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英['lɪs(ə)n] 美['lɪsn]
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草莓小菇凉:说的非常好,十分有道理,棒棒棒!

06-08 15:44:55

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TPO 49-L3 .Squirrel's ability 点击收藏

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    Listen to part of a lecture in a biology class.

    Okay,so that's how the arctic ground squirrel's able to cope in this extreme environment.

    Now let's talk about your reading assignment,about reindeer,also typically found in Siberia and other far northern regions.

    Who would like to start off?Yes,Mike?

    Well,for one thing,they've got thick hair all over their body,even on their noses.

    Yes.They are very well insulated,and the thickness of their fur varies depending on the season.

    Good.Yes?

    Um...newborn reindeer are very adult-like,like they can stand as soon as they're born,

    and by their second day they can already run as fast as a human.

    Critical.Food is very scarce in far north so reindeer herds have to cover lots of ground every day.

    And in the fall they might easily trek a thousand kilometers or more to get to their winter feeding site.

    So if you are a newborn you've got to get up to speed fast.

    Okay Other adaptations?

    Also reindeer don't have to keep their legs as warm as their main body,so they don't have to use up as much energy keeping them warm.

    Yes,so that means they can allocate less energy to heating their extremities and more energy to maintaining stable temperature in their body core where their vital organs are located.

    And you know I don't think it is mentioned in your textbook,

    but even different parts of a reindeers leg are adapted for optimal cold weather performance.

    The fat in the lower part of their legs,the part that gets coldest,that fat has a different chemical structure from the fat in the upper parts of the leg.

    So it doesn't get hard,even at temperatures down around freezing,it stays kind of gel-like,kind of oily.

    Okay, good.What about food?

    What do you remember about that?

    Well,they are pretty flexible.

    OK,can you explain that a little more?

    Well,they can eat a lot of different kinds of plants,so that improves their chances of coming across something they can eat.

    I think they said that they found that the reindeer in one herd had something like 37 different kinds of plants.

    OK,yes.You've really done your reading.

    And reindeer also eat a number of different plant species that most animals are not very interested in.

    Which means?

    They don't have a lot of competition when it comes to that food?

    That's right.

    In particular,your reading mentions lichens.

    Lichens are plants you'll find growing on rocks in the far north,sometimes referred to as reindeer moss.

    They look pretty basic you know,just a little moss on a rock.

    But lichens are actually quite complex.

    They are not just a single organism.

    They're actually kind of combination of some sort of fungus and some sort of algae that lire together in a symbiotic relationship.

    Anyway...Okay,reindeer,um,oh,oh yes,and one more thing about lichens.

    They crank out a lot of chemicals,which is probably at least part of the reason why they are not considered all that tasty by most animals.

    Anyway,does anyone remember what your reading said about them?

    Yeah,somehow when reindeer eat lichens they're able to draw a lot more nutrients from them than other animals.

    Like if a cow or a sheep eats lichens,they're only gonna get like half as much nutrition out af them as a reindeer would.

    That's right,and in winter,lichens are crucial for reindeer because their supply energy,

    but they don't have all the proteins and minerals the reindeer need.

    Um,so when reindeer get to the end of the long winter they are often very thin with low levels of minerals.

    In spring they have to eat different plants and replenish what they've lost over the winter,

    so what reindeer have done is they've developed the ability to digest different plants in different seasons by adjusting the microbes in their digestive systems.

    As you know microbes are micro-organisms like bacteria that help to digest or break down food.

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