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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 [email protected], 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 WorkBy 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.
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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 [email protected].
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NATIONAL GEOGRAPHIC EXPLORER!May 2008, Vol. 7, No. 7, pp. 2+
Copyright © 2008 NATIONAL GEOGRAPHIC SOCIETY. All rights reserved. Reprinted with permission.
Layers of LifeBy 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.
(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.
Giant Amazon Water Lilypads
A giant Amazon water lily is strong enough for a person to stand on. (Credit: Will & Deni McIntyre/Getty Images)
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(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.
Jaguar in Amazon Rain Forest
Jaguars are the largest cats in the Americas. (Credit: Claus Meyer/Minden Pictures/Getty Images)
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(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.
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)
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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
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Copyright © 2002, Crinkles. Published by LMS Associates LLC. March/April 2002, pp. 40-43. http://www.crinkles.com.
Tundra Summers--Arctic Wintersby 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?
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(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.
What Is Permafrost?
Permafrost is soil that is permanently frozen. The permafrost in the tundra is what keeps trees from being able to send their roots deep into the soil. Permafrost also accounts for the many lakes and marshes in the tundra in the warm months. Even though snowfall is not excessive, the many lakes are formed when the snow melts and can't seep into the soil because of the permafrost.
What Other Features Can You See?
Another interesting feature of tundra landscape is called a pingo. A pingo is formed when a lake is covered with debris and then freezes. The water trapped underneath the debris expands and pushes the land above it up into a hill called a pingo.
Large geometric patterns of cracked land also make up part of the tundra. They are formed by ice. When the ice melts and then freezes again, season to season, the land contracts and expands. This cycle of contracting and expanding makes cracks in the land. These cracks fill with water. When the water expands, it makes the cracks grow even larger, creating the huge "polygons" that are visible in the tundra from the sky. They are too large to notice from ground level.
Alpine Tundra
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What Are the Seasons Like in the Tundra?
Winter weather in the tundra lasts for eight or nine months of the year. The other three to four months are the growing and mating season in the tundra. During the warm months temperatures vary, but most days average about 50 degrees Fahrenheit.
The tundra is a fragile ecosystem. Life is very interdependent. Since there is a short growing season, a single change can affect an area for years. Many books have been written about the tundra. The land where the sun never sets for several weeks in the summer and never rises for several weeks in the winter lends itself to great tales.
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GOBAR TIMES (New Delhi, India) Sept. 30, 2006, Issue No. 63, pp. 66-67
Copyright © CSE Centre for Science and Environment www.gobartimes.org. Gobar Times. Sept. 30, 2006. For comments, please visit www.gobartimes.org/gt_write-us.htm.
The Forest Folks When people think of forests, the first things that come to the mind are large trees, bears, eagles, gorillas, and tigers. But there's plenty more. Forest plants and organisms, such as bacteria and fungi, are also jungle dwellers!
In fact, each part of the forest supports life...
Plants: Forest plants include trees, shrubs, vines, herbs, grasses, and a variety of other plants to be found among the trees.
Plants are real all-rounders! Their most crucial benefit is that plants (leaves) produce oxygen, which is essential for every living organism. Moreover, plants provide shelter and food to the animals living in the forest, and benefit human beings as well.
Amphibians: Amphibians include frogs, toads, and salamanders. Amphibians begin their lives in the ponds (where they hatch from the eggs) and can spend their entire adult lives on dry ground. Sometimes these ponds are tiny pools of water between the leaves of a plant, or they are large expanses of wetlands within the forest (riparian zones).
Fish: Fish in a forest? Well, not exactly in the forest but, in the rivers and streams that run through them. Rivers, ponds, and bogs are all integral parts of natural forests, and there are often complex relationships between the animals in the water and the animals in the trees. Fish and the variety of insects in the water attract reptiles and birds.
Mammals: The huge variety of mammal species living in forests range from the tiny, mouse-like shrews to acrobatic primates! Many forest mammals are brilliant climbers, and use trees for food, shelter, and as travel routes.
