Photosynthesis in Higher Plants Complete NCERT Notes, Important Questions & PYQs for NEET 2026

Photosynthesis is one of the most important chapters in Class 11 Biology and carries significant weightage in NEET. Every year, multiple questions are asked directly from NCERT concepts, diagrams, and terminology. If you master this chapter, you can easily secure valuable marks in Biology.

What is Photosynthesis?

Photosynthesis is the process by which green plants prepare their own food using sunlight, carbon dioxide, and water.

Chemical Equation

6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O

Photosynthesis occurs in the chloroplasts of green plant cells.

Why is Photosynthesis Important?

Primary source of food on Earth

Releases oxygen into the atmosphere

Maintains carbon dioxide balance

Converts solar energy into chemical energy

Supports all ecosystems

Factors Necessary for Photosynthesis

External Factors

Light

Carbon dioxide

Water

Temperature

Internal Factors

Chlorophyll content

Leaf anatomy

Protoplasmic condition

Enzyme activity

Site of Photosynthesis

Photosynthesis occurs in the chloroplast.

Structure of Chloroplast

Outer membrane

Inner membrane

Stroma

Grana

Thylakoids

NCERT Point

Grana contain chlorophyll pigments and are the site of light reactions.

Photosynthetic Pigments

Chlorophyll a

Primary pigment

Blue-green color

Reaction center pigment

Chlorophyll b

Accessory pigment

Yellow-green color

Carotenoids

Carotenes

Xanthophylls

NCERT Important Line

Chlorophyll a is the chief pigment involved in photosynthesis.

Light Reaction

Occurs in the thylakoid membrane.

Major Events

Absorption of light energy

Splitting of water (Photolysis)

Oxygen release

ATP formation

NADPH formation

Photolysis of Water

2H₂O → 4H⁺ + 4e⁻ + O₂

Products

ATP

NADPH

Oxygen

Photosystems

Photosystem II (PS II)

Reaction center P680

First photosystem to function

Photosystem I (PS I)

Reaction center P700

Produces NADPH

NEET Favorite Question

Which photosystem participates first in light reaction?

Answer: Photosystem II

Electron Transport System

Electrons move through:

PS II → PQ → Cyt b6f → PC → PS I → Fd → NADP

This movement generates ATP.

Cyclic and Non-Cyclic Photophosphorylation

Feature

Cyclic

Non-Cyclic

Photosystem

PS I

PS I & PS II

ATP

Produced

Produced

NADPH

Not produced

Produced

Oxygen

Not released

Released

Dark Reaction (Calvin Cycle)

Occurs in the stroma.

Three Phases

Carboxylation

Reduction

Regeneration

Key Enzyme

RuBisCO

RuBisCO is the most abundant enzyme on Earth.

First Stable Product

3-Phosphoglyceric Acid (3-PGA)

C3 Plants

Examples:

Wheat

Rice

Sunflower

Characteristics

First product: 3-PGA

Calvin cycle only

Less efficient under high temperature

C4 Plants

Examples:

Maize

Sugarcane

Sorghum

Characteristics

First product: Oxaloacetic Acid (OAA)

Kranz anatomy present

Higher photosynthetic efficiency

NCERT Important Line

Kranz anatomy is a characteristic feature of C4 plants.

Photorespiration

Occurs when RuBisCO acts as oxygenase.

Consequences

Loss of fixed carbon

Energy wastage

Reduced productivity

Absent In

C4 plants

C3 vs C4 Plants

Feature

C3

C4

First Product

3-PGA

OAA

Kranz Anatomy

Absent

Present

Photorespiration

High

Negligible

Efficiency

Lower

Higher

Most Important NCERT Points

Remember These

Chlorophyll a is the chief pigment.

PS II functions before PS I.

RuBisCO is the most abundant enzyme.

ATP and NADPH are produced during light reaction.

Calvin cycle occurs in the stroma.

Kranz anatomy is present in C4 plants.

Photorespiration reduces plant productivity.

NEET PYQ-Based Questions

Q1. Which pigment acts as the reaction center in Photosystem I?

A. Chlorophyll b

B. P700

C. P680

D. Carotene

Answer: B. P700

Q2. First stable product of Calvin cycle is:

A. OAA

B. RuBP

C. PGA

D. PEP

Answer: C. PGA

Q3. Kranz anatomy is found in:

A. Wheat

B. Rice

C. Maize

D. Sunflower

Answer: C. Maize

Q4. Most abundant enzyme on Earth is:

A. DNA Polymerase

B. ATP Synthase

C. RuBisCO

D. Pepsin

Answer: C. RuBisCO

Final Revision Tips for NEET

Read every NCERT line carefully.

