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All living things on earth, from the tiniest creatures to the tallest of trees, are made
of microscopic parts called cells.
Living things can be made of just one cell, or have many.
Whether it's a plant, or an animal, cells are the basic structures they are composed of.
That's why cells are sometimes called the 'building blocks of life!'
Although there are many, many different types of cells that all have different jobs to do,
most cells have some things in common.
For now, we will be dealing with two types of cells: plant cells and animal cells.
Both plant cells and animal cells are surrounded by a cell membrane.
The cell membrane is a thin, flexible layer that separates the inside of the cell from
the outside of the cell.
It protects the cell, and controls what is allowed to go in (food) and come out (waste).
Plant cells have an extra layer called a cell wall that surrounds the membrane.
The cell wall is tough, and stronger than a membrane.
Cell walls provide support for plants to grow and keep their shape.
An elephant has a skeleton to support it as it grows - a redwood tree doesn't.
Cell walls are what allows them to stand so tall.
Inside the cell membrane, cells have smaller parts called organelles.
Organelles are like tiny organs, and they each do specific jobs inside the cell.
Some organelles bring in food, get rid of waste, repair the cell, and help it grow and
reproduce.
All of the organelles are held in a special gel called cytoplasm.
Cytoplasm is usually colorless and about 80% water.
Major organelles of a cell include the nucleus, vacuole, mitochondria, ribosomes, endoplasmic
reticulum, golgi apparatus, and - only in plant cells - chloroplast.
Let's talk about the nucleus first!
The nucleus is the control center of the cell, and acts kind of like the brain.
The nucleus contains the DNA or genetic material that determines everything about the cell
- like what kind of cell it will be and when it will divide.
Next, let's talk about the vacuole.
Vacuoles are basically storage tanks that the cell uses to hold water or other materials.
A plant cell usually has one large vacuole, while animal cells may have several smaller
ones, called vesicles.
Vacuoles are often the largest organelle in a plant cell, and when plants do not get enough
water, their vacuoles shrink, and the plant begins to wilt.
Mitochondria are famously the powerhouse of the cell, but they are important because they
take food and turn it into energy that the rest of the cell can use.
This process of using oxygen to break down sugars into chemical energy is called cellular
respiration.
Ribosomes are shaped like tiny balls, but work like tiny factories.
They make things that the cell needs, like proteins!
The cell can use proteins made by the ribosomes to build new structures, repair damage, and
direct chemical reactions.
Some ribosomes float free in the cytoplasm, while others are attached to the endoplasmic
reticulum.
Endoplasmic reticulum, sometimes called 'ER,' is a cellular highway!
It's a transportation network that takes molecules where they need to go.
The endoplasmic reticulum helps transport proteins made by the ribosomes to the Golgi
apparatus.
The Golgi apparatus looks a little bit like a stack of pancakes, and it can be thought
of as the post office of the cell.
What it does is take things like proteins or other molecules that needs to be transported
around or out of the cell and inspects them for flaws, packages them up, and sends them
where they need to go.
Finally, let's look at the chloroplast.
Chloroplasts are found only in plant cells and contain chlorophyll - the substance that
allows photosynthesis to take place.
In photosynthesis, chlorophyll absorbs energy from sunlight and creates sugar to feed the
plant.
Simple plant cells may have only one or two chloroplasts in them, but more complex ones
may have hundreds.
Cells and the tiny organelles inside them do the work that allows living things to live and function.
Without cells, there would be no life on Earth!
hope you enjoyed learning about cells today. Goodbye till next time!