Part B · Food tests and food energy Key concepts in biology mind map

Food tests

• Prepare: Crush with distilled water; separate portions; filter if needed
• Starch: Iodine: orange-brown → blue-black
• Reducing sugar: Benedict’s + water-bath heat → coloured precipitate
• Protein: Biuret reagents → lilac / purple; peptide bonds
• Lipid: Ethanol then water → white emulsion; no flames
• Controls: Known positive / water negative; same volumes and heating

Calorimetry

• Measure: Known water mass; temperature rise; food mass actually burned
• Water energy: E = mcΔT; c = 4.2 J/(g °C) when m is in grams
• Per gram: Water energy ÷ food burned; 1,260 J ÷ 0.5 g = 2,520 J/g
• Limits: Heat losses / incomplete burning underestimate; improve / repeat

Connections

• Food tests → Calorimetry: Food composition and burning energy answer different questions.
• Calorimetry → Food tests: Both investigations require controlled comparisons and valid measurements.