Memorize diagrams of chloroplast and Calvin cycle.

Practice previous year questions.

Focus on C3 vs C4 differences.

Revise photosystems and photophosphorylation repeatedly.

Conclusion

Photosynthesis in Higher Plants is one of the highest-scoring chapters in NEET Biology. Most questions are directly based on NCERT concepts, diagrams, and terminology. A strong understanding of light reaction, Calvin cycle, C3 plants, C4 plants, and photorespiration can help you secure easy marks in the exam.

Respiration in Plants Complete NCERT Notes, Important Questions & PYQs for NEET 2026

Respiration in Plants is one of the most important chapters for NEET Biology. Questions are frequently asked from glycolysis, Krebs cycle, electron transport system (ETS), respiratory quotient (RQ), and ATP production. Most NEET questions are directly based on NCERT concepts.

What is Respiration?

Respiration is the process of oxidation of food molecules to release energy in the form of ATP.

General Equation

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP)

Why is Respiration Important?

Releases energy for life processes

Supports growth and development

Powers active transport

Essential for cell division

Maintains metabolism

Types of Respiration

1. Aerobic Respiration

Occurs in presence of oxygen

Complete oxidation of glucose

Produces maximum ATP

2. Anaerobic Respiration

Occurs without oxygen

Partial oxidation of glucose

Produces less ATP

Example

Yeast: Glucose → Ethanol + CO₂ + Energy

Glycolysis

Definition

Breakdown of glucose into pyruvate.

Site

Cytoplasm

Important Facts

First step of respiration

Occurs in all living cells

Does not require oxygen

End Products

2 Pyruvate

2 ATP (Net gain)

2 NADH

NCERT Point

Glycolysis is also known as EMP pathway.

Fate of Pyruvate

Pyruvate can undergo three pathways:

1. Lactic Acid Fermentation

Muscle cells

Pyruvate → Lactic Acid

2. Alcoholic Fermentation

Yeast

Pyruvate → Ethanol + CO₂

3. Aerobic Respiration

Pyruvate enters mitochondria.

Krebs Cycle (Citric Acid Cycle)

Site

Mitochondrial Matrix

Starting Molecule

Acetyl CoA

Products from One Acetyl CoA

3 NADH

1 FADH₂

1 ATP

2 CO₂

NCERT Important Line

Krebs cycle was discovered by Hans Krebs.

Electron Transport System (ETS)

Site

Inner mitochondrial membrane

Components

Complex I

Complex II

Complex III

Complex IV

Function

Transfers electrons and generates ATP.

Final Electron Acceptor

Oxygen

Product Formed

Water

Oxidative Phosphorylation

ATP formation during ETS is called oxidative phosphorylation.

ATP Synthase

Responsible for ATP production.

NCERT Point

ATP synthase is located on the inner mitochondrial membrane.

ATP Yield

Aerobic Respiration

One glucose molecule produces approximately:

36–38 ATP

Anaerobic Respiration

Only:

2 ATP

Amphibolic Pathway

Respiration is called an amphibolic pathway because it participates in:

Catabolism

Anabolism

NEET Favorite Concept

Why is respiration called amphibolic?

Because it acts in both breakdown and synthesis pathways.

Respiratory Quotient (RQ)

Formula

RQ = CO₂ Released / O₂ Consumed

Carbohydrates

RQ = 1

Fats

RQ < 1

Organic Acids

RQ > 1

Mitochondria: Powerhouse of Cell

Structure

Outer membrane

Inner membrane

Cristae

Matrix

Function

ATP production

NCERT Point

Cristae increase surface area for ATP generation.

Aerobic vs Anaerobic Respiration

Feature

Aerobic

Anaerobic

Oxygen

Required

Not Required

ATP Yield

36–38

2

Oxidation

Complete

Partial

End Products

CO₂ + H₂O

Ethanol/Lactic Acid

Most Important NCERT Points

✔ Glycolysis occurs in cytoplasm.

✔ Krebs cycle occurs in mitochondrial matrix.

✔ ETS occurs in inner mitochondrial membrane.

✔ Oxygen is final electron acceptor.

✔ ATP synthase produces ATP.

✔ Respiration is amphibolic.

✔ RQ for carbohydrates is 1.

