We are family: Scientists suspect that a large DNA-based virus took up residence inside a bacterial cell more than a billion years ago to create the first cell nucleus.
病毒跟我们是一家人：科学家认为，十多亿年前一个大的DNA病毒在细菌细胞内居住并形成了第一个细胞核。
Out on the horizon, you should see a large blue object. That is the nucleus of the cell.
在地平线上，你应该会看到一个大蓝色的东西，这就是是细胞核。
They are usually small, with dense protoplasm, large central nucleus and few vacuoles. Their cell walls are thin and without secondary deposits. They have large Numbers of mitochondria and ribosomes.
它们体积细小，细胞质浓，细胞核大，无大液胞，细胞壁薄，具有较多粒线体和核糖体，能不断进行细胞分裂。
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