Carbohydrates Flashcards – AQA A-Level Biology - (7402)

How does a disaccharide form in a condensation reaction?

Two monosaccharides join by a glycosidic bond, releasing a molecule of water.

How does hydrolysis break the linkage in a disaccharide?

Water is used to break the glycosidic bond.

Which monosaccharides make up maltose?

Two glucose units.

Which monosaccharides make up sucrose?

Glucose and fructose.

Which monosaccharides make up lactose?

Glucose and galactose.

What is starch?

A plant storage polysaccharide formed by condensation of many $\alpha$-glucose units.

What is the structure of amylose?

An unbranched, coiled chain with $\alpha$-1,4 glycosidic bonds.

What is the structure of amylopectin?

A branched chain with $\alpha$-1,4 glycosidic bonds and $\alpha$-1,6 bonds at branch points.

How does starch's compactness benefit glucose storage?

It allows glucose to be stored in a small space.

What are the two consequences of starch being insoluble in cells?

It does not substantially affect cell water potential or diffuse out of cells.

How is glucose released from starch?

Its glycosidic bonds are hydrolysed.

What role do amylopectin's branches play in its breakdown?

They provide ends where breakdown can occur.

What is glycogen?

A storage polysaccharide in animal cells, formed by condensation of many $\alpha$-glucose units.

Which glycosidic bonds occur in glycogen chains and at their branch points?

$\alpha$-1,4 bonds occur in the chains; $\alpha$-1,6 bonds occur at branch points.

How does the branching of glycogen compare with that of amylopectin?

Glycogen is more highly branched than amylopectin.

How does glycogen’s compact structure help with glucose storage?

It allows glucose to be stored in a small space.

What are the two consequences of glycogen being insoluble in cells?

It does not substantially affect cell water potential or diffuse out of cells.

How do glycogen’s many branch ends help release glucose when needed?

They allow glycosidic bonds to be hydrolysed rapidly, releasing glucose.

What is cellulose made from, and how are its units joined to form the polymer?

Cellulose is a structural polysaccharide formed by condensation of many β-glucose units.

What type of glycosidic bond joins glucose units in cellulose?

β-1,4 glycosidic bonds.

How are alternate glucose units arranged in cellulose, and what shape does this give the chains?

Alternate units are rotated relative to one another, producing straight, unbranched chains.

How are cellulose chains grouped into strong microfibrils?

Hydrogen bonds form between neighbouring chains.

How do cellulose microfibrils help prevent plant cells from bursting when water enters?

They give cell walls tensile strength, helping them resist pressure from the cell contents.

What reagent is added to a sample to test for starch?

Iodine dissolved in potassium iodide solution.

What colours indicate positive and negative results in the iodine test for starch?

• Positive: blue-black
• Negative: yellow-brown