Lesson Plan - Get It!
We know when something is alive, but what makes something alive?
Everything around you can be classified into three groups: living, once-living, and non-living.
Things that can be classified as living must possess the following characteristics of life:
- All living things are made of cells. A cell is the basic unit of function and structure in an organism. Cells are made of chemicals. Water is the most abundant chemical, and carbohydrates provide energy.
Organisms that are made of only one cell are called unicellular. Organisms that are made of more than one cell are called multicellular.
- All living things have levels of organization. Cells are organized into cells, tissue, organs, organ systems, and organisms.
- All living things use energy. Organisms use energy to grow, move, reproduce, and carry out other functions needed to live. The foods they eat provide them with energy. The sun provides energy for the plants that many animals eat. These animals grow, and thus provide nutrients for larger animals, creating the food chain and balance within the ecosystems.
- All living things reproduce (or have the ability to reproduce). Organisms can produce offspring that are similar to the parent organisms. Organisms like bacteria reproduce by making an exact copy of themselves and splitting into two new cells. Multicellular organisms like cats need two parents, and the offspring (kittens) are similar to the parents.
- All living things develop and grow. Once a new organism is produced, it continues to grow and develop by continuing to increase the number of cells they have. Multicellular organisms grow and go through many changes during their lifetime. All the changes that an organism goes through during its lifetime is called development. Can you think of ways you have changed physically during your lifetime?
Note: All living things grow, repair themselves, and reproduce according to genetic code found in DNA (Deoxyribonucleic Acid).
- All living things have a system of self regulation in place. This system helps maintain the steady internal balance required for the organism to stay alive. This balance includes such factors as internal temperature, pH, moisture balance, hormone levels, etc. The scientific term for this system is homeostasis. A few examples of homeostasis at work in the human body are sweat and the body's ability to send blood-thickening platelets to the scene of a cut to slow the bleeding and form a scab. In order to maintain homeostasis, the body responds to certain conditions with either positive or negative feedback. When the body is too hot, the body must release some of its water stores in the form of sweat to cool down. This is an example of negative feedback. The process of the body's ability to slow bleeding by sending platelets to a wounded area is an example of positive feedback.
- All living things respond to, and adapt to, their environment. A stimulus is an environmental change that triggers a response.
Print the Living Things Notebook from Downloadable Resources in the right-hand sidebar. You will be answering questions from this section in this notebook.
All living things grow by increasing their number of cells. This can be a slow process, and is very hard to see in a short time frame. However, there are some organisms, such as bacteria, that can undergo cell division in as little as 20 minutes! In order for living things to grow, they must maintain stable internal conditions — this is referred to as homeostasis. All of this takes energy that is provided by food or the sun. Living things must also respond to changes in the environment in order to maintain homeostasis.
In the Got It? section, you will investigate how living things use energy. When you first look at the yeast, they don't appear to be alive, but when you add hot water and sugar, they prove otherwise! Try it yourself!