Glycogen is a branched chain polymer of $\alpha$-D-glucose units in which chain is formed by C1-C4 glycosidic linkage whereas branching occurs by the formation of C1-C6 glycosidic linkage. Structure of glycogen is similar to _______. (i) amylose (ii) amylopectin (iii) cellulose (iv) glucose

> [!TLDR] > Glycogen is the animal storage polysaccharide, structurally analogous to amylopectin (the branched component of starch) — both have $\alpha$-1,4 chains with $\alpha$-1,6 branch points. The correct option is **(ii)**. The question tests your grasp of polysaccharide architecture — specifically, which plant polymer shares glycogen’s branching pattern. Let’s build the picture from the ground up. 1. **Recall the key structural features of glycogen.** Glycogen is a homopolymer of $\alpha$-D-glucose. The backbone consists of $\alpha$-1,4 glycosidic linkages (C1–C4), forming linear chains. Branching occurs via $\alpha$-1,6 linkages (C1–C6) every 8–12 residues. This creates a highly branched, compact molecule — ideal for rapid glucose release in animals. 2. **Now examine the options one by one.** - **Amylose** is the linear component of starch. It has only $\alpha$-1,4 linkages — no branching at all. So it cannot match glycogen’s structure. - **Amylopectin** is the branched component of starch. It has $\alpha$-1,4 chains with $\alpha$-1,6 branch points, exactly like glycogen. The only difference is that amylopectin branches less frequently (every 24–30 residues) and has a slightly different overall shape. But the *type* of linkages is identical. - **Cellulose** is a polymer of $\beta$-D-glucose with $\beta$-1,4 linkages. The $\beta$ configuration makes it linear and rigid — no branching, and the glycosidic bond is stereochemically opposite to glycogen’s $\alpha$ bonds. - **Glucose** is a monosaccharide, not a polymer. It doesn’t have glycosidic linkages at all. 3. **Identify the correct match.** The question explicitly says: “Structure of glycogen is similar to _______.” The similarity lies in the *pattern of glycosidic linkages* — both $\alpha$-1,4 and $\alpha$-1,6. That pattern is shared only with amylopectin among the given options. > [!WARNING] > A common mistake is to pick amylose because both are storage polysaccharides.

Glycogen is a branched chain polymer of α-D-glucose units in which chain is formed by C1-C4 glycosidic linkage

NCERT Exemplar · Q1

\alpha

(i) amylose

(ii) amylopectin

(iii) cellulose

(iv) glucose

Punjab PsebMCQ· 1mImportance★★★★★

31% · 34/110 Questions

✓ Free question

Concept understanding — Carbohydrate Functions Plants

Carbohydrates in Plants: Why They Matter

Think of a plant as a factory that builds itself out of thin air and sunlight. The raw material is carbon dioxide from the air, the energy comes from sunlight, and the first product it makes is glucose — a simple sugar. That glucose is the starting point for everything else.

Now, glucose is useful, but it's also fragile and reactive. A plant can't just leave piles of glucose lying around. It needs to store that energy for later (like a battery), and it needs to build strong structures (like a skeleton). This is where carbohydrates come in — they are glucose molecules linked together in different ways to serve different purposes.

The Two Big Jobs of Carbohydrates in Plants

1. Energy Storage (The Battery)

Plants make glucose during the day when the sun shines. But they need energy at night too, and during cloudy days, and when they're growing new leaves or making seeds. So they pack glucose molecules into a long, branched chain called starch.

Note

Starch is to plants what glycogen is to animals — a compact, insoluble way to store glucose. It's stored in roots (potatoes), seeds (rice, wheat), and stems (sugarcane).

When the plant needs energy, it breaks starch back down into glucose, which it then burns (respires) to get ATP — the energy currency of cells.

2. Structural Support (The Skeleton)

Plants don't have bones. Instead, they build rigid cell walls from cellulose — a completely different arrangement of glucose molecules. Cellulose chains lie flat and hydrogen-bond to each other, forming incredibly strong, rope-like fibres.

Watch out

Humans cannot digest cellulose. We lack the enzyme (cellulase) to break the bonds between its glucose units. That's why grass and wood pass right through us — they're structural, not food for us.

Cellulose gives plant cells their shape, allows trees to grow tall, and makes leaves stiff enough to catch sunlight.

