PASSAGE 1
Interested people are needed to participate in a one-year study to assess the effects of long dark winters on the vitamin D and calcium levels of Fairbanks residents.
So began a recruitment poster Meredith Tallas created 25 years ago. Now living in Oakland, California, Tallas was a University of Alaska Fairbanks student in 1983 who wanted to study how levels of a vitamin related to sun exposure fluctuated in people living so far from the equator. "The most obvious vitamin to study in Alaska is vitamin D, because of the low light in winter," Tallas said recently over the phone from her office in Berkeley.
Forty-seven people responded to Tallas' 1983 request, and her master's project was underway. By looking at the blood work of those Fairbanks residents every month and analyzing their diets, she charted their levels of vitamin D, which our skin magically produces after exposure to a certain amount of sunshine. We also get vitamin D from foods, such as vitamin-D enriched milk and margarine, and fish (salmon are a good source). Vitamin D is important for the prevention of bone diseases, diabetes, and other maladies.
If you live at a latitude farther north than about 42 degrees (Boston, Detroit, or Eugene, Oregon), the sun is too low on the horizon from November through February for your skin to produce vitamin D, according to the National Institutes of Health. Tallas also saw another potential Alaska limitation on the natural pathway to vitamin D production.
"Most outdoor activity requires covering all but the face and hands approximately seven months of the year,” she wrote in her thesis. “During the summer months residents keep much of their bodies clothed because of the persistent and annoying mosquitoes and biting flies and because of this, an Alaskan summer suntan becomes one of the face and hands.”
But even over bundled people like Alaskans show signs of enhanced vitamin D production from the sun. Tallas found the highest levels of vitamin D in the Fairbanks volunteers' blood in July, and the lowest levels in March. Tallas attributed the July high occurring about a month after summer solstice to the time needed for the body's processing of sunlight and the conversion to vitamin D. In Tallas' study, volunteers showed low levels of vitamin D in the winter months, but most got sufficient doses of vitamin D from sources other than the sun. Tallas also found that males had an average of 16 percent more vitamin D in their blood throughout the study, which she attributed in part to men being outside more.
In charting an average for people's time outside (you can't convert sunlight to vitamin D through windows), she found December was the low point of sunlight exposure when the sun struck the skin of her volunteers for less than 20 minutes per day. People spent an average of more than two hours exposed to Alaska sunlight in June and July. They seemed to hunker down in October when time outside in the sun dropped to about half an hour after almost two hours of daily sun exposure in September.
In her thesis, Tallas wrote that a midwinter trip to somewhere close to the equator would be a good thing for boosting Alaskans' vitamin D levels. “Presuming that an individual's lowest circulating vitamin D level is found in March or April, such trips could potentially have a very significant effect in improving late winter vitamin D status,” she wrote in her thesis. "Unfortunately a majority of Alaskan residents do not take such trips often.” An easy alternative for Alaskans not travelling southward during the winter is eating foods rich in vitamin D or taking vitamin D supplements, Tallas said.
PASSAGE 2
The Canada goose is the most widely distributed in North America. The breeding grounds of the geese cover the stretch from eastern Labrador to Western Alaska, and it is the only goose in North America to breed south of 49°N. The geese are known to occupy a wide range of habitats in temperate to low arctic areas including The Tundra which is not so rich in geographical features, The Boreal forest, The Parklands, The Prairies, meadows, and the higher mountains.
For most goose populations, nesting areas in the Arctic are secure; however, the development of gas and oil industries poses a danger to these groups. During migration, the geese head for warmer places where food is readily available. Canada geese migrate in the V- formation and are always in large groups. Scientists believe that geese travel in V-formation because of what is called the 'drafting effect.' It aids the birds to preserve their energy as they cover long distances. The same paths are followed by the migrating birds each year. The name given to these paths is 'flyways' or 'routes'. The four flyways that the Canada Geese use are: the Atlantic Flyway which is along the eastern coast of North America, the Mississippi Flyway, the Central Flyway which spans the Rocky Mountains, and the Pacific Flyway which is the route along the west of the Rocky Mountains.
Canada geese follow seasonal patterns of migration. The autumn migration is seen from September to the starting of November. The early migrant geese are likely to migrate faster as they spend less time at the designated rest stops. Some geese are known to return year after year to the same nesting grounds and lay their eggs with their partners. The chicks are raised in the same way every year. We know this from the records of many geese that have been tagged by scientists on the East Coast. However, It has been noticed that a few migratory populations of the Canada Goose are not flying as far south in the winter months as they used to. This Northward range shift is probably because of the availability of waste grain in the fall and winter months.
Agricultural fields offer food that is available in abundance and is also of superior quality for the geese compared to natural crops. Changing weather patterns and hunting pressure are the other reasons.
Every autumn, the snow geese move from their chief breeding area in central Canada to Squaw Creek National Wildlife Refuge where they make a stopover before moving to their destination in the Gulf of Mexico. They breed during the Arctic summers and then migrate to Mexico to spend the winter. During the summer, the young geese grow rapidly and become ready to fly. By the end of August, the birds make their journey to Mexico with the young ones on their first migration. They travel back to Canada in late spring along with their young ones. Some birds make the entire journey without stopping for rest, making it a journey of 70 straight hours of flying. Most of the geese are not inclined to make a stop on their return journey north as they are eagerly waiting to mate.
The Squaw Creek National Park is an essential stopover for the geese on the Central Flyway migratory route. The area was a private hunting area, but now the wildlife here is protected by law.
