14 Questions
What is the general formula for carbohydrates?
C(H2O)n
What is the role of carbohydrates in plants?
They provide structure to the plant cell wall
What is another name for carbohydrates?
Saccharides
What is the function of carbohydrates in the human body?
They are a source of energy
What type of carbohydrate contains two monosaccharide units?
Disaccharide
What is the term for carbohydrates that contain 3-9 monosaccharide units?
Oligosaccharide
What is the minimum number of monosaccharide units a polysaccharide can contain?
More than 9
Which type of sugar contains a free aldehyde or ketose group?
Reducing sugar
What is the purpose of Molisch's test?
To detect the presence of carbohydrates
What is the principle behind Benedict's test?
Reduction of cupric ion in an alkaline medium
What is the purpose of Barfoed's test?
To distinguish between mono- and disaccharides
What is the purpose of Seliwanoff's test?
To distinguish between ketoses and aldoses
Which of the following is an example of a non-reducing sugar?
Sucrose
What is the common characteristic of all monosaccharides?
They are reducing sugars
Study Notes
Carbohydrates
- Organic molecules containing carbon, hydrogen, and oxygen
- Formed by green plants during photosynthesis from CO2 and water
- General formula: C(H2O)n, meaning "watered carbon"
- Also known as "saccharide" or sugars
- Major source of energy from diet
Importance of Carbohydrates
- Widely distributed in nature
- Key intermediates of metabolism (sugars)
- Structural components of plants (cellulose)
- Central to industrial products (paper, fibers)
- Key component of food sources (sugars, flour, vegetable fiber)
Classification of Carbohydrates
- Simple sugars (monosaccharides): contain one unit (e.g., glucose, fructose)
- Complex sugars:
- Disaccharides: contain two units (e.g., sucrose, lactose, maltose)
- Oligosaccharides: contain 3-9 units (e.g., raffinose)
- Polysaccharides: contain more than 9 units (e.g., starch)
Reducing and Non-Reducing Sugars
- Reducing sugars: have free aldehyde or ketose group (e.g., glucose, galactose, fructose, lactose, maltose)
- Non-reducing sugars: lack free aldehyde or ketose group (e.g., sucrose, oligosaccharides, polysaccharides)
Tests for Carbohydrates
Molisch's Test
- General test for all carbohydrates
- Principle: dehydration of carbohydrates into furfural compounds in strong acid, reacting with α-naphthol to form a violet-colored ring
- Procedure: 1 ml sugar, 5 drops α-naphthol, 10 drops H2SO4 slowly
Benedict's Test
- Test for reducing sugars
- Principle: reduction of cupric ion into cuprous oxide in hot alkaline medium, causing color change and red precipitate formation
- Procedure: 0.5 ml sugar solution, 1 ml Benedict's reagent, boiling water bath for 3 minutes
Barfoed's Test
- Distinguishes mono from disaccharides
- Principle: reduction of cupric ion in Barfoed's reagent faster by monosaccharides than disaccharides in hot acidic medium
- Procedure: 1 ml sugar solution, 1 ml Barfoed's reagent, boiling water bath for 2-3 minutes
Seliwanoff's Test
- Distinguishes between ketoses and aldoses
- Principle: ketoses are more rapidly dehydrated than aldoses when heated
- Used to identify ketoses and aldoses
Learn about carbohydrates, their definition, formation, and importance. Explore their structure, function, and role as a major source of energy.
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