What is Biomacromolecules?

Biomacromolecules are large biomolecules with molecular weights greater than 10,000 Da. They are found in the acid-insoluble fraction of cells and include proteins, nucleic acids (DNA and RNA), and polysaccharides. These are generally polymeric molecules made up of repeating smaller units (monomers).

The acid-soluble fraction contains micromolecules, such as amino acids, sugars, nucleotides, and other small molecules, with molecular weights ranging from 18 to about 800 Da.

Although lipids have low molecular weights (usually less than 800 Da), they are present in the acid-insoluble fraction because they are organized into cell membranes. When cells are broken, membrane fragments form insoluble vesicles, causing lipids to separate with the acid-insoluble fraction. Therefore, lipids are not true biomacromolecules.

Key Facts (NEET/CBSE)

Micromolecules: Molecular weight < 1000 Da (acid-soluble fraction).
Biomacromolecules: Molecular weight > 10,000 Da (acid-insoluble fraction).
Examples of biomacromolecules: Proteins, nucleic acids, polysaccharides.
Lipids are an exception: Present in the acid-insoluble fraction but not true macromolecules.
Water is the most abundant chemical in living organisms.

Primary and Secondary Metabolites NEET Concepts

Here are the most important facts from NCERT Class 11 Biology – Biomolecules (Primary and Secondary Metabolites) for NEET and CBSE.

Primary Metabolites

Definition: Compounds directly involved in the growth, development, reproduction, and survival of an organism.
They are essential for life.
Found in all living organisms (plants, animals, fungi, and microbes).
Usually present in large quantities.
Produced continuously during normal metabolism.
They have well-defined physiological functions.

Examples

Carbohydrates (glucose, starch)
Proteins
Amino acids
Lipids
Nucleic acids (DNA, RNA)
Vitamins
ATP

Functions

Provide energy
Form cell structures
Store genetic information
Catalyse reactions (enzymes)
Growth and repair of tissues

Secondary Metabolites

Definition: Organic compounds that are not directly required for growth and reproduction, but help the organism survive in its environment.
Mainly found in plants, fungi, and microorganisms.
Usually present in small amounts.
Often species-specific.
Many have commercial and medicinal importance.

Examples (NCERT)

Alkaloids
Flavonoids
Rubber
Essential oils
Antibiotics
Coloured pigments
Scents
Gums
Spices

Functions

Defence against herbivores and pathogens
Attract pollinators
Seed dispersal
Protection from UV radiation
Ecological interactions
Communication between organisms

Human Uses of Secondary Metabolites

💊 Medicines (antibiotics, alkaloids)
🌶️ Spices (pepper, clove, cinnamon)
🌸 Perfumes (essential oils)
🎨 Natural dyes and pigments
🚗 Rubber industry
🍬 Food flavouring

Difference Between Primary and Secondary Metabolites

Primary Metabolites	Secondary Metabolites
Essential for life	Not directly essential for growth
Found in all organisms	Mainly in plants, fungi and microbes
Large quantity	Small quantity
Direct role in metabolism	Ecological and protective role
Common to most species	Often species-specific
Examples: Glucose, proteins, DNA	Alkaloids, flavonoids, antibiotics, rubber

NCERT Facts to Remember

Primary metabolites have identifiable functions in normal physiological processes.
Functions of many secondary metabolites are still not fully understood.
Many secondary metabolites are valuable for human welfare.
Some secondary metabolites have ecological importance.

NEET One-Liners

Primary metabolites = Essential for life.
Secondary metabolites = Helpful for survival, defence, and ecological interactions.
Antibiotics, alkaloids, flavonoids, rubber, essential oils, gums, spices and pigments are secondary metabolites.
Glucose, amino acids, proteins, lipids and nucleic acids are primary metabolites.

Memory Trick

Primary = “P for Personal Survival” (essential for the organism)

Secondary = “S for Survival in Surroundings” (defence, attraction, ecological role, and human use)

When carboxylic acid is called a fatty acid?

A carboxylic acid is called a fatty acid when it has a long hydrocarbon chain attached to the carboxyl group (-COOH).

where R is a long hydrocarbon chain, usually containing 4 to 36 carbon atoms (most common are 12–22 carbons).

