Energy for Life
Applying Energy for Life
As a heterotroph, you get all of your energyglossary term (opens in a new window) from eating food. No matter what you consume, all foods provide a source of energy called calories. A calorie is the amount of thermal energyglossary term (opens in a new window) needed to raise the temperature of 1 gram of water by 1°C. The Calories referred to on food labels are actually kilocalories—each is worth 1,000 calories (notice the uppercase “C” in the term). This information can sometimes be misinterpreted. For example, a hard-boiled egg contains 80 Calories of energy. However, since the units are actually kilocalories, the egg has 80,000 calories. Not to worry, though. The recommended caloric intake is 2,000 Calories a day, but since the units have been reduced for simplicity, the number of calories needed is actually two million! (Don’t take that as an excuse to go eat everything in sight).
In order to maintain your weight and keep the body functioning properly, caloric intake should be balanced with energy output. This means the number of calories taken in as food should equal the number of calories used or released as energy. This energy could be released as heat, as kinetic energy when you move, or as chemical energyglossary term (opens in a new window) in the compounds you excrete or defecate. If you wish to gain weight, you need to eat more food calories than the energy you use. If you wish to lose weight, eat fewer calories than you use. It’s all a matter of energy balance.
While there are several different opinions on how many calories one should consume a day, the overall idea is that most weight loss is a numbers game. For example, one of the recommended matrices used for weight maintenance is to take your body weight and multiply it by 12 for men and 11 for women. This will then give you an idea of how many calories a day you need to maintain your weight. How many do you need? Let’s say a man weighs 180 pounds. Doing the math (180 x 12), that means this man will need 2,160 Calories per day to maintain his weight. If he consumes less than that, he will lose weight. If he consumes more, he will gain weight. Additionally, the amount of exercise needs to be considered. If this man burns 400 calories a day running, then that increases the number of calories he can consume. The bottom line is that weight loss is all about the calories.
What is the ideal weight? All people, except identical twins, have genetic differences. This means their bodies and metabolism are different. However, studies of a large number of people have led scientists to create a tool that help individuals to determine a healthy body weight. This tool is called the body mass index, or BMI. The BMI is an estimate of body fat based on height and weight. It is not a precise figure, but it does tell you where you would fall compared to others. It may overestimate body fat in athletes who have a muscular build and underestimate body fat for individuals who have a low muscle mass. BMI can be determined using tables or special calculators available on the Internet.
The key to reaching and holding a healthy weight isn’t about short term changes in diet. It’s not about fad diets that promise quick results. It is about healthy eating and physical activity, balancing the calories you eat with the number of calories your body uses—energy in and energy out.
STEM and Energy for Life
Converting chemical energy into kinetic energy is the basis of how cars move. The potential energyglossary term (opens in a new window) stored in petroleum products is used to power the automobile engine. This combustion produces waste products that pollute the environment and is a non-renewable resource. This means that it will eventually get used up. Alternative fuel sources for cars are currently being researched.
Biofuels are fuels produced from biological sources. Biofuels can include using agricultural waste products, sawdust, and even corn to generate fuel such as ethanol. Corn is of particular interest because of its abundance and ease of converting into ethanol. The corn is cooked with different enzymes to convert its starch into simple sugars.
Corn production has reached all-time highs in the United States. Of the 1.5 billion bushels of corn produced in 2011, 600 million were used for biofuel. This is good news for the environment.
To meet the ever-growing demand for biofuels, crop science has become more and more popular as a course of study. Crop scientists conduct research on crops and other agricultural products to find new and improved ways to use these for fuel. A crop scientist may test several types of perennial grasses to see which can be most efficiently broken down into simple sugars. Crop scientists also work to improve crop yields by using techniques that could enhance feedstock production efforts. A career in this field would require a strong biology background, as well as a lot of field training.
Teacher Note
Use this summative assessment as a concluding activity after discussing the concepts of BMI, body weight, and energy. Have the students work on it together and then share their findings with the class.
