 These things are alive. These things are not alive. Have you ever thought about what makes something alive? Biology is the study of life. Life is defined by seven properties or characteristics. Order. Living things display an ordered organization. Reproduction. Living things reproduce more of their own kind. Growth and development. Things that are alive, grow and develop. Energy processing. Living things take in energy and convert it to useful forms in order to perform work. Response to the environment. Living things respond to stimuli. Regulation. Living things have systems in place to maintain a constant internal environment despite fluctuating external conditions. This property of life is sometimes also called homeostasis. Evolutionary adaptation. Populations of living things evolve over time in order to adapt to their environment. Let's look at some examples of the properties of life. These sunflowers display an ordered organization seen in the fruits in the center of the flower. An order can also be seen in the petals surrounding them. Living things also reproduce more of their own kind. These orangutan parents and their offspring are an example of living things reproducing. Another property of life is growth and development. This time lapse video shows the growth and development of a lithops flower, also called a pebble plant. This rhinoceros is demonstrating energy processing. As the rhino takes in chemical energy in the form of food, it converts that energy to energy that can be used to do work, like movement. All organisms respond to stimuli in their environment. This Venus flytrap closes around the insect as it senses its presence. Living things maintain a constant internal environment. For example, this dog pants in order to cool down as it walks. Even if the external environment temperature is high, the dog has a system to control its internal temperature, displaying the property of regulation. These organisms have evolved in order to be camouflaged in their surroundings. Adaptations like these evolve in populations of living things over time, where organisms that are well suited to their environment have a reproductive advantage. In cases like these, the camouflage enables these organisms to avoid predation because they can't be seen. Remember at the beginning of the video when we said these things were not alive? Now we will consider a few of these non-living things and determine why they cannot be considered alive. First, let's look at a rock. Does a rock display order? Maybe, some rocks are striated for example. Does a rock reproduce? No. Grow and develop? No. Is a rock able to process energy? No. A rock also can't respond to stimuli or regulate its internal environment. Have rocks evolved over time? No. So as you can see, a rock doesn't display the properties of life and therefore cannot be considered alive. Another example of a non-living thing is a building. Let's consider the properties of life as they apply to a building. Does a building display order? Yes, most buildings are organized. Does a building reproduce? No. Grow and develop? Sometimes, buildings might have additions built. Can a building process energy? No. Energy enters the building in the same form it is used. Does a building respond to the environment? No. Are there systems in a building used to regulate its internal environment? Yes. Buildings have systems to regulate their temperature for example. Have buildings evolved over time? No. Sometimes, non-living things like the building display some of the properties of life. But in order for something to be considered alive, it must display all the properties we talked about. In summary, living things like flowers, animals and trees display the seven properties of life, while things like cars, buildings and rocks don't and are therefore not alive. So when we study living things, we study the things that display the seven properties.