Food Energy & Basal Metabolic Rate Why do we need to eat?
Why do we need to eat? • Nutrients in food (carbs, fat, and protein) provide the raw materials necessary for growth and maintenance of our bodies. • Nutrients contain chemical energy (= bond energy) that cells use to fuel biological processes and physical activity • Warm-blooded animals expend a great deal of energy to maintain body temperature
Metabolism • Metabolism: • The set of chemical reactions that occur in living organisms that are necessary to maintain life • It is the rate at which your body converts stored energy into working energy • Two general types of reactions involved • Catabolism – chemical and physical breakdown of materials • Anabolism: building large, complex molecules from smaller, simpler molecules
Demo: Chemical Bond Energy • Decomposition of sucrose (table sugar) sugar water + carbon dioxide C12H22O11 (s) 11 H2O(g) + 12 C(s) • Predict: should energy be absorbed or released? Why? • Do your observations support your prediction?
Factors Affecting Metabolism • Physical activity –More strenuous activity requires more energy • Body size – larger bodies require more energy • Body surface area: Higher surface area means more heat is lost • Body composition: Muscle burns more energy than fat • Sex: Males require more energy • Age: Metabolic rate decreases with age • Genetics: Naturally use energy faster/slower
Measuring Energy • Energy is measured in: • joules (J) or kilojoules (kJ) 1 kJ = 1000 J • calories (c) or Calories (C) 1 Cal = 1000 cal • Calorie (with a big ‘C’) is listed on food labels • Defined as “the amount of energy required to raise the temperature of 1 L of water by one degree Celsius) • 1 Cal = 4.18 kJ
Basal Metabolic Rate (BMR) • BMR - Amount of energy required by an organisms at rest • Daily basal energy requirement is estimated based on: height, weight, age, sex
Mini-Investigation • Calculate your BMR using Harris- Benedict equation. You will need: • Height in cm • Weight in kilograms (1 kg = 2.2 lb)