Examples

Compound	Formula	Fatty Acid?	Reason
Formic acid	HCOOH	❌ No	No hydrocarbon chain
Acetic acid	CH₃COOH	❌ No	Only 2 carbons
Propionic acid	CH₃CH₂COOH	❌ No	Too short
Butyric acid	CH₃(CH₂)₂COOH	✔️ Yes (short-chain fatty acid)	4 carbons
Palmitic acid	C₁₅H₃₁COOH	✔️ Yes	16 carbons
Stearic acid	C₁₇H₃₅COOH	✔️ Yes	18 carbons
Oleic acid	C₁₇H₃₃COOH	✔️ Yes	18 carbons, one double bond

Classification of fatty acids

Short-chain: 4–6 carbons
Medium-chain: 8–12 carbons
Long-chain: 14–20 carbons
Very long-chain: 22 or more carbons

Saturated vs Unsaturated

Saturated fatty acid (no C=C bond)

Palmitic acid (C₁₆:0)
Stearic acid (C₁₈:0)

Unsaturated fatty acid (one or more C=C bonds)

Oleic acid (C₁₈:1)
Linoleic acid (C₁₈:2)
Linolenic acid (C₁₈:3)

NEET/JEE Definition

Fatty acids are aliphatic monocarboxylic acids containing a long hydrocarbon chain. They may be saturated or unsaturated and are the building blocks of fats and oils (triglycerides).

Important Note

There is no strict carbon-number cutoff in chemistry, but in biology and biochemistry, carboxylic acids with long hydrocarbon chains (typically C₄ and above, especially C₁₂–C₂₂) are referred to as fatty acids. Acetic acid and propionic acid are carboxylic acids, but they are generally not considered fatty acids in the context of fats and oils.

Difference between fats and lipids?

The terms lipids and fats are related, but they are not the same. Fats are a type of lipid, while lipids are a broader group of biological molecules.

Feature	Lipids	Fats
Definition	A broad class of water-insoluble biomolecules	A specific type of lipid (mainly triglycerides)
Composition	Includes fats, oils, waxes, phospholipids, steroids, etc.	Made of one glycerol molecule and three fatty acids (triglycerides)
Examples	Cholesterol, phospholipids, waxes, fats, oils	Butter, ghee, lard, animal fat
Functions	Energy storage, cell membrane formation, hormones, insulation, waterproofing	Mainly long-term energy storage and insulation
Physical State	Can be solid or liquid	Usually solid at room temperature (animal fats); liquid forms are often called oils
Found In	All living organisms	Mainly animals, though plants also produce fats and oils

Key Points

Lipids = Umbrella term
- Fats
- Oils
- Waxes
- Phospholipids
- Steroids (e.g., cholesterol)
Fats = One category of lipids
- Store excess energy.
- Protect organs.
- Help maintain body temperature.

Easy Analogy

Lipids are like “vehicles.”
Fats are like “cars.”

Just as every car is a vehicle but not every vehicle is a car, every fat is a lipid, but not every lipid is a fat.

Exam Tip (NEET/CBSE)

All fats are lipids, but all lipids are not fats. This is a commonly asked conceptual question in biology and chemistry.

Fats are esters?

More specifically, fats are triesters (triglycerides or triacylglycerols) formed by the reaction of glycerol with three fatty acid molecules.

Formation of a fat (esterification)

$\text{Glycerol} + 3\ \text{Fatty acids} \rightarrow \text{Triglyceride (fat)} + 3\ \text{H}_2\text{O}$

For example: $\text{Glycerol} + 3\ \text{Stearic acid} \rightarrow \text{Tristearin} + 3\ \text{H}_2\text{O}$

Difference between oils and fats?

Fats and oils are both triglycerides (triacylglycerols)—they are esters of glycerol and three fatty acids. The main difference is the type of fatty acids they contain, which determines whether they are solid or liquid at room temperature.

