Passage 1
Caffeine, the stimulant(興奮劑) in coffee, has been called “the most widely used psychoactive(對心理有顯著影響的) substance(物質) on Earth.” Synder, Daly, and Bruns have recently proposed that caffeine affects behavior by countering the activity in the human brain of a naturally occurring chemical called adenosine. (第一段之主題句,作者藉由Synder的研究指出一個研究結論,Caffeine中的adenosine來降低腦細胞的活動量) Adenosine normally depresses neuron(神經細胞) firing(可視為acting) in many areas of the brain.(說明主題的細節,還是得讀) It apparently does(指的是adenosine depresses,前句若能讀通,此句是講述細節的細節,可以不讀) this by inhibiting(抑制) the release of neurotransmitters, chemicals that carry nerve impulses from one neuron to the next. Like many other agents that affect neuron firing, adenosine must first bind to specific receptors(感覺器官) on neuronal membranes(細胞薄膜)(like之後的子句比like本身更重要,要優先讀,至於本句意思則是說,adenosine 必須先附著到神經薄膜的接收器上,才能展開抑制腦細胞活動的任務). There are at least two classes of these receptors, which have been designated A1 andA2. Snyder et al propose that caffeine, which is structurally similar to adenosine, is able to bind to both types of receptors, which prevents adenosine from attaching there and allows the neurons to fire more readily than they otherwise would.
[總結第一段,Although adenosine can depresses neuron, caffeine reduce the activity of adenosine,so caffeine make neuron act more readily.]
For many years, caffeine’s effects have been attributed to its inhibition(抑制) of the production of phosphodiesterase(講述一個過去就被接受的因果關係,是因為一個叫P的酵素,這P可以分解AMP,讓AMP無法作用,但caffeine卻是壓抑P的作用), an enzyme that breaks down the chemical called cyclic AMP. A number of neurotransmitters exert their effects by first increasing cyclic AMP concentrations in target neurons(總結第二段前兩句,可以得出作者引述過去看法,認為AMP的升高可以使neutron更興奮). Therefore, prolonged periods at the elevated concentrations, as might be brought about by a phosphodiesterase inhibitor(只要AMP上升,P就會受壓抑), could lead to a greater amount of neuron firing and, consequently, to behavioral stimulation.(若前兩句能讀懂,就不必再讀本句) But Snyder et al point out that(非常強烈的語氣轉折,必讀) the caffeine concentrations needed to inhibit the production of phosphodiesterase in the brain are much higher than those that produce stimulation.(確認Caffeine能使P的作用降低) Moreover, other com-pounds that block phosphodiesterase’s activity are not stimulants.
[總結第二段,作者提出一個過去的看法,強調caffeine might reduce the P,and the less P exists, the more AMP act. Then make human being be more stimulated.]
To buttress(strengthen) their case that caffeine acts instead by preventing adenosine binding, Snyder et al compared the stimulatory effects of a series of caffeine derivatives with their ability to dislodge(remove) adenosine from its receptors in the brains of mice.(前兩句是加強結論,可以略讀) “In general,” they reported, “the ability of the compounds to compete at the receptors correlates with their ability to stimulate locomotion in the mouse; i.e., the higher their capacity to bind at the receptors, the higher their ability to stimulate locomotion.”(實驗發現,結果,一定必讀) Theophylline, a close structural relative of caffeine and the major stimulant in tea, was one of the most effective compounds(指的是the ability of the compounds and the ability to stimulate這兩種能力) in both regards. (提出新例證,還是必讀)
[第三段總結:作者進一步說明這三位科學家的發現,顯示作者也能認同,也就是Caffeine reduce Adenosine,間接造成腦細胞更興奮。此外,作者以Theophylline為例,顯示作者認為Caffeine和Theophylline一般兼具附著在細胞薄膜及引起刺激的能力。]
There were some apparent exceptions to the general correlation observed between adenosine-receptor binding and stimulation(承續第三段最後提出的Theophylline,但引出例外補充說明). One of these was a compound called3-isobuty1-1-methylxanthine(IBMX), which bound very well but actually depressed mouse locomotion. Snyder et al suggest that this is not a major stumbling block to their hypothesis(不會成為他們假設的障礙). The problem is that the compound has mixed effects in the brain, a not unusual occurrence with psychoactive drugs. Even caffeine, which is generally known only for its stimulatory effects, displays this property, depressing mouse locomotion at very low concentrations and stimulating it at higher ones.
