Carbohydrates

Question 1

Carbohydrates are chemically classified as:
A) Polyhydroxy aldehydes and ketones
B) Amino acids
C) Lipids
D) Nucleic acids

Answer 1

A

Question 2

The process by which plants synthesize carbohydrates is called:
A) Fermentation
B) Photosynthesis
C) Respiration
D) Hydrolysis

Answer 2

B

Question 3

The molecular formula of glucose is:
A) C5H10O5
B) C6H12O6
C) C7H14O7
D) C8H16O8

Answer 3

B

Question 4

The main product of photosynthesis is:
A) Starch
B) Glucose
C) Fructose
D) Protein

Answer 4

B

Question 5

Which of the following is NOT a property of carbohydrates?
A) Soluble in water
B) Have a sweet taste
C) Contain nitrogen
D) Can be used as an energy source

Answer 5

C

Question 6

The main source of carbon in the formation of carbohydrates in plants is:
A) Carbon dioxide
B) Water
C) Oxygen
D) Sunlight

Answer 6

A

Question 7

Which functional group is present in glucose?
A) Amine
B) Hydroxyl and Carbonyl
C) Carboxyl
D) Ester

Answer 7

B

Question 8

The process of carbohydrate metabolism in animals is known as:
A) Glycolysis
B) Photosynthesis
C) Fermentation
D) Hydrolysis

Answer 8

A

Question 9

Which element is NOT a major component of carbohydrates?
A) Carbon
B) Hydrogen
C) Oxygen
D) Nitrogen

Answer 9

D

Question 10

The breakdown of glucose to release energy occurs in:
A) Photosynthesis
B) Cellular respiration
C) Polymerization
D) None of the above

Answer 10

B

Question 11

What are carbohydrates?

Answer 11

Carbohydrates are polyhydroxy aldehydes or ketones that serve as a primary energy source in living organisms.

Question 12

What is the molecular formula of glucose?

Answer 12

The molecular formula of glucose is C₆H₁₂O₆.

Question 13

What is the main product of photosynthesis?

Answer 13

The main product of photosynthesis is glucose.

Question 14

What are the reactants of photosynthesis?

Answer 14

Carbon dioxide (CO₂) and water (H₂O) are the reactants of photosynthesis.

Question 15

What functional groups are present in glucose?

Answer 15

Glucose contains hydroxyl (-OH) and carbonyl (C=O) functional groups.

Question 16

What role do carbohydrates play in metabolism?

Answer 16

Carbohydrates serve as an energy source, being broken down in cellular respiration to produce ATP.

Question 17

Why are carbohydrates soluble in water?

Answer 17

Carbohydrates have multiple hydroxyl (-OH) groups that form hydrogen bonds with water molecules, making them soluble.

Question 18

What is the difference between an aldose and a ketose?

Answer 18

Aldoses have an aldehyde (-CHO) group, while ketoses have a ketone (C=O) group.

Question 19

How do plants produce carbohydrates?

Answer 19

Plants synthesize carbohydrates through photosynthesis, using CO₂, H₂O, and sunlight.

Question 20

What is the chemical equation for photosynthesis?

Answer 20

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (in the presence of sunlight).

Question 21

Define carbohydrates and explain their general chemical composition.

Answer 21

Carbohydrates are organic compounds composed of carbon (C), hydrogen (H), and oxygen (O), usually in a ratio of 1:2:1. They are classified as polyhydroxy aldehydes or ketones because they contain multiple hydroxyl (-OH) groups and either an aldehyde (-CHO) or a ketone (C=O) functional group. The general formula for carbohydrates is (CH₂O)n, where n ≥ 3.

Question 22

Differentiate between aldose and ketose carbohydrates with suitable examples.

Answer 22

Aldoses are carbohydrates that contain an aldehyde (-CHO) functional group at the terminal carbon.
Example: Glucose (C₆H₁₂O₆), an aldohexose.
Ketoses are carbohydrates that contain a ketone (C=O) functional group usually at the second carbon.
Example: Fructose (C₆H₁₂O₆), a ketohexose.
Both glucose and fructose have the same molecular formula but differ in functional groups, making them structural isomers.

Question 23

Describe the process of photosynthesis and explain how it contributes to carbohydrate formation.