Insects: Insects are the most abundant group of pollinators and are thus vital to both plants and other animals. They also decompose the piles of dead organic matter, which the fungi cannot decompose alone. Insect
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larvae work their way into fallen trees and help the forest floor store moisture.
Birds: There are two main groups of birds: the permanent residents and the migrants. The permanent residents use the forest for food and shelter. Birds feed on insects, and on seeds and fruits found in forests. The migrating birds distribute seeds as they travel great distances every day.
Reptiles: Snakes and lizards are the most common forest reptiles. There are approximately 2000 species of snakes on earth! Lizards have species ranging from tiny geckos to the huge iguanas.
Both have very interesting defense mechanisms. Snakes use their venom and camouflage. And lizards shed their tails when attacked! Even after separating from the lizard, the tail continues to move! This distracts the predator and the now tailless lizard escapes!
Epiphytes: Do you know that there are certain plants that grow in the branches of large trees? They can make up over 50 percent of the plant species in a tropical rainforest! They come in all shapes--hanging, sprawling vines, bushy clumps of water-catching leaves, even cactus-like plants. In some temperate coastal forests, trees are carpeted with layers of epiphytic moss and lichenes!
Fungi: Do you like mushrooms? Do you know that mushrooms are the "fruits" of an underground network of fungus? Yes, fungus!
Trees and the fungi (that mainly grow around tree roots) are interdependent for certain nutrients. If a tree is cut down, the fungi around its roots die. If a new tree is then planted in the same spot, it cannot grow well because the soil would lack the important fungus!
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SCIENCE MADE SIMPLE April 2004, pp. 1-4
Reprinted with permission from Science Made Simple.
What Is the Environment? Why Is It Important? Air, water, food and shelter--these are the basic necessities of life. And they are provided for us by our planet Earth.
All of these things--our surroundings--are part of our "environment." The term "environment" is used to describe both the natural world, and our man-made surroundings. When we use it here, we will mean the natural environment.
Ecology
The study of how living things depend on each other and their environment is called ecology. Scientists who study ecology are called ecologists. Not only do they study animals and plants, but they also study humans in the environment.
The environment includes the air we breathe, the land and water that surround us and all the living things: plants, animals, insects, even bacteria. The environment also includes climate and location. A place can be warm and rainy or dry and hot. It can be near the ocean, in a forest or desert, or high up in the mountains. Your environment is not only the space immediately around you, but is as big as planet Earth itself.
Ecosystems and Niches
Organisms (living things) exist in many different kinds of environments. For example, polar bears live in the freezing cold of the Arctic, while certain bacteria live in hot springs at temperatures close to 100 degrees C, the boiling point of water. The kind of place where a plant or animal normally lives and grows is called its "habitat." Polar bears and the thermophilic ("ther-muh-fill-ik," meaning grows in high heat) bacteria live in very different habitats.
Many different kinds of animals live within each type of habitat. These animals live together in an interdependent group called a "community," just like people in a town or city are a community. The organisms in a community and all of their non-living surroundings are called an "ecosystem." An ecosystem can be as small as a rock pool on the beach, or as big as the Arctic.
The organisms that live within each ecosystem are perfectly adapted to survive there. Polar bears only live in the Arctic. Their thick, white fur keeps them warm and blends in with the snow. The bottoms of their broad feet are hairy, so they can walk on ice without slipping. Their food includes the seals, fish and birds that live there. They also eat plants that grow in the spring and early summer. Polar bears find everything they need to survive in their Arctic habitat.
Green turtles are adapted to a very different habitat. These large marine turtles live all around the world in tropical and subtropical oceans. They swim near the coastline, feeding on seaweed and algae. The females go ashore to lay their eggs in the warm sand. Their
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environment provides everything they need to survive.
Polar bears and green turtles live in very different environments, but like all other plants and animals, each is well adapted to its own habitat.
Every living thing fills an ecological "niche" within their ecosystem. This means that they don't simply take up space, but they have a function, or role to play in the community. For example, polar bears fill a niche in their Arctic ecosystem. They eat smaller animals, keeping the populations under control. Without the bears, the number of seals or birds might grow too large for the amount of food available to them. There are many different species of dung beetles, which feed on animal waste. In their niche, they perform a very important role in cleaning and maintaining their ecosystems.
