About this video
Living things can be classified in three ways: by number of cells (unicellular or multicellular), by whether the cell has a nucleus (prokaryote or eukaryote), and by how they get energy (autotroph or heterotroph). Using a backyard compost bin as the example, the video shows that bacteria are unicellular prokaryotes, while plants, earthworms and mushrooms are multicellular eukaryotes, and that plants make food from sunlight while the decomposers consume it.
You'll be able to
- classify organisms as unicellular or multicellular and explain the difference in how the cells work.
- distinguish prokaryotes, which have no nucleus, from eukaryotes, which do.
- distinguish autotrophs, which make their own food, from heterotrophs, which consume other organisms.
Key words
- Unicellular
- Made of just a single cell, which must carry out all the functions needed for life on its own.
- Multicellular
- Made of many cells, which can perform different jobs such as movement, structure or obtaining energy.
- Prokaryote
- A cell or organism without a nucleus, so its DNA sits in the cytoplasm, such as bacteria.
- Eukaryote
- A cell or organism whose DNA is housed inside a nucleus, such as earthworms, mushrooms and humans.
- Autotroph
- An organism that makes its own food, usually from sunlight through photosynthesis, such as a plant.
Transcript
- [Instructor] If you open a backyard compost bin, at first glance, it just looks like a pile of old food and nothing else. But if we could zoom in, we would see that it's filled with living organisms, all working together to break down that pile. Some, like the earthworm, the mushrooms, the maggots, they're all large enough to spot with our eyes, while others are so tiny that we would need a microscope to see them.
So how do scientists sort and compare the many different living things on Earth? How do they classify organisms? Let's find out. One way to classify organisms is based on the number of cells. You probably know, all living things are made of cells. And organisms can either be unicellular or multicellular.
Unicellular organisms are made of just a single cell. For example, bacteria that are helping break down that food scraps, they are unicellular. On the other hand, multicellular organisms are the ones that have multiple cells, more than one cells. Examples include those earthworms or mushrooms, maggots, and it also includes animals and plants and you and me.
We're all multicellular organisms. In a unicellular cell, one cell must do everything on its own. The single cell carries out all the functions needed for life. But in multicellular organisms, different cells can perform different jobs. Some cells can help with movement, others can provide structure, or you know, other cells could help obtain energy and so on and so forth.
Okay, so this is one way to classify organisms. Is there any other way to do that? Yeah. Let's compare a cell of a bacteria with that of an earthworm, for example. Now, there are a lot of differences, but here is a big one. You can see the DNA over here, which contains all the instructions to help the organism grow and function and reproduce, is housed inside a compartment.
This compartment is called the nucleus. But if you look at the bacterial cell, you can see that DNA does not have that compartment. There is no nucleus. The DNA is just sitting in the cytoplasm, you know, the gel-like material that fills the entire cell. So this is another way we can classify organisms.
We can classify it based on whether the nucleus is present or not. If the nucleus is not present, we call such cells prokaryotes or prokaryotic organisms. And organisms whose cells do have a nucleus, we call them eukaryotes or eukaryotic organisms. So bacteria are prokaryotic.
They don't have a nucleus. Whereas most other living organisms we saw in the compost bin, like the earthworms, the mushrooms, and the maggots, they're all eukaryotic. They do have a nucleus. Okay, so far, we've discussed classifying organisms based on the number of cells and whether the cells have a nucleus.
But there is another way to classify organisms based on how they produce energy. Remember that all organisms need energy to survive. They need energy to grow and repair themselves, and you know, carry out all kinds of life processes. But how do they produce that energy?
How do they get it? Well, some organisms can make their own food. We call them autotrophs or autotrophic organisms. The most common example are the plants. Most autotrophs, like these plants, they use the energy from the sunlight to make their own food. This process is called photosynthesis.
Think about all the fruits and the vegetables that were tossed into this compost bin. Before they became food scraps, they were part of the living plants. Those plants were the autotrophs. They captured the energy from the sunlight and used it to make their own food.
On the other hand, organisms that cannot make their own food, they're called heterotrophs or heterotrophic organisms. They get their energy by consuming other organisms or organic matter. The bacteria, the fungi, the earthworms, they're all heterotrophs. They obtain energy by breaking down the dead fruits and vegetables and leaves in the compost.
So look, all the pieces of our compost story is connecting together. The plants that grew using the sunlight were the autotrophs. Those plants eventually became fruits and vegetables, and after the fruits and vegetables were discarded, they ended up in the compost bin.
Then the bacteria, the fungi, the earthworms and so many more, which are all heterotrophs, they began breaking them down. Okay, what about us, human beings, are we autotrophs or heterotrophs? Well, we like to say we make our own food in our daily conversations, for example, but that's not the same thing that we're talking about over here.
Even we eat fruits and vegetables and meat. When we say we make our own food in everyday language, we're just talking about the way we cook. We can cook them however we want. We can cook food all by ourselves, but we don't strictly create our own food, right? Which means we too are heterotrophs.
So look, even though these organisms are very different from one another, scientists can compare them using the exact same set of characteristics. So to quickly summarize everything that we've learned: Some organisms are unicellular, which means they're made of just one cell, while others are multicellular, made of many cells.
Some organisms are prokaryotes, meaning they don't have a nucleus protecting the DNA. Others are eukaryotes or eukaryotic organisms, which means they do have a nucleus protecting the DNA. And finally, we have autotrophs, which can produce their own food, usually from the sunlight.
And then there are the heterotrophs that cannot make their own food. They obtain energy by consuming other organisms.
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