[第四段總結:提出一種特殊的情況,會有極強的附著效果,但卻反而壓抑老鼠的活動力,但作者也以IBMX藉機表示,藥效一體兩面,若是很強,當然可以刺激,但若是很弱,則反而壓抑。]
1. The primary purpose of the passage is to
A. discuss a plan for investigation of a phenomenon that is not yet fully understood
B. present two explanations of a phenomenon and reconcile the differences between them
C. summarize two theories and suggest a third theory that overcomes the problems encountered in the first two
D. describe an alternative hypothesis and provide evidence and arguments that support it
E. challenge the validity of a theory by exposing the inconsistencies and contradictions in it
主題類型題目。由於本篇沒有態度,所以有態度的字都先刪除E;另外本題沒有三種理論,再刪C;至於AB則是既無”not yet understood”, 也沒有”reconcile”,所以再刪
2. According so Snyder et al, caffeine differs from adenosine in that caffeine
A. stimulates behavior in the mouse and in humans, whereas adenosine stimulates behavior in humans only(亂寫,見第四段)
B. has mixed effects in the brain, whereas adenosine has only a stimulatory effect(並未提出)
C. increases cyclic AMP concentrations in target neurons, whereas adenosine decreases such concentrations(adenosine不會影響AMP)
D. permits release of neurotransmitters when it is bound to adenosine receptors, whereas adenosine inhibits such release(正確,見原文第21-25行)
E. inhibits both neuron firing and the production of phosphodiesterase when there is a sufficient concentration in the brain, whereas adenosine inhibits only neuron firing(亂寫)
3. In response to experimental results concerning IBMX, Snyder et al contended that it is not uncommon for psychoactive drugs to have(原文第53行、基本拿分題)
A. mixed effects in the brain(直接定位就可找到)
B. inhibitory effects on enzymes in the brain
C. close structural relationships with caffeine
D. depressive effects on mouse locomotion(小心別選到這個選項,這是IBMX,而非所有精神用藥)
E. the ability to dislodge caffeine from receptors in the brain
4. According to Snyder et al, all of the following compounds can bind to specific receptors in the brain EXCEPT(基本拿分題)
A. IBMX
B. caffeine
C. adenosine
D. theophylline
E. phosphodiesterase(第二段有專文介紹)
5. Snyder et al suggest that caffeine’s ability to bind to A1 and A2 receptors can be at least partially attributed to which of the following?
A. The chemical relationship between caffeine and phosphodiesterase
B. The structural relationship between caffeine and adenosine
C. The structural similarity between caffeine and neurotransmitters
D. The ability of caffeine to stimulate behavior
E. The natural occurrence of caffeine and adenosine in the brain
本題請見第一段,因為文章己經說了,caffeine比adenosine更容易附著在傳導細胞的薄膜上,所以才會有刺激的效果
6. The author quotes Snyder et al in lines 38-43 most probably in order to
A. reveal some of the assumptions underlying their theory
B. summarize a major finding of their experiments
C. point out that their experiments were limited to the mouse
D. indicate that their experiments resulted only in general correlations
E. refute the objections made by supporters of the older theory
從38-43行可清楚判定,這是要說明三位科學家的見解是正確的,基本假設要找積極正面的,因此看到有否定態度[C E]、不確定態度[A]、限定態度(都可刪除)