托福阅读真题+题目+答案：Bumblebee Heat Regulation

托福阅读真题+题目+答案：Bumblebee Heat Regulation

While flying,bumblebees have a body temperature that is generally well above that of the air around them,and tends to be constant at about 35 C.Keeping warm is harder the smaller you are. Small creatures,like bees,have a vast surface area relative to their volume,and lose heat incredibly quickly.Yet bumblebees can keep themselves warm even when the surrounding air is 30C cooler than their body temperature.Scientist Bernd Heinrich found that the answer to bees'ability to retain heat is in two parts:keeping heat in, and generating it in the first place.Keeping warm is helped if you have insulation,and of course bumblebees have furry coats.The vital thing for a bumblebee is to keep its thorax (the middle section)warm, because this is where the flight muscles are;unless the thorax is warm enough,the muscles cannot contract sufficiently fast,and the bee cannot take off.The temperature of the abdomen does not matter much in flight.The abdomen and thorax in a bumblebee are connected by a very narrow waist,and the front part of the abdomen contains a sac of air,so heat loss from the thorax to the abdomen is minimal (air is a poor conductor).A bumblebee's heat is generated by the contractions of the flight muscles.In flight a bumblebee flaps its wings 200 times per second.This generates a lot of heat,but of course comes at a cost:bumblebee flight is enormously expensive in terms of the energy that it uses.Consequently,bumblebees have to eat almost continually to keep warm.

1.According to paragraph 1,all of the following help bumblebees generate heat or stay warm EXCEPT

O their furry coats

O the contraction of their flight muscles

O the movements of their abdomen during flight

O the sac of air at the front of their abdomen

2.According to paragraph 1,which of the following is true of bumblebees?

O Bumblebees save energy by not flying when they are cold.

O Bumblebees must eat almost constantly in order to maintain their body heat.

O The body temperature of bumblebees is often 30 degrees cooler than the surrounding air.

O Bumblebees expend an enormous amount of energy during takeoff but not during flight.

A bumblebee's dense furry coat has obvious advantages,but it can create problems when the weather is warm.Bumblebees cannot help but produce lots of heat when they fly,which can be difficult to get rid of if the air temperature is also high. ⬛ This is probably why bumblebees are not common in Mediterranean countries. ⬛ If their body temperature exceeds 44 C they will die;as they approach this lethal limit,their metabolism collapses and they become unable to fly. ⬛ It is noticeable that those species of bumblebee that occur in warmer climates tend to have shorter fur,while those from high latitudes and altitudes tend to be very large and very furry. ⬛ Hence the huge size and long shaggy coat of the world's largest bumblebee,Bombus dahlbomii,which inhabits the high Andes of South America.

3.In paragraph 2,why does the author note that Bombus dahlbomii has a long shaggy coat and is the world's largest bumblebee?

A To argue against the claim that a furry,dense coat can cause problems for large bees

B To help support the idea that a bumblebee's size and the density of its fur depends on the climate of its habitat

C To provide evidence that bumblebees of the Andes are closely related to those from high latitudes in other parts of the world

D To provide an example of how bumblebees get rid of excess heat when air temperatures are high

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