Back To CourseCampbell Biology: Online Textbook Help
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Adrianne has taught high school and college biology and has a master's degree in cancer biology.
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.
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.
Most responses to stimuli are in an effort to do our next characteristic of life, which is maintain homeostasis. Homeostasis is a stable internal environment where organisms function best. You actually know a little more about this than you think you do. Do you know your normal body temperature? Sure, it's 98.6 degrees F. That is one aspect of homeostasis in your body.
Just like there is a certain temperature at which your body works best, there are also certain oxygen levels, blood volume, number of breaths per minute, etc. All living organisms have a set internal environment that is preferred for ideal function. Living organisms will do whatever is necessary to stay within those limits.
If you spend any time studying a species over time, then you will realize that they have changed over time to adapt to the environment in which they live. This means they evolve in order to ensure the species will continue to live and thrive. The more variety that exists in a species, the more likely it is to survive. This is the reason why living organisms continue to change over time. This also helps to make sure resources like mates, food, and space to live in don't run out for a species. When there is variety, then every member of the species will have slightly different needs due to their differences.
The last characteristic shared by all living organisms is that we use energy in order to maintain life and grow. Bacteria acquire energy by breaking down things in their environment or taking broken-down nutrients from organisms they are living in. People eat food, and plants use the sun to get energy to convert into a form of energy that can be used. This energy is essential in order to carry out the functions of life.
By now, you should have a grasp on the study of living things, better known as biology. The scientists that study biology are biologists. Biologists that study how organisms interact with each other and their environments are called ecologists, and the study of how organisms interact with each other and their environments is ecology. There are eight characteristics that all living organisms share. All living organisms are:
Organisms made with only one cell are unicellular organisms, and organisms with more than one cell are multi-cellular organisms. The two types of reproduction are sexual reproduction, which is reproduction using gametes during mating, and asexual reproduction, which is reproduction without using gametes.
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Back To CourseCampbell Biology: Online Textbook Help
56 chapters | 510 lessons