Answer 23

Photosynthesis is the biological process by which green plants, algae, and some bacteria convert light energy into chemical energy in the form of carbohydrates. The process occurs in the chloroplasts of plant cells and involves two stages:

Light-dependent reactions – Occur in the thylakoid membrane, where sunlight is absorbed to produce ATP and NADPH.
Light-independent reactions (Calvin Cycle) – Occur in the stroma, where CO₂ is fixed using ATP and NADPH to form glucose.

Question 24

Write the balanced chemical equation for the synthesis of glucose via photosynthesis and explain each reactant and product.

Answer 24

The balanced equation for photosynthesis is:

6
C
O
2
+
6
H
2
O
→
sunlight
C
6
H
12
O
6
+
6
O
2
6CO
2
​
+6H
2
​
O
sunlight
​
C
6
​
H
12
​
O
6
​
+6O
2
​

Reactants:
CO₂ (Carbon dioxide): Absorbed from the atmosphere.
H₂O (Water): Absorbed from the soil.
Sunlight: Provides the energy required for the reaction.
Products:
C₆H₁₂O₆ (Glucose): A simple sugar stored as energy.
O₂ (Oxygen): Released into the atmosphere as a byproduct.
This process is crucial for producing organic compounds that serve as food for plants and other organisms.

Question 25

Discuss the significance of hydroxyl (-OH) and carbonyl (C=O) functional groups in carbohydrates.

Answer 25

The hydroxyl (-OH) groups make carbohydrates highly polar and soluble in water, allowing easy transport in biological systems. They also participate in hydrogen bonding, stabilizing carbohydrate structures. The carbonyl (C=O) group determines whether the carbohydrate is an aldose (aldehyde) or ketose (ketone). It is highly reactive and plays a key role in the formation of ring structures in sugars. These functional groups make carbohydrates versatile biomolecules involved in energy storage, signaling, and structural functions.

Question 26

Explain why carbohydrates are considered the primary source of energy in most living organisms.

Answer 26

Answer: Carbohydrates serve as a primary energy source because: They can be easily broken down into simpler sugars (e.g., glucose) that undergo cellular respiration to produce ATP, the energy currency of the cell. Glycogen (animals) and starch (plants) act as storage forms of carbohydrates, ensuring a readily available energy supply. Unlike proteins and fats, carbohydrates provide quick and efficient energy metabolism, making them the preferred energy source for the brain and muscles.

Question 27

Describe the structural difference between glucose and fructose.

Answer 27

Answer: Glucose is an aldohexose with an aldehyde (-CHO) functional group at carbon 1. Fructose is a ketohexose with a ketone (C=O) functional group at carbon 2. Both sugars have the same molecular formula (C₆H₁₂O₆) but differ in their functional groups and structural arrangement.

Question 28

How does the polyhydroxy nature of carbohydrates contribute to their solubility in water?

Answer 28

Answer: Carbohydrates contain multiple hydroxyl (-OH) groups, which form hydrogen bonds with water molecules. These interactions make them highly hydrophilic (water-soluble), allowing carbohydrates like glucose to dissolve easily in biological fluids for transport and metabolism.

Question 29

Discuss the role of carbohydrates in plant metabolism and storage.

Answer 29

Answer: Carbohydrates play several essential roles in plants: Energy storage: Glucose is converted into starch for long-term storage. Structural support: Cellulose, a carbohydrate polymer, forms the cell wall, providing rigidity. Metabolism: Carbohydrates act as fuel in cellular respiration to generate ATP for plant growth and development. Transport: Sucrose (a disaccharide) transports energy from leaves to other parts of the plant via the phloem.

Question 30

Explain the importance of glucose in biological systems and how it is utilized in cellular respiration.

Answer 30

Glucose is the primary metabolic fuel in living organisms. In cellular respiration, it is broken down through three key steps: Glycolysis: Occurs in the cytoplasm, breaking glucose into pyruvate, producing ATP and NADH. Krebs Cycle (Citric Acid Cycle): Takes place in mitochondria, generating electron carriers NADH and FADH₂. Electron Transport Chain (ETC): Produces ATP through oxidative phosphorylation. The overall equation for cellular respiration is: C 6 H 12 O 6 + 6 O 2 → 6 C O 2 + 6 H 2 O + A T P C 6 ​ H 12 ​ O 6 ​ +6O 2 ​ →6CO 2 ​ +6H 2 ​ O+ATP Glucose is vital for ATP production, fueling cellular processes such as muscle contraction, nerve function, and biosynthesis.

