问题 问答题 简答题

进行酶活力测定时应注意什么?为什么测定酶活力时以测初速度为宜?

答案

参考答案:

提示:⑴.进行酶活力测定时应注意以下几点:①使酶促反应在最适条件下进行,最适pH、最适温度;②对特异性不强的酶应选择最适底物;③防止激活剂与抑制剂对酶活性的干扰;④通常测定产物的生成量比较准确,但检测方法要灵敏。

⑵.为什么测定酶活力时测初速度最好:因为在最初一段时间内酶促反应速度能保持恒定,随着时间的推移酶活性会受到影响,如底物浓度降低,产物的抑制作用,pH及温度条件对酶的破坏。

阅读理解

The computer keyboard helped kill shorthand---a system of rapid handwriting, and now it's threatening to finish off handwriting as a whole. When handwritten essays were introduced on the SAT exams for the class of 2011, just 15% of the most 1.5 million students wrote their answers in cursive (草写字母).The rest? Block letters.

And those college hopefuls are just the first edge of a wave of US students who no longer get much handwriting instructions in the primary grades, frequently 10 minutes a day or less. As a result, more and more students struggle to read and write cursive.

At Keene Mill Elementary School in Springfield, all their poems and stories are typed. Children in Fairfax County schools are taught keyboarding beginning in kindergarten. Older students who never mastered handwriting say it doesn't affect their grades.

There are those who say the culture is at a crossing, turning from the written word to the typed one. If handwriting becomes a lost form of communication, does it matter?

It was at University of Virginia that researchers recently discovered a previously unknown poem by Robert, written in his unique script. Handwritten documents are more valuable to researchers, historians say, because their authenticity (真实性)can be confirmed. Students also find them more fascinating.

The loss of handwriting also may be a cognitive (认知的)opportunity missed. Several academic studies have found that good handwriting skills at a young age can help children express their thoughts better-a lifelong benefit.

It doesn't take much to teach better handwriting skills. At some schools in Prince George's County, elementary school students use a program called Handwriting Without Tears for 15 minutes a day. They learn the correct formation of manuscript letters through second grade, and cursive letters in third grade.

There are always going to be some kids who struggle with handwriting because of their particular neurological (神经系统的)wiring, learning issues or poor motor skills. Educators often point to this factor in support of keyboarding.

小题1:What is the author concerned about after 2011 SAT exams?

A.Keyboarding.

B.Shorthand

C.Handwriting.

D.Block letters.小题2:A poem by Robert mentioned in the passage is used to _________.

A.prove how valuable handwriting is

B.explain what a famous poet he is

C.show how unique his poem is

D.stress how fascinating the documents are小题3:The example of Handwriting Without Tears helps to argue that_________.

A.the schools are responsible for the loss of handwriting

B.the loss of handwriting is a cognitive opportunity missed

C.it doesn't take much to teach better handwriting skills

D.the culture is turning from the written word to the typed one小题4: According to the author, when is a perfect time to learn handwriting?

A.Kindergarten.

B.Primary school.

C.High school.

D.College.小题5:What is the author’s attitude towards this debate?

A.Devotion.

B.Encouragement.

C.critical.

D.Objective.

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