Hey there, fellow multicellular being!
Did you realize
that you are made up of almost 30 trillion cells?
Most of these, about 90%, are red blood cells,
but you still have about 200 different kinds of cells
in your body.
You are not a giant blob or single-celled organism.
You are made up of many different cells,
each with a specialized job or function.
Interestingly enough, you also have
about the same number of microbial cells in your body
as you have of your own cells.
Microbes are single-celled organisms.
Wait, what?!
Can you believe that?
You are a walking biome for microbes.
In fact, we humans rely on these microbes to keep us healthy.
We need them as part of our personal ecosystem.
Let's take a look at cells.
Cells are the definition of life.
If you want to study living things or biology,
you need to understand cells first and foremost.
Some living organisms, like bacteria,
are only one cell.
When you put cells together,
you make much bigger living organisms,
like most of the plants and animals you see around us.
However, there are organisms, like the Portuguese man-of-war,
that is sometimes thought to be one, multicellular organism,
like a jellyfish,
but it is actually a colony of single-cells called polyps.
It is a siphonophore,
an animal made up of a colony of organisms working together.
Right now, let's review the fundamentals of the cell theory.
The cell is the basic unit of life;
all cells come from pre-existing cells;
all living things are made up of one or more cells.
Since cells are the fundamental unit of life,
they need to be able to do everything
a multicellular organism can do, but on a much smaller scale.
Cells need to process energy, remove wastes,
and repair themselves and reproduce.
If a cell is a plant, it will produce its own energy,
or glucose, through photosynthesis.
If the cell is an animal,
it will need to consume energy from another source.
Cells need a way to remove waste products
generated when they use energy.
Cells also need the ability
to reproduce and produce other cells.
Now, at some point, you are probably going to be asked
to make a cell model out of food,
toys or everyday objects.
Don't do it!
Unless you know why you are making this model,
it won't be that useful.
Plus, it might turn you off candy for a bit.
We make cell models to learn about
all the bits and pieces inside the cell.
We call these organelles.
Organelles are small structures inside the cell
that perform specialized functions.
We also learn about other structures
like the cell membrane and cell wall
that are not inside the cell, but surround it.
The cell's organelles perform similar functions
to the large organs in our body.
But, while organs work
on a macroscopic, full-body level,
organelles act on a microscopic, cellular level.
In multicellular organisms,
our kidneys and liver remove toxins,
our brain gives our body instructions
and our stomach breaks down food
that provides the energy for our cells.
Cells have organelles that perform similar functions.
Organelles make proteins,
give us usable energy from glucose,
clean up the inside cell environment,
and send out instructions to the cell
so it will have a specialized function.
Each cell in your body has the same instructions
found inside the nucleus.
These instructions are in the form of DNA.
Most multicellular organisms
result from the union of two gametes.
Once these two cells unite,
the organism should have a full set of chromosomes
or DNA instructions.
These instructions tell the dividing cells
what they need to "know" to reproduce and specialize.
In a developing organism,
stem cells, or unspecialized cells,
become many different types of cells in the adult.
This is called "cell differentiation",
the process where a cell changes from one cell type to another.
These specialized cells group together to form tissues,
and eventually become our organs.
Our organs will group together in organ systems,
like the digestive system or the nervous system.
Plants also have specialized cells, tissues and organs.
A cell becomes specialized because certain parts of the DNA
are turned on or off to make the cell become a certain type.
Based on our current knowledge,
all living organisms have cells in common.
Biologists consider cells to be the essential unit of life.
It is important that we treat our cells and our bodies well
so we can continue to learn
and maybe find life in other forms.