Question 31

can a carbohydrate contain both aldehyde and ketone groups

Answer 31

No, a carbohydrate cannot naturally contain both an aldehyde (-CHO) and a ketone (C=O) functional group at the same time. Explanation: Carbohydrates are classified based on their functional groups: Aldoses: Contain an aldehyde (-CHO) group at carbon-1. Ketoses: Contain a ketone (C=O) group, usually at carbon-2. Mutual Exclusion: In a monosaccharide, only one carbonyl functional group can be present—either an aldehyde or a ketone, but not both. If a molecule had both, it would not be classified as a simple carbohydrate (monosaccharide) but rather a derivative or a chemically modified carbohydrate. Exceptions in Special Cases: Some derivatives of carbohydrates may be chemically modified to contain both an aldehyde and a ketone group, but this does not occur in naturally occurring simple sugars.

Question 32

can a carbohydrate contain two carbon atoms

Answer 32

No, a naturally occurring carbohydrate cannot contain only two carbon atoms because the smallest possible carbohydrate must have at least three carbon atoms (a triose). Explanation: General Carbohydrate Formula: Carbohydrates follow the empirical formula (CH₂O)n, where n ≥ 3. The smallest naturally occurring monosaccharides are trioses (C₃H₆O₃), such as: Glyceraldehyde (an aldose) Dihydroxyacetone (a ketose) Why Not C₂H₄O₂? A two-carbon (C₂) compound following the (CH₂O)n rule would be C₂H₄O₂, which does not fit the structure of a carbohydrate. It would lack the necessary polyhydroxy (multiple -OH) and carbonyl (-CHO or C=O) features that define carbohydrates. Are There Any C₂ Sugar-Like Compounds? There exist two-carbon sugar derivatives, such as glycolaldehyde (C₂H₄O₂), but they are not classified as true carbohydrates. Glycolaldehyde is a simple aldehyde with hydroxyl groups, but it does not fit the polyhydroxy definition of carbohydrates. Conclusion: Carbohydrates must have at least three carbon atoms, making C₂ carbohydrates impossible under the standard biochemical definition.

Question 33

Stereoisomers in Carbohydrates

Answer 33

Stereoisomers are compounds with the same molecular formula and sequence of bonded atoms but different 3D orientations. Example: D-Glucose and L-Glucose D-Glucose and L-Glucose are stereoisomers because they have the same molecular formula (C₆H₁₂O₆) but differ in their spatial arrangement.

Question 34

Enantiomers (Mirror Images) Definition: Enantiomers are non-superimposable mirror images of each other.

Answer 34

Example: D-Glucose and L-Glucose are enantiomers. They are mirror images but cannot be rotated to look exactly the same. Most naturally occurring sugars in living organisms are D-sugars.

Question 35

Diastereomers (Non-Mirror Stereoisomers)

Answer 35

Definition: Diastereomers are stereoisomers that are not mirror images of each other. Example: D-Glucose and D-Mannose are diastereomers because they differ at C-2 but are not mirror images. D-Glucose and D-Galactose are also diastereomers (differ at C-4).

Question 36

Epimers (A Type of Diastereomer)

Answer 36

Definition: Epimers are diastereomers that differ at only one chiral carbon. Examples: D-Glucose and D-Mannose (C-2 epimers) D-Glucose and D-Galactose (C-4 epimers)

Question 37

Anomers (A Type of Epimer)

Answer 37

Definition: Anomers are epimers that differ specifically at the anomeric carbon (C-1 in aldoses, C-2 in ketoses) when the sugar is in its cyclic form. Examples: α-D-Glucose and β-D-Glucose are anomers because they differ at C-1: α-anomer: -OH group on C-1 is down in Haworth projection. β-anomer: -OH group on C-1 is up in Haworth projection. Anomers exist in equilibrium due to mutarotation in aqueous solutions.

Question 38

isomerism in carbohydrates

Answer 38

Question 39

Define monosaccharides and explain their significance in biological systems.

Answer 39

Monosaccharides are the simplest form of carbohydrates, consisting of a single sugar unit. They are polyhydroxy aldehydes or ketones that cannot be hydrolyzed into simpler sugars. Significance: They are the building blocks of larger carbohydrates like disaccharides and polysaccharides. They serve as quick energy sources in metabolic processes like glycolysis. Some, like ribose, are essential for nucleic acids (DNA & RNA).