The Precise Statement

\alpha

There's also a third, less famous role: sucrose (table sugar) is the main form in which plants transport glucose from leaves to other parts. It's a disaccharide — two glucose-like units stuck together — that dissolves easily in sap and doesn't react as readily as pure glucose.

A Quick Comparison Table

Carbohydrate	Monomer	Bond type	Function	Where found
Starch	$\alpha$ -glucose	$\alpha$ -(1,4) and $\alpha$ -(1,6)	Energy storage	Roots, tubers, seeds
Cellulose	$\beta$ -glucose	$\beta$ -(1,4)	Structural support	Cell walls
Sucrose	Glucose + fructose	$\alpha$ -(1,2)	Transport	Phloem sap

The Key Insight

The difference between starch and cellulose is just one tiny twist in the shape of the glucose molecule ( $\alpha$ vs $\beta$ ). That twist changes everything: starch is digestible, soluble, and good for storage; cellulose is indigestible, insoluble, and strong enough to hold up a redwood tree. Same building block, completely different function — that's the elegance of carbohydrate chemistry in plants.

The distinct roles of starch, cellulose and sucrose in plants are grounded in the NCERT Class 11 Biology curriculum on biomolecules and plant physiology, a common source of short-answer questions in CBSE board exams. Anyone revising "functions of carbohydrates in plants class 11 biology" or the starch-versus-cellulose comparison will find this alpha- versus beta-glucose explanation matches the textbook's own framing.

Why this formula?

Carbohydrate Functions in Plants: Why They Matter

Carbohydrates are not just energy sources — they are the structural backbone and chemical currency of plant life. Let’s break down why each key function works the way it does.

1. Photosynthesis: The Source of All Carbohydrates

Key equation:

6CO_2 + 6H_2O \xrightarrow{\text{light, chlorophyll}} C_6H_{12}O_6 + 6O_2

Why this holds:

Carbon fixation: Plants use light energy to split water ( $H_2O$ ) into protons, electrons, and oxygen. The electrons reduce $CO_2$ to form glucose ( $C_6H_{12}O_6$ ).
Energy storage: Glucose is the first stable carbohydrate — it stores chemical energy in its C–H bonds. The 6-carbon skeleton is ideal because it can be easily polymerised into starch or cellulose.
Oxygen as byproduct: The oxygen comes from water, not $CO_2$ — proven by isotope labelling ( $^{18}O$ in water appears in $O_2$ ).

Exam tip: Remember — the light reaction produces ATP and NADPH; the Calvin cycle uses them to reduce $CO_2$ to sugar.

2. Starch: Energy Reserve (Why Glucose is Stored as Starch)

Key formula:

\text{Glucose} \xrightarrow{\text{condensation}} \text{Amylose} + \text{Amylopectin} \ (\text{Starch})

Why starch, not free glucose?

Osmotic problem: Free glucose would draw water into cells via osmosis, causing swelling or bursting. Starch is insoluble — it doesn’t affect water potential.
Compact storage: Starch granules pack many glucose units in a small volume. Amylose is helical (tight), amylopectin is branched (even denser).
Quick mobilisation: Enzymes (amylases) can rapidly break starch back to glucose when energy is needed (e.g., at night, during germination).

Derivation insight: The $\alpha$ -(1→4) and $\alpha$ -(1→6) glycosidic bonds in starch are hydrolysable — this is why starch is a reserve, not a structural material.

3. Cellulose: Structural Support (Why Glucose is Polymerised Differently)

Key formula:

\text{Glucose} \xrightarrow{\beta\text{-(1→4) bonds}} \text{Cellulose} \ (\text{linear chains})

Why $\beta$ bonds instead of $\alpha$ ?

$\beta$ -(1→4) linkage flips every alternate glucose molecule 180°. This allows hydrogen bonding between parallel chains, forming strong microfibrils.
Rigidity: Cellulose is crystalline — it resists tensile stress. This is why plant cell walls can withstand turgor pressure.
Indigestibility: Most animals (including humans) lack cellulase enzymes. Only ruminants and termites (with microbial symbionts) can break $\beta$ bonds.

Key contrast: Starch = $\alpha$ bonds (flexible, digestible). Cellulose = $\beta$ bonds (rigid, indigestible). This is a classic exam comparison.

