AP Biology Unit 1 Topic 1.4: Carbohydrates Structure and Function — Monosaccharides, Disaccharides, Polysaccharides

Question 1

What are carbohydrates and what elements do they contain?

Accepted Answer

Carbohydrates are organic molecules made of carbon, hydrogen, and oxygen, usually in a ratio of one carbon to two hydrogens to one oxygen. Their general formula is approximately C H two O repeated. They serve as energy sources, energy storage, and structural materials in cells.

Question 2

What is a monosaccharide?

Accepted Answer

A monosaccharide is the simplest carbohydrate, a single sugar molecule that cannot be broken down into smaller sugars. Common examples are glucose, fructose, and galactose, all of which share the molecular formula C six H twelve O six but differ in their structure. They are the monomers of all carbohydrates.

Question 3

Why is glucose the most important monosaccharide for living organisms?

Accepted Answer

Glucose is central because it is the primary fuel for cellular respiration, the process that produces ATP. It can also be converted to other sugars or stored as glycogen or starch. Almost all organisms can metabolize glucose, making it the universal currency of carbohydrate energy.

Question 4

What is a disaccharide?

Accepted Answer

A disaccharide is a carbohydrate made of two monosaccharides joined by a glycosidic bond formed through dehydration synthesis. Common examples are sucrose, which is glucose plus fructose; lactose, which is glucose plus galactose; and maltose, which is two glucose units.

Question 5

What is a glycosidic bond?

Accepted Answer

A glycosidic bond is the covalent bond that links two sugar molecules together. It is formed by dehydration synthesis, with the loss of a water molecule, and broken by hydrolysis. The orientation of the bond, called alpha or beta, has major consequences for whether the resulting carbohydrate is digestible and how it functions.

Question 6

What is a polysaccharide?

Accepted Answer

A polysaccharide is a large carbohydrate built from many monosaccharide units linked by glycosidic bonds. Polysaccharides serve two main roles: storing energy and providing structural support. The four most important polysaccharides for AP Biology are starch, glycogen, cellulose, and chitin.

Question 7

What is starch and what is its function?

Accepted Answer

Starch is the energy storage polysaccharide of plants, made of glucose monomers linked by alpha glycosidic bonds. It comes in two forms: amylose, which is unbranched, and amylopectin, which is branched. Starch is broken down by amylase into glucose during digestion.

Question 8

What is glycogen and how does it differ from starch?

Accepted Answer

Glycogen is the energy storage polysaccharide of animals and fungi, also made of glucose with alpha bonds. It is more highly branched than starch, allowing it to release glucose rapidly when energy is needed. In humans, glycogen is stored mainly in the liver and skeletal muscles.

Question 9

What is cellulose and why can humans not digest it?

Accepted Answer

Cellulose is the main structural polysaccharide of plant cell walls. It is made of glucose monomers linked by beta glycosidic bonds, which create straight chains that bundle into strong fibers. Humans lack the enzyme cellulase needed to break these beta bonds, so cellulose passes through our digestive system as fiber.

Question 10

What is chitin and where is it found?

Accepted Answer

Chitin is a structural polysaccharide found in the exoskeletons of arthropods like insects and crustaceans, and in the cell walls of fungi. It is similar to cellulose but contains a nitrogen-containing functional group on each monomer, which makes it stronger and more durable.

Question 11

How does the alpha versus beta bond orientation affect carbohydrate function?

Accepted Answer

Alpha glycosidic bonds produce coiled chains like those in starch and glycogen, which are easy to break down for energy. Beta glycosidic bonds produce straight chains like those in cellulose, which pack tightly into fibers and resist digestion. This is why starch is food and cellulose is fiber.

Question 12

Why are carbohydrates so important biologically?

Accepted Answer

Carbohydrates serve as the primary short-term energy source for most cells, the long-term energy storage in plants and animals through starch and glycogen, and the structural backbone of cell walls and exoskeletons. They also play roles in cell-to-cell recognition through glycoproteins on cell surfaces.

---