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Course: Middle school biology > Unit 1
Lesson 1: Cells and organismsCells and organisms
All living things are made up of cells, which is the smallest unit that can be said to be alive. An organism may consist of one single cell (unicellular) or many different numbers and types of cells (multicellular). Created by Khan Academy.
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- If cells can survive on their own, why are there multi-cellular organisms?(31 votes)
- in multi-cellular organisms, groups of cells differentiating will take on specialized functions.(33 votes)
- What are Cells made of?(17 votes)
- Cells are made up of certain organelles that help it survive and function. Functions such as controlling what comes in an out of the cell, producing food for the cell, and going through the complex processes such as mitosis are only some of the things a cell's "insides" can do.(43 votes)
- Are viruses alive?(32 votes)
- This is quite a debate. Generally, viruses are classified as not alive. There are many different definitions of the criteria something has to fill in order to be classified as alive. Something must fulfill all of these criteria to be considered alive. Khan Academy has their criteria here
https://www.khanacademy.org/science/biology/intro-to-biology/what-is-biology/a/what-is-life
I personally, prefer this organization of four requirements.
1. An organism must have DNA
2. An organism must be able to take energy from its surroundings and convert it into a form that it can use.
3. An organism must be able to sense and respond to changes in its surroundings.
4. An organism must be able to reproduce
Viruses do not (completely) fit any of this criteria.
1.Some viruses have RNA instead of DNA. However this does not make the ones with DNA alive, as they do not fulfill the other criteria.
2. Viruses don't metabolize energy. They depend on energy from their host cell, and they don't convert it to a usable form themselves.
3. To be honest, this is a maybe. We don't really know, and this is kind of a topic of debate. My personal view is that until it is absolutely proven that viruses respond to stimuli, I will classify this as a no.
4. Not really. Viruses can't reproduce themselves. Instead, they inject their genetic material into a host cell, which basically takes over the cell and forces it to make more viruses. But the viruses don't do it themselves. If there is not a viable host cell, the viruses won't be able to reproduce.
In conclusion, viruses are not really classified as alive, because something living must fulfill all the criteria for life. Keep in mind that this is my personal list of requirements for life. However, viruses do not fill any full list of criteria for life. Khan Academy has an article about whether a virus is alive or dead here
https://www.khanacademy.org/test-prep/mcat/cells/viruses/a/are-viruses-dead-or-alive
I encourage you to read the other article before this one though.
I apologize for the long response, but hopefully you understand a bit better.(77 votes)
- Can cells die? if they can if cells die in our body would we get sick and or die?(17 votes)
- Yes, cells can die. In fact, hair is made up of dead cells stacked up on each other!
To answer your other question, we might get sick if A LOT of our cells died, but one is certainly not enough to make us even feel anything.
Good Question! I hope this helps!(31 votes)
- At2:50when she says that "most multicellular objects can be seen by the naked eye," are there any examples of multicellular organisms that can't be seen by the naked eye?(14 votes)
- Yes. Certain fungi cannot be seen but are multicellular.(9 votes)
- hiya, is dna a cell? if so, how?(6 votes)
- no its not cells just contain dna(12 votes)
- Is any living thing an organism? Or only a living thing with organs? So are bacteria organisms or only plants and animals - since they have organs?(9 votes)
- Any living thing is considered an organism, not just any complex multicellular one.(10 votes)
- Do cells make up humans?(6 votes)
- Yes! Cells make up all of your organs and tissues.(13 votes)
- What was the first living cell(6 votes)
- Prokaryotes were one of the first living cells, which were found in Earth's oceans.(8 votes)
- Do cells and organisms live in stuff like rocks or dirt/sand and other natural substances(6 votes)
- Anything that is non-living do not have any cells in it. Rocks, dirt and sand are all non-living so therefore no cells will be found inside them.(6 votes)
Video transcript
- [Narrator] Hi, everyone. In this video, we are going to be talking about one of the most fascinating
and complex features of life on Earth, cells. But before we do, I'd like to take us way back
to when I was a little kid. Now I know that for me, at least, I had a great time playing
with toy building blocks, and creating things out of them. I used blocks of
different shapes and sizes to make all kinds of things like houses, cars, even spaceships, and airplanes. You're probably thinking, what does this have to do with cells? Well, cells are considered
the building blocks of life. Like my blocks, cells can
come in a variety of shapes, and they have different features too. They can also stand alone, or they can come together
to build something larger. So let's dive deeper into this
fascinating topic of cells. So all living things, or organisms, like you, me, your pet dog, the birds in the sky, the fish in the sea, all organisms are made of
these basic units called cells. Take this moss plant, for
example, if we zoom way in, we can see that it's actually
made up of many smaller units. These units are cells. Each cell contains a flurry of activity, as it works to carry out the functions that keep the organism alive. In fact, cells are the smallest
unit that can carry out all the tasks necessary for life. For instance, all cells can
take up nutrients and water, get rid of waste, use energy, and interact with the things around them in their environment. These functions, plus many
others that cells carry out, are what make life possible. There are many different kinds of cells. For instance, take a look at these cells that make up an onion's outer skin, or these really cool red blood cells, or even these bacterial cells. This type of bacteria is called e-coli, which you might've heard
can be a safety hazard found in our food. So cells are fascinating to look at, but we generally can't see
them with our eyes alone. Most cells are so small that we need a microscope to see them. In fact, all of these
pictures of cells here were taken with the aid of microscopes. And something else that I find really cool is that some organisms are
made up of only a single cell, while others are made up of many cells. So organisms that are made up of one cell are called unicellular, and organisms that are
made up of many cells are called multicellular. Uni telling us that
there is only one cell, and multi telling us that
there are many cells. So an example of a unicellular organism would be the e-coli bacteria
that I mentioned a minute ago. Each bacterium is a single cell that's responsible for taking
in nutrients, reproducing, and doing all the things
that it needs to stay alive. So an example of a multicellular organism would be you, me, or
most any other organism that you can see with the naked eye. And the cells of multicellular organisms are often specialized to
carry out specific functions. So for example, some cells help the
organism absorb nutrients, while others transmit information, or defend against bacteria and viruses. So going back to our comparison between building blocks and cells, specialized cells are like
different building blocks of different sizes, shapes, and colors. And these different blocks can come together to
build something larger, like this airplane here. Similarly, cells with different structures and functions come together
to make something larger, an organism like this
adorable kitten right here. So to sum up cells and organisms, today, we learned that cells
are the smallest unit of life. We talked about how all
organisms are made up of cells, and that organisms can be
unicellular or multicellular. So I hope that now you
have a good understanding of cells and organisms, as well as a new perspective
about building blocks, not the toys, but the cells
that make up life itself.