Meiosis halves; fertilisation restores
הוצג| English | משמעות |
|---|---|
| meiosis/meɪˈəʊsɪs/ | מיוזיס |
| fertilisation/ˌfɜːtɪlaɪˈzeɪʃn/ | הטחאה |
What would explain this observation?
- If gametes kept the ordinary body-cell chromosome number, fusion would double it each generation. Meiosis 减数分裂 solves that problem before fertilisation 受精.
Build the model
- Cells in reproductive organs divide by meiosis to form gametes.
- Genetic information is copied and the cell divides twice, forming four gametes.
- Each has one set of chromosomes and the gametes are genetically different.
- GCSE Biology requires this overall account, not recall of named meiotic stages or detailed chromosome-exchange mechanisms.
- meiosis: Division producing gametes with one chromosome set.
- fertilisation: Fusion of gametes restoring the normal chromosome number.
A model species has 24 chromosomes in ordinary cells. What number should a gamete contain?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
A gamete carries half the ordinary number - one chromosome from each pair - so 24 becomes 12. Keeping 24 would make it a body cell, and 48 would double it.
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
- Fusion of two gametes restores the normal number of chromosomes in the new cell.
- The new cell divides by mitosis, increasing the number of cells.
- As the embryo develops, cells differentiate and become specialised.
- Copying DNA before division does not mean the final gametes keep two chromosome sets.
In the lab: Use coloured chromosome cards to represent sets, label a body cell and gamete clearly, and trace two gametes into one fertilised cell. Keep chromosome number separate from the number of cells. State that a simple card model demonstrates number conservation rather than all mechanisms producing variation.
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: in a fictional species, an ordinary cell has 18 chromosomes.
- Each gamete has 9.
- Fertilisation combines 9+9 to restore 18; later mitosis maintains 18 in each ordinary daughter cell.
- Four gametes each having 9 means 36 chromosomes across four separate cells, not 36 within each gamete.
Your turn: A fictional species has 32 chromosomes in ordinary cells. Find the number in a gamete.
A fictional species has 32 chromosomes in ordinary cells. Find the number in a gamete.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 16 chromosomes. Known: ordinary cells have 32 chromosomes. Meiosis halves the number: gamete = 32/2 = 16 chromosomes. Fertilisation of two such gametes restores 32.
Check the conclusion and its limits
- Meiosis does not make four identical ordinary body cells.
- Fertilisation is fusion rather than a division.
- The four-cell outcome is the specification’s overall model; detailed gamete development and stage names are outside this objective.
Not true: Fertilisation halves the chromosome number. Meiosis halves the chromosome number to make gametes; fertilisation FUSES two gametes and so doubles the number back to the full set. The directions must not be reversed.
- Cells in reproductive organs divide by meiosis to form gametes.
- Fusion of two gametes restores the normal number of chromosomes in the new cell.
- Watch for: meiosis does not make four identical ordinary body cells.
Meiosis halves the chromosome number to make gametes; fertilisation FUSES two gametes and so doubles the number back to the full set.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
True. Meiosis halves the chromosome number to make gametes; fertilisation FUSES two gametes and so doubles the number back to the full set. The directions must not be reversed.
Division producing gametes with one chromosome set: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
meiosis means Division producing gametes with one chromosome set.