Cellular Composition
Cells are the building blocks to life. From single-celled organisms such as bacteria to multicellular organisms such as human beings, all living things are composed of cells. If you look at the cells of two organisms that are very different, such as a whale and a mouse, it may be difficult to tell them apart under a microscope. Both eukaryotic and prokaryotic organisms are living things.
Growth and Change
Living things grow and change on a daily basis, but also over many generations. The largest redwood trees began as tiny seeds that grew a little more each day. But redwood trees have also adapted to their environment over millions of years, making them resistant to wildfires and tree rot. Redwoods, like all living things, are capable of growing and changing in the short term and evolving in the long term.
Genetics and Heredity
Although all living things are different at the genetic level, it doesn’t change the fact that they all carry DNA. This DNA serves as an instruction guide for growth, development and individual traits. It’s present in every cell in the organism’s body and regulates all physical aspects of that organism’s life. Even when an organism is taken from its natural environment, its DNA controls much of its behavior and instincts.
Maintains Homeostasis
Homeostasis is the process in which living things maintain a stable internal environment. Cells keep an organism at a constant temperature by balancing biological substances and chemicals and ridding the body of waste. Homeostasis is necessary for an organism to complete many cellular processes, and losing homeostasis can endanger its life. No matter how big, small, simple, or complex a living thing is, its cells are constantly working to keep it in homeostasis.
Metabolism
Fungi process energy from dead leaves, sharks receive energy from eating smaller fish, and flowers create energy through photosynthesis. All living things, also known as biotic factors in an ecosystem, require energy to survive. Heterotrophs, including carnivores, herbivores, omnivores, and decomposers, find food from other organisms. Autotrophs, such as phytoplankton and iron bacteria, make their own food. But all of these organisms use sustenance to create energy through chemical reactions, which maintain nutrition and health.
Movement
You may be surprised to hear that all living things can move – especially plants. But it’s true! Plants can rotate their leaves toward the sun, close flower petals and bend their stems as needed. Animals can move their location quickly, in the case of a cheetah, or slowly, in the case of a snail. Even coral, which are also living things, can move with ocean currents and move as they grow. Having the ability to move is a key characteristic of life.
Responds to Stimuli
Animals, plants, fungi, bacteria, and all living things are sensitive to their environments. They can react to stimuli, which are changes in their environment, to protect themselves. Environmental stimuli might include temperature changes, smells that indicate a predator is nearby, or noises from distressed offspring. Living things may also respond to pain, hunger, thirst, or discomfort. This sensitivity helps an organism survive in their environments.
Sexual or Asexual Reproduction
One of the most important characteristics of life is an organism’s ability to reproduce. All living things reproduce sexually, with a partner, or asexually, by themselves. Sexual reproduction involves each parent providing half of the genes to the offspring, while asexual parents provide an exact copy of their DNA to their offspring through mitosis. Living things have a prevailing drive for reproduction that keeps them alive long enough to perpetuate their species.
Living Things in Context
You may be able to think of non-living things that fit one or two of these characteristics. Clouds can grow, for example, and dormant volcanoes appear to maintain homeostasis. But unless an object possesses all of the above qualities, it is not alive. Next, see how these living things fit into the context of the classification of living things. You can also see how all living things are divided into these kingdom examples.