NEET PYQ Practice Questions

Q1. Glycolysis occurs in:

A. Nucleus

B. Cytoplasm

C. Mitochondria

D. Ribosome

✅ Answer: B. Cytoplasm

Q2. Final electron acceptor in ETS is:

A. Carbon dioxide

B. NADH

C. Oxygen

D. FAD

✅ Answer: C. Oxygen

Q3. Krebs cycle occurs in:

A. Cytoplasm

B. Chloroplast

C. Mitochondrial Matrix

D. Nucleus

✅ Answer: C. Mitochondrial Matrix

Q4. Respiratory Quotient of carbohydrates is:

A. 0.7

B. 0.9

C. 1

D. 1.5

✅ Answer: C. 1

Q5. ATP synthase is located in:

A. Outer membrane

B. Ribosome

C. Inner mitochondrial membrane

D. Matrix

✅ Answer: C. Inner mitochondrial membrane

Final Revision Strategy for NEET

Focus On

Glycolysis steps

Krebs cycle products

ATP calculation

ETS diagram

Respiratory Quotient

Aerobic vs Anaerobic comparison

Conclusion

Respiration in Plants is a high-yield NEET chapter that often contributes direct questions from NCERT. Master glycolysis, Krebs cycle, ETS, ATP production, and RQ concepts to secure easy marks in Biology.

Read NCERT line by line, revise diagrams, and solve PYQs regularly for maximum NEET success. 🚀

Plant Kingdom Complete NCERT Notes, Important Questions & PYQs for NEET 2026

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The Plant Kingdom chapter is one of the most important chapters in Class 11 Biology for NEET aspirants. Questions are frequently asked from algae, bryophytes, pteridophytes, gymnosperms, angiosperms, life cycles, and NCERT examples.

Introduction to Plant Kingdom

Plants are multicellular, eukaryotic organisms possessing chlorophyll and performing photosynthesis.

Basis of Classification

Plants are classified based on:

Body differentiation

Vascular tissues

Seed formation

Nature of life cycle

Classification of Plant Kingdom

1. Algae

Characteristics

Chlorophyll-bearing organisms

Mostly aquatic

Photosynthetic

Simple thalloid body

Types of Algae

Green Algae (Chlorophyceae)

Examples:

Chlamydomonas

Volvox

Ulothrix

Spirogyra

Brown Algae (Phaeophyceae)

Examples:

Ectocarpus

Dictyota

Laminaria

Sargassum

Red Algae (Rhodophyceae)

Examples:

Porphyra

Polysiphonia

Gelidium

NCERT Point

Red algae contain phycoerythrin pigment.

2. Bryophytes

Characteristics

Amphibians of Plant Kingdom

Require water for fertilization

No vascular tissue

Examples

Riccia

Marchantia

Funaria

NCERT Point

Bryophytes are called amphibians because they need water for sexual reproduction.

3. Pteridophytes

Characteristics

First vascular plants

Possess xylem and phloem

Reproduce through spores

Examples

Selaginella

Equisetum

Pteris

Dryopteris

NCERT Point

Pteridophytes are the first terrestrial vascular plants.

4. Gymnosperms

Characteristics

Naked seeds

No fruits

Well-developed vascular tissues

Examples

Cycas

Pinus

Cedrus

Ginkgo

Important Feature

Seeds remain exposed.

NCERT Point

Gymnosperm seeds are not enclosed within fruits.

5. Angiosperms

Characteristics

Flowering plants

Seeds enclosed within fruits

Most advanced plants

Examples

Mango

Wheat

Rose

Pea

Monocots vs Dicots

Character

Monocots

Dicots

Cotyledons

One

Two

Venation

Parallel

Reticulate

Root System

Fibrous

Tap Root

Floral Parts

Multiple of 3

Multiple of 4 or 5

Plant Life Cycles

Haplontic

Dominant phase:

Haploid

Example:

Chlamydomonas

Diplontic

Dominant phase:

Diploid

Example:

Gymnosperms

Angiosperms

Haplodiplontic

Both phases multicellular.

Examples:

Bryophytes

Pteridophytes

Important NCERT Examples

Green Algae

Volvox

Spirogyra

Ulothrix

Bryophytes

Riccia

Marchantia

Funaria

Pteridophytes

Selaginella

Equisetum

Gymnosperms

Cycas

Pinus

Angiosperms

Wheat

Mango

Most Important NCERT Points

✔ Algae are primary producers.

✔ Bryophytes are amphibians of plant kingdom.

✔ Pteridophytes are first vascular plants.

✔ Gymnosperms possess naked seeds.

✔ Angiosperms are flowering plants.

✔ Cycas shows coralloid roots.

✔ Pinus possesses winged pollen grains.

