There are many creations in this beautiful world, both large and small. Sometimes very, very small!
Take a look at the shortest tree in the world, the dwarf willow, which grows only six centimeters
tall. Animals come in small sizes too, such as the chihuahua, the smallest dog breed in the
world. The littlest dog ever measured was only 9.6 centimeters tall and weighed less than a kilogram.
As tiny as that is, it's not even close to the smallest mammal in the world.
This is the bumble bee bat which grows to just
over two centimeters in length and weighs only two grams, about the weight of a single dime.
Of course, there are many things more minuscule than that in our world, but how can we see them?
Scientists believe that the human eye with no assistance can see objects as small as
0.1 millimeters. That's about the thickness of a piece of paper, a strand of human hair,
or a fine grain of sand. For thousands of years, humankind was limited to observing things with
only the naked eye. But that all changed with the invention of the microscope in the 17th century.
Many discoveries were made through the lens of a microscope, revealing an entire microscopic world
that no one had ever seen before. In 1665, Robert Hook, a scientist from England, was experimenting
with one of the first primitive microscopes. As he studied a piece of cork under magnification,
he noticed that the cork was divided into tiny microscopic sections. Hook named
these tiny divisions cells. This small discovery would change science forever.
All living things are made up of these cells. They are the smallest working unit of living organisms.
Because of this, cells are known as the building blocks of life. Some living
things in our world are made up of only one single cell, like this single building brick.
These organisms are called unicellular and entire kingdoms of life are made up of these
one-cell creatures. Unicellular organisms are also known as microorganisms.
They are everywhere, but they are so small that you cannot see them without a microscope.
Just as you build something bigger out of blocks by snapping them together, cells can also be
combined. The resulting multicellular organisms are much larger and more complex than unicellular
organisms. Plants and animals are examples of organisms made of many cells working together. The
biggest difference between a unicellular organism and a multicellular organism is that the single
cell creature has only one vulnerable cell with no protecting cells around it. If the cell dies,
the organism also dies. On the other hand, a multicellular organism has many specialized cells.
If one cell dies, the organism can still survive. For example, the human body is made up of
trillions of cells and every second a million of them die and are replaced by new cells.
There are two defining types of cells on earth: prokaryote and eukaryote.
The main difference between these two types of cells is that eukaryotic cells have specialized
organelles including a membrane-bound nucleus. An organelle is a membranous structure inside
the cell that performs a specific job, and the most important organelle in a eukaryotic cell
is the nucleus. The nucleus contains the genetic material for the cell and is the control center,
similar to a brain, directing the cell's activities and functions.
The genetic material of the prokaryote floats freely within the cell's cytoplasm
along with organelles less complex than those found within a eukaryote.
The cell is the most basic part of your body and is part of an amazing organizational system.
A single cell joins together with many other similar cells to form tissues,
like the tissues that make up your muscles. These tissues are grouped together to form organs,
like your heart, which is a special muscle that beats 100,000 times each day.
Different organs work together to form an organ system, such as your cardiovascular system,
where your heart and blood vessels work together to pump blood, oxygen,
and nutrients throughout your body. In turn, these various organ systems group together to form you,
a living organism. Your body is made up of about 200 different types of cells,
each with a different purpose. Some of these cells include blood cells, skin cells, and brain cells,
to name just a few. Each type of cell has a different function in your body. For example,
the main job of red blood cells is to transport oxygen from your lungs to the rest of your body,
while the function of skin cells is to form a protective barrier between you and the rest of the
world. Each individual type of cell contributes to the miracle that is a working body. Although they
aren't visible, cells are everywhere. They are the building blocks of life, making up
every organism around you, even the ones you can't see. The invention of the microscope opened up a
whole new microscopic landscape for learning and studying and cells are just the beginning.