2022 英语周报 八年级 GDY 5答案

书面表达One possible version:NOTICEA sports meeting will be held in the playground of our school from next Thursday to FridayAs you know, the pressure of study is very heavy now, especially for those senior 3. So the purpose of the sports meeting is to letevery student get relaxed, as a result of which we students can live happily and heal thilyEveryone is welcome to take part in it. Those who perform excellently at the sports meeting will get prizes. But don' t take theresults so serously because taking part is more important than the result. Good luck to everyone!

37.(15分,除标注外,每空2分)(1)小于(1分)用滤膜过滤除菌(2)氮源琼脂鉴别(3)黑色菌落偏低两个或多个大肠杆菌连在一起时,平板上只能观察到一个菌落【解析】(1)分析图解可知,实验将待测水样进行过滤,转移滤膜进行微生物培养,因此水中的大肠杆菌应留在滤膜上,即图甲中滤膜的孔径应小于大肠杆菌的直径。受此启发,对某些不耐高温的试剂可以用滤膜过滤除菌。(2)培养基的基本成分一般包括水、无机盐、碳源、氮源,另外鉴别培养基是固体培养基,必须加入凝固剂琼脂,图中乳糖为碳源,因此培养基中还应该加入氮源。(3)在伊红美蓝培养基上,可以鉴定出菌落为黑色的大肠杆菌,因此该小组通过统计黑色菌落的数目,计算出单位体积样品中大肠杆菌数目,由于培养基中两个或多个大肠杆菌连在一起时,平板上只能观察到一个菌落,因此理论上他们的统计值比实际值偏低

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