Two different kinds of animals can not fill the same niche in the same ecosystem. For example, grey squirrels and red squirrels are very closely related. They usually live in the same type of woodland habitats, fill the same niches, and eat the same acorns, seeds and berries as food. Until the early 1900's, only red squirrels lived in the woods and forests of England. Then grey squirrels were brought over from America. Unfortunately for the red squirrels, there is only room in each niche for one type. The grey squirrels were more aggressive, eating the food and excluding the reds from the broad-leaf forests. The red squirrels had to find another niche to survive. They moved northward, where they were able to adapt to living in the evergreen forests found there.
Each ecosystem, and the plants and animals within it, exists in a delicate balance. Changing the environment, and adding or removing any part can upset that balance. The whole ecosystem could collapse. The survival of all living things on the planet, even humans, depends on maintaining a healthy ecosystem and keeping the balance of all of the living things within it.
Biomes--Different Kinds of Habitats
The main thing that controls the type of plants growing in any location is the climate. Climate is the normal weather conditions (temperature, precipitation, wind) over a long period of time. Since similar climates exist in many different places on Earth, similar habitats can be found in different locations.
These related areas across the globe are called "biomes." Scientists have not agreed on a single classification system for biomes, so you may see different types listed in other sources or references. One way to classify biomes is to split them into 5 different types: water (aquatic), desert, forest, grassland, and tundra. These 5 main types can each be split further. The aquatic biome has freshwater and marine biomes. The marine biome can be divided into estuaries, oceans and coral reefs. Forest biomes can be divided into temperate (seasonal), rainforest, and others.
In each type of biome, you will find similar kinds of organisms and ecosystems, no matter where on the planet it is found. For example, you can find bears not only in California forests, but also in Russian and Chinese woodlands.
The Earth's Natural Cycles
The planet Earth is always changing, and yet it maintains a delicate balance that supports all life here. Some of these changes, like the weather, can happen very quickly. Others, like the
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changing of the seasons, happen more slowly and on a regular and predictable basis. And still others, such as the climate changes of the Ice Ages, take thousands of years.
When the Earth's natural cycles change slowly over time, the plants and animals have to change too. This is a process known as adaptation. For example, the fur of the arctic fox thickens and turns white each winter to blend in better with its surroundings. If an area of the African tundra gradually becomes drier over several years, the animals learn to look elsewhere for water. Given enough time, they may be able to find other sources of water, or they may move to a wetter location.
On the other hand, if a change in these natural cycles is very sudden or drastic then the animals and plants that relied on a regular pattern might not have time to adapt, and may not survive as a consequence. Floods and droughts are examples of the type of sudden natural change in environment that can be disastrous to the living things within it. These changes are often simply part of a natural cycle, but sometimes people affect and alter the environment in harmful ways.
In addition to these types of changes, there are a number of continuous cycles which support and maintain life. The air, water and all living things are part of one huge ecosystem, each piece dependent on all of the other parts.
The Water Cycle
The Earth's water is constantly on the move in a continuous cycle. In fact, the water you drink today may be the same water a dinosaur drank! Every river and stream, every ocean, lake and puddle, contains droplets of water that have circulated, or recycled around the planet for billions of years.
The cycle starts when water evaporates from the oceans, lakes and rivers. Heat from the Sun turns the liquid water into water vapor that rises up into the air. When the water vapor reaches the cooler layers high in the atmosphere, it condenses into tiny water droplets and forms clouds.
(See picture, "Water Cycle.")
Winds in the atmosphere push the clouds along. The tiny droplets grow, and eventually fall as rain, snow or hail, often many hundreds of miles away from where the cloud was formed. Some of this water soaks into the ground where it flows into "aquifers," underground layers of permeable rock, sand or gravel. Some makes its way into streams and ponds, flowing into Water Cycle
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lakes and rivers, and back to the sea. Anywhere along the way, the water may evaporate and the cycle starts over again.
