How Do We Know if Something is Living or Not? Well...it depends on who you ask We are going to say there are six. Living things are made of cells. Living things respond to their environment. Living things reproduce. Living things use energy. Living things eliminate waste. Living things grow and mature. 1. Living Things are Made of Cells We will later learn about the structure and function of cells. A cell is the smallest thing to be alive. Some living things (organisms) are only one cell. Others are multicellular. We often call cells the building blocks of life. Examples of single-celled organisms Examples of Cells from Multicellular Organisms 2. Living Things Respond to their Environment All organisms have the ability to “sense” the world around them so that they may survive. The things they sense are called stimuli and may include light, temperature, pressure, gravity, odor, sound, color, water and so many other conditions. Living Things Respond (continued) Organisms need to sense their environment in order to maintain HOMEOSTASIS. This is the ability of an organism to maintain “body function” in response the environmental changes. We shiver and sweat to keep our body temperature and its healthy temperature. Examples of Response to Stimuli Sensing fewer daylight hours and lower temperatures, many animals begin to hoard food and may undergo some level of hibernation in order to save energy until spring returns. Plants move their leaves toward the sun’s rays so they maximize photosynthesis. Many bird species migrate in order to access food and nesting resources as seasons and competition change. 3. Living Things Reproduce They make more of themselves. More about this later. 4. Living Things Use Energy 5. Living Things Eliminate Waste During the process of photosynthesis, leaves give off oxygen and H2O. Middle school students think of feces. It is an example. Kidneys filter waste from blood. It is eliminated as urine. Legume plants have “nodules” for bacteria to live. Some waste from bacteria is Nitrogen in a form that plants and animals need. Living Things Grow and Mature Living Versus Non-Living Living things will have all of the six characteristics (at some time). NON-living things may have “some” of these characteristics, but NOT all.