# Option B. Human Biochemistry B.1. all living things require the input of energy to exist – this energy is used to drive the thousands of biochemical reactions.

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Option B. Human Biochemistry B.1

all living things require the input of energy to exist – this energy is used to drive the thousands of biochemical reactions that occur to allow the organism to grow, reproduce and sustain life – this energy comes almost always from the Sun, in the first instance – energy from sunlight is captured by photosynthetic organisms (e.g. plants, algae, certain bacteria) and converted into carbohydrates. these are then broken down by a process called cellular respiration, to produce energy-rich molecules (e.g. adenosine triphosphate, or ATP) that release energy to drive biochemical reactions. – photosynthetic organisms can by ingested by nonphotosynthetic animals, and the carbohydrates (and other biomolecules) can be broken down and used for cellular respiration – in general an average man requires about 10,500 kilojoules (2500 kilocalories) per day, while an average woman needs approximately 8400kJ (2000 kcal) per day Introduction

a food (or bomb) calorimeter can be used, which measures the heat of combustion a known mass of a particular food is ignited and completely burnt in the presence of oxygen. Energy value of food using enthalpy of combustion data

energy contained in the food can be calculated using the following equation: q = mcΔT – q = heat evolved (J) – m = mass of water (g) – c = specific heat capacity of water (4.18 J g −1 K −1 or 4.18 J g −1 °C −1 ) – Δ T = temperature change of the water (in °C or K)

Worked example When 1.00 g of tomato soup was burnt in a food calorimeter containing 100 g water, it raised the temperature of the water from 20.4 °C to 28.0 °C. Calculate the energy content of 100 g of tomato soup. – q = mcΔT m = 100 g of water c = 4.18 J g −1 K −1 ΔT = 7.6 °C – therefore: q = 100 × 4.18 × 7.6 = 3176.8 J or 3.18 kJ – so, in 100 g of tomato soup… there will be 3.18 kJ(100g) of tomato soup = 318 kJ

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