PASSAGE 3
One of the most alluring natural events of the year in many areas throughout North America is the leaves falling during autumn. They come in beautiful colours. But the question is why some trees turn yellow or orange, and others red or purple. This is something that has confused scientists for a long time.
During summers, leaves are green because they are filled with chlorophyll, the molecule that uses sunlight to convert energy into new building materials for the tree. When fall starts in the northern hemisphere, the solar energy reaching the surface reduces considerably. Except for evergreen conifers many trees stop photosynthesis till the spring starts. So instead of making food for the leaves, the tree sheds its leaves and saves its precious resources. Before shedding its leaves, the tree breaks down its chlorophyll molecules and sends the nitrogen back into the branches. When the chlorophyll is exhausted, other colours that have been dominated by the chlorophyll during the summer start to show. This phenomenon explains the yellow and orange colours during autumn, but not the bright red and purple colours found in maple or sumac trees.
The red colour is created by anthocyanins which are water-soluble plant pigments reflecting the spectrum from red to blue. They are a part of a class of sugar-based chemical compounds known as flavonoids. What's puzzling is that anthocyanins are newly made in the leaves at the time when the tree is preparing to drop them. But the production of anthocyanins does not make sense.
Why should a tree try to make new chemicals in its leaves when it's trying to shed and save the old ones?
Scientists have argued that anthocyanins might act as a chemical defence against attacks by insects or fungi, or that they might attract fruit-eating birds and that it might increase a leaf's tolerance to freezing. But some problems with these theories include the fact that leaves are red for a very short period of time and that the energy needed to manufacture the anthocyanins is more than any anti-fungal or anti-herbivore activity achieved.
It has also been suggested that trees may exhibit bright red colours to trick herbivorous insects into thinking that they are healthy and would be easily able to create chemical defences against infestation. When the insects pay attention to such things, they are tempted to lay their eggs on a duller, and presumably less resistant host. The fault in the theory lies in the lack of evidence to back it. No one has as yet discovered whether more robust trees sport the brightest leaves, or whether insects make choices according to colour intensity.
The reason behind why leaves take the trouble of making anthocyanins before the winter is the theory known as the 'light screen' hypothesis. It sounds contradictory because the idea behind this hypothesis is that the red pigment is produced in autumn leaves to protect chlorophyll in leaves from too much light. But why does it need protection when chlorophyll is the world's best light absorber? Why does the tree protect the chlorophyll when it is breaking it down to save as much of it as possible?
Even though Chlorophyll is equipped to capture the energy of sunlight, it can sometimes be engulfed by it, especially during droughts, low temperatures, or nutrient deficiency. Moreover, the problem of oversensitivity to light is even more severe during the fall, when the leaf is busy preparing for winter by dismantling its internal machinery. In summer, the energy collected by the chlorophyll molecules of the fragile fall leaf is not instantly channelled into useful products and processes. The weakened fall leaf is then exposed to the severe damages of the oxygen produced by the stimulated chlorophyll molecules.
There are hints everywhere, even if you had no idea what was going on as the leaves turned crimson. On many trees, the leaves on the side of the tree are the reddest and get the most sun. Not only that, the crimson on the upper side of the leaf is brighter. For many years, it has been said that the best conditions for bright red colours are dry, sunny days and cool nights, which are similar to the conditions that make leaves vulnerable to excessive light. Finally, as you travel to the north in the northern hemisphere, trees such as maples become considerably redder. It's cooler there, they're more stressed, their chlorophyll is more sensitive, and more sunscreen is required.
The reason why some trees start to produce red pigments while others don't bother and simply reveal their orange or yellow hues is still unknown. It is not known whether these trees have other ways to dispose to stop being exposed to more light in autumn. This will remain a subtle and complex thing
Questions 1 - 7
Complete the sentences below.
Write ONE WORD ONLY from the passage for each answer.
1 Tallas invited Fairbank residents to her through an advertisement.
2 Tallas examined the food intake as well as samples of the subjects to record their vitamin D levels.
3 As you move up , there is insufficient availability of sunlight.
4 To avoid insect bites, Alaskans remain almost entirely .
5 Spending more time led to higher vitamin D levels in male volunteers.
6 At its lowest, Alaskans are exposed to the sun for only a few every day.
7 A to sunny regions during winters can surge the vitamin D levels of Alaskans.
Questions 1 - 8
Complete the sentences below.
Write NO MORE THAN TWO WORDS from the passage for each answer.
1 The geese live in various types of .
2 Extraction of and in the Arctic can be a threat to goose population.
3 Migrating geese can save energy due to the created by flying in V-formation.
4 Some groups of Canada goose do not migrate to the far south anymore because they can get plentiful on farmlands.
5 After in central Canada, Snow geese migrate to Mexico for the winters.
6 The return journey to Canada takes place by the end of .
7 Some geese do not take as they fly back to the north.
8 is not allowed in the Squaw Creek National Park.
Questions 1 - 5
Complete the sentences below.
Choose NO MORE THAN TWO WORDS AND/OR A NUMBER from the passage for each answer.
1 During summers, leaves are green because they are filled with .
2 During fall in the northern hemisphere, the solar energy reaching the surface .
3 The red colour in leaves is created by which are water-soluble plant pigments reflecting the spectrum from red to blue.
4 Anthocyanins might act as a chemical defence against attacks by insects or fungi, or that they might attract fruit-eating birds and that it might increase a leaf's tolerance to .
5 In , the energy collected by the chlorophyll molecules of the fragile fall leaf is not instantly channelled into useful products and processes.