题干

如图为某工厂工人生产能力频率分布直方图,则估计此工厂工人生产能力的平均值为____

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133.8

同类题3

某生物兴趣小组开展探究实验,课题是“培养液中酵母菌种群数量与时间的变化关系”.

实验材料、用具:菌种和无菌培养液、试管、血球计数板 (计数室为1mm×1mm方格,由400个小格组成)、滴管、无菌水、台盼蓝染液(对活细胞无染色效果)、显微镜等.

酵母菌的显微计数方法:

①血球计数板:是带有微小方格刻度的玻璃片,用于在显微镜下对微生物的计数.

②将含有酵母菌的培养液滴在计数板上,计数一个方格内的酵母菌数量,再以此为根据,估算试管中的酵母菌总数.连续观察7d,并记录每天的数值.

根据以上叙述回答下列问题:

(1)本实验没有另设对照实验,原因是____ .该实验____(填“需要”或“不需要”) 重复实验,原因是____ .

(2)在吸取培养液计数前,要轻轻震荡几次试管,原因是____ .如果一个小方格内酵母菌过多,难以数清,应当采取的措施是____ 

(3)某同学第5天在使用血球计数板计数时做法如下:

①振荡摇匀试管,取1mL培养液并适当稀释(稀释样液的无菌水中加入了几滴台盼蓝染液).

②先将____ 放在计数室上,用吸管吸取稀释后的培养液滴于其边缘,让培养液自行渗入,多余培养液用滤纸(吸水纸)吸去,制作好临时装片.

③显微镜下观察计数:在观察计数时只计____ (填“被”或“不被”)染成蓝色的酵母菌.在用血球计数板对某一稀释10倍样品进行计数时,发现在一个小方格内(盖玻片下的培养液厚度为0.1mm)酵母菌平均数为5,据此估算10mL培养液中有酵母菌____ 个.

同类题5

完形填空

    I fell in love with Yosemite National Park the first time I saw it, when I was 13. My parents took us there for camping. On the way out, I asked them to wait while I ran up to E1 Capitan, a1 rock of 3,300 feet straight up. I touched that giant rock and knew 2 I wanted to climb it. That has been my life's passion (钟爱) ever since—3 the rocks and mountains of Yosemite. I've long made Yosemite my 4.

    About 15 years ago I started seeing a lot of 5 like toilet paper, beer cans, and empty boxes, around the area. It's6 me why visitors started respecting the place 7 and treated such a beautiful home-like place this way.

    I tried 8 trash (垃圾) myself, but the job was too big. I would9 an hour or two on the job, only to find the area trashed all over again weeks later. Finally, I got so 10 it that I decided something had to change.

    As a rock-climbing guide, I knew 11about organizing any big event. But in 2014, together with some climbers, I set a date for a 12. On that day, more than 300 people 13 Over three days we collected about 6,000 pounds of trash. It was amazing how much we were able to14 I couldn't believe the15we made —the park looked clean!

    Each year volunteers come for the cleanup from everywhere. In 2016 alone, 2,945 people picked up 42,330 pounds of trash and16132 miles of roadway.

    I often hear people17about their surroundings. If you are one of them, I would say the only way to change things is by 18rather than complaining. We need to teach by 19.You can't blame others 20 you start with yourself.