Eukaryotes and prokaryotes: location of genetic material
| English | Français |
|---|---|
| plasmid/ˈplæzmɪd/ | plasmide |
| prokaryote/ˈprɒkərɪəʊt/ | procaryote |
What would explain this observation?
- A bacterium and a plant cell both contain DNA. Their genetic material is arranged differently, and a bacterium is usually much smaller.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Plant and animal cells are eukaryotic: their genetic material is enclosed in a nucleus. A bacterial cell is prokaryotic and has no nucleus. It contains cytoplasm, a cell membrane and a surrounding cell wall. Its main genetic material is a single DNA loop, and it may also contain small DNA rings called plasmids 质粒.
- prokaryote 原核生物: An organism whose cells lack a nucleus enclosing the main genetic material; plasmid: A small DNA ring that can occur in a bacterial cell.
Which observation supports identifying the model as a bacterial cell?
Use structures rather than size alone to identify a cell type. A plant cell has a cellulose cell wall, but a bacterial wall is not made of cellulose. Not every bacterium has a plasmid. A small cell image can be enlarged, so image size cannot by itself show real cell size.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Use structures rather than size alone to identify a cell type. A plant cell has a cellulose cell wall, but a bacterial wall is not made of cellulose. Not every bacterium has a plasmid. A small cell image can be enlarged, so image size cannot by itself show real cell size.
- Inspect teacher-provided labelled images with scale bars. For a size comparison, convert both real dimensions into one unit before dividing. One millimetre is 1,000 micrometres; one micrometre is 1,000 nanometres. State whether the ratio concerns length, area or volume.
Which two habits make the investigation or model in this case more defensible?
Inspect teacher-provided labelled images with scale bars. For a size comparison, convert both real dimensions into one unit before dividing. One millimetre is 1,000 micrometres; one micrometre is 1,000 nanometres. State whether the ratio concerns length, area or volume.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: a bacterial cell is 2 micrometres long and a plant cell is 40 micrometres long. Length ratio = 40/2 = 20. In metres these are 2×10⁻⁶ m and 4×10⁻⁵ m. The plant cell is twenty times longer in this example, not twenty times larger in every possible measure.
A 30 micrometre plant cell is compared with a 3 micrometre bacterial cell. Find the length ratio plant/bacterium. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A 30 micrometre plant cell is compared with a 3 micrometre bacterial cell. Find the length ratio plant/bacterium.
The result is 10 . Known: a bacterial cell is 2 micrometres long and a plant cell is 40 micrometres long. Length ratio = 40/2 = 20. In metres these are 2×10⁻⁶ m and 4×10⁻⁵ m. The plant cell is twenty times longer in this example, not twenty times larger in every possible measure.
Check the conclusion and its limits
- Prokaryotes have DNA even though they lack a nucleus. Magnification changes the displayed size; it does not turn one cell type into another. Order-of-magnitude estimates give a scale comparison rather than a precise identity test.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
A bacterial cell has no genetic material because it has no nucleus. This claim is false: Prokaryotes have DNA even though they lack a nucleus. Magnification changes the displayed size; it does not turn one cell type into another. Order-of-magnitude estimates give a scale comparison rather than a precise identity test.
Eukaryotes and prokaryotes: location of genetic material: Use structures rather than size alone to identify a cell type. A plant cell has a cellulose cell wall, but a bacterial wall is not made of cellulose. Not every bacterium has a plasmid. A small cell image can be enlarged, so image size cannot by itself show real cell size.
A bacterial cell has no genetic material because it has no nucleus.
Prokaryotes have DNA even though they lack a nucleus. Magnification changes the displayed size; it does not turn one cell type into another. Order-of-magnitude estimates give a scale comparison rather than a precise identity test.
An organism whose cells lack a nucleus enclosing the main genetic material: write the technical term.
prokaryote means An organism whose cells lack a nucleus enclosing the main genetic material.