Biology: The Study of Life

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  • 0:01 Biology
  • 1:11 Characteristics of Life
  • 6:15 Lesson Summary
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Lesson Transcript
Instructor: Adrianne Baron

Adrianne has taught high school and college biology and has a master's degree in cancer biology.

This lesson is going to discuss the basics of biology. We will discuss the study of biology, including the characteristics that are shared by all living organisms.


You likely became familiar with some of the ways you are different from other members of your family as you were growing up. When in school, you and your friends may have also compared yourselves to one another. What you probably didn't do is compare yourself to your dog or cat. And it is even less likely that you thought about what you do and don't have in common with the trees in your yard or the bacteria that caused you to get sick.

The interesting thing, though, is that you actually have several things in common with them. First of all, you, your dog, the trees, and bacteria are all living. This has been proven through biology, which is the study of life. The scientists that study biology are called biologists. Biologists have spent hundreds of years studying every aspect of living things. They have learned about the internal and external structure as well as the function of living organisms to gain a better understanding of life.

Beyond that, there is a specific field of biology that is the study of how living organisms interact with each other and their environments called ecology. The biologists that study ecology are called ecologists.

Characteristics of Life

So, you are still questioning what you have in common with those icky bacteria. Let's get to that now. There are eight characteristics that all living organisms share.

First, all living organisms are composed of one or more cells. Every single living thing can be broken down into its most basic unit, which is the cell. Some living organisms are composed of only one cell. They are known as unicellular organisms. Examples include bacteria and protozoa.

Other organisms, like you and your dog, are multi-cellular organisms, which means they're composed of more than one cell. Unicellular organisms do all of their processing within the one cell. Multi-cellular organisms have different types of cells that perform a particular function, and they all work together for that organism.

Luckily, we all display organization. How we are organized varies greatly from one organism to the next, but all living organisms are put together based on an organization plan. There is organization within and outside of the cells. Each cell has certain organelles that have a distinct function, and they accomplish a set goal. This is the end of the organization for unicellular organisms.

For multi-cellular organisms, the cells are organized into tissues, which are organized into organs. The organs work together to make an organ system that has a particular function, and then all organ systems work together to carry out all functions of the organism.

The next thing that all living things do is grow and develop. This is quite evident when you look at your pictures from when you were born. You don't look the same way, and you certainly aren't the same size. You may have even had the chance to watch your dog from the time it was a puppy or your cat from when it was a kitten, and you have seen it change a lot over the years. This occurs in all living organisms. If it is unicellular, then the one cell grows, and if it is multi-cellular, then the cells divide to increase in number, causing the organisms to grow.

Now, you personally may or may not have experienced this next characteristic, but other humans have. Reproduction must occur within each species in order for it to continue to exist. Every single member of a species may not reproduce, but reproduction is possible and is a characteristic of every living organism. Some organisms create offspring by mating with other members of the same species using gametes, while other organisms create offspring on their own without mating. When mating occurs using gametes to create offspring, this is called sexual reproduction. Creation of offspring without mating or gametes is asexual reproduction.

Have you ever accidentally touched something that was hot and then yanked your hand away? When you did, you were doing our next characteristic, which is respond to stimuli. This basically covers behaviors that are displayed.

Are you confused about how plants and trees can respond to stimuli? Think about this. If you were to place a plant in a room next to a window where the sun only shines in one direction, then the plant will grow towards the sun. Still not convinced? If you were to rotate the plant so the sun is on the other side it was growing away from, then the plant will change the direction it is growing in. That is a direct response to stimuli.

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