Small Molecular Weight Organic Compounds in Living Tissues (NEET Biology Notes)
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| Biomolecules in Living Tissues: Complete NEET study chart covering carbohydrates, amino acids, lipids, nucleotides, DNA and RNA. |
Introduction
Living organisms are made up of different types of organic molecules. These molecules are called biomolecules because they are essential for life.
The four major groups of biomolecules are:
Carbohydrates (Sugars)
Proteins (Amino acids)
Lipids (Fats and Oils)
Nucleic Acids (DNA & RNA building blocks)
These molecules perform different functions such as providing energy, building body tissues, storing food, and carrying genetic information.
1. Carbohydrates (Sugars)
What are carbohydrates?
Carbohydrates are the main source of energy in living organisms.
They are made up of three elements:
Carbon (C)
Hydrogen (H)
Oxygen (O)
General formula:
(CH₂O)ₙ
Examples shown in the figure
(A) Glucose
Molecular Formula:
C₆H₁₂O₆
Important Points
Most common sugar in living cells.
Also called blood sugar.
Primary source of energy.
Produced during photosynthesis.
Stored as glycogen in animals.
Stored as starch in plants.
NEET Facts
✔ Monosaccharide
✔ Six-carbon sugar (Hexose)
✔ Easily soluble in water
(B) Ribose
Molecular Formula:
C₅H₁₀O₅
Important Points
Five-carbon sugar.
Present in RNA.
Forms part of nucleotides.
NEET Facts
✔ Pentose sugar
✔ Present in RNA
✔ DNA contains deoxyribose instead of ribose.
Functions of Carbohydrates
Immediate source of energy
Energy storage
Structural component of cells
Formation of nucleic acids
2. Amino Acids
What are amino acids?
Amino acids are the building blocks (monomers) of proteins.
Each amino acid contains:
Amino group (–NH₂)
Carboxyl group (–COOH)
Hydrogen atom
Variable side chain (R-group)
General structure
NH₂—CH(R)—COOH
Examples shown
(A) Glycine
Features
Simplest amino acid
Side chain = H
NEET Fact
✔ Smallest amino acid
(B) Alanine
Features
Side chain = CH₃
It is slightly larger than glycine.
(C) Serine
Features
Side chain = CH₂OH
Contains a hydroxyl (–OH) group.
Functions of Amino Acids
Protein synthesis
Growth and repair
Enzyme formation
Hormone formation
Antibody production
Protein Formation
Many amino acids join together by peptide bonds to form proteins.
Amino acid + Amino acid
↓
Dipeptide
↓
Polypeptide
↓
Protein
3. Lipids (Fats and Oils)
What are lipids?
Lipids are molecules that:
Store energy
Form cell membranes
Provide insulation
Protect organs
Lipids are insoluble in water.
(A) Fatty Acid
Example shown:
Palmitic Acid
Formula:
CH₃(CH₂)₁₄COOH
Features
Saturated fatty acid
Long hydrocarbon chain
One carboxyl group
NEET Fact
Common saturated fatty acid.
(B) Glycerol
Structure
CH₂OH
|
CHOH
|
CH₂OH
Features
Three-carbon alcohol
Has three hydroxyl groups
Formation of Triglyceride
Three fatty acids combine with one glycerol molecule.
3 Fatty acids
1 Glycerol
↓
Triglyceride
This reaction releases 3 molecules of water.
Triglycerides
Functions
Long-term energy storage
Insulation
Protection of internal organs
Phospholipid (Lecithin)
Structure
Contains:
Glycerol
Two fatty acids
Phosphate group
Nitrogen-containing group
Importance
Major component of:
✔ Cell membrane
NEET Fact
Phospholipids form the lipid bilayer of cell membranes.
Cholesterol
What is cholesterol?
A steroid lipid found in animal cells.
Functions
Maintains membrane fluidity
Forms steroid hormones
Helps in Vitamin D synthesis
Helps in bile salt formation
NEET Fact
Plants do not contain cholesterol.
Functions of Lipids
Energy storage
Cell membrane formation
Hormone synthesis
Insulation
Protection
4. Nitrogen Bases
Nitrogen bases are components of nucleic acids.
They contain nitrogen atoms.
Types
Purines (Double Ring)
Adenine (A)
Guanine (G)
Pyrimidines (Single Ring)
Cytosine (C)
Thymine (T)
Uracil (U)
Figure Examples
Adenine
Purine
Double-ring nitrogen base.
Uracil
Pyrimidine
Found only in RNA.
Nucleosides
What is a nucleoside?
A nucleoside is formed when:
Nitrogen base
Sugar
↓
Nucleoside
No phosphate group is present.
