IB DP Biology- D3.1 Reproduction - IB Style Questions For SL Paper 2 - FA 2025
▶️ Answer/Explanation
a.
- Data Trend: The box plot shows that the sperm count in the 2000s is slightly higher than in the 1980s, or at least not significantly lower. This does not support the hypothesis that pollution has reduced sperm production.
- Limitations:
- The data lacks information about actual pollution levels, which makes it hard to establish a direct link.
- The sample is limited to Kolkata only, and there’s no mention of sample size or variation in individual health/lifestyle.
- Conclusion: The data presented is insufficient to confirm a negative effect of pollution on spermatogenesis. Other aspects of sperm quality (like motility or morphology) may still be affected.
b.i.
- Measured length on the image = 62 mm
Magnification = ×400
\[
\text{Actual size} = \frac{62 \, \text{mm}}{400} = 0.155 \, \text{mm} = 155 \, \mu\text{m}
\]
b.ii. Spermatogonium
- The cell labelled Z is located at the edge of the seminiferous tubule, near the basement membrane.
- These are diploid stem cells that divide by mitosis to give rise to spermatocytes.
Markscheme
a. Evaluation of Pollution Hypothesis:
1. Data Interpretation: Hypothesis not supported — sperm counts show slight increase/no significant difference between 1980s and 2000s.
2. Limitations:
• No data on pollution levels or sample sizes.
• Confounding factors (e.g., lifestyle changes) not considered.
• Geographically limited to Kolkata.
3. Alternative: Pollution might affect other aspects of spermatogenesis (e.g., motility).
b.i. Seminiferous Tubule Size Calculation:
62 mm ÷ 400 (magnification) = 0.155 mm or 155 μm (micrometers).
Note: Accept answers in cm (0.0155 cm).
b.ii. Cell Identification:
Cell Z: Spermatogonium or Primary spermatocyte.