Cell measurements and scale
הוצג| English | משמעות |
|---|---|
| magnification/ˌmæɡnɪfɪˈkeɪʃn/ | הגדלה |
| resolution/ˌrezəˈluːʃn/ | רזולוציה |
What would explain this observation?
- A cell can look larger on a screen without changing its real size. Two photographs at different zoom settings cannot be compared by eye alone.
Build the model
- Eukaryotic cells contain a nucleus.
- Prokaryotic cells have genetic material but no membrane-bound nucleus.
- A bacterial cell is a living cell; a virus depends on a host cell to reproduce.
- magnification 放大倍数: Image length divided by actual length.
- resolution 分辨率: Ability to distinguish two close points.
Which comparison of two cell images is reliable?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Reliable comparison needs a shared real scale. Converting each image length with its own scale bar gives real sizes that can be compared; screen lengths alone depend on zoom, which differs between the images.
Match each technical term to its precise meaning.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- A scale bar provides a known real distance in the same image.
- Convert the image length and real length to the same unit before dividing.
- Magnification is a ratio and has no unit.
In the lab: Focus a prepared slide at low power first. Move to a higher power and use fine focus. Make a clear line drawing, label structures with straight lines, and record the scale rather than shading the image.
Which two habits make the investigation or model in this case more defensible?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: a cell image is 30 mm long and represents a 50 micrometre cell.
- Use magnification = image size / actual size.
- Convert 30 mm to 30,000 micrometres.
- Magnification = 30,000 / 50 = 600.
- A separate 10 mm scale bar representing 20 micrometres gives 10,000 / 20 = 500, and that magnification applies to every object in its image.
Your turn: An image is 12 mm long; the cell is 40 micrometres long. Calculate magnification.
An image is 12 mm long; the cell is 40 micrometres long. Calculate magnification.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 300 . Known: image length 12 mm; actual length 40 micrometres. Use magnification = image size / actual size with both lengths in the same unit. Convert 12 mm to 12,000 micrometres. Magnification = 12,000 / 40 = 300. The image is 300 times the real cell length; the ratio has no unit.
Check the conclusion and its limits
- A nucleus is not the only cell structure.
- Do not claim bacteria have no DNA, or that more magnification always means better resolution.
Not true: Every bacterial cell has a membrane-bound nucleus. Bacterial cells are prokaryotic: their genetic material lies free in the cytoplasm, not inside a membrane-bound nucleus. Only eukaryotic cells have a true nucleus.
- Eukaryotic cells contain a nucleus.
- A scale bar provides a known real distance in the same image.
- Watch for: A nucleus is not the only cell structure.
Every bacterial cell has a membrane-bound nucleus.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Bacterial cells are prokaryotic: their genetic material lies free in the cytoplasm, not inside a membrane-bound nucleus. Only eukaryotic cells have a true nucleus.
Image length divided by actual length: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
magnification means Image length divided by actual length.