Characteristics of Life - Online Tutor, Practice Problems & Exam Prep

All living organisms share eight key characteristics: they are composed of cells, organized into complex structures, respond to environmental stimuli, maintain homeostasis, reproduce, acquire and utilize energy, contain genetic information (DNA), and evolve over time. These traits distinguish life from non-living entities, emphasizing the importance of cellular structure and function, energy acquisition, and adaptability in various environments. Understanding these characteristics is fundamental to studying biology and the diversity of life on Earth.

Characteristics of Life

In this video, we're going to talk about the characteristics of life. All living organisms, regardless of whether they are unicellular or multicellular, share 8 characteristics that distinguish these living organisms from the nonliving things that surround them. If we take a look at our table down below, notice we're listing the 8 characteristics that are shared by all living organisms, and we'll go through each one of these 8 characteristics one by one. The first characteristic shared by all living organisms is that all living organisms are composed of cells, or in other words, all living organisms are cellular. Recall from some of our previous lesson videos that we define cells as the smallest or the most basic fundamental unit of life, meaning that nothing smaller than the cell displays all of the characteristics of life and thus nothing smaller than the cell is considered alive. Notice over here we're showing you an image that is showing you cells. As we move forward in our course, we're going to talk a lot more about the structure and function of different types of cells. For now, you should just know that all living organisms are composed of cells.

The second characteristic that all living organisms share is that all living organisms are organized, and this organization allows all living organisms to use smaller structures to build larger, more complex structures. Those larger, more complex structures allow living organisms to survive. Just like over here in this image where this large brick wall is being built by using smaller individual bricks that are organized in a very specific way, all living organisms are also going to be organized. Later in our course, we're going to talk about the organizational hierarchy of life, which discusses how living things are organized on our planet.

The third characteristic that's shared by all living organisms is that all living organisms are able to respond to environmental stimuli, or in other words, all living organisms can respond to changes in the environment. The environment is constantly changing. For example, over here on the right, we're showing you a plant that is growing on the windowsill and notice that the plant is growing towards the window where the sunlight is shining through. This plant is responding to the environmental stimuli, which is the sunlight, and it is growing towards the sunlight. All living organisms are able to respond to environmental stimuli in one way or another.

The fourth characteristic shared by all living organisms is the ability to maintain homeostasis. This refers to the ability of all living organisms to stabilize or maintain suitable living conditions. Not only are all living organisms capable of responding to environmental stimuli, but they're capable of responding to the stimuli in such a way that it allows them to stabilize or maintain suitable living conditions. The environment surrounding living organisms is constantly changing. Some days when we go outside it's super hot, and other days it's really wet or really cold. The environment that's changing may not be the best environment for living organisms. Living organisms have to be able to respond to the changing environments in such a way that it allows them to maintain suitable living conditions. A classic example of maintaining homeostasis is when the human body sweats. In really hot environments, like on a hot summer day, your body will start to sweat in order to cool off and maintain living conditions. Sweating helps to cool off your body and allows your body to maintain more suitable living conditions, and once again all living organisms are capable of maintaining homeostasis.

The fifth characteristic shared by all living organisms is the ability to reproduce. Reproduction refers to the capacity to produce life or the ability to produce more life, and reproduction can either occur sexually or it can occur asexually. Sexually, of course, means that there are going to be two parents involved in the reproduction, and asexually means that there will only be one parent involved in the reproduction. We'll get to talk a lot more about the reproduction abilities of living organisms much later in our course when we're discussing mitosis and meiosis. But for now, you should just know that all living organisms have the ability to reproduce and create more life. Over here, notice that we're showing you an image of a baby to remind you of this characteristic of reproduction.

The sixth characteristic shared by all living organisms is the ability for all organisms to acquire and utilize energy from the environment or from the surroundings. Over here, we're showing you this kid that is eating a carrot to obtain energy from its environment. All living organisms have the ability to do this, obtain energy from their environment.

The seventh characteristic shared by all living organisms is that all living organisms contain genetic information, which is essentially hereditary information that can be passed down from one generation to the next. The molecule that serves as the genetic material is going to be DNA. We'll get to talk a lot more about DNA and genetics as we move forward in our course, but for now note that all living organisms contain genetic information, specifically DNA. Over here, we're showing you an image that represents the structure of DNA.

The eighth and final characteristic shared by all living organisms is the ability to evolve. Evolution refers to changes in the DNA of a population over really long periods of time, which allows the population to adapt and improve their survival in their environments. Evolution occurs in all living organisms and all populations of living organisms. We'll get to talk a lot more about evolution later in our course, but notice over here we're showing you a classic image that represents evolution, and how characteristics can be acquired and changed over time to lead to new species.

