Your Skin
Quick! What's the body's biggest organ?
You might be surprised to find out it's the skin, which you might not think of as
an organ. No matter how you think of it, your skin is very important. It covers
and protects everything inside your body. Without skin, people's muscles, bones,
and organs would be hanging out all over the place. Skin holds everything
together. It also:
• protects our bodies
• helps keep our bodies at just the right temperature
• allows us to have the sense of touch
Don't Miss Your Epidermis
The skin is made up of three layers, each with its own important parts. The layer
on the outside is called the epidermis (say: eh-pih-dur-mis). The epidermis is
the part of your skin you can see.
Look down at your hands for a minute. Even though you can't see anything
happening, your epidermis is hard at work. At the bottom of the epidermis, new
skin cells are forming.
When the cells are ready, they start moving toward the top of your epidermis.
This trip takes about 2 weeks to a month. As newer cells continue to move up,
older cells near the top die and rise to the surface of your skin. What you see on
your hands (and everywhere else on your body) are really dead skin cells.
Bye-Bye Skin Cells
These old cells are tough and strong, just right for covering your body and
protecting it. But they only stick around for a little while. Soon, they'll flake off.
Though you can't see it happening, every minute of the day we lose about
30,000 to 40,000 dead skin cells off the surface of our skin.
So just in the time it took you to read this far, you've probably lost about 40,000
cells. That's almost 9 pounds (4 kilograms) of cells every year! But don't think
your skin might wear out someday. Your epidermis is always making new skin
cells that rise to the top to replace the old ones. Most of the cells in your
epidermis (95%) work to make new skin cells.
And what about the other 5%? They make a substance called melanin (say:
mel-uh-nun). Melanin gives skin its color. The darker your skin is, the more
melanin you have. When you go out into the sun, these cells make extra melanin
to protect you from getting burned by the sun's ultraviolet, or UV, rays.
That's why your skin gets tan if you spend a lot of time in the sun. But even
though melanin is mighty, it can't shield you all by itself. You'll want to wear
sunscreen and protective clothing, such as a hat, to prevent painful sunburns.
Protecting your skin now also can help prevent skin cancer when you get older.
Taken from: KidsHealth.org
Nervous System Includes: Brain, Spinal Cord and Nerves
You Have Some Nerve!
So the brain is boss, but it can't do it alone. It needs some nerves — actually a
lot of them. And it needs the spinal cord, which is a long bundle of nerves inside
your spinal column, the vertebrae that protect it. It's the spinal cord and nerves
— known as the nervous system — that let messages flow back and forth
between the brain and body.
If a spiky cactus falls off a shelf headed right for your best friend, your nerves
and brain communicate so that you jump up and yell for your friend to get out of
the way. If you're really good, maybe you're able to catch the plant before it hits
your friend!
But you might wonder about these nerves, which you can't see without a
microscope. What are they anyway? The nervous system is made up of millions
and millions of neurons (say: NUR-onz), which are microscopic cells. Each neuron
has tiny branches coming off it that let it connect to many other neurons.
When you were born, your brain came with all the neurons it will ever have, but
many of them were not connected to each other. When you learn things, the
messages travel from one neuron to another, over and over. Eventually, the
brain starts to create connections (or pathways) between the neurons, so things
become easier and you can do them better and better.
Think back to the first time you rode a bike. Your brain had to think about
pedaling, staying balanced, steering with the handlebars, watching the road, and
maybe even hitting the brakes — all at once. Hard work, right? But eventually, as
you got more practice, the neurons sent messages back and forth until a pathway
was created in your brain. Now you can ride your bike without thinking about it
because the neurons have successfully created a "bike riding" pathway.
Taken from: KidsHealth.org
Plant Biology: Roots, Shoots, Stems, and Leaves
By Peter Mikulecky, Michelle Rose Gilman, and Brian Peterson from AP Biology For
Dummies
Your basic vascular plant parts are roots, shoots, stems, and leaves. Of course, there's a
wealth of variety within these types or parts, but it boils down to those four. Each part has
distinct functions. Together, these parts reflect how vascular plants evolved to inhabit two
distinct environments at the same time: the soil and the air. Why would plants do such a
thing? The soil offers water and vital minerals. The air offers carbon dioxide and the energy of
sunlight. To forge the successful lifestyles they enjoy today, plants evolved systems to tap
into all these resources, both above and below the ground. In short, plants evolved roots and
shoots. Shoots, in turn, can develop stems and leaves.
Roots
Roots are branched, underground structures that serve two major functions. First, somewhat
obviously, roots firmly anchor the plant to a fixed spot. Once a plant takes root and begins to
grow in an area with good access to moisture, soil nutrients, and light, it pays to stay.
Second, roots serve as transport systems, allowing the plant to suck up water and dissolved
nutrients from the soil to support the plant's growth. Roots have specialized parts that
develop from the three major types of plant tissue: ground, dermal, and vascular.
Shoots
Shoots target the above-ground business of the plant. Very young plants may possess only
simple, undeveloped shoots. As a plant grows, however, these tender shoots develop into
stems and leaves. So, stems and leaves are really part of the shoot system. Stems and
leaves are so different and specialized that it is worth considering them separately. Overall,
the shoot system enables a plant to grow taller to gain access to energy-giving light, and
allows the plant to convert that light energy into the chemical energy of sugar. Like roots,
shoots develop from ground, dermal, and vascular tissues.
Stems
Stems are sturdy structures that grow in order to give a plant a fighting chance to spread its
leaves in the sun. Stem growth can add to the plant's height, broaden the area covered by
the leaves, or even direct growth from a dark area toward one with more light. To provide
mechanical support for a growing plant, stems need to be strong. To help move water and
nutrients to the furthest reaches of the plant, stems are stuffed with little transport pipes in the
form of xylem and phloem.
Leaves
Leaves are the original solar panels, capturing energy from sunlight in a biochemical process
called photosynthesis. The cells within leaf tissues are hectic with biochemistry, importing
water and nutrients to support their frantic work, and exporting sugar to provide energy to the
remainder of the plant. The import/export business conducted by the leaves is supported by
xylem and phloem pipelines, which explains why leaves are so richly veined.
The "Typical" Plant Body
The Root System
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•
•
•
•
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Underground (usually)
Anchor the plant in the soil
Absorb water and nutrients
Conduct water and nutrients
Food Storage
The Shoot System
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•
•
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◦
◦
•
Above ground (usually)
Elevates the plant above the soil
Many functions including:
photosynthesis
reproduction & dispersal
food and water conduction
Note: the shoot system includes the leaves and the reproductive organs, although these
will be covered in more detail separately