NEET PYQ Questions

Q1. Amphibians of Plant Kingdom are:

A. Algae

B. Bryophytes

C. Gymnosperms

D. Angiosperms

✅ Answer: B. Bryophytes

Q2. Naked seeds occur in:

A. Bryophytes

B. Pteridophytes

C. Gymnosperms

D. Angiosperms

✅ Answer: C. Gymnosperms

Q3. First vascular land plants are:

A. Algae

B. Bryophytes

C. Pteridophytes

D. Angiosperms

✅ Answer: C. Pteridophytes

Q4. Red color in red algae is due to:

A. Chlorophyll b

B. Carotene

C. Phycoerythrin

D. Fucoxanthin

✅ Answer: C. Phycoerythrin

Q5. Which plant has coralloid roots?

A. Pinus

B. Cycas

C. Mango

D. Funaria

✅ Answer: B. Cycas

Last Minute NEET Revision Tips

Must Revise

NCERT examples

Plant life cycles

Monocot vs Dicot differences

Algae classification

Gymnosperm features

Bryophyte and Pteridophyte characteristics

Conclusion

Plant Kingdom is a high-scoring NEET chapter with direct NCERT-based questions. Focus on classification, examples, life cycles, and characteristic features to maximize your Biology score.

Cell: The Unit of Life – Complete NCERT Notes | Class 11 Biology | NEET 2026

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The cell is the fundamental structural and functional unit of life. All living organisms are made up of cells. This chapter is highly important for NEET because many questions are directly asked from NCERT diagrams, organelles, and cell theory.

What is a Cell?

A cell is the basic unit of life capable of performing all life processes.

Examples

Amoeba → Single cell

Human body → Trillions of cells

Cell Theory

Proposed by:

Matthias Schleiden

Theodor Schwann

Modified by:

Rudolf Virchow

Main Points

All organisms are made of cells.

Cell is the basic unit of life.

Every cell arises from a pre-existing cell.

NCERT Line

Omnis cellula e cellula (Every cell originates from another cell.)

Types of Cells

Prokaryotic Cells

Examples:

Bacteria

Cyanobacteria

Features

No true nucleus

No membrane-bound organelles

Circular DNA

Small size

Eukaryotic Cells

Examples:

Plants

Animals

Fungi

Protists

Features

True nucleus present

Membrane-bound organelles present

Linear chromosomes

Cell Shape

Cell shape depends upon function.

Examples:

Cell

Shape

RBC

Biconcave

Neuron

Long and branched

Muscle Cell

Elongated

Amoeba

Irregular

Structure of Cell

Major Components:

Plasma Membrane

Cytoplasm

Nucleus

Plasma Membrane

Outer boundary of cell.

Functions

Selectively permeable

Regulates transport

Protection

Fluid Mosaic Model

Proposed by:

S. J. Singer

Garth Nicolson

Cell Wall

Present in plant cells.

Composition

Cellulose

Hemicellulose

Pectin

Functions

Protection

Mechanical support

Middle Lamella

Made of calcium pectate.

Osmosis

Movement of water through a semipermeable membrane from higher water potential to lower water potential.

Important Terms

Hypotonic

Hypertonic

Isotonic

NCERT Point

Plant cells become turgid in hypotonic solution.

Cytoplasm

Semi-fluid matrix between nucleus and plasma membrane.

Contains:

Organelles

Cytosol

Inclusions

Endoplasmic Reticulum (ER)

Rough ER

Ribosomes present

Protein synthesis

Smooth ER

Lipid synthesis

Detoxification

Golgi Apparatus

Discovered by:

Camillo Golgi

Functions

Packaging

Secretion

Formation of lysosomes

Lysosomes

Known as:

"Suicidal Bags"

Contain hydrolytic enzymes.

Function

Intracellular digestion.

Mitochondria

Powerhouse of Cell

Structure

Outer membrane

Inner membrane

Cristae

Matrix

Functions

ATP production

Cellular respiration

NCERT Point

Mitochondria possess their own DNA and ribosomes.

Plastids

Present only in plant cells.

Types

Chloroplast

Photosynthesis

Chromoplast

Colored pigments

Leucoplast

Storage

Chloroplast Structure

Grana

Thylakoids

Stroma

NCERT Point

Chlorophyll is present in thylakoid membranes.

Ribosomes

Site of Protein Synthesis

Types

70S (Prokaryotes)

80S (Eukaryotes)

Centrosome

Present in animal cells.

Function

Spindle formation during cell division.

Cilia and Flagella

Function

Movement

Example

Cilia → Trachea

Flagella → Sperm

Nucleus

Control center of the cell.

Components

Nuclear membrane

Nucleoplasm

Chromatin

Nucleolus

Chromosomes

Made of:

DNA

Proteins

Human Chromosomes

46 chromosomes

(23 pairs)

Chromatin Types

Euchromatin

Lightly stained

Transcriptionally active

Heterochromatin

Darkly stained

Inactive

Microbodies

Examples:

Peroxisomes

Glyoxysomes

Function

Metabolic activities

Plant Cell vs Animal Cell

Feature

Plant Cell

Animal Cell

Cell Wall

Present

Absent

Chloroplast

Present

Absent

Vacuole

Large

Small

Centrosome

Absent

Present

Most Important NCERT Points

✔ Cell is the structural and functional unit of life.