It is important to note that viruses, such as the coronavirus, for example, are not considered alive. This is because viruses lack some of the characteristics of life, mainly the ability to reproduce on their own without having to hijack other cells. We'll get to talk a lot more about viruses later in our course, but for now, you should note that viruses are generally not considered alive because they lack some of these characteristics of life. This concludes our brief lesson on the characteristic of life, and all living organisms from single-celled bacteria to you and I display these characteristics of life. We'll be able to get some practice applying these concepts as we move forward, so I'll see you all in our next video.

Characteristics of Life Example 1

Alright. So here we're looking at an example problem that's asking which of the following is not a characteristic of life, and we've got these four potential answer options down below. Because we're looking for the option that is not a characteristic of life, we're looking for the false answer option because it's going to be the one that is not a characteristic of life. Option a says, the structure of an organism is based on a hierarchy of organization. We know that one of the major characteristics of life is that they have organization, and so option a, to say that the structure of an organism is based on a hierarchy of organization, is actually a true statement. This is because it's referring to the organization characteristic. Because it is true, it's not the false answer option that we're looking for, so we can eliminate answer option a.

Moving on to option b, it says the ability to establish a constant internal temperature, despite the fact that the temperatures of the environment are constantly changing. This is referring to the ability to maintain homeostasis. Maintaining homeostasis is definitely a characteristic of life. So this is once again a true answer option, which means that we can eliminate answer option b because it's not the false answer option that we're looking for. Now we're between either option c or option d, and notice option c says, the ability to convert sunlight energy into chemical energy, whereas d says DNA molecule that stores genetic and hereditary information.

Recall that the hereditary information of using DNA is a characteristic shared by all living organisms. All living organisms use a DNA molecule as the hereditary molecule to store hereditary information. So once again, we're saying that option d here is true, again because it's referring to hereditary information and DNA. We can go ahead and eliminate answer option d because it's not the false answer option that we're looking for. This only leaves answer option c here as the false answer option that we're looking for. The ability to convert sunlight into chemical energy is something that some living organisms have, but it is not a characteristic of life shared by all living organisms. For that reason, this is actually the false answer option that we were looking for.

So we can go ahead and mark c as the answer that we were looking for, and that concludes this practice or this example. So I'll see you guys in our next practice problem.

All of the following are characteristics of life EXCEPT:

• A. Evolution
• B. Multicellularity
• C. Homeostasis
• D. Reproduction

Salt concentration in blood remains relatively steady, regardless of a person's diet. This best illustrates:

• A. Homeostasis.
• B. Life's organizational hierarchy.
• C. Autotrophy.
• D. Evolution.

Here’s what students ask on this topic:

What are the eight characteristics of life that distinguish living organisms from non-living things?

The eight characteristics of life that distinguish living organisms from non-living things are: 1) composed of cells, 2) organized, 3) responsive to environmental stimuli, 4) maintain homeostasis, 5) reproduce, 6) acquire and utilize energy, 7) contain genetic information (DNA), and 8) evolve over time. These traits are essential for defining life and understanding the biological processes that sustain it. For example, all living organisms, from single-celled bacteria to humans, exhibit these characteristics, which help them survive, grow, and reproduce in their environments.

Why are viruses not considered living organisms?

Viruses are not considered living organisms because they lack several key characteristics of life. Most notably, they cannot reproduce independently; they must hijack the cellular machinery of a host organism to replicate. Additionally, viruses do not maintain homeostasis, do not have cellular structures, and do not acquire or utilize energy in the same way living organisms do. While they do contain genetic material (DNA or RNA) and can evolve, their inability to perform essential life processes on their own excludes them from being classified as living organisms.

How do living organisms maintain homeostasis?

Living organisms maintain homeostasis through various physiological processes that stabilize their internal environment despite external changes. For example, humans sweat to cool down when it's hot, maintaining a stable body temperature. Similarly, when blood sugar levels rise, the pancreas releases insulin to help cells absorb glucose, keeping blood sugar levels within a narrow range. These mechanisms ensure that conditions within the organism remain suitable for survival, allowing it to function effectively in changing environments.

What is the role of DNA in living organisms?

DNA (deoxyribonucleic acid) serves as the genetic material in all living organisms. It contains the hereditary information that is passed from one generation to the next. DNA is responsible for coding the instructions for the development, functioning, growth, and reproduction of organisms. It ensures that offspring inherit traits from their parents and plays a crucial role in the process of evolution by allowing genetic variations to occur over time, which can lead to adaptations and the emergence of new species.

How do living organisms acquire and utilize energy?

Living organisms acquire and utilize energy through various metabolic processes. Autotrophs, like plants, capture energy from sunlight through photosynthesis, converting it into chemical energy stored in glucose. Heterotrophs, like animals, obtain energy by consuming other organisms and breaking down their organic molecules through cellular respiration. This process releases energy stored in chemical bonds, which is then used to power cellular activities, growth, and reproduction. Efficient energy acquisition and utilization are vital for maintaining life processes and overall organismal health.