题干

科学家用32P标记的噬菌体侵染未被标记的大肠杆菌,侵染一段时间后搅拌,离心得到上清液和沉淀物,检测上清液中放射性32P约占初始标记噬菌体放射性的30%.在侵染时间内,被侵染细菌的存活率接近100%.据此判断不正确的是(    )

A:在噬菌体遗传特性的传递过程中DNA起作用

B:上清液的放射性基本不来自大肠杆菌的裂解

C:搅拌使吸附的噬菌体与大肠杆菌分离

D:离心后大肠杆菌主要分布在上清液中

上一题 下一题 0.0难度 选择题 更新时间:2015-07-28 11:51:05

答案(点此获取答案解析)

D

同类题1

阅读下列短文, 从给的四个选项 (A、B、C和D) 中, 选出最佳选项。   

    More over smart phone, the intelligent watch is about to take your spot as the latest hi­tech current, allowing wearers to glance at messages and even take calls without touching their phones. The i'm Watch, available since 2011, is the flagship product of an Italian company—i'm. This smart watch is an assist to the smart phone, with which it can communicate by Bluetooth wireless technology. It means you can leave your phone in your pocket as you answer or reject a call, review e­mails or read updates from friends on Twitter or Facebook.

    The i'm Watch also has its own applications, such as i'm Sport, which links with a heart rate detector (检测器) to allow a runner to check his pulse. Such functions already exist in specialized sports watches but not on watches that are linked to smart phones.

    With a square shape, a 3.8­centimeter touch screen and various colors, the i'm Watch sells for a minimum of 300 Euros ($390) for the basic model and prices climb to 16 000 Euros for a luxury model in silver or decorated with diamonds.

    So far, the watch has already found 30 000 buyers, 80 percent of whom are men aged 25 to 50. “Seventy percent are iPhone users, 25 percent Samsung and the rest are other telephones using Google's Android operating system,” said Massimiliano Bertolini, a manager of the company, which aims to sell more than 200 000 watches this year. The company's target market is the person who is always glued to his smart phone, even in meetings or at the movies, or people who wish to keep an eye on their heartbeat during exercise. They will especially target women with advertisements emphasizing its design rather than its technology.