题干

下表中表示某培养基的配方,下列叙述正确的是
成分
蛋白胨
葡萄糖
K2HPO4
伊红
美蓝
蒸馏水
含量
10g
10g
2g
0.4g
0.065g
1000mL

A:从物理性质看该培养基属于液体培养基,从用途看该培养基属于选择培养基

B:该培养基中缺少提供生长因子的物质

C:培养基调好pH后就可以接种菌种

D:培养基中属于碳源的物质主要是葡萄糖,属于氮源的物质是蛋白胨

上一题 下一题 0.0难度 选择题 更新时间:2015-03-26 11:24:10

答案(点此获取答案解析)

D

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    Are you sick of going to bed late and waking up tired? Then grab your hiking boots and a tent. A new study suggests that camping in the great outdoors for a couple of days can reset your body clock and help you get more sleep.

    The body clock is an internal system that tells our bodies when it's time to go to sleep and when it's time to wake up. Scientists track this clock by measuring the amount of melatonin (褪黑激素) circulating in a person's blood at any given time.

    In a healthy sleeper, melatonin levels rise a few hours before bedtime, stay high through the night, and then settle back down when it's time to wake up.

    In our modern society, however, most of us stay up many hours past sunset and would probably sleep in many hours after sunrise if we could. And the trouble is, your melatonin levels may still be high when your alarm clock goes off in the morning, which leads to fatigue. It may also have other health consequences as well, such as diabetes (糖尿病), overweight and heart disease.

    Professor Kenneth Wright of the University of Colorado in the US wanted to see if our body clocks can be reset by a short stay in nature. His team recruited (招募) fourteen physically active volunteers in their 20s and 30s. Nine went on a weekend camping trip, while the other five stayed home. At the end of the weekend, the researchers reported that in just two days, the campers' body clocks had shifted so that their melatonin levels began to rise more than an hour earlier than they did before they left on the trip. By contrast, the body clocks of the group that stayed home shifted even later over the course of the weekend.

    “This tells us we can reset our clocks fast,” Wright said.

    Therefore, if you want to change your sleep patterns you could try to increase your exposure to natural light during the day and decrease the amount of artificial light you see at night. And if that doesn't work,there's always camping.