Standard One: Terrestrial and Aquatic Ecosystems

Standard Two: Terrestrial and Aquatic Ecosystems

How Stuff Works Mar 3, 2009, n.p. Copyright © 2009, How Stuff Works. All rights reserved. Reprinted with permission. Distributed by McClatchy-Tribune Information Services. For reprints, email , call 800-374-7985 or 847-635-6550, send a fax to 847-635-6968, or write to The Permissions Group Inc., 1247 Milwaukee Ave., Suite 303, Glenview, IL 60025, USA.

How Stuff Works: How Stem Cells Work

By Marshall Brain

HowStuffWorks.com (MCT)

Think about some of the big medical breakthroughs that have changed the human condition for the better. There is the invention of the vaccine, which has nearly eliminated deadly viral diseases like smallpox, polio, measles and mumps. There's the rise of antibiotics, which can rapidly heal all sorts of bacterial infections. There are surgical procedures like heart surgery and brain surgery. Even the common appendectomy has saved millions of lives.

Those are all huge medical advancements, many of which we now take completely for granted. Together they have helped to double the average human lifespan.

Stem cells research promises to open up a new area of medical advancement that could be just as important. Once we understand and harness their full potential, stem cells will improve millions of lives. Which leads to the obvious question: what is a stem cell?

Here is a simple definition: A stem cell is a cell that has the potential to turn into many different kinds of cells. To understand that, think about your own body. It contains dozens of different cell types. You have skin cells, which are completely different from liver cells, which are different from the cells that create tooth enamel, which are all different from muscle cells. But all those different types of cells came originally from stem cells.

You started out in your mother's womb as a single cell--a fertilized egg. That little spark of life divided into a tiny clump of stem cells (known as embryonic stem cells). Then those stem cells started dividing and differentiating into the specific cell types that make up your body today.

Obviously stem cells were important when you were developing in your mother's womb, but how can they be therapeutic for you today? Let's look at a few examples.

The idea of a bone marrow transplant is actually a stem cell therapy of sorts. Bone marrow contains stem cells for creating new red and white blood cells. But in certain diseases, the bone marrow stops doing its job correctly. Or bone marrow can be destroyed in the process of treating an aggressive cancer. So the stem cells in the marrow are replaced with new stem cells from a donor.

One classic situation where stem cells will probably be useful is the treatment of Parkinson's disease. Parkinson's disease is caused when a certain type of brain cell (called a dopaminergic neuron) stops working. Dopaminergic neurons produce dopamine, and without dopamine your brain loses its ability to control your muscles. The hope is that stem cells can be injected into the brain, and that they can differentiate into the proper types of cells to replace the lost dopamine.

Another place where stem cells might help is in the treatment of paralysis. Imagine that you were to fall and sever your spinal cord. Depending on where the break occurs, this accident will paralyze your legs or your arms and legs. You will be paralyzed for life because the nerve cells in the spinal cord will not grow back on their own. With stem cells, there may be a way to coax new cells to repair the damage.

Another area of stem cell research is organ replacement. Since stem cells are undifferentiated, they have the potential to turn into specific cell types. What if you could coax stem cells into growing a new heart or a new kidney? One of the first successes in the new era of organ replacement came in 2008, when scientists grew a woman a new wind pipe using stem cells. They started with a piece of donated wind pipe three inches long. They stripped off its outer cells to create a scaffold for new cells. Then they seeded the scaffold with stem cells from the woman needing treatment. The stem cells covered the scaffolding and created a new piece of windpipe that her body would not reject. Surgeons inserted the replacement windpipe and eliminated a significant problem for her.

It is easy to imagine many new techniques that become possible with stem cells. But at this moment, the research in this area is still very new. Scientists and doctors have a long way to go before they completely understand stem cells and how to use them. It is hoped that, by opening up research, new treatments will become available in the near future.

Looking for more? For extra info on this or the scoop on other fascinating topics, go to HowStuffWorks.com. Contact Marshall Brain, founder of HowStuffWorks, at .

NATIONAL GEOGRAPHIC EXPLORER!May 2008, Vol. 7, No. 7, pp. 2+

Layers of Life

By Susan Blackaby

• Explore the Amazon rain forest from the ground to the treetops.

The air is steamy. A giant anteater hunts for insect nests in the soil. An eagle flies high above. Between these two creatures lie layers of rain forest.

Each layer of these warm woods has a different mix of life. Together, they form a colorful ecosystem. That is a group of living and nonliving things that affect one another.

This is the Amazon rain forest. It covers much of South America. It is the largest rain forest on Earth. The Amazon rain forest is home to half the kinds of plants and animals on Earth. Let's explore it. We'll start at the floor of the rain forest.

The Forest Floor

The forest floor is dark. Ants and termites build nests. Earthworms feast on dead plants and animals. Other critters do, too. Yet new plants rise up.

Many of the plants have huge leaves. Big leaves can catch what little sunlight comes down this low. Water lilies, for instance, have giant pads.

Giant Amazon Water Lilypads
A giant Amazon water lily is strong enough for a person to stand on. (Credit: Will & Deni McIntyre/Getty Images)

(See picture, "Giant Amazon Water Lilypads.")

The Understory

The layer just above the forest floor is the understory. Bushes, vines, and small trees grow here. Not much sun gets through to this layer. Wild cats walk in the inky darkness. Bats, owls, spiders, and poison frogs also share the understory.

Jaguar in Amazon Rain Forest
Jaguars are the largest cats in the Americas. (Credit: Claus Meyer/Minden Pictures/Getty Images)

(See picture, "Jaguar in Amazon Rain Forest.")