Feature	Fats	Oils
Physical state (25°C)	Solid or semi-solid	Liquid
Fatty acids	Rich in saturated fatty acids	Rich in unsaturated fatty acids
Carbon–carbon bonds	Mostly single bonds (C–C)	One or more double bonds (C=C)
Packing of molecules	Pack tightly	Do not pack tightly because of bends caused by double bonds
Melting point	Higher	Lower
Common source	Mostly animals (butter, ghee, lard)	Mostly plants and fish (mustard oil, sunflower oil, olive oil)
Examples	Butter, ghee, tallow	Olive oil, coconut oil*, sunflower oil

Why are oils liquid?

Unsaturated fatty acids contain C=C double bonds, usually in the cis configuration. These create kinks (bends) in the hydrocarbon chains, preventing the molecules from packing closely together. As a result, the intermolecular forces are weaker, so they melt at lower temperatures and remain liquid.

Why are fats solid?

Saturated fatty acids have no C=C double bonds, so their chains are straight. They pack closely together, leading to stronger intermolecular forces and a higher melting point, making them solid at room temperature.

CBSE Class 12 Biology – Origin and Evolution of Man (NCERT) Important Facts

These are the highest-yield NCERT facts for CBSE Class 12 Board Exams, useful for MCQs, 1-mark, 2-mark, Assertion-Reason, and Case-Based Questions.

Evolution of Humans (NCERT Timeline)

Time	Organism	Important Feature
15 mya	Dryopithecus	Ape-like
15 mya	Ramapithecus	More man-like
3–4 mya	Early hominids	Walked upright
2 mya	Australopithecines	Used stone tools, mainly fruit eaters
~2 mya	Homo habilis	First human-like being, brain 650–800 cc
1.5 mya	Homo erectus	Brain ~900 cc, probably ate meat
100,000–40,000 years ago	Neanderthal man	Brain ~1400 cc, buried dead
75,000–10,000 years ago	Homo sapiens	Modern humans developed

1. Dryopithecus

Lived about 15 million years ago (mya).
Hairy and walked like modern apes.
More ape-like than human-like.

2. Ramapithecus

Lived about 15 mya.
More man-like than Dryopithecus.
Considered closer to the human lineage in NCERT.

3. Early Hominids

Fossils found in Ethiopia and Tanzania.
Lived about 3–4 mya.
Walked upright (bipedal).
About 4 feet tall.

4. Australopithecines

Lived about 2 million years ago.
Found mainly in East African grasslands.
Used stone tools.
Mainly fruit eaters.

5. Homo habilis

Considered the first human-like being in NCERT.
Brain capacity: 650–800 cc.
Probably did not eat meat.

6. Homo erectus

Fossils discovered in Java (1891).
Lived about 1.5 million years ago.
Brain capacity: ~900 cc.
Probably ate meat.

7. Neanderthal Man

Lived between 100,000–40,000 years ago.
Brain capacity: ~1400 cc.
Used animal hides for clothing.
Buried their dead, indicating social and cultural behavior.

8. Homo sapiens

Originated in Africa.
Migrated to different continents.
Developed into different human populations.

9. Ice Age

Lasted from about 75,000 to 10,000 years ago (as per NCERT context).
Modern Homo sapiens became widespread during this period.

10. Cave Art

Developed around 18,000 years ago.
Indicates advanced thinking and creativity.

11. Agriculture

Began about 10,000 years ago.
Led to:
- Permanent settlements
- Farming
- Development of civilizations

Evolution Sequence (Very Important)

Dryopithecus
⬇
Ramapithecus
⬇
Early Hominids
⬇
Australopithecines
⬇
Homo habilis
⬇
Homo erectus
⬇
Neanderthal Man
⬇
Homo sapiens (Modern Humans)

Brain Capacity (Frequently Asked)

Organism	Brain Capacity
Homo habilis	650–800 cc
Homo erectus	~900 cc
Neanderthal man	~1400 cc

One-Mark Questions

Q1. Which primate was more ape-like?
Answer: Dryopithecus.

Q2. Which primate was more man-like?
Answer: Ramapithecus.

Q3. Where were early hominid fossils found?
Answer: Ethiopia and Tanzania.

Q4. Which species is considered the first human-like being in NCERT?
Answer: Homo habilis.

Q5. What was the brain capacity of Homo habilis?
Answer: 650–800 cc.