✔ Fluid mosaic model explains plasma membrane.

✔ Middle lamella contains calcium pectate.

✔ Ribosomes are sites of protein synthesis.

✔ Mitochondria possess DNA and ribosomes.

✔ Chloroplasts contain chlorophyll.

✔ Lysosomes contain hydrolytic enzymes.

✔ Centrosome helps in spindle formation.

NEET PYQ Practice Questions

Q1. Fluid Mosaic Model was proposed by:

A. Watson & Crick

B. Singer & Nicolson

C. Schleiden & Schwann

D. Virchow

✅ Answer: B

Q2. Powerhouse of the cell is:

A. Golgi Body

B. Ribosome

C. Mitochondria

D. Lysosome

✅ Answer: C

Q3. Site of protein synthesis:

A. Lysosome

B. Ribosome

C. Vacuole

D. Centrosome

✅ Answer: B

Q4. Cell wall middle lamella contains:

A. Cellulose

B. Chitin

C. Calcium Pectate

D. Lignin

✅ Answer: C

Q5. Which organelle possesses its own DNA?

A. Ribosome

B. Golgi Body

C. Lysosome

D. Mitochondria

✅ Answer: D

Last-Minute NEET Revision

Focus on:

Cell Theory

Fluid Mosaic Model

Cell Organelles

Mitochondria

Chloroplast

Ribosomes

Nucleus

Plant vs Animal Cell

NCERT Diagrams

Molecular Basis of Inheritance – Complete NCERT Notes | Class 12 Biology | NEET 2026

Keywords

Molecular Basis of Inheritance Notes, Class 12 Biology Notes, DNA Replication Notes, Transcription and Translation NEET, Lac Operon Notes, Human Genome Project Notes, DNA Fingerprinting Notes, Molecular Basis of Inheritance PYQ, NEET 2026 Biology Notes.

The chapter Molecular Basis of Inheritance is one of the highest-weightage chapters in NEET Biology. Questions are frequently asked from DNA structure, replication, transcription, translation, operon concept, genetic code, and Human Genome Project.

Introduction

Inheritance occurs through genetic material called DNA (Deoxyribonucleic Acid).

DNA stores, transmits, and expresses genetic information.

Search for Genetic Material

Griffith's Experiment (1928)

Organism:

Streptococcus pneumoniae

Observation

R strain → Non-virulent

S strain → Virulent

Heat-killed S strain + Live R strain → Mouse died

Conclusion

Some transforming principle transferred genetic information.

Avery, MacLeod and McCarty Experiment

Conclusion

DNA is the genetic material.

Hershey and Chase Experiment

Organism:

Bacteriophage

Conclusion

DNA enters bacterial cells and acts as genetic material.

NCERT Point

DNA is the genetic material in most organisms.

Structure of DNA

Proposed by:

James Watson

Francis Crick

Based on X-ray diffraction studies of:

Rosalind Franklin

Features of DNA

Double helix structure

Two antiparallel strands

Sugar-phosphate backbone

Nitrogenous bases

Base Pairing

A ↔ T

G ↔ C

Chargaff's Rule

A = T

G = C

DNA Packaging

Human DNA length:

Approximately 2.2 meters per cell

Packaging protein:

Histones

Nucleosome

DNA wrapped around histone octamer.

NCERT Point

Nucleosome is the repeating unit of chromatin.

DNA Replication

DNA replication is semiconservative.

Confirmed by:

Matthew Meselson

Franklin Stahl

Steps

Unwinding

Complementary base pairing

Formation of daughter strands

Important Enzyme

DNA Polymerase

NCERT Point

Replication occurs in 5' → 3' direction.

Transcription

Process of formation of RNA from DNA template.

Enzyme

RNA Polymerase

Types of RNA

mRNA

tRNA

rRNA

NCERT Point

Only one strand acts as template strand.

Genetic Code

Properties:

Triplet Code

One amino acid = Three nucleotides

Degenerate

Multiple codons code for same amino acid.

Universal

Same in almost all organisms.

Start Codon

AUG

Stop Codons

UAA

UAG

UGA

Translation

Process of protein synthesis from mRNA.

Site

Ribosomes

Main Steps

Activation of amino acids

Initiation

Elongation

Termination

NCERT Point

AUG codes for Methionine.