All animals need water to survive, but clean, fresh water is a limited resource. The majority of water on the planet's surface, in the form of oceans and seas, is salt water. Only around 1% of the Earth's water is fresh liquid water.
In many places, people get their water directly from lakes or rivers. Surface water is often diverted into human-made reservoirs for storage and use. In some areas, people use wells to get fresh water from the underground aquifers. No matter where your drinking water comes from, you can see how important it is to protect our limited sources of fresh, clean water.
The Food Chain
We mentioned earlier how all living things on the planet interact and depend on each other. A good example of that is the food chain.
The food chain begins with energy from the sun. Plants use this energy, along with carbon dioxide (CO2) from the air, and water and nutrients from the soil, to produce everything they need to live and grow. Green plants are called the "energy fixers." Using a series of chemical reactions called photosynthesis, plants turn water and carbon dioxide into simple sugars. The sugars store energy for later use. They are also used as building blocks for more complex molecules, such as other carbohydrates, proteins, fats and cellulose (a structural material in plant cell walls).
(See picture, "Food Chain.")
Plants also provide food for animals. Herbivores are animals that eat vegetation, but not meat. Examples are rabbits and other small rodents, some insects, certain birds, and ruminant animals such as sheep and cows. The herbivores themselves may become food if eaten by carnivores or omnivores. Carnivores are strictly meat eaters, while omnivores eat both plants and animals. Cats, foxes and birds of prey are carnivorous. Most humans are omnivores, although some, called vegetarians, are herbivores.
Nothing in the food chain is wasted. When plants and animals die, the remains are recycled
Food Chain
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by the "decomposers." The decomposition process often begins with worms and certain insects (beetles and grubs), and is then completed by fungi and bacteria in the soil. The decomposers break down the dead material, and the waste products that all animals produce. They take what they need to live, and the rest is returned as nutrients to the soil. New generations of plants will use those nutrients to grow, starting the cycle all over again.
The Carbon Cycle
Carbon is one of the most common elements in the universe. It is the building block of life here on Earth. Even though carbon makes up only a small fraction of the Earth's total mass (about 0.001%), the human body is about 18% carbon.
Carbon is found in the atmosphere, oceans, soil, rocks and the planet's interior, as well as in all living things. It moves from place to place in two natural cycles, the geological and the biological-physical carbon cycles.
(See picture, "Carbon Cycle.")
Our planet is constantly changing, and the geological carbon cycle operates over millions of years. Carbon dioxide in the atmosphere reacts with minerals in rocks and soil to form carbon-containing chemicals, called carbonates. Through weathering and erosion, these carbonates are washed away to the ocean where they settle on the bottom.
The surface of the planet is not solid, but is covered in "tectonic plates" that fit together like a jigsaw puzzle. These plates move very slowly over time. In some areas of the ocean floor, the plates are moving
apart. Molten rock flows up through the cracks, then cools to form new ocean floor. Where two plates come together, one of the plates slides under the other, returning surface material to the interior of the planet. This is called "subduction."
The carbonates, as part of the seabed, are returned to the planet's interior through subduction. There, the material melts and more reactions take place, forming carbon dioxide. The carbon dioxide gas is returned to the atmosphere when volcanoes erupt.
Carbon Cycle
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The Biological Carbon Cycle: Respiration & Photosynthesis
In the earlier section on the food chain, we discussed photosynthesis. It turns out that this process is also part of the carbon cycle. Plants take in atmospheric carbon dioxide and produce sugar and food. The reactions which occur during photosynthesis release oxygen back into the air. Humans and animals need this oxygen (O2) to live. Land animals get their oxygen from the air they breathe. Most aquatic animals absorb oxygen from the water in which they live.
The oxygen is used in reactions which provide our bodies with energy. During those reactions, the oxygen is converted to carbon dioxide (CO2). Exhaled as a waste gas, this CO2 is returned to the atmosphere. This process of taking in and using oxygen and exhaling carbon dioxide waste is called "respiration." The exhaled CO2 is available for plants to use, starting the cycle over again.