Q6. Where was Homo erectus discovered?
Answer: Java.

Q7. Which human ancestor buried their dead?
Answer: Neanderthal man.

Q8. Where did Homo sapiens originate?
Answer: Africa.

Q9. When did agriculture begin?
Answer: About 10,000 years ago.

NCERT Keywords for Board Exams

Dryopithecus
Ramapithecus
Hominids
Australopithecines
Homo habilis
Homo erectus
Neanderthal Man
Homo sapiens
Bipedalism
Stone Tools
Cave Art
Agriculture
Brain Capacity
Ethiopia
Tanzania
Java
Africa

High-Yield NCERT Facts to Remember

Dryopithecus → More ape-like.
Ramapithecus → More man-like.
Australopithecines → Used stone tools, mainly fruit eaters.
Homo habilis → First human-like being; 650–800 cc brain.
Homo erectus → ~900 cc brain; probably ate meat.
Neanderthal man → ~1400 cc brain; buried the dead.
Homo sapiens → Originated in Africa.
Cave art → Around 18,000 years ago.
Agriculture → Around 10,000 years ago.

CBSE Class 12 Biology – Brief Account of Evolution (NCERT) Important Facts

These are the highest-yield NCERT facts for CBSE Board Exams (MCQs, 1-mark, 2-mark, Assertion-Reason, and Case-Based Questions).

Evolution Timeline (NCERT)

Time (Million Years Ago, mya)	Evolutionary Event
2000 mya	First cellular life appeared
500 mya	Invertebrates became abundant
350 mya	Jawless fishes evolved
350 mya	Fish with strong fins moved onto land
320 mya	Seaweeds and early land plants existed
200 mya	Fish-like reptiles (Ichthyosaurs) evolved
65 mya	Dinosaurs became extinct

Board Tip: Remember the sequence rather than only the dates.

1. First Cellular Life

Appeared about 2000 million years ago (mya).
Some early cells released oxygen (O₂) through a photosynthesis-like process.
Oxygen gradually accumulated in the atmosphere.

2. Multicellular Organisms

Single-celled organisms gradually evolved into multicellular organisms.

3. Invertebrates

Appeared around 500 mya.
They were the first major group of complex animals.

4. Jawless Fishes

Evolved around 350 mya.
Among the earliest vertebrates.

5. First Plants on Land

Plants were the first organisms to colonize land.
They spread on land before animals.

6. Transition from Water to Land

Some fishes developed strong, stout fins.
These enabled movement on land and back to water.
They gave rise to the first amphibians.

7. Coelacanth

A living fossil.
Thought to be extinct until rediscovered in 1938 off the coast of South Africa.
Belongs to the lobe-finned fishes.

Important Board Fact: Coelacanth provides evidence for the transition from fishes to amphibians.

8. Amphibians

First vertebrates to live on both land and water.
Ancestors of modern frogs and salamanders.

9. Reptiles

Evolved from amphibians.
Laid thick-shelled eggs, preventing drying on land.
Modern descendants include:
- Turtles
- Tortoises
- Crocodiles

10. Dinosaurs

Reptiles dominated the Earth for about 200 million years.
Largest dinosaur mentioned in NCERT:
- Tyrannosaurus rex
About 20 feet tall with large, dagger-like teeth.
Became extinct around 65 mya.

11. Ichthyosaurs

Reptiles that returned to water.
Evolved around 200 mya.
Fish-like in appearance.

12. Giant Ferns

Giant pteridophytes formed dense forests.
Their remains gradually formed coal deposits.

13. Birds

Some scientists suggest birds evolved from reptiles (including dinosaurs).
NCERT notes that the exact reason for dinosaur extinction is still uncertain.

14. Mammals

Characteristics:

Viviparous (give birth to live young).
Young develop inside the mother’s body.
More advanced nervous system and better parental care.

The earliest mammals resembled shrews.

15. Continental Drift

South America later joined North America.
South American mammals were largely replaced by North American species.
Australia’s isolation allowed marsupials (pouched mammals) to survive due to reduced competition.

16. Aquatic Mammals

Examples:

Whale
Dolphin
Seal
Sea cow

Despite living in water, they are mammals.

