ENERGY ABILITY TO DO WORK © PDST Home Economics

Energy Energy is the ability to do a task Energy is the ability to do a task The food we eat gives the body energy The food we eat gives the body energy Food is the fuel for the body Food is the fuel for the body

Measuring Energy Energy is measured in calories or joules Energy is measured in calories or joules We usually refer to kilocalories or kilojoules because a calorie or a joule is a very small amount We usually refer to kilocalories or kilojoules because a calorie or a joule is a very small amount A kilocalorie is the amount of heat energy it takes to raise a litre of water by 1ºC A kilocalorie is the amount of heat energy it takes to raise a litre of water by 1ºC 1kilocalorie = 4.2 kilojoules 1kilocalorie = 4.2 kilojoules

Getting energy from food Energy is got from food in a process called cellular respiration (oxidation). Energy is got from food in a process called cellular respiration (oxidation). Digested food and oxygen go into the body cells and react together to produce energy Digested food and oxygen go into the body cells and react together to produce energy Food + Oxygen → Energy + water + CO 2 Food + Oxygen → Energy + water + CO 2 Food labels tell us how much energy 100g of a food will give us.

Energy Content of Food All foods give us energy. All foods give us energy. Some food will give more energy than others it depends on the kind of nutrients in the food. Some food will give more energy than others it depends on the kind of nutrients in the food. Protein, Fats and Carbohydrates give a lot of energy but Water, Minerals and Vitamins give very little Protein, Fats and Carbohydrates give a lot of energy but Water, Minerals and Vitamins give very little 100g Cabbage = 22 kilocalories 100g Cabbage = 22 kilocalories 100g Cheddar cheese = 412 kilocalories 100g Cheddar cheese = 412 kilocalories Fats give the most energy Fats give the most energy

Energy Value of Nutrients 1g Protein = 4 kilocalories or 17 kilojoules of energy 1g Protein = 4 kilocalories or 17 kilojoules of energy 1g Carbohydrate = 4 kilocalories or 17 kilojoules of energy 1g Carbohydrate = 4 kilocalories or 17 kilojoules of energy 1g Fats = 9 kilocalories or 38 kilojoules of energy 1g Fats = 9 kilocalories or 38 kilojoules of energy

Amount of energy needed A basic amount of energy is needed just to keep the body alive ….. Heart, Lungs, Brain. A basic amount of energy is needed just to keep the body alive ….. Heart, Lungs, Brain. This basic amount of energy is called the Basal Metabolic Rate (BMR). This basic amount of energy is called the Basal Metabolic Rate (BMR).

Energy Needs Everyone needs a different amount of energy. The factors that decide how much energy you need are Age Age Size Size Activity Activity Gender Gender Climate Climate Pregnancy/ breast feeding Pregnancy/ breast feeding

Energy Balance To keep your body at the same weight, the amount of energy you take in must equal the amount of energy you use up To keep your body at the same weight, the amount of energy you take in must equal the amount of energy you use up If you eat more calories then you use you gain weight If you eat more calories then you use you gain weight If you eat less calories than you use you loose weight If you eat less calories than you use you loose weight

Functions of Energy All activities, including working internal organs All activities, including working internal organs Keeping body temperature at 37ºC Keeping body temperature at 37ºC Working of cells and nerves Working of cells and nerves Making new cells … growth Making new cells … growth

How much Energy do you need Girls 9 – 18 need 2300 kcals. per day Girls 9 – 18 need 2300 kcals. per day Boys 12 – 15 need 2800 kcals. per day Boys 12 – 15 need 2800 kcals. per day Boys 15 – 18 need 3000 kcals per day Boys 15 – 18 need 3000 kcals per day

How much energy? Activity done for 1 hour Sleeping - 70 kcals Writing kcals Housework kcals Walking fast kcals Swimming kcals Running kcals