There are also other sources of carbon in the biological carbon cycle. Carbon that makes up the plants and bodies of animals is released after death by decomposition. Forest fires, and burning wood or fossil fuels, release carbon dioxide into the air. Even the oceans play a role, absorbing and holding large amounts of dissolved carbon dioxide.
So, animals and plants depend on each other for survival. The "waste" gases from plants keep animals alive and the "waste" gases from animals keep plants alive.
The balance between how much C02 is produced and how much is reabsorbed is essential to all living things. If this is altered, either by a change in natural cycles or because of humankind's influence, the consequences could be disastrous.
We All Need Each Other
All of the planet's natural cycles are interlinked. For example, the CO2 cycle depends on photosynthesis from plants and respiration from animals, which also require water from the water cycle. Both CO2 and water are also part of the food cycle. Changes in any one of these cycles will therefore have an effect on all of the Earth's dynamic systems. A healthy balance within each is vital for the health of the entire planet and all of the living things it supports through these natural cycles!
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HIGHLIGHTS FOR CHILDREN July 2008, Vol. 63, No. 7, pp. 6-7
Copyright © Highlights for Children. July 2008. All rights reserved. Reprinted with permission.
What Good Is the Big Bad Wolf?
This predator helps its habitat.
By Linda Zajac
One by one, Stoney, Betty, and the other wolves in their pack trudged down a snowy bank into the bone-chilling waters of the Cascade River. The wolves had not eaten anything for several days. Now, dinner was waiting across the water. They could smell it. In silence they moved, dripping in the darkness.
While the wolves trailed their next meal through Banff National Park in Canada, scientists were coming to track the wolves. At daybreak, Dr. Mark Hebblewhite and his co-workers drove through the valley to the base of the Rocky Mountains. Hebblewhite has been studying wolves for years and is now a scientist at the University of Montana.
Over 15 years, the researchers had trailed the wolves on cross-country skis or snowshoes. They trekked among pine trees and jagged snow-capped peaks. At times, the tracks ended at a river, where crossing wasn't always possible. Sometimes, the threat of crashing snow forced the scientists to turn back.
"Avalanches can kill people and wolves," Hebblewhite said.
But in time the research team learned where the wolves went and how many elk they ate.
A Natural Experiment
Banff National Park is the site of a "natural experiment" that shows the role that a predator can play in its habitat. The experiment was set up by accident. In fact, it began when people tried to kill off wolves.
Wolves cause problems for farmers and ranchers. But over many years, the predators' reputation became worse than they deserved. In legends and folklore,
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wolves blew down houses and ate grandmothers, too. They were blamed for a disease they didn't spread. "Many people hated wolves," said Hebblewhite.
People began to kill wolves. In fact, until 1969, killing wolves was part of every warden's job in the park. Soon any wolves that had survived had left the park.
But wolves can travel long distances, and by 1986, wolves from other areas had begun to move into the park.
Time had changed the town of Banff, which is in the middle of the park. The town had grown much bigger. Elk roamed freely in the town and park, but when the wolves came back, very few wolves went near the town. Most chose wilderness areas.
Now scientists could compare two types of areas, just as they might in an experiment that they had set up themselves. In the town, they could see what happened in a habitat that had lots of elk but almost no wolves. In the wild areas, they could study what happened to that same kind of habitat as wolves moved in and began to hunt the elk.
Up and Down the Food Chain
Why study these habitats--one with wolves and one without? To learn more about food chains.
Scientists already know how energy moves up a food chain. Plants (such as the aspen and willow trees) capture energy from sunlight and use it to make their food. Plant eaters (such as elk) eat the plants, taking the plants' food energy. Then meat eaters (wolves) eat the plant eaters, taking in energy that was once sunlight.
But plants, elk, and wolves are not the only living things in these habitats. Songbirds and beavers also use the trees that the elk eat. The scientists wanted to know more about how meat eaters at the top of a food chain affect plants and other animals in the park. In other words, do wolves help keep nature in balance?