17. Evolution of Humans

NCERT identifies the evolution of humans as one of the most successful evolutionary stories because of:

Language
Intelligence
Self-consciousness

Evolution Sequence (Very Important)

First Cells
⬇
Multicellular Organisms
⬇
Invertebrates
⬇
Jawless Fishes
⬇
Lobe-finned Fishes (Coelacanth-type)
⬇
Amphibians
⬇
Reptiles
⬇
Birds and Mammals
⬇
Humans

One-Mark Questions

Q1. When did the first cellular life appear?
Answer: About 2000 million years ago (mya).

Q2. Which organisms first invaded land?
Answer: Plants.

Q3. What is Coelacanth?
Answer: A lobe-finned fish regarded as a living fossil, rediscovered in 1938.

Q4. Which vertebrates first lived on both land and water?
Answer: Amphibians.

Q5. Which reptiles returned to water?
Answer: Ichthyosaurs.

Q6. When did dinosaurs become extinct?
Answer: Around 65 million years ago.

Q7. Name two modern reptiles mentioned in NCERT.
Answer: Turtles and crocodiles (also tortoises).

Q8. Name two aquatic mammals.
Answer: Whale and dolphin (also seals and sea cows).

NCERT Keywords for Board Exams

First Cellular Life
Oxygen Evolution
Multicellular Organisms
Invertebrates
Jawless Fish
Coelacanth
Lobe-finned Fish
Amphibians
Reptiles
Thick-shelled Eggs
Dinosaurs
Tyrannosaurus rex
Ichthyosaurs
Pteridophytes
Coal Formation
Mammals
Viviparous
Continental Drift
Marsupials
Aquatic Mammals
Human Evolution

High-Yield NCERT Facts to Memorize

2000 mya: First cellular life.
500 mya: Invertebrates became abundant.
350 mya: Jawless fishes and transition of vertebrates toward land.
Plants colonized land before animals.
Coelacanth is a living fossil rediscovered in 1938.
Reptiles evolved from amphibians and laid thick-shelled eggs.
Dinosaurs became extinct about 65 mya.
Earliest mammals resembled shrews.
Australia’s marsupials survived because of geographic isolation and reduced competition.

CBSE Class 12 Biology – Hardy–Weinberg Principle (NCERT) Important Facts

These are the highest-yield NCERT facts for CBSE Board Exams (MCQs, 1 Mark, 2 Marks, Assertion-Reason, and Case-Based Questions).

1. Hardy–Weinberg Principle

Proposed by:

G.H. Hardy
Wilhelm Weinberg

Definition

The allele frequencies in a population remain constant from generation to generation if no evolutionary forces act on the population.

This state is called Genetic Equilibrium.

2. Gene Pool

Gene pool =

Total collection of all genes and their alleles present in a population.

3. Genetic Equilibrium

When allele frequencies remain constant from one generation to the next, the population is said to be in Hardy–Weinberg equilibrium.

4. Hardy–Weinberg Equation

If:

p = frequency of dominant allele (A)
q = frequency of recessive allele (a)

Then,

Allele Frequency

p + q = 1

Genotype Frequency

p² + 2pq + q² = 1

Where:

p² = AA (Homozygous dominant)
2pq = Aa (Heterozygous)
q² = aa (Homozygous recessive)

Board Tip: Memorize both equations exactly as given in NCERT.

5. Importance

Helps determine whether evolution is occurring in a population.
If observed genotype frequencies differ from expected values, it indicates evolutionary change.

6. Factors Affecting Hardy–Weinberg Equilibrium

There are five major factors:

Gene Migration (Gene Flow)
Genetic Drift
Mutation
Genetic Recombination
Natural Selection

7. Gene Flow (Gene Migration)

Movement of individuals (or their genes) from one population to another.
Introduces new alleles into the receiving population.
Changes allele frequencies in both populations.

8. Genetic Drift

Random changes in allele frequencies due to chance.
More significant in small populations.
Can eventually lead to speciation.

9. Founder Effect

Occurs when:

A small group separates from a larger population.
This small group establishes a new population.
Its allele frequencies differ from the original population due to genetic drift.

