Slide 1 There are two laws of thermodynamics that will be important for you to understand so that you understand cellular metabolism. The first law of thermodynamics can be stated in several ways. We can say that the amount of energy in the universe is constant. Or we can say that energy can neither be created nor destroyed, but only converted from one form to another Another way to say this law is to sat that the energy used and released in any reaction must be balanced. Some people even describe this law as "there is no free lunch" - this means that energy must come from somewhere and it isn't free! Slide 2 One of the goals of this course is to improve your critical thinking skills. This has relevance not only in the classroom but in your everyday life. There are always con artists who are willing to take your money through promises of miraculous medical cures or, as seen here, the promise of free electricity through the use of perpetual motion machines. Perpetual motion refers to the movement of a machine without any input of external energy. A basic scientific understanding of the first law of thermodynamics along with some critical thinking skills tells us that this is not possible! Perpetual motion is not physically possible here on earth. Slide 3 The closest I have come to believing in perpetual motion is when watching my Chihuahua Speedy. As you can see in this picture - he is blurry because he never stops moving! But I have to feed him so even with a Chihuahua there is no such thing as a free lunch or pepetual motion. Slide 4 The Second Law of Thermodynamics refers to the tendency of the universe to tend toward disorder. Like the first law, it can be stated in many different ways. We can say that matter is becoming more random. Or we can point out that entropy is increasing in the universe. Entropy is a measure of disorder. Another way of stating the second law is to say that all energy in the universe is tending toward heat. Heat is the most random form of energy. But it may be best to think about the second law in terms of familiar observations. This image shows a nice red shed. If no energy is put into maintaining this shed it will fall into disarray as disorder or entropy increases. To return the shed to good order - energy must be put into the system. This shed is a good analogy for our cells and our bodies. If we do not take in energy to do cell work and maintain our cells and bodies - we fall into disrepair. As work is done on the shed or as we do cellular work - heat is returned to the environment. As the most random form of energy - this heat is not useful to drive biological processes. Luckily we have a constant input of energy into the biosphere in the form of sunlight. Slide 5 Our sun provides energy to plants and other photosynthetic organisms. These organisms produce high energy compounds such as glucose that provide energy to all other organims. So, as long as the sun is shining on earth - we will have energy that we can use. Slide 6 But what happens when the sun stops shining....