Examples
Adenosine
Adenine
Ribose
↓
Adenosine
Uridine
Uracil
Ribose
↓
Uridine
Nucleotides
What is a nucleotide?
A nucleotide consists of:
Nitrogen base
Pentose sugar
Phosphate group
↓
Nucleotide
Example
Adenylic Acid (AMP)
Contains:
Adenine
Ribose
Phosphate
Difference Between Nitrogen Base, Nucleoside and Nucleotide
| Feature | Nitrogen Base | Nucleoside | Nucleotide |
|---|---|---|---|
| Sugar | ❌ | ✔ | ✔ |
| Phosphate | ❌ | ❌ | ✔ |
| Example | Adenine | Adenosine | AMP |
DNA vs RNA
| Feature | DNA | RNA |
|---|---|---|
| Sugar | Deoxyribose | Ribose |
| Bases | A, T, G, C | A, U, G, C |
| Strands | Double | Usually Single |
| Function | Genetic information | Protein synthesis |
NEET Important Points
Carbohydrates
Glucose = Hexose sugar
Ribose = Pentose sugar
Main source of energy
Amino Acids
Building blocks of proteins
Contain amino and carboxyl groups
Joined by peptide bonds
Lipids
Fatty acid + Glycerol = Fat
Triglycerides store energy
Phospholipids form cell membranes
Cholesterol is a steroid lipid
Nucleic Acids
Nitrogen base + Sugar = Nucleoside
Nucleoside + Phosphate = Nucleotide
Nucleotides form DNA and RNA
Flow Chart (Easy Revision)
Biomolecules
│
├── Carbohydrates
│ ├── Glucose
│ └── Ribose
│
├── Proteins
│ └── Amino Acids
│ ├── Glycine
│ ├── Alanine
│ └── Serine
│
├── Lipids
│ ├── Fatty Acid
│ ├── Glycerol
│ ├── Triglyceride
│ ├── Phospholipid
│ └── Cholesterol
│
└── Nucleic Acids
├── Nitrogen Base
├── Nucleoside
└── Nucleotide
NEET One-Line Revision
Glucose → Main energy source.
Ribose → Sugar of RNA.
Amino acids → Building blocks of proteins.
Glycine → Simplest amino acid.
Palmitic acid → Saturated fatty acid.
Glycerol → Three-carbon alcohol.
Triglyceride → Main storage fat.
Phospholipid → Forms cell membrane.
Cholesterol → Steroid lipid in animals.
Adenine → Purine base.
Uracil → Pyrimidine base found only in RNA.
Nucleoside = Base + Sugar.
Nucleotide = Base + Sugar + Phosphate.
DNA and RNA are polymers made of nucleotides.
These notes cover all the biomolecules shown in the figure in a simple, NEET-focused manner suitable for beginners.
CBSE Class 11 Biology
Chapter: Biomolecules
Question Bank (Part 1)
Topics Covered:
✔ Carbohydrates
✔ Amino Acids
✔ Lipids
✔ Nitrogen Bases
✔ Nucleosides
✔ Nucleotides
Section A : Multiple Choice Questions (MCQs)
Section B : Very Short Answer Questions (1 Mark)
Section C : Short Answer Questions (2–3 Marks)
| Glucose | Ribose |
|---|---|
| It is a hexose sugar (6 carbon atoms). | It is a pentose sugar (5 carbon atoms). |
| Molecular formula: C6H12O6 | Molecular formula: C5H10O5 |
| Main source of energy. | Present in RNA. |
| Produced during photosynthesis. | Forms part of nucleotides. |
- Provide immediate energy to living cells.
- Store food in plants (starch) and animals (glycogen).
- Form structural components of cells and nucleic acids.
Amino acids are organic compounds containing one amino group (-NH2) and one carboxyl group (-COOH). They are called the building blocks of proteins.
Functions:- Help in protein synthesis.
- Required for growth and repair of body tissues.
- Help in enzyme and hormone formation.
- Essential for antibody production.
A triglyceride is formed when one molecule of glycerol combines with three molecules of fatty acids through ester bonds.
Components:- One glycerol molecule
- Three fatty acid molecules
- Stores long-term energy.
- Provides insulation.
- Protects internal organs.
| Nucleoside | Nucleotide |
|---|---|
| Contains sugar and nitrogen base. | Contains sugar, nitrogen base and phosphate group. |
| No phosphate group is present. | Phosphate group is present. |
| Example: Adenosine | Example: AMP (Adenylic acid) |
- Store energy.
- Provide thermal insulation.
- Protect internal organs.