NCERT Point: The original drifted population becomes the founders, and this phenomenon is called the Founder Effect.

10. Mutation

Sudden, random, heritable changes in DNA.
Produces new alleles.
Alters allele frequencies and contributes to evolution.

11. Genetic Recombination

Occurs during gamete formation (meiosis).

Creates:

New combinations of genes.
Genetic variation.

12. Natural Selection

Natural selection:

Acts on heritable variations.
Individuals with favourable traits survive and reproduce more.
Changes allele frequencies over generations.

13. Types of Natural Selection

A. Stabilising Selection

Favours average (mean) individuals.
Reduces extreme variations.
Mean phenotype is maintained.

Example: Average birth weight in humans.

B. Directional Selection

Favours one extreme phenotype.
Population mean shifts toward that extreme.

Example: Evolution of antibiotic-resistant bacteria.

C. Disruptive Selection

Favours both extreme phenotypes.
Intermediate phenotypes are selected against.
Can lead to speciation.

Flow Chart

Variation
⬇
Mutation / Recombination / Gene Flow / Genetic Drift
⬇
Change in Allele Frequency
⬇
Natural Selection
⬇
Evolution
⬇
Speciation

One-Mark Questions

Q1. What is the Hardy–Weinberg Principle?
Answer: Allele frequencies remain constant from generation to generation in the absence of evolutionary forces.

Q2. Define gene pool.
Answer: The total collection of all genes and their alleles in a population.

Q3. Write the Hardy–Weinberg equation.
Answer: p² + 2pq + q² = 1.

Q4. What does p represent?
Answer: Frequency of the dominant allele (A).

Q5. What does q² represent?
Answer: Frequency of homozygous recessive genotype (aa).

Q6. Name the five factors affecting Hardy–Weinberg equilibrium.
Answer: Gene flow, genetic drift, mutation, genetic recombination, and natural selection.

Q7. What is genetic drift?
Answer: Random changes in allele frequencies due to chance, especially in small populations.

Q8. What is the founder effect?
Answer: A form of genetic drift in which a small group establishes a new population with different allele frequencies.

NCERT Keywords for Board Exams

Hardy–Weinberg Principle
Genetic Equilibrium
Gene Pool
Allele Frequency
Genotype Frequency
Gene Flow
Gene Migration
Genetic Drift
Founder Effect
Mutation
Genetic Recombination
Natural Selection
Stabilising Selection
Directional Selection
Disruptive Selection

Most Important Equations

Allele frequencies: p + q = 1
Genotype frequencies: p² + 2pq + q² = 1

CBSE Class 12 Biology – Mechanism of Evolution (NCERT) Important Facts

1. Mechanism of Evolution

Mechanism of evolution explains:

How variation arises.
How new species (speciation) are formed.

2. Origin of Variation

Variation is the raw material of evolution.

Variation arises due to:

Mutation
Genetic recombination
Gene flow
Genetic drift

NCERT emphasis (this section): Mutation

3. Hugo de Vries

Dutch botanist.
Worked on Evening Primrose (Oenothera lamarckiana).
Proposed the Mutation Theory of Evolution.

4. Mutation

Mutation is:

A sudden, random, heritable change in the genetic material.

Characteristics:

Random
Directionless
Sudden
Heritable

5. Mutation Theory

According to Hugo de Vries:

Evolution occurs because of mutations.
New species may arise through large mutations.
Evolution can occur suddenly, not gradually.

6. Saltation

Saltation means:

Evolution by a single large mutation.

This was proposed by Hugo de Vries.

7. Darwin vs Hugo de Vries

Darwin	Hugo de Vries
Evolution is gradual	Evolution is sudden
Small heritable variations	Large mutations
Natural selection is the main force	Mutation is the main force
Directional variation	Random mutation
Slow evolution	Saltation (single-step evolution)

8. Darwin’s View

Darwin believed:

Small inherited variations accumulate over generations.
Natural selection acts on these variations.
Evolution is slow and gradual.

9. Mutation Characteristics

Mutation is:

Sudden
Random
Heritable
Directionless

It may be:

Beneficial
Harmful
Neutral

10. Speciation

Speciation is:

Formation of a new species from an existing species.

