Food stores chemical energy 7

Objectives Distinguish between kinetic and potential energy. Explain what chemical energy is and how cells release it from food. Define calories and kilocalories as units of energy.

Key Terms kinetic energy potential energy thermal energy chemical energy calorie

Energy is the ability to perform work. The two basic forms of energy are kinetic energy and potential energy. While you climb the stairs, you have kinetic energy, the energy of motion. Anything that is moving has kinetic energy.kinetic energy Once you reach the top of the stairs and are standing still, you have low kinetic energy. Where has the energy gone? Although it is not possible to destroy or create energy, energy can be converted from one form to another.

By climbing the stairs, your body converted kinetic energy to potential energy. Potential energy is energy that is stored due to an object's position or arrangement. As you climb higher against the force of gravity, your body gains potential energy due to its position—its higher location. The potential energy is converted back to kinetic energy as you move down the slide.Potential energy

What becomes of the energy once you have splashed into the pool and come to a stop? As you go down the slide, your body collides with air and water molecules, increasing their motion. And when you splash into the pool, the rest of your motion is transferred to the water. The air and water molecules transfer their motion in random directions as they collide again and again. This type of kinetic energy— random molecular motion—is called thermal energy. (Thermal energy that is transferred from a warmer object to a cooler one is referred to as heat.)thermal energy

You cannot retrieve this thermal energy and put it to work again. So, to climb the stairs again, you need a fresh supply of energy. That energy is provided by food.

Chemical Energy How do the organic compounds in food provide energy for a climb up a water slide? Just like the molecules in gasoline and other fuels, these organic compounds have a form of potential energy called chemical energy. In the case of chemical energy, the potential to perform work is due to the arrangement of the atoms within the molecules.chemical energy Chemical energy depends on the structure of molecules. Organic molecules such as the carbohydrates, fats, and proteins have structures that make them especially rich in chemical energy

Figure 7-6 compares potential energy due to position and chemical structure (chemical energy). In the case of potential energy due to position, the potential energy is converted to kinetic energy in the forms of motion and thermal energy (which is released to the surroundings as heat). In the case of chemical energy, the rearrangement of atoms during chemical reactions releases the potential energy. This energy is then available for work such as contracting a muscle.

Putting Chemical Energy to Work The organic molecules in food are high in chemical energy, just as the organic molecules in gasoline are. Cells and automobile engines make chemical energy available for work through similar processes. In both cases, a complex molecule is broken into smaller molecules that have less chemical energy than the original substance

Calories: Units of Energy You have probably heard the term calorie used to refer to food or exercise. A calorie is the amount of energy required to raise the temperature of 1 gram (g) of water by 1 degree Celsius (°C). However, a calorie is such a tiny unit of energy that it is not very practical for measuring the energy content of food. Instead, people usually express the energy in food in kilocalories. One kilocalorie (kcal) equals 1,000 calories. The "calories" shown on a food label are actually kilocalories.calorie