Estructura celular
Diploma del Bachillerato Internacional · IB Diploma · Biology · SL Tema 3 3:50 Narración en inglés · Subtítulos en inglés + 中文 quemados en pantalla
Capítulos
Transcripción
A cell can look larger on a screen without changing its real size.
细胞在屏幕上可能看起来更大，但其实际大小并未改变。
Two photographs at different zoom settings cannot be compared by eye alone.
两张不同放大倍率下的照片无法仅凭肉眼进行比较。
Eukaryotic cells contain a nucleus.
真核细胞含有细胞核。
Prokaryotic cells have genetic material but no membrane-bound nucleus.
原核细胞有遗传物质，但没有膜包被的细胞核。
A bacterial cell is a living cell.
细菌细胞是活细胞。
A virus depends on a host cell to reproduce.
病毒依赖宿主细胞进行繁殖。
Magnification: image length divided by actual length.
放大倍数：图像长度除以实际长度。
Resolution: ability to distinguish two close points.
分辨率：分辨两个靠近点的能力。
A scale bar provides a known real distance in the same image.
比例尺提供了同一图像中已知的实际距离。
Convert the image length and real length to the same unit before dividing.
在相除之前，请将图像长度和实际长度转换为同一单位。
Magnification is a ratio and has no unit.
放大倍数是一个比值，没有单位。
In the lab: Focus a prepared slide at low power first.
在实验室中，首先使用低倍镜对焦已制备好的玻片。
Move to a higher power and use fine focus.
然后切换到高倍镜并使用细准焦螺旋进行调焦。
Make a clear line drawing, label structures with straight lines, and record the scale rather than shading the image.
绘制清晰的线条图，用直线标注结构，并记录比例尺，而不是对图像进行阴影处理。
Known: a cell image is 30 mm long and represents a 50 micrometre cell.
已知：细胞图像长度为30毫米，代表一个50微米的细胞。
Use magnification equals image size divided by actual size.
使用放大倍数等于图像大小除以实际大小。
Convert 30 mm to 30,000 micrometres.
将30毫米转换为30,000微米。
Magnification equals 30,000 divided by 50, which is 600.
放大倍数等于30,000除以50，即600。
A separate 10 mm scale bar representing 20 micrometres gives 10,000 divided by 20, which is 500, and that magnification applies to every object in its image.
另一条10毫米的标尺代表20微米，计算为10,000除以20，即500，该放大倍数适用于其图像中的每个物体。
Your turn: An image is 12 mm long; the cell is 40 micrometres long.
轮到你了。 图像长度为 12 mm，细胞长度为 40 μm。
Calculate magnification.
请计算放大倍数。
Pause the video and work it out.
请暂停视频，自己算一算。
Check: 12 millimetres is 12,000 micrometres; divided by 40 gives a magnification of 300 times.
核对：12 毫米 = 12000 微米，除以 40，放大倍数为 300 倍。
A nucleus is not the only cell structure.
细胞核并非唯一的细胞结构。
Do not claim bacteria have no DNA, or that more magnification always means better resolution.
不要声称细菌没有DNA，也不要认为放大倍数越高分辨率就越好。
Not true: Every bacterial cell has a membrane-bound nucleus.
不正确：并非所有细菌细胞都有膜包被的细胞核。
Bacterial cells are prokaryotic: their genetic material lies free in the cytoplasm, not inside a membrane-bound nucleus.
细菌细胞是原核生物，其遗传物质游离在细胞质中，而不是位于膜包被的细胞核内。
Only eukaryotic cells have a true nucleus.
只有真核细胞才具有真正的细胞核。
Eukaryotic cells contain a nucleus.
真核细胞含有细胞核。
A scale bar provides a known real distance in the same image.
标尺在同一图像中提供了已知的实际距离。
Watch for: A nucleus is not the only cell structure.
注意：细胞核并非唯一的细胞结构。
An image is 18 millimetres long and the cell is 25 micrometres long.
图像长度为18毫米，细胞长度为25微米。
Find the magnification.
求放大倍数。
A bacterial cell has no membrane-bound nucleus.
细菌细胞没有膜包被的细胞核。
The result is a magnification of 720.
结果是放大倍数720倍。
Cover the quantity you want.
遮住你要求的量。
Magnification is image size divided by actual size, and both lengths must be in the same unit before you divide.
放大倍数等于图像大小除以实际大小，相除之前两个长度必须换算成同一单位。
A displayed cell is 18 mm long and its scale bar is 6 mm for 20 micrometres.
图中显示的细胞长度为18毫米，其比例尺为6毫米代表20微米。
Find cell length.
求该细胞的真实长度。
The display is enlarged by 50%; does the real length change?
若图像被放大50%，细胞的真实长度是否改变？
The length is 18 over 6, times 20, which is 60 micrometres.
长度等于 18 除以 6 再乘以 20，即 60 微米。
Both image and bar enlarge together; their ratio and inferred real length stay unchanged.
图像和比例尺一起放大，二者的比值以及推算出的实际长度都不变。
An isolated image length without its scale would be insufficient.
只有图像长度而没有比例尺，就不足以得出结论。
Pause and check yourself. Explain each point on screen in your own words, then change one number in the last example and say which assumption must still hold.
暂停一下，自我检查：用自己的话解释屏幕上的每个要点，再改动最后一个例子中的一个数字，说明哪个假设仍然必须成立。