Lac Operon

Proposed by:

François Jacob

Jacques Monod

Components

Regulatory gene

Promoter

Operator

Structural genes

Inducer

Lactose

NCERT Point

Lac operon is an inducible operon.

Human Genome Project (HGP)

Objectives

Identify all genes

Determine DNA sequences

Store information

Facts

Human genome contains approximately 3.2 billion base pairs.

Around 20,000–25,000 genes.

DNA Fingerprinting

Developed by:

Alec Jeffreys

Principle

Based on polymorphism in DNA sequences.

Applications

Forensic science

Paternity testing

Criminal identification

Important Scientists for NEET

Scientist

Contribution

Griffith

Transformation

Avery, MacLeod & McCarty

DNA as genetic material

Hershey & Chase

DNA proof

Watson & Crick

DNA structure

Meselson & Stahl

Semiconservative replication

Jacob & Monod

Lac Operon

Alec Jeffreys

DNA Fingerprinting

Most Important NCERT Lines

✔ DNA is the genetic material in most organisms.

✔ DNA replication is semiconservative.

✔ AUG is the initiation codon.

✔ UAA, UAG and UGA are stop codons.

✔ Genetic code is universal and degenerate.

✔ Nucleosome is the repeating unit of chromatin.

✔ Lac operon is inducible.

✔ DNA fingerprinting is based on polymorphism.

NEET PYQ Practice Questions

Q1. DNA double helix model was proposed by:

A. Griffith

B. Watson and Crick

C. Hershey and Chase

D. Jacob and Monod

✅ Answer: B

Q2. Start codon is:

A. UAA

B. AUG

C. UGA

D. UAG

✅ Answer: B

Q3. DNA replication is:

A. Conservative

B. Dispersive

C. Semiconservative

D. Random

✅ Answer: C

Q4. DNA fingerprinting was developed by:

A. Watson

B. Crick

C. Alec Jeffreys

D. Griffith

✅ Answer: C

Q5. Inducer in lac operon is:

A. Glucose

B. Lactose

C. DNA

D. RNA

✅ Answer: B

Last-Minute NEET Revision

Focus on:

DNA structure

Chargaff's rule

DNA replication

Transcription

Translation

Genetic code

Lac operon

Human Genome Project

DNA fingerprinting

Organisms and Populations – Complete NCERT Notes | Class 12 Biology | NEET 2026

Organisms and Populations Notes, Class 12 Ecology Notes, Organisms and Populations NCERT Notes, Population Growth NEET, Ecology Notes NEET, Population Interactions Notes, Organisms and Populations PYQ, NEET 2026 Biology Notes.

Organisms and Populations is an important Ecology chapter for NEET. Questions are frequently asked from adaptations, population growth, population interactions, and ecological principles. Most NEET questions are directly based on NCERT examples.

Organism and Its Environment

Every organism interacts continuously with its environment.

Environment Includes

Biotic factors

Abiotic factors

Major Abiotic Factors

1. Temperature

Most important ecological factor.

Organisms Based on Temperature

Eurythermal

Can tolerate wide temperature range.

Examples:

Humans

Tiger

Stenothermal

Can tolerate narrow temperature range.

Examples:

Coral reefs

2. Water

Essential for all living organisms.

Organisms Based on Water Availability

Xerophytes

Adapted to dry conditions.

Examples:

Cactus

Opuntia

Hydrophytes

Adapted to aquatic habitat.

Examples:

Hydrilla

Lotus

3. Light

Affects:

Photosynthesis

Flowering

Growth

NCERT Point

Many plants depend on photoperiod for flowering.

4. Soil

Important characteristics:

pH

Mineral composition

Topography

Responses to Abiotic Factors

1. Regulate

Maintain constant body temperature.

Examples:

Birds

Mammals

2. Conform

Body temperature changes with surroundings.

Examples:

Amphibians

Reptiles

3. Migrate

Move temporarily to favorable habitats.

Examples:

Birds

4. Suspend

Dormancy during unfavorable conditions.

Examples:

Spores

Seeds

Adaptations

Adaptations help organisms survive in their habitat.

Desert Adaptations

Kangaroo Rat

Meets water requirement through metabolism

Rarely drinks water

Camel

Conserves water efficiently

Opuntia

Leaves modified into spines

Stem performs photosynthesis

Population

Population refers to a group of individuals of the same species living in a particular area.

Example:

All humans living in India.

Population Attributes

1. Natality

Birth rate.

Formula

Births per population per unit time.

2. Mortality

Death rate.

3. Sex Ratio

Number of males and females.

4. Age Distribution

Population categories:

Pre-reproductive

Reproductive

Post-reproductive

Population Growth

Exponential Growth

Occurs when resources are unlimited.