It occurs due to:

Accumulation of variations
Natural selection
Mutation
Reproductive isolation (covered later in NCERT)

One-Mark Questions

Q1. Who proposed the Mutation Theory?
Answer: Hugo de Vries.

Q2. On which plant did Hugo de Vries work?
Answer: Evening Primrose (Oenothera lamarckiana).

Q3. What is mutation?
Answer: A sudden, random, heritable change in genetic material.

Q4. What is saltation?
Answer: Evolution by a single large mutation.

Q5. According to Darwin, evolution is ________.
Answer: Gradual.

Q6. According to Hugo de Vries, evolution occurs by ________.
Answer: Mutation.

NCERT Keywords for Board Exams

Mechanism of Evolution
Mutation
Hugo de Vries
Evening Primrose
Saltation
Speciation
Heritable Variation
Natural Selection
Gradual Evolution
Random Mutation

Most Important NCERT Differences

Darwin’s Theory	Mutation Theory (de Vries)
Small, heritable variations	Large, sudden mutations
Gradual evolution	Sudden evolution (saltation)
Natural selection drives evolution	Mutation drives evolution
Variations are selected over time	New species may arise in one major step

Board Exam Tip

Remember these four high-yield facts:

Mutation Theory was proposed by Hugo de Vries.
He worked on Evening Primrose (Oenothera lamarckiana).
Mutation is a random, sudden, heritable change.
Saltation means evolution by a single large mutation.

CBSE Class 12 Biology – Biological Evolution (NCERT) Important Facts

1. Biological Evolution

Biological evolution began after the origin of the first cellular life forms.
Evolution occurs through Natural Selection.

2. Darwin’s Theory of Natural Selection

The two main concepts are:

Branching descent
Natural selection

3. Branching Descent

All organisms evolved from common ancestors.
New species arise by divergence from ancestral species.

4. Natural Selection

Nature selects individuals having favourable inherited variations.

These individuals:

Survive better.
Reproduce more.
Leave more offspring.

5. Fitness

According to Darwin,

Fitness = Reproductive success

It does NOT mean:

Physical strength
Body size
Intelligence

It means ability to survive and produce more offspring.

6. Genetic Basis of Evolution

Adaptation is heritable.
Fitness has a genetic basis.
Only inherited variations can be selected by nature.

Board Point: Acquired characters are not inherited.

7. Adaptation

Adaptation means characteristics that help an organism survive in its environment.

Example:

Antibiotic-resistant bacteria.
Camouflage in insects.

8. Example of Bacteria Evolution

A bacterial colony has natural variations.
When the environment changes, only bacteria with favourable traits survive.
They reproduce rapidly.
Eventually, the new type dominates the population.

Reason: Bacteria divide very quickly.

9. Rate of Evolution

Rate depends on generation time.

Fast Evolution

Bacteria
Viruses

Slow Evolution

Birds
Fish
Mammals

10. Lamarck’s Theory

Proposed by Jean Baptiste Lamarck.

Theory:

Evolution occurs by use and disuse of organs.
Acquired characters are inherited.

Example

Giraffes developed long necks by stretching to reach leaves.

Current Status: Rejected.

11. Darwin vs Lamarck

Darwin	Lamarck
Natural Selection	Use and Disuse
Heritable variations are selected	Acquired characters inherited
Accepted	Rejected

12. Thomas Malthus

His work on population growth influenced Darwin.
Natural resources are limited.
Organisms compete for survival.

13. Observations of Darwin

Organisms produce more offspring than can survive.
Resources are limited.
Population size remains relatively stable.
Individuals show variations.
Most variations are inherited.
Competition exists among organisms.

14. Struggle for Existence

Due to limited resources, organisms compete for:

Food
Space
Shelter
Mates

15. Survival of the Fittest

Only organisms with favourable inherited traits survive and reproduce more successfully.

16. Evolution is Gradual

Evolution occurs:

Slowly
Over many generations
By accumulation of favourable variations

Flow Chart (Very Important)

Variation
⬇
Competition
⬇
Natural Selection
⬇
Survival
⬇
More Reproduction
⬇
Inheritance
⬇
Evolution
⬇
New Species

One-Mark Questions

Q1. What is fitness according to Darwin?
Answer: Reproductive fitness (ability to leave more offspring).

