Why are carbohydrates called energy molecules?

Carbohydrates provide immediate energy in the form of glucose, which is oxidized to produce ATP during cellular respiration.

What is the difference between starch and cellulose?

Starch is a storage polysaccharide in plants and is digestible by humans, whereas cellulose is a structural polysaccharide and cannot be digested due to the absence of cellulase enzyme.

Carbohydrates – Structure, Classification & Functions

Carbohydrates are one of the most important biomolecules essential for life. They serve as the primary source of energy and play key structural and metabolic roles in living organisms.

What Are Carbohydrates?
Classification of Carbohydrates
Functions of Carbohydrates
Common Examples
Biological Importance
Exam Tips & Pitfalls
MCQs + Answers
True / False
Fill in the Blanks
FAQs
कार्बोहाइड्रेट (Hindi)

What Are Carbohydrates?

Carbohydrates are organic biomolecules composed of carbon (C), hydrogen (H), and oxygen (O). They are the most abundant organic compounds in nature and act as the primary source of energy for living organisms.

General Formula: C_n(H₂O)_n (mainly applicable to monosaccharides)

Classification of Carbohydrates

1. Monosaccharides

Simple sugars that cannot be hydrolyzed further.

Examples: Glucose, Fructose, Galactose

2. Disaccharides

Formed by the condensation of two monosaccharide units.

Sucrose (Glucose + Fructose)
Lactose (Glucose + Galactose)

3. Oligosaccharides

Contain 3–10 monosaccharide units and are often involved in cell recognition.

4. Polysaccharides

Long chains of monosaccharides serving storage or structural roles.

Starch – Plant storage
Glycogen – Animal storage
Cellulose – Plant cell wall

Functions of Carbohydrates

Provide quick energy (glucose)
Structural support (cellulose, chitin)
Components of nucleic acids (ribose & deoxyribose)
Main fuel for the brain and nervous system
Act as metabolic intermediates

Common Examples

Monosaccharides: Glucose, Fructose
Disaccharides: Sucrose, Lactose
Polysaccharides: Starch, Glycogen, Cellulose

Biological Importance

Ribose forms RNA backbone
Glycogen stores energy in liver and muscles
Cellulose maintains plant rigidity
Interconversion with fats during metabolism

Exam Tips & Pitfalls (NEET / CBSE)

Do not confuse starch (storage) with cellulose (structural)
Glucose is the main fuel of the brain
Sucrose is a non-reducing sugar

MCQs

Q1. The general formula of carbohydrate is:

(a) CnH2nOn (b) CnH2n-2On (c) CnH2n+2On (d) None

Answer: (a)

Q2. Storage carbohydrate in animals is:

Answer: Glycogen

True / False

Glucose is a polysaccharide ❌
Cellulose is digestible by humans ❌

Fill in the Blanks

Plant storage carbohydrate is Starch
Sugar in milk is Lactose

FAQs

Why are carbohydrate called energy molecules?
They provide immediate energy in the form of glucose for ATP synthesis.

Difference between starch and cellulose?
Starch is digestible storage polysaccharide, cellulose is indigestible structural polysaccharide.

कार्बोहाइड्रेट (Hindi)

कार्बोहाइड्रेट कार्बन, हाइड्रोजन और ऑक्सीजन से बने जैविक यौगिक हैं। ये शरीर में ऊर्जा का मुख्य स्रोत होते हैं। उदाहरण: ग्लूकोज़, स्टार्च, ग्लाइकोजन।

Carbohydrates – Wikipedia

Carbohydrates