XXIV. Read the following paragraphs on the nitrogen cycle. Some of the sentences have numbers after them. Write that number in the corresponding box in the picture below.
Almost 80% of the air is nitrogen gas. But most living things cannot use nitrogen in this form. It must first be changed into nitrogen compounds. The process whereby nitrogen gas is changed into nitrogen compounds is called nitrogen fixation. The nitrogen cycle is the movement of nitrogen through an ecosystem.
There are two ways that nitrogen is fixed (changed from nitrogen gas to nitrogen compounds). The first is through lightning. As lightning passes through the air, it causes nitrogen to combine with oxygen to form nitrates (1). These compounds are washed out of the air to the earth by rain. Then plants and animals can use nitrogen in this form.
The second way that nitrogen can be fixed is by the actions of certain microorganisms called blue-green bacteria (2). After the nitrogen has been fixed, plants use this form of nitrogen (3). Then, animals eat the plants (4). When the animals die, the nitrogen in their bodies returns to the soil (5).
In order to complete the cycle, there has to be some nitrogen gas returned to the air so the process can start again. This is done by denitrifying bacteria (6). These bacteria live in the soil and change nitrogen compounds back into nitrogen gas.
XXV. Now read the following passage about the carbon and oxygen cycle.
The movement of carbon dioxide and oxygen through an ecosystem is called the carbon and oxygen cycle. In this passage, we will focus on the cycle of carbon dioxide. There are two ways that carbon dioxide is removed from the atmosphere. The first is through the ocean, which is like a huge reservoir that absorbs much of the gas. The second way is by plants that take in carbon dioxide through the process of photosynthesis.
In a natural system, carbon dioxide is released back into the atmosphere through respiration when an animal, such as a deer, breaks down food and energy is released. Carbon dioxide is also put back into the atmosphere through a process called decomposition. This process occurs when dead plants and animals are broken down by the actions of bacteria.
Human activity, however, has seriously affected this cycle by releasing more carbon dioxide into the atmosphere than is taken away. This extra carbon dioxide is released into the atmosphere in two ways. The first is through the burning of fossil fuels, such as coal, oil, and gas. The second is through deforestation, where trees are either cut or burned, releasing all the stored carbon dioxide into the air.
XXVI. Retell the text using this picture.
XXVII. Final test
1. Describe the structure of an ecosystem.
2. List various physical factors and describe how they affect the distribution of living things
3. Describe a typical food chain
4. Explain how energy flows through an ecosystem
5. Explain how materials cycle in an ecosystem
RART III
Texts for Individual Reading
Text 1
Tundra plants can be, classified into five main groups. Lichens are primitive plants without stems, leaves, or roots. They are a combination of algae and fungi that grow on rocks and the ground. A second group of plants are the mosses, which are usually found in cracks in rocks. Arctic cotton grass is a kind of grass, the third group of alpine plants, which produces a ball of white fluff that helps the plant stay warm. The tundra's most delicate-looking plants—the small flowering plants—are often the toughest. For example, the Arctic poppy has thin petals that remain on the flower even when it is extremely windy. Finally, a typical shrub in the alpine tundra is the ground willow.
Birds in the tundra are either migratory or permanent. The snowy owl, the ptarmigan, and the raven are birds that live in the tundra all year long. They have learned to survive the cold and the darkness of the winter. Two of these birds, the snowy owl and the ptarmigan, turn white in the winter. They change color so that they match the snowy background, which will help protect them from predators. With the coming of spring, however, other birds migrate to the tundra. Some of these typical migratory birds include geese, ducks, and terns.
Mammals are also both migratory and permanent residents of the tundra. The permanent residents can be further classified into three types: mammals that roam the open tundra year-round, mammals that hibernate, or mammals that dig tunnels under the snow. A typical migratory animal is the caribou, which migrates from the taiga in the spring. The chief predator of the caribou is the wolf, and this animal roams the open tundra year-round. Two other animals that roam the open tundra year-round are the Arctic hare—or snowshoe hare—and the Arctic fox. The hare and the fox turn white in the winter, just like the snowy owl and the ptarmigan, to protect themselves from predators or to surprise their prey. Grizzly bears and ground squirrels are animals that hibernate, but bears will sometimes come out of their dens during the winter. Finally, lemmings, which are small furry herbivores that look like hamsters, dig tunnels under the snow and live their lives much as they do above the ground in the summer
Text2
Acid Precipitation in Québec
In the 1980s, a lot was said in the media about acid precipitation. The strong interest in the phenomenon stemmed from the fact that our lakes, rivers and forests were located on highly sensitive soils and received highly acidic depositions. This interest was all the more significant that acid precipitation had an immediate impact on sport fishing as it resulted in the disappearance of certain vulnerable fish species from our lakes, which proved acidic. Also, in our forests acidification contributed to sugar maple dieback. But the 1980s was also the decade where countermeasures were implemented. Lake monitoring and precipitation measurement networks were set up to better define the problem and its impact on the environment. National and international agreements aimed at reducing pollutant emissions worldwide were discussed, while legislative tools to help Québec meet the reduction goals set forth in the agreements were adopted. Since the end of the 1980s, Québec has managed to lower its SO2 emissions by more than 60% with respect to 1980 levels. While Ontario has reached a similar goal, the United States will have reduced its SO2 emissions by 40% (1980 reference year) by 2010. It would appear, however, that these achievements will not be sufficient to recover the resources affected by acidification. Québec is therefore committed to seek an agreement with the other Eastern Canadian provinces for an additional 50% reduction in SO2 emissions. The government of Québec has signed a similar agreement with the Eastern Canadian Provinces and New England States addressing the problems of acid precipitation and mercury specifically. |
Text3