4. Sucrose: Transport Sugar (Why Not Glucose?)

Key formula:

\text{Glucose} + \text{Fructose} \xrightarrow{\text{glycosidic bond}} \text{Sucrose} + H_2O

Why sucrose for transport?

Non-reducing sugar: Sucrose has no free aldehyde/ketone group — it doesn’t react with proteins or other molecules during transport. Glucose would.
Energy efficiency: Sucrose carries two hexoses per molecule — twice the energy per transport event.
Phloem loading: Sucrose is actively loaded into sieve tubes via SUT transporters (sucrose uptake transporters). This creates osmotic flow (pressure flow hypothesis).

Derivation note: The glycosidic bond between glucose (C1) and fructose (C2) blocks both reducing ends — this is why sucrose is non-reducing.

5. Cell Wall Polysaccharides: Pectin and Hemicellulose

Key formula (pectin):

\text{Galacturonic acid} \xrightarrow{\alpha\text{-(1→4) bonds}} \text{Pectin}

Why pectin?

Gel-forming: Pectin’s negative charges (from uronic acids) bind $Ca^{2+}$ ions, forming a gel that cements adjacent cell walls.
Flexibility: Unlike cellulose, pectin is amorphous — it allows cell expansion during growth.
Fruit ripening: Enzymes (pectinases) break pectin, softening fruit — a key agricultural concept.

Summary Table: Why Each Carbohydrate Exists

Carbohydrate	Function	Why this form?
Glucose	Immediate energy	Soluble, easily metabolised
Starch	Long-term storage	Insoluble, compact, mobilisable
Cellulose	Structural support	Strong $\beta$ bonds, crystalline
Sucrose	Transport	Non-reducing, energy-dense
Pectin	Cell adhesion	Gel-forming, flexible

Final Exam-Ready Takeaway

Every carbohydrate’s structure is a direct consequence of its function.

Starch = $\alpha$ bonds → storage (easy to break).

Cellulose = $\beta$ bonds → structure (hard to break).

Sucrose = blocked reducing ends → safe transport.

If you understand why the bonds differ, you can derive the function — no rote memorisation needed.

Glycogen is the animal storage polysaccharide, structurally analogous to amylopectin (the branched component of starch) — both have $\alpha$ -1,4 chains with $\alpha$ -1,6 branch points. The correct option is (ii).

The question tests your grasp of polysaccharide architecture — specifically, which plant polymer shares glycogen’s branching pattern. Let’s build the picture from the ground up.

Recall the key structural features of glycogen.

Glycogen is a homopolymer of $\alpha$ -D-glucose. The backbone consists of $\alpha$ -1,4 glycosidic linkages (C1–C4), forming linear chains. Branching occurs via $\alpha$ -1,6 linkages (C1–C6) every 8–12 residues. This creates a highly branched, compact molecule — ideal for rapid glucose release in animals.
Now examine the options one by one.
- Amylose is the linear component of starch. It has only $\alpha$ -1,4 linkages — no branching at all. So it cannot match glycogen’s structure.
- Amylopectin is the branched component of starch. It has $\alpha$ -1,4 chains with $\alpha$ -1,6 branch points, exactly like glycogen. The only difference is that amylopectin branches less frequently (every 24–30 residues) and has a slightly different overall shape. But the type of linkages is identical.
- Cellulose is a polymer of $\beta$ -D-glucose with $\beta$ -1,4 linkages. The $\beta$ configuration makes it linear and rigid — no branching, and the glycosidic bond is stereochemically opposite to glycogen’s $\alpha$ bonds.
- Glucose is a monosaccharide, not a polymer. It doesn’t have glycosidic linkages at all.
Identify the correct match.

The question explicitly says: “Structure of glycogen is similar to _______.” The similarity lies in the pattern of glycosidic linkages — both $\alpha$ -1,4 and $\alpha$ -1,6. That pattern is shared only with amylopectin among the given options.

Watch out

A common mistake is to pick amylose because both are storage polysaccharides. But amylose is unbranched — it lacks the $\alpha$ -1,6 linkages that define glycogen’s branching. Storage function alone is not structural similarity.

Tip

A quick memory aid: Glycogen and amylopectin both have “glyc” or “pectin” — both are branched $\alpha$ -glucans. Amylose is the “odd one out” among starch components because it’s linear.

