What is Life? What does it mean to be alive? Though it may sound like a straightforward question, finding the line between living and non-living can be quite complex. Is there a “life defining line” between a rock, a virus, a bacterium, a plant, a fungus, an animal, a cell phone, a robot, or chat bot software? If so, what is that line? What do you think is more important for defining life, what it does, or what it’s made of? Let’s list 5 key characteristics that most scientists agree are common to all known life. All Living Things: ▪ ___________________________________________________________________________ ▪ ___________________________________________________________________________ ▪ ___________________________________________________________________________ ▪ ___________________________________________________________________________ ▪ ___________________________________________________________________________ A Closer Look at the Characteristics of Life Use of Energy Living things use energy to create order. They organize their molecules and chemical processes. The molecules on the surface of Mars are relatively homogenous and disordered. The molecules in this rainforest are highly varied. They are complex, organized, and performing specific functions. Nearly all of the energy used by living things on Earth comes from the sun. Name the chemical process that traps energy from the sun: ____________________________________ This solar energy is trapped and stored in molecules of ____________________________________ Photosynthesis carbon dioxide + water glucose (sugar) + oxygen Name the chemical process that living things use to release energy from sugars: _________________________________________________ Cellular Respiration glucose (sugar) + oxygen carbon dioxide + water Growth and Reproduction Living things grow bigger, repair damage, and make offspring to persist through time. There are two different modes of reproduction: Asexual Reproduction Sexual Reproduction What is it? Main advantage Example organisms Respond and Adapt to Environment Living things respond to stimuli. This can be quick and simple like squinting in the sun, or slow and complex like developing a tan when exposed to the sun. Over many generations, the offspring of organisms change in response to the conditions in their environment. This is known as evolution. Can you think of or research some interesting ways that different organisms respond to stimuli? Species / Group Stimulus response Mammals Cold temperature shivering Living things often maintain their internal conditions within a range. This is called: ___________________________________ What are some examples of conditions that the human body maintains within homeostasis? _______________________________________ _______________________________________ _______________________________________ The Production of Wastes The collection of chemical processes taking place within in living things is known as their metabolism. During metabolism, and while processing food, organisms produce and release waste products. As an example lets examine human wastes: Waste product from deriving energy from sugar via cellular respiration: _______________________________ Waste product from food digestion: _______________________________ Waste products filtered out of blood by the kidneys: _______________________________ Made of Cells This is increasingly a topic of debate. What defines a cell? Is cellular life the only kind of life that can exist? Evidence suggests that all life on earth is either composed of, or derived from cells. This includes you. There are two main types of cells: Prokaryotic Cells Eukaryotic Cells Uncertainty: Are Viruses Alive? • Using the above characteristics that define living things, explore whether you think a virus would be considered living, or non-living • Viruses have living and non-living characteristics: Living Characteristics Non-Living Characteristics Use the space below to describe why you think viruses may be considered living, or non-living and explain why. _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ Watch this video: https://www.statedclearly.com/videos/what-is-life/ What is NASA’s proposed new definition of life? “A self-sustaining chemical system capable of Darwinian evolution.” Does their new definition of life include viruses? _________________ Do you think their new definition of life could include artificial intelligence? _______________________ Explain: _____________________________________________________________________________________ _____________________________________________________________________________________ Watch this video to review and extend on today’s lesson: https://www.youtube.com/watch?v=cQPVXrV0GNA&vl=en “Amoeba Sisters: Characteristics of Life”