Q2. Name the two key concepts of Darwinism.
Answer: Branching descent and natural selection.

Q3. Why do bacteria evolve faster than mammals?
Answer: Because bacteria have a very short generation time and reproduce rapidly.

Q4. Which scientist proposed the theory of use and disuse?
Answer: Jean Baptiste Lamarck.

Q5. Who influenced Darwin’s ideas on population?
Answer: Thomas Malthus.

Q6. What is adaptation?
Answer: An inherited characteristic that helps an organism survive and reproduce in a particular environment.

NCERT Keywords for Board Exams

Biological Evolution
Natural Selection
Branching Descent
Variation
Adaptation
Fitness
Reproductive Success
Heritable Variation
Lamarckism
Use and Disuse
Acquired Characters
Thomas Malthus
Struggle for Existence
Survival of the Fittest

Exam Tip: CBSE frequently asks the differences between Darwin’s theory and Lamarck’s theory, the meaning of fitness, and the role of variation and natural selection in evolution.

CBSE Class 12 Biology – Evolution of Life Forms (NCERT) Important Facts

Theory of Special Creation

According to religious literature:

All living organisms were created in their present form.
Species have remained unchanged since creation.
Earth is about 4000 years old.

CBSE Fact: These ideas were challenged during the 19th century.

Charles Darwin

Travelled around the world on H.M.S. Beagle.
Observed plants, animals, and fossils.
Proposed the Theory of Evolution by Natural Selection.

Important Observation

Living organisms show similarities with one another.
Present-day organisms also resemble extinct organisms.
Species have changed gradually over millions of years.

Evolution

Evolution is the gradual change in living organisms over long periods of time, leading to the formation of new species.

Variation

Every population has inherited variations.
Variations make individuals different from one another.
Variation is the raw material for evolution.

Natural Selection

Darwin proposed Natural Selection as the mechanism of evolution.

Principle

Individuals with favourable variations survive and reproduce more successfully.

This is also known as:

“Survival of the Fittest.”

Fitness (According to Darwin)

Fitness means reproductive fitness, not physical strength.

A fit organism:

Survives better.
Produces more offspring.
Passes favourable traits to the next generation.

Important Board Point: Fitness = Ability to leave more progeny.

Natural Selection Process

Variation
⬇
Competition
⬇
Survival of better-adapted individuals
⬇
More reproduction
⬇
Natural selection
⬇
Evolution

Alfred Russel Wallace

Worked in the Malay Archipelago.
Independently proposed the idea of Natural Selection.
Published similar conclusions around the same time as Darwin.

Extinction

Many organisms that lived millions of years ago no longer exist.
New species evolved while others became extinct.

Common Ancestor

All present-day organisms share common ancestors.
Different groups diverged over millions of years.

Geological and Biological History

NCERT states:

Geological history of Earth closely matches the biological history.
Evolution occurred over billions of years.

Important Keywords for Board Exams

Evolution
Natural Selection
Variation
Adaptation
Reproductive Fitness
Common Ancestor
Extinction
H.M.S. Beagle
Alfred Russel Wallace
Survival of the Fittest
Theory of Special Creation

Frequently Asked One-Mark Questions

Q1. Name the ship on which Darwin travelled.
Answer: H.M.S. Beagle

Q2. Who independently proposed Natural Selection besides Darwin?
Answer: Alfred Russel Wallace

Q3. What is meant by fitness according to Darwin?
Answer: Reproductive fitness (ability to leave more offspring).

Q4. What is the raw material of evolution?
Answer: Variation.

Q5. What is Natural Selection?
Answer: The process by which individuals with favourable variations survive and reproduce more successfully.

Q6. What does “Survival of the Fittest” mean?
Answer: Better-adapted individuals survive and produce more offspring.

NCERT Statements Often Asked in Boards

Evolution is a gradual process.
Variation exists in every population.
Natural selection is the mechanism of evolution.
Fitness refers to reproductive success.
All organisms share common ancestors.
Geological history correlates with biological history.
Earth is billions of years old, not thousands.