✓Final answer

The correct option is (ii) amylopectin .

Concept: Polysaccharide Structure — Branching in Starch vs Glycogen

Method: Structural Comparison of Storage Polysaccharides

Step 1: Recall the key structural features of glycogen

Glycogen is a highly branched polymer of $\alpha$ -D-glucose.
Linear chains: $\alpha$ ‑1,4 glycosidic linkages (C1–C4).
Branch points: $\alpha$ ‑1,6 glycosidic linkages (C1–C6).

Step 2: Compare with the given options

Polysaccharide	Linkages	Branching
Amylose	Only $\alpha$ ‑1,4	No branching (linear)
Amylopectin	$\alpha$ ‑1,4 (chains) + $\alpha$ ‑1,6 (branches)	Branched (but less frequent than glycogen)
Cellulose	$\beta$ ‑1,4	Linear, no branching
Glucose	Monomer, not a polymer	—

Step 3: Identify the closest match

Both glycogen and amylopectin have:
- $\alpha$ ‑D-glucose units
- $\alpha$ ‑1,4 chains
- $\alpha$ ‑1,6 branch points
The difference is only in degree of branching (glycogen is more highly branched), but the type of structure is identical.

Step 4: Conclusion

The structure of glycogen is similar to amylopectin.

Final Answer:

(B) amylopectin

Common Mistakes & How to Avoid Them

Mistake 1: Confusing Glycogen with Amylose

Why students make this mistake:

Students often remember that both glycogen and starch are storage polysaccharides of glucose, and assume "storage" means the same structure. Amylose is the unbranched component of starch, so it seems like a plausible answer.

How to avoid:

Focus on branching: Glycogen is highly branched (C1–C6 links every 8–12 residues). Amylose is completely unbranched (only C1–C4 links).
Key fact: Amylose = linear; Glycogen = branched. They are structurally opposite.

Mistake 2: Choosing Cellulose

Why students make this mistake:

Cellulose is also a glucose polymer, and students sometimes confuse "structural similarity" with "same monomer." They see "polymer of glucose" and pick cellulose without checking linkage type.

How to avoid:

Check the anomeric form: Glycogen uses α-D-glucose; cellulose uses β-D-glucose.
Linkage difference: Glycogen has α-1,4 and α-1,6 bonds; cellulose has β-1,4 bonds only.
Rule: α-linkages → digestible storage; β-linkages → structural (indigestible).

Mistake 3: Picking "Glucose" (Option D)

Why students make this mistake:

Some students misread the question as "glycogen is made of which monomer?" and answer glucose. The question asks for structural similarity, not composition.

How to avoid:

Read carefully: The question says "Structure of glycogen is similar to _______."
Remember: Glucose is a monomer, not a polymer. Glycogen is a polymer — compare it with other polymers.

Mistake 4: Not Knowing the Difference Between Amylopectin and Glycogen

Why students make this mistake:

Both amylopectin and glycogen are branched α-glucose polymers with α-1,4 and α-1,6 links. Students may think they are identical.

How to avoid:

Degree of branching:
- Amylopectin: branches every 25–30 glucose units.
- Glycogen: branches every 8–12 glucose units (more highly branched).
Structure is similar, not identical — but among the options, amylopectin is the closest match.

✓ Correct Answer: Amylopectin (Option B)

Why:

Both glycogen and amylopectin are branched polymers of α-D-glucose with C1–C4 chains and C1–C6 branch points. The only difference is branching frequency — glycogen is more densely branched.

Quick memory tip:

"Glycogen is like amylopectin on steroids — same structure, just more branches."

←Previous section · answersAnswers to Intext Questions →Next questionQ2 — Which of the following polymers is stored in the liver of animals? (i)…

Q.Glycogen is a branched chain polymer of α\alphaα-D-glucose units in which chain is formed by C1-C4 glycosidic linkage whereas branching occurs by the formation of C1-C6 glycosidic linkage. Structure of glycogen is similar to _______.

🎓Unlock everything free for 14 days

Q.Glycogen is a branched chain polymer of $\alpha$ -D-glucose units in which chain is formed by C1-C4 glycosidic linkage whereas branching occurs by the formation of C1-C6 glycosidic linkage. Structure of glycogen is similar to _______.

Unlock everything free for 14 days