Photosynthesis and Carbohydrates Quiz

Photosynthesis

• Green plants use sunlight to convert carbon dioxide and water into glucose and oxygen.

Carbohydrates

• Three main types: monosaccharides, disaccharides, polysaccharides.

Monosaccharides

• Single sugar unit.
• Chemical formula: C₆H₁₂O₆.
• Examples: glucose, fructose, galactose.

Disaccharides

• Formed by joining two monosaccharides through a condensation reaction (water loss).
• Chemical formula: C₁₂H₂₂O₁₁.
• Examples: maltose, sucrose, lactose.

Polysaccharides

• Formed by joining three or more monosaccharides through repeated condensation reactions.
• Can be straight or branched chains.
• Examples: starch, pectin, cellulose, gums, glycogen.
• Non-starch polysaccharides (NSPs) are also known as dietary fibre or roughage.

Starch

• Composed of:
  • Amylose (straight chains).
  • Amylopectin (branched chains).

Non-starch Polysaccharides (NSPs/Dietary Fibre)

• Cannot be digested by the body.
• Absorbs large amounts of water.
• Aids waste removal through peristalsis (muscular gut movements).
• Sources: wholemeal bread, brown rice, wholemeal pasta.

Properties of Sugars

• Solubility: Soluble in water; solubility increases with heating.
• Aeration: Denatures egg proteins for aeration (e.g., sponge cakes).
• Crystallization: Forms when more sugar is added than the liquid can absorb; crystals form on cooling.
• Caramelization: Heating produces brown caramel through gradual chemical changes (104°C to 177°C).
• Maillard Reaction: Sugar + amino acid + dry heat = browning.
• Sweetness: Fructose is significantly sweeter than lactose.
• Hydrolysis: Chemical breakdown by adding water to form smaller molecules (reverse of condensation).
• Inversion: Hydrolysis of sucrose into glucose and fructose (invert sugar); used in jam production.

Properties of Starch

• Flavour: Not sweet.

• Solubility: Insoluble in cold water.

• Hygroscopic: Absorbs moisture from the air (e.g., biscuits).

• Dextrinization: Heating forms shorter dextrin chains, and then brown pyrodextrins (e.g., toasting bread).

• Gelatinization: Heating in water causes swelling, bursting, and liquid absorption, thickening the mixture. Forming a sol that turns into a gel upon cooling.

Properties of Non-starch Polysaccharides (NSPs)

• Solubility: Insoluble in water.

• Bulk: Adds bulk to diet for feeling of fullness.

• Pectin: Found in fruit and vegetables; used in setting jams and jellies.

• Pectin Extraction: Rich fruits like blackcurrants and apples are heated, and an acid like lemon juice is added to change protopectin to pectin.

• Gel Formation: When heated with acid and sugar, pectin forms a gel by trapping water.

Effects of Heat on Carbohydrates

• Dry Heat: Browning from dextrins, caramelisation of sugar, and Maillard reactions.
• Moist Heat: Softening of cellulose, gelatinization of starch (thickening), pectin extraction (e.g., jam).

Culinary Uses of Carbohydrates

• Sugar: Sweetener, preservative, caramelisation, fermentation (bread), gel formation (jam), colour prevention, thickener, hygroscopic, dextrinization.

• NSPs: Gel formation (jam), bulkiness (texture), absorption of moisture.

Biological Functions of Carbohydrates

• Energy Source: Provides heat and energy for body functions.
• Protein Sparing: Allows proteins to be used for growth and repair instead of energy production.
• Energy Storage: Excess carbohydrate is stored as glycogen in the liver and muscles, or as fat.
• Cellulose: Speeds up waste removal; prevents bowel disorders like constipation.

Digestion of Carbohydrates

• Mouth: Chewing and salivary amylase breaks down starch to maltose.
• Pancreas: Amylase continues breaking down starch to maltose.
• Small Intestine: Maltase, sucrase, and lactase break down disaccharides into monosaccharides (glucose, fructose, galactose).

Absorption and Utilisation of Carbohydrates

• Monosaccharides are absorbed by the small intestine.
• Hepatic portal vein transports to the liver.
• Liver converts fructose and galactose to glucose.
• Glucose is used for energy, stored as glycogen, or converted to fat.

Test your knowledge on photosynthesis and the different types of carbohydrates, including monosaccharides, disaccharides, and polysaccharides. This quiz covers their definitions, structures, and examples, providing a comprehensive overview of vital concepts in plant biology and nutrition.