3. starch & cellulose

flashcards notes

What is the main role of starch in plants?

Energy storage.

Why is starch insoluble, and why is this important?

Insoluble → does not affect water potential or diffuse out of cells.

What two polymers make up starch?

Amylose and Amylopectin.

How is amylose structured, and how does this help storage?

Long unbranched α-glucose chains with α(1→4) glycosidic bonds → coils into a compact helix for dense energy storage.

How is amylopectin structured, and how does this help energy release?

Branched α-glucose chains with α(1→4) and α(1→6) bonds → branches increase surface area, allowing enzymes to release glucose quickly.

Where is glycogen stored in animals?

Liver and muscle cells.

How does glycogen’s structure differ from amylopectin?

More highly branched and compact.

Why does glycogen need to be more branched than starch?

Animals require rapid glucose release (e.g., during exercise) → branches allow faster hydrolysis by enzymes.

What type of bonds are present in glycogen?

α(1→4) glycosidic bonds in chains, α(1→6) bonds at branches.

What role does cellulose play in plants?

Provides structural support in cell walls and maintains cell turgidity.

What monomer makes cellulose, and how are they arranged?

β-glucose molecules joined by β(1→4) glycosidic bonds.

β-glucose molecules joined by β(1→4) glycosidic bonds.

To allow straight, unbranched chains to form.

How are cellulose chains strengthened?

Hydrogen bonds form between chains, creating microfibrils → very strong yet flexible.

Why is cellulose suited for cell wall strength?

Microfibrils provide tensile strength, resisting osmotic pressure and giving rigidity to plant cells.

What key difference explains why starch/glycogen are for storage but cellulose is structural?

α-glucose polymers coil or branch for compact storage and rapid hydrolysis, while β-glucose forms straight chains with hydrogen bonds for strength.

Which properties of starch and glycogen make them good storage molecules?

Compact, insoluble, and easily hydrolysed to glucose.