET Point**

**Regulate** Homeostasis by physiological/behavioral means Human 37°C, Birds, Mammals Only 1% animals are regulators

**Conform** No internal temp regulation 99% animals, All plants Heat loss/gain = simple & energy efficient

**Migrate** Move to less stressful habitat Siberian cranes → Bharatpur Keoladeo National Park, Rajasthan

**Suspend** Escape in time. Dormancy Bears = Hibernation, Snails = Aestivation Zooplankton = Diapause in suspended development

### *3. Adaptations - Morphological, Physiological, Behavioral*  

1. *Desert*: Kangaroo rat meets water need from internal fat oxidation. No drinking water ever.  

2. *Plants*: Opuntia = no leaves, photosynthetic stem. Thick cuticle, CAM, sunken stomata.  

3. *Cold*: Allen’s Rule = Shorter limbs/ears in cold mammals. Blubber in seals.  

4. *Altitude*: Body compensates low O₂ by ↑ RBC production, ↑ breathing rate, ↓ Hb binding affinity.  

5. *Behavioral*: Desert lizard basks in sun, moves to shade when hot.  

### *4. Population Attributes*  

- *Population*: Group of individuals of same species in a geographical area, sharing resources.  

- *Natality & Mortality*: Birth & Death rate. Decide population size.  

- *Sex Ratio*: 1000 males : X females.  

- *Age Pyramids*: 3 types  

    1. *Expanding*: Pre-reproductive > Reproductive. India.  

    2. *Stable*: Pre = Reproductive. Bell shaped.  

    3. *Declining*: Pre < Reproductive. Urn shaped. Japan.  

- *Population Density*: D = N/S. Measured by % cover, biomass, pugmarks, counting.  

### *5. Population Growth Models*  

1. *Exponential/J-shaped*: Unlimited resources. Food & space unlimited.

N_t = N_0e^{rt}

\frac{dN}{dt} = rN

  

   r = b - d. Darwin showed slow growing animal like elephant can reach enormous numbers.  

2. *Logistic/S-shaped*: Verhulst-Pearl Logistic Growth. Resources limited.

\frac{dN}{dt} = rN \left( \frac{K-N}{K} \right)

  

   K = Carrying capacity. Asymptote. _Most realistic model_.  

   Lag phase → Acceleration → Deceleration → Asymptote.  

### *6. Population Interactions* `NEET ka Sabse Fav Topic`

**Interaction** **A** **B** **Imp Examples for NEET**

**Mutualism** + + 1. Lichen: Algae + Fungi  2. Mycorrhiza: Glomus + Plants  3. Fig & Wasp  4. Pollination

**Competition** - - 1. Flamingoes vs Fish in S. American lakes  2. Abingdon tortoise extinct due to goats

**Predation** + - 1. Tiger-Deer  2. Sparrow-Seed  3. Prickly pear cactus controlled by moth

**Parasitism** + - 1. Ectoparasite: Lice, Ticks  2. Endoparasite: Plasmodium, Tapeworm  3. Brood: Cuckoo-Crow

**Commensalism** + 0 1. Orchid on Mango branch  2. Barnacles on Whale  3. Cattle Egret & Grazing cattle

**Amensalism** - 0 1. Penicillium kills bacteria  2. Black walnut secretes juglone

*NEET Traps + PYQ Gold:*  

1. *Gause’s Exclusion Principle*: 2 species cannot coexist if resources same. _Paramecium expt_.  

2. *Resource Partitioning*: 5 warbler species on same tree avoid competition by foraging differently.  

3. *Co-evolution*: Fig has only 1 wasp pollinator. Both cannot live without each other.  

4. *Predator Functions*: 1. Keeps prey population under control  2. Helps in species diversity.  

5. *Plant Defenses*: Thorns = Acacia, Cactus. Calotropis = Cardiac glycosides. Nicotine, Caffeine, Quinine.  

6. *Pseudocopulation*: Mediterranean Orchid Ophrys employs sexual deceit. Petal = female bee.  

### *7. PYQ Hotspots 2020-2025*  

1. *Amensalism example* → Penicillium & Staphylococci = NEET 2024.  

2. *Expanding age pyramid* → Triangular shape = NEET 2023.  

3. *Mycorrhiza* → Absorb phosphorus from soil = NEET 2022.  

4. *Allen’s Rule* → Mammals from colder climates = shorter ears/limbs = NEET 2021.  

5. *S-shaped curve* → Logistic growth = NEET 2020.  

*Ch-11 se 3Q pakka*: 1Q Growth curve, 1Q Interactions table, 1Q Adaptations.