Equation

Nt = N₀eʳᵗ

Graph

J-shaped curve

Logistic Growth

Occurs when resources become limited.

Graph

S-shaped curve

Carrying Capacity (K)

Maximum population size supported by environment.

NCERT Point

Logistic growth is more realistic.

Population Interactions

One of the most important topics for NEET.

1. Mutualism (+,+)

Both species benefit.

Examples

Lichen (Algae + Fungus)

Mycorrhiza

Fig and Wasp

2. Commensalism (+,0)

One benefits, other unaffected.

Examples

Orchid on Mango Tree

Cattle Egret and Grazing Cattle

3. Parasitism (+,-)

Parasite benefits, host harmed.

Examples

Cuscuta

Tapeworm

Lice

NCERT Point

Many parasites show host specificity.

4. Predation (+,-)

Predator kills prey.

Examples

Tiger and Deer

Bird and Insect

Importance

Controls prey population.

5. Competition (-,-)

Both species harmed.

Example

Two species competing for same resource.

NCERT Point

Competition may occur even if resources are abundant.

6. Amensalism (-,0)

One harmed, other unaffected.

Example

Penicillium inhibiting bacterial growth.

Important NCERT Examples

Concept

Example

Mutualism

Lichen

Commensalism

Orchid on Mango Tree

Parasitism

Cuscuta

Predation

Tiger and Deer

Amensalism

Penicillium

Desert Adaptation

Kangaroo Rat

Most Important NCERT Points

✔ Organisms respond to environmental changes through regulation, conformity, migration, or suspension.

✔ Kangaroo rat rarely drinks water.

✔ Logistic growth is more realistic than exponential growth.

✔ Carrying capacity determines maximum population size.

✔ Lichen is a mutualistic association.

✔ Cuscuta is a parasitic plant.

✔ Competition may occur even when resources are abundant.

NEET PYQ Practice Questions

Q1. Growth curve under unlimited resources is:

A. S-shaped

B. J-shaped

C. Circular

D. Linear

✅ Answer: B. J-shaped

Q2. Carrying capacity is associated with:

A. Exponential Growth

B. Logistic Growth

C. Natality

D. Mortality

✅ Answer: B. Logistic Growth

Q3. Example of Mutualism:

A. Cuscuta

B. Tapeworm

C. Lichen

D. Tiger

✅ Answer: C. Lichen

Q4. Example of Commensalism:

A. Orchid on Mango Tree

B. Cuscuta

C. Lichen

D. Tapeworm

✅ Answer: A. Orchid on Mango Tree

Q5. Kangaroo rat is adapted to:

A. Aquatic habitat

B. Desert habitat

C. Forest habitat

D. Polar habitat

✅ Answer: B. Desert habitat

Last-Minute NEET Revision

Must Revise

Abiotic factors

Adaptations

Population attributes

Exponential vs Logistic growth

Carrying Capacity

Population interactions

NCERT examples

Conclusion

Organisms and Populations is a scoring Ecology chapter with direct NCERT-based questions. Master the population interactions, growth curves, and adaptation examples to score easy marks in NEET Biology.

Principles of Inheritance and Variation – Complete NCERT Notes | Class 12 Biology | NEET 2026

Keywords

Principles of Inheritance and Variation Notes, Mendelian Genetics Notes, Class 12 Genetics Notes, Inheritance and Variation NCERT Notes, Blood Group Genetics, Sex Linked Inheritance Notes, Genetic Disorders Notes, NEET 2026 Biology Notes, Mendel Laws PYQ.

Principles of Inheritance and Variation is one of the highest-scoring chapters in NEET Biology. Questions are frequently asked from Mendel's laws, monohybrid cross, dihybrid cross, incomplete dominance, codominance, blood groups, linkage, and genetic disorders.

Introduction

Inheritance is the transmission of traits from parents to offspring.

Variation refers to differences among individuals of the same species.

Gregor Johann Mendel

Known as:

Father of Genetics

Experimented on:

Garden Pea (Pisum sativum)

Why Mendel Chose Pea Plant?

Easy cultivation

Short life cycle

Self-pollinating

Distinct contrasting characters

Seven Contrasting Traits

Character

Dominant

Recessive

Seed Shape

Round

Wrinkled

Seed Color

Yellow

Green

Flower Color

Violet

White

Pod Shape

Inflated

Constricted

Pod Color

Green

Yellow

Flower Position

Axial

Terminal

Stem Height

Tall

Dwarf

Important Terms

Gene

Unit of inheritance.

Alleles

Alternative forms of a gene.

Example:

T = Tall

t = Dwarf

Homozygous

Same alleles.

Examples:

TT

tt

Heterozygous

Different alleles.

