Unit 2.1 Dynamic Cell PDF

Unit 2 THE DYNAMIC CELL UNIT 2.1 WHAT IS ENERGY? Learning Outcomes Distinguish between potential and kinetic forms of energy. Define the two laws of thermodynamics. Summarize how the laws of thermodynamics and the concept of entropy relate to living organisms. WHAT IS ENERGY?  Ene...

Unit 2 THE DYNAMIC CELL UNIT 2.1 WHAT IS ENERGY? Learning Outcomes Distinguish between potential and kinetic forms of energy. Define the two laws of thermodynamics. Summarize how the laws of thermodynamics and the concept of entropy relate to living organisms. WHAT IS ENERGY?  Energy is defined as the capacity to do work— to make things happen. Without a source of energy, life, including humans, would not exist on our planet. The biosphere receives energy from the sun, which is converted through life processes. Two basic forms of energy are potential and kinetic energy.  Potential energy is stored energy, while kinetic energy is the energy of motion. Potential energy is constantly converted to kinetic energy, and vice versa. An example is a diver converting potential energy into kinetic energy during a dive. Explanation: ✓ Food contains potential energy, which a diver can convert to kinetic energy to climb a ladder. ✓ Height is potential energy due to location, which the diver converts to kinetic energy when she jumps. Every conversion to kinetic energy loses some potential energy as heat. Measuring Energy Chemists use the joule unit to measure energy, but it is common to measure food energy in terms of calories. A calorie is the amount of heat required to raise the temperature of 1 gram of water by 1 degree Celsius. This isn’t much energy, so the caloric value of food is listed in nutrition labels and diet charts in terms of kilocalories (1,000 calories). On food label, and in scientific studies, an upper- case C (Calorie) indicates 1,000 calories. How much energy do you need per day to sustain life? Explanation: The measurement of the minimum energy requirements needed to sustain life is called the basal metabolic rate, or BMR. The BMR is responsible for activities such as maintaining body temperature, heartbeat, and basic nervous functions. The BMR varies widely, depending on the age and sex of the individual, as well as body mass, genetics, and activity level. BMR values may be as low as 1,200 and as high as 2,000 kilocalories per day. Energy Laws Two energy laws govern energy flow and help us understand the principles of energy conversion. Collectively, these are called the laws of thermodynamics Example Energy acquisition and conversion occur before a process, as seen in the diver's energy acquisition and conversion. Example Energy is frequently converted between forms at the cellular level, such as in muscles storing complex carbohydrate glycogen and converting it to kinetic energy for muscle contraction. Entropy ▪ The second law of thermodynamics states that energy cannot be changed without a loss of usable energy. ▪ Many forms of energy are usable, such as the energy of the sun, food, and ATP. ▪ Heat is the least usable form of energy, resulting in a loss of usable energy in the form of heat. ▪ Energy transformations lead to an increase in disorganization or disorder, referred to as entropy. ▪ Entropy refers to the relative amount of disorganization. ▪ The only way to bring about or maintain order is to add more energy to a system. Example 1 ▪ A tidy room is more organized and less stable than a messy room, which is disorganized and more. ▪ In other words, your room is much more likely to stay messy than it is to stay tidy. Why? Unless you continually add energy to keep your room organized and neat, it will inevitably become less organized and messy. All energy transformations, including those in cells, lead to an increase in entropy. ▪ Hydrogen ions (H+) that have accumulated on one side of a membrane tend to move to the other side unless they are prevented from doing so by the addition of energy. Why? Because when hydrogen ions are distributed equally on both sides of the membrane, no additional energy is needed to keep them that way, and the entropy, or disorder, of their arrangement has increased. The result is a more stable arrangement of H+ ions in the cell. Example 2 The second law of thermodynamics states that entropy (disorder) always increases. Therefore, (a) a tidy room tends to become messy and disorganized, and (b) hydrogen ions (H+) on one side of a membrane tend to move to the other side so that the ions are equally distributed. Both processes result in a loss of potential energy and an increase in entropy. Reactions in cells that progress from disorder to order require energy input. Example 3 Plant cells can make glucose out of carbon dioxide and water. How do they do it? Energy provided by the sun allows plants to make glucose, a highly organized molecule, from the more disorganized water and carbon dioxide. Even this process, however, involves a loss of some potential energy. When light energy is converted to chemical energy in plant cells, some of the sun’s energy is always lost as heat. In other words, the organization of a cell has a constant energy cost that also increases the entropy of the universe. END!