The cell cycle: prepare, divide the nucleus, divide the cell
הוצג| English | משמעות |
|---|---|
| mitosis/maɪˈtəʊsɪs/ | מיטוזה |
| cell cycle/sel ˈsaɪkl/ | מחזור תאי |
What would explain this observation?
- A cell must copy genetic material before distributing it to two daughter cells. Growth alone cannot provide each daughter with a complete genetic set.
Build the model
- Before division, a cell grows and increases its sub-cellular structures, including ribosomes and mitochondria.
- Its DNA replicates to give two copies of each chromosome.
- During mitosis 有丝分裂, one set is pulled to each end and the nucleus divides.
- Finally, cytoplasm and cell membranes divide, forming two genetically identical daughter cells under the normal model.
- mitosis: Nuclear division distributing chromosome copies into genetically identical nuclei.
- cell cycle 细胞周期: The sequence of cell growth, DNA copying and division.
Which event must occur before chromosome copies are separated?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Copies can be separated only after they exist: DNA replication comes first, then mitosis distributes the copies. Losing all chromosomes would kill the cell, and gametes are made by meiosis, not mitosis.
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
- Use three overall stages: growth and DNA copying, mitosis, then cell division.
- AQA does not require the named phases within mitosis at this point.
- Mitosis supports growth and development in multicellular organisms and repair or replacement in mature animals; it does not produce genetically varied haploid gametes.
In the lab: Observe school-prepared dividing-tissue images or use chromosome-copy models. Trace one copied chromosome through nuclear division and into each daughter. Identify whether an example describes more cells, specialized cell functions or gamete formation before naming its process.
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 model cell has eight chromosomes before DNA replication.
- The copied genetic material is shared through mitosis so each daughter normally has eight chromosomes.
- If one starting cell completes four successive ideal division rounds with no loss, cell number is 2⁴=16.
- Each cell still has the model chromosome number eight.
Your turn: Three model starting cells each complete three division rounds. Calculate the final number.
Three model starting cells each complete three division rounds. Calculate the final number.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 24 cells. Known: 3 starting cells; three division rounds each. Each starting cell gives 2^3 = 8 cells, so the final number = 3 x 8 = 24 cells.
Check the conclusion and its limits
- Mitosis divides a nucleus; the complete cell cycle includes preparation and division of the cell. “Identical” concerns the normal copied genetic information in this model, not a claim that every cell is physically the same size at every moment.
Not true: Mitosis normally halves the chromosome number of each daughter cell. Mitosis conserves the chromosome number: after DNA replication the copies are shared so each daughter normally gets the full set. Halving belongs to meiosis.
- Before division, a cell grows and increases its sub-cellular structures, including ribosomes and mitochondria.
- Use three overall stages: growth and DNA copying, mitosis, then cell division.
- Watch for: mitosis divides a nucleus; the complete cell cycle includes preparation and division of the cell. “Identical” concerns the normal copied genetic information in this model, not a claim that every cell is physically the same size at every moment.
Mitosis normally halves the chromosome number of each daughter cell.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Mitosis conserves the chromosome number: after DNA replication the copies are shared so each daughter normally gets the full set. Halving belongs to meiosis.
Nuclear division distributing chromosome copies into genetically identical nuclei: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
mitosis means Nuclear division distributing chromosome copies into genetically identical nuclei.