Example:

Tt

Monohybrid Cross

Cross involving one character.

Example

TT × tt

F₁ Generation

All Tall (Tt)

F₂ Generation

Genotypic Ratio:

1 TT : 2 Tt : 1 tt

Phenotypic Ratio:

3 Tall : 1 Dwarf

Law of Dominance

States that in a heterozygote, one allele expresses itself and suppresses the other.

Example

T dominates over t.

Law of Segregation

Alleles separate during gamete formation.

NCERT Point

Also called Law of Purity of Gametes.

Dihybrid Cross

Cross involving two characters.

Example

Round Yellow × Wrinkled Green

F₂ Phenotypic Ratio

9 : 3 : 3 : 1

Law of Independent Assortment

Genes of different characters assort independently during gamete formation.

Derived From

Dihybrid cross.

Incomplete Dominance

Neither allele completely dominant.

Example

Snapdragon (Antirrhinum)

Red × White

↓

Pink

F₂ Ratio

1 Red : 2 Pink : 1 White

Codominance

Both alleles express simultaneously.

Example

Human ABO Blood Group

IA and IB are codominant.

Multiple Alleles

More than two alleles govern a character.

Example

ABO Blood Group

Alleles:

IA

IB

i

Blood Groups

Blood Group

Genotype

A

IAIA or IAi

B

IBIB or IBi

AB

IAIB

O

ii

NCERT Point

AB blood group shows codominance.

Pleiotropy

One gene influences multiple traits.

Example

Phenylketonuria

Chromosomal Theory of Inheritance

Proposed by:

Walter Sutton

Theodor Boveri

Main Idea

Genes are located on chromosomes.

Linkage

Genes present on same chromosome tend to inherit together.

Discovered by

Thomas Hunt Morgan

Recombination

Formation of new gene combinations.

Occurs due to crossing over.

Sex Determination

Human Sex Determination

Male:

XY

Female:

XX

NCERT Point

Father determines sex of child.

Sex-Linked Inheritance

Genes present on sex chromosomes.

Haemophilia

Cause

Recessive gene on X chromosome.

Symptoms

Blood clotting defect.

Colour Blindness

Cause

X-linked recessive trait.

Symptoms

Inability to distinguish colors.

Pedigree Analysis

Study of inheritance pattern across generations.

Symbols

Square = Male

Circle = Female

Filled Symbol = Affected

Mendelian Disorders

Haemophilia

Blood clotting disorder.

Colour Blindness

Vision disorder.

Phenylketonuria

Metabolic disorder.

Sickle Cell Anaemia

Mutation in β-globin gene.

NCERT Point

Autosomal recessive disorder.

Chromosomal Disorders

Down Syndrome

Cause

Trisomy 21

Chromosomes

47

Klinefelter Syndrome

Karyotype

XXY

Chromosomes

47

Turner Syndrome

Karyotype

XO

Chromosomes

45

Most Important NCERT Points

✔ Mendel is Father of Genetics.

✔ Monohybrid ratio = 3:1

✔ Dihybrid ratio = 9:3:3:1

✔ Law of Segregation = Purity of Gametes.

✔ AB blood group shows codominance.

✔ Snapdragon demonstrates incomplete dominance.

✔ Father determines sex of child.

✔ Down syndrome = Trisomy 21.

✔ Sickle cell anaemia is autosomal recessive.

NEET PYQ Practice Questions

Q1. Father of Genetics is:

A. Darwin

B. Mendel

C. Morgan

D. Sutton

✅ Answer: B. Mendel

Q2. Phenotypic ratio in monohybrid cross:

A. 9:3:3:1

B. 1:2:1

C. 3:1

D. 1:1

✅ Answer: C. 3:1

Q3. Example of incomplete dominance:

A. Pea Plant

B. Snapdragon

C. Blood Group

D. Colour Blindness

✅ Answer: B. Snapdragon

Q4. AB Blood Group exhibits:

A. Dominance

B. Recessiveness

C. Codominance

D. Linkage

✅ Answer: C. Codominance

Q5. Down Syndrome results from:

A. Trisomy 21

B. XO

C. XXY

D. Mutation

✅ Answer: A. Trisomy 21

Last-Minute NEET Revision

Must Revise

Mendel's Laws

Monohybrid Cross

Dihybrid Cross

Blood Groups

Linkage

Pedigree Analysis

Sex-linked Inheritance

Genetic Disorders

Chromosomal Disorders

Conclusion

Principles of Inheritance and Variation is one of the most important NEET chapters. Questions are directly asked from Mendelian genetics, blood groups, linkage, and genetic disorders. Master the ratios, examples, and NCERT terminology to score easy marks in NEET Biology.