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What is a carbohydrate?

A carbohydrate is an organic molecule made of carbon (C), hydrogen (H), and oxygen (O) in a 1:2:1 ratio. It serves as a primary energy source for living organisms.

What is the monomer of a carbohydrate?

The monomer of a carbohydrate is a monosaccharide (simple sugar).

List the pentose monosaccharides. What are the respective functions?

Ribose – A component of RNA and ATP.

Deoxyribose – A component of DNA.

List the hexose monosaccharides. What are the respective functions?

Glucose – Primary energy source for cells.

Fructose – Found in fruits; converted to glucose in the body.

Galactose – Component of lactose; converted to glucose in metabolism.

List the disaccharides. What are the respective functions?

Maltose (glucose + glucose) – Found in germinating grains; broken down into glucose.

Lactose (glucose + galactose) – Found in milk; provides energy.

Sucrose (glucose + fructose) – Table sugar; major energy source.

List the polysaccharides. What are the respective functions?

Starch – Storage form of glucose in plants.

Glycogen – Storage form of glucose in animals.

Cellulose – Structural component of plant cell walls (not digestible by humans).

Chitin – Structural component in fungi and exoskeletons of arthropods.

What is an enzyme?

An enzyme is a biological catalyst that speeds up chemical reactions without being consumed.

What polysaccharide can humans not digest because we lack the enzyme?

Cellulose (humans lack the enzyme cellulase).

What is the name of the reagent (chemical) used to test for reducing sugars?

Benedict’s reagent.

What metal does it contain?

Copper (Cu²⁺).

What color solution indicates high reducing sugar content? Medium reducing sugar content? Low reducing sugar content? No reducing sugar content?

High – Brick red or orange

Medium – Yellow

Low – Green

None – Blue

Which disaccharide is NOT a reducing sugar?

Sucrose.

What is a control? What is a positive control? What is a negative control?

Control – A sample used as a standard for comparison.

Positive control – Contains the substance being tested and should give a positive result.

Negative control – Lacks the substance being tested and should give a negative result.

What solution did we use as a positive control?

A solution containing a known reducing sugar (e.g., glucose solution).

What solutions did we use for negative controls?

Distilled water or a solution without reducing sugar.

Indicate positive and negative control from the following picture.

(You would need to analyze the color results in the tubes; generally, blue indicates a negative control, and red/orange/yellow indicates a positive control.)

What reducing sugar is found in milk?

Lactose.

What reducing sugar is found in apple juice?

Fructose and glucose.

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