The Canopy

The next layer is the canopy. It is like a roof above the forest floor. It is formed by treetops.

Leaves here get lots of water. Too much water could make a leaf rot. So each leaf grows a point called a drip tip. It helps extra water flow off.

The trees carry vines upward to the sunlight. The trees also hold plants called epiphytes. These are plants that get water and food from air. Many orchids and ferns are epiphytes.

Some plants are not the best guests for a tree to have. The strangler vine, for instance, steals food from its host. Its leaves block sunlight. Over time, the host tree dies.

Animals in the Treetops

Most rain forest animals live in the canopy. Its branches, vines, and leaves provide food and shelter for animals. In the treetops, fruit bats eat berries. Birds called toucans pick fruit. Macaws crack open nuts.

Animals that eat meat live here, too. Emerald tree boas wrap around animals and squeeze them to death.

The animals of the canopy have body parts that help them live in the trees. Sloths have hooked claws for hanging upside down. Tree frogs have sticky fingers and toes. They can even stick to wet leaves and branches. Monkeys' long tails can hold onto branches.

The Top Layer

The highest part of the forest is the emergent layer. It is formed by the tops of the very tallest trees.

Waterfall in Amazon Rain Forest, Ecuador
A stream crashes over rocks in the eastern part of the Amazon rain forest. (Credit: Pete Oxford/Minden Pictures/Getty Images)

(See picture, "Waterfall in Amazon Rain Forest, Ecuador.")

Some of these trees stand 18 stories high. Rain and wind pound the trees' leaves. Sunlight bakes them.

These trees' leaves are small and waxy. That helps them hold onto water. Otherwise, the water would be lost to the sun and wind.

The top layer of the forest is home mainly to things with wings. Butterflies dance in the air. Eagles nest in tree branches.

Below them, monkeys play. Even farther down, the anteater hunts for insects. From top to bottom, the rain forest is home for wild wonders.

Wordwise

canopy: roof-like layer formed by the tops of most rain forest trees

ecosystem: group of living and nonliving things that affect one another

emergent layer: layer formed by the tops of the tallest trees

understory: layer just above the rain forest floor

About the Story

Students explore the Amazon rain forest, Earth's largest, from the ground to the treetops, meeting some of the creatures that live in each layer.

Fast Facts

• Rain forests cover only about 6 percent of Earth's surface, yet they are home to more than half the planet's plant and animal species.

• Scientists identified some 280 different tree species in a single hectare (2.5 acres) of rain forest in South America.

• The second largest rain forest is in central Africa.

Vocabulary

Compounds: Have students find the word anteater in the first sentence of the article. Ask if they recognize any smaller words within it (ant + eater). Explain that anteater is a compound word. That is a word made of two or more shorter words. Then have students search the page for treetops and earthworms. Have them identify the smaller words that make up these compounds (tree + tops, earth + worms). Point out that thinking about the meanings of the two smaller words can sometimes help them understand the compound word.

CRINKLESMarch/April 2002, pp. 40-43

Tundra Summers--Arctic Winters

by Jennifer Galvin

The seal blubber lamp filled the room with smoke. Russel sat listening to Oogruk, his teacher, tell about the old ways of the Eskimo. Russel learned to hunt with a bow and arrow. When Oogruk gave him a sled and dogs, Russel knew it was time to embrace these ways. He crossed mountains, tundra, and ice floes always looking for his own song. How does he save himself from a threatening polar bear? How does he survive in the wilderness? Read Dogsong by Gary Paulsen. (Bradbury Press, 1985. 177p. Newbery Honor book)

It is now June. The temperature has been getting gradually warmer. Life is becoming easier. The birds are returning from their long migrations. Some animals are emerging from their winter hibernation. Others are shedding their white camouflage and acquiring new coats or feathers to blend in with the summer colors. This is the tundra where the months for growing are few and the cold months are long.

The tundra has been a favored setting for many authors. What makes them want to write stories in such harsh places? Perhaps it is the difficulty of survival that makes the struggle so real. The people and animals living there must cope with harsh weather, other animals, and rough terrain. They survive in spite of the cold and often severe temperatures.

What Is Tundra?

According to Donna Walsh Shepherd in Tundra, the word "tundra" comes from the Laplanders, the Sami native people of northern Scandinavia, and the Russians. It means "marshy plain" and "land of no trees."

Is All Tundra the Same?

There are two types of tundra--Alpine Tundra and Arctic Tundra. Both types of tundra appear above the treeline which is the place between where trees can exist and where the climate is too harsh for them to grow. It really isn't a line. It is an area where the trees grow smaller and smaller when the growing conditions grow harsher and harsher closer to the Arctic. Soon no trees can grow at all. Trees need to send their roots deep into the soil to support their large trunks and branches. When the ground is frozen most of the year, this isn't possible. Do you want to know more?

Alpine Tundra

(See picture, "Alpine Tundra.")

Where Is the Tundra?

Alpine Tundra appears at the peaks of very tall mountains all over the world. The land close to the Arctic and the North Pole is also called tundra or Arctic Tundra. It exists all around the Arctic Circle. Tundra covers parts of Canada, Alaska, Russia, China, Northern Europe, Greenland, and Iceland.

What Does the Tundra Look Like?

The tundra is a land of few trees. Instead, it is covered with grasses and fields of flowers. The tundra is full of plants that have adapted to grow quickly in the short summer months. The plants that live here have to be able to survive in the small layer of soil that is above the permafrost.