- Form cell membranes.
Nitrogen bases are classified into two groups.
Purines (Double-ring nitrogen bases)- Adenine (A)
- Guanine (G)
- Cytosine (C)
- Thymine (T)
- Uracil (U)
Phospholipids are important lipids that form the plasma membrane of cells.
Importance:- Form lipid bilayer.
- Maintain membrane structure.
- Control movement of substances across the membrane.
- Help in cell signaling.
Section D : Long Answer Questions (5 Marks)
Carbohydrates are organic compounds made up of carbon, hydrogen and oxygen. They are the main source of energy for living organisms.
Examples- Glucose
- Ribose
- Provide energy.
- Store food.
- Help in nucleic acid formation.
- Provide structural support.
- Glucose – Blood sugar
- Starch – Plant storage carbohydrate
- Glycogen – Animal storage carbohydrate
Lipids are water-insoluble biomolecules composed mainly of carbon, hydrogen and oxygen.
Types- Fatty acids
- Glycerol
- Triglycerides
- Phospholipids
- Cholesterol
- Energy storage.
- Formation of plasma membrane.
- Thermal insulation.
- Protection of organs.
- Hormone synthesis.
- Vitamin D synthesis.
Nucleoside is formed by the combination of a nitrogen base and a pentose sugar.
Example: Adenine + Ribose = Adenosine
Nucleotide is formed when one phosphate group is added to a nucleoside.
Example: Adenosine + Phosphate = AMP (Adenylic Acid)
Importance- Building blocks of DNA.
- Building blocks of RNA.
- Carry genetic information.
- Essential for protein synthesis.
Section E : Assertion and Reason Questions
Directions: Choose the correct option.
- A. Both Assertion (A) and Reason (R) are true, and R is the correct explanation of A.
- B. Both Assertion (A) and Reason (R) are true, but R is not the correct explanation of A.
- C. Assertion (A) is true, but Reason (R) is false.
- D. Assertion (A) is false, but Reason (R) is true.
Assertion (A): Glucose is the primary source of energy in living cells.
Reason (R): Glucose is easily oxidized during cellular respiration to produce ATP.
Assertion (A): Ribose is present in RNA.
Reason (R): Ribose is a pentose sugar.
Assertion (A): Amino acids are the building blocks of proteins.
Reason (R): Proteins are polymers formed by peptide bonds between amino acids.
Assertion (A): Phospholipids form the plasma membrane.
Reason (R): Phospholipids have hydrophilic heads and hydrophobic tails.
Assertion (A): Cholesterol is a steroid lipid.
Reason (R): Cholesterol is present only in animal cells.
Assertion (A): Uracil is present in DNA.
Reason (R): Uracil is a pyrimidine nitrogen base.
Assertion (A): Glycerol is a three-carbon alcohol.
Reason (R): Glycerol combines with fatty acids to form triglycerides.
Assertion (A): Nucleotides are the building blocks of nucleic acids.
Reason (R): A nucleotide contains a nitrogen base, pentose sugar and phosphate group.
Section F : Fill in the Blanks
Section G : Match the Columns
| Column A | Column B |
|---|---|
| Glucose | Energy source |
| Ribose | RNA sugar |
| Glycine | Simplest amino acid |
| Alanine | Amino acid |
| Palmitic acid | Saturated fatty acid |
| Glycerol | Three-carbon alcohol |
| Lecithin | Phospholipid |
| Cholesterol | Steroid lipid |
| Adenine | Purine |
| Uracil | Pyrimidine |
Answer Key
| Column A | Correct Match |
|---|---|
| Glucose | Energy source |
| Ribose | RNA sugar |
| Glycine | Simplest amino acid |
| Alanine | Amino acid |
| Palmitic acid | Saturated fatty acid |
| Glycerol | Three-carbon alcohol |
| Lecithin | Phospholipid |
| Cholesterol | Steroid lipid |
| Adenine | Purine |
| Uracil | Pyrimidine |
Section E : Assertion and Reason Questions
Directions: Choose the correct option.
- A. Both Assertion (A) and Reason (R) are true, and R is the correct explanation of A.
- B. Both Assertion (A) and Reason (R) are true, but R is not the correct explanation of A.
- C. Assertion (A) is true, but Reason (R) is false.
- D. Assertion (A) is false, but Reason (R) is true.
Assertion (A): Glucose is the primary source of energy in living cells.
Reason (R): Glucose is easily oxidized during cellular respiration to produce ATP.
Assertion (A): Ribose is present in RNA.
Reason (R): Ribose is a pentose sugar.
Assertion (A): Amino acids are the building blocks of proteins.