(See picture, "Food Chain in Banff National Park.")
For 15 years after wolves had returned to the park, the research team studied the two kinds of habitat. They measured willow twigs and examined young aspen trees. Every winter they hovered in helicopters, counting elk. They also tracked five wolf packs.
The research team discovered that the food chain was out of balance in the town. Without wolves to prey on the elk, the elk herd had grown out of control. Elk roamed in the roads, grazed in gardens, and ripped through aspen and willow trees like a river overflowing its banks. Many trees died.
Warblers nest in willow trees. As the trees died, many songbirds vanished.
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Beavers use willows to build their homes. As the trees died, there were fewer beaver dams.
The Good Wolf?
But in wild areas, the habitats looked different. Where the wolves lived, they ate some of the elk. Now there were fewer elk to eat the trees. As more trees survived, more beavers and warblers came back and built lodges and nests.
The answer was clear. Wolves kept the food chain and the habitat in balance. "Wolves affected elk, which influenced plants like aspen and willow, which had impacts on birds and beavers," said Hebblewhite.
Now it seems that the wolf never deserved its old reputation for being "big and bad." As this study and many others show, the wolf plays an important role in its habitat.
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SCIENCE NEWS FOR KIDS April 4, 2007, n.p.
Copyright © April 4, 2007 Science Service, Incorporated. All rights reserved. Reprinted with permission.
Food Web WoesBy Emily Sohn
Food Chain in Banff National Park
In Banff National Park, wolves have a ripple effect through their habitat. By taking some elk, they save some plants for other animals. (Credit: WikiMedia Commons (wolf); (c) Cliff Nietvelt (elk, beaver and plants))
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Sharks are scary--no doubt about it. Just ask anyone who's seen Jaws or other films that feature these sharp-toothed creatures.
But there's something that might be just as scary as meeting up with a shark--at least from an environmental perspective. It's the thought of what might happen if sharks disappeared from the oceans. That's because sharks are important players in delicate food webs, suggests a new study out of Canada.
Fishing companies have been killing large sharks for decades. Sometimes they've done it on purpose, and sometimes they've done it by mistake. Because of these kills, the animals that sharks eat have boomed. And that's bad news for the creatures even lower on the food web.
Along the East Coast of the United States, only sharks that are at least 2 meters (6.6 feet) long are tough enough to eat a lot of the medium-size sharks, rays, and skates living in those waters. Eleven large shark species in the region fit into that category.
Researchers led by Ransom Myers in Nova Scotia reviewed 17 surveys that counted big sharks and their prey during the past 35 years. They found that numbers of all 11 species have dropped since 1972.
As the big sharks disappear, most of the smaller sharks, rays, and skates have increased in number. Surveys have shown increases in 12 of 14 species of these sea creatures over the past 30 years. The populations of some of these species are 10 times as high as they were three decades ago.
Researcher Charles H. Peterson recently heard fishermen in North Carolina complaining that cownose rays were eating up all the region's bay scallops. He and his colleagues at the University of North Carolina's Institute of Marine Sciences at Morehead City decided to test whether this was really happening.
To keep rays from eating scallops in certain areas, the scientists put a protective ring of poles around the scallops. Rays are wider than most sea creatures and won't usually swim between poles that are spaced closely together. (The rays could turn sideways and fit through, but they don't usually do this.) Other animals, however, swim easily through the gaps between poles.
In 2002 and 2003, at the beginning of the fall season, researchers found populations of bay scallops that were healthy and dense. But after rays migrated through, the scallops nearly disappeared in areas that were not surrounded by poles. Within protected areas, only half of the scallops were gone. It's not even certain that the missing ones got eaten, Peterson says, since they might just have swum away.
The study suggests that efforts to replace declining populations of shellfish, such as scallops and oysters, might require extra levels of protection against predators.
The findings reinforce the message from a 1998 study of a food web in Alaska. In that area, killer whales can normally eat otters. Otters eat sea urchins. And sea urchins
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eat kelp. When the whales ate more otters, the study found, sea urchins thrived, and the kelp suffered.
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