Reason (R): Proteins are polymers formed by peptide bonds between amino acids.
Assertion (A): Phospholipids form the plasma membrane.
Reason (R): Phospholipids have hydrophilic heads and hydrophobic tails.
Assertion (A): Cholesterol is a steroid lipid.
Reason (R): Cholesterol is present only in animal cells.
Assertion (A): Uracil is present in DNA.
Reason (R): Uracil is a pyrimidine nitrogen base.
Assertion (A): Glycerol is a three-carbon alcohol.
Reason (R): Glycerol combines with fatty acids to form triglycerides.
Assertion (A): Nucleotides are the building blocks of nucleic acids.
Reason (R): A nucleotide contains a nitrogen base, pentose sugar and phosphate group.
Section F : Fill in the Blanks
Section G : Match the Columns
| Column A | Column B |
|---|---|
| Glucose | Energy source |
| Ribose | RNA sugar |
| Glycine | Simplest amino acid |
| Alanine | Amino acid |
| Palmitic acid | Saturated fatty acid |
| Glycerol | Three-carbon alcohol |
| Lecithin | Phospholipid |
| Cholesterol | Steroid lipid |
| Adenine | Purine |
| Uracil | Pyrimidine |
Answer Key
| Column A | Correct Match |
|---|---|
| Glucose | Energy source |
| Ribose | RNA sugar |
| Glycine | Simplest amino acid |
| Alanine | Amino acid |
| Palmitic acid | Saturated fatty acid |
| Glycerol | Three-carbon alcohol |
| Lecithin | Phospholipid |
| Cholesterol | Steroid lipid |
| Adenine | Purine |
| Uracil | Pyrimidine |
Section L : Diagram-Based Questions
Q1. Observe the structure of glucose and answer the following questions.
- Write the molecular formula of glucose.
- How many carbon atoms are present?
- Which biomolecule group does glucose belong to?
- State one important function of glucose.
- C6H12O6
- Six
- Carbohydrates
- Provides immediate energy.
Q2. Observe the structure of glycine.
- Name the amino acid.
- Which functional groups are present?
- Why is it called the simplest amino acid?
- Glycine
- Amino group (-NH2) and Carboxyl group (-COOH)
- Because its side chain is only one hydrogen atom.
Q3. Observe the structure of glycerol.
- How many carbon atoms are present?
- How many hydroxyl (-OH) groups are present?
- Which important lipid is formed from glycerol?
- Three
- Three
- Triglyceride
Section M : True / False Questions
Section N : Revision Questions
Section O : Important NEET & CBSE One-Liners
- Glucose is the universal respiratory substrate.
- Ribose is the sugar present in RNA.
- Deoxyribose is the sugar present in DNA.
- Proteins are polymers of amino acids.
- Peptide bond joins two amino acids.
- Glycine is the smallest amino acid.
- Alanine contains a methyl (-CH3) side chain.
- Serine contains a hydroxyl (-OH) group.
- Palmitic acid is a saturated fatty acid.
- Glycerol is a three-carbon alcohol.
- Three fatty acids + One glycerol = One triglyceride.
- Lecithin is a phospholipid.
- Phospholipids form the plasma membrane.
- Cholesterol is a steroid lipid.
- Adenine and Guanine are purines.
- Cytosine, Thymine and Uracil are pyrimidines.
- Uracil is present only in RNA.
- DNA contains thymine instead of uracil.
- Nucleoside = Sugar + Nitrogen Base.
- Nucleotide = Sugar + Nitrogen Base + Phosphate.
- DNA and RNA are polymers of nucleotides.
Section P : Exam Tips
- Learn all molecular formulas carefully.
- Remember the difference between nucleoside and nucleotide.
- Practice diagram-based questions regularly.
- Revise purines and pyrimidines thoroughly.
- Memorize important examples like glucose, ribose, glycine, glycerol, palmitic acid and cholesterol.
- Read NCERT diagrams carefully as many CBSE and NEET questions are directly based on them.
★★★★★ Complete Biomolecules Question Bank Finished ★★★★★
CBSE Class 11 Biology + NEET Preparation
Includes:
✔ MCQs (15)
✔ Very Short Answer Questions
✔ Short Answer Questions
✔ Long Answer Questions
✔ Assertion & Reason
✔ Fill in the Blanks
✔ Match the Columns
✔ Statement-Based Questions
✔ Case Study Questions
✔ HOTS Questions
✔ Competency-Based Questions
✔ Diagram-Based Questions
✔ True/False Questions
✔ Revision Questions
✔ Important One-Liners
✔ Exam Tips
✔ Complete Answer Key
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