▶️ 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.
[3]▶️ Answer/Explanation
a.
The plant T. grandiflora belongs to the phylum Angiospermophyta.
A visible recognition feature is the presence of flowers used for reproduction.
b.i.
The structure labelled X is the ovule.
b.ii.
The relationship between the bee and the T. grandiflora flower is mutualistic.
- The bee gains nectar or pollen as a food source.
- In return, the flower is pollinated, as pollen sticks to the bee when it enters and is transferred to the stigma of the same or another flower.
c.
To investigate a variable affecting seed germination:
- Independent Variable: Temperature (use different temperatures for each Petri dish).
- Place an equal number of seeds in each Petri dish on moistened absorbent cotton balls.
- Keep other variables constant such as light, oxygen, and water.
- Record the number of seeds that germinate over a set time (e.g. 5 days).
- Include a control group with optimal germination conditions (e.g. 25°C, moisture, light).
Markscheme
a. Angiospermophyta/Angiosperms
AND
flowers «as reproductive organs» ✔
Both required.
b.i. ovule ✔
b.ii.
a. mutualistic relationship
OR
bee gets nectar/pollen «as food» AND flower is pollinated/fertilized ✔ Both needed.
b. when bee enters, pollen from anther sticks to it ✔
c. pollen is picked up by stigma «of same or other flower» ✔
c.
a. different values for the named independent variable ✔ Name of the independent variable must be included, eg temperature.
b. large / equal number of seeds in each Petri dish ✔
c. control of other variables «than seeds» ✔
d. mentions how germination will be determined eg appearance of radicle.
OR
how germination rate/percentage will be measured ✔ eg number germinated over time/in a set time. Do not accept measurement of growth of stem/number of leaves.
e. includes a control giving seeds all factors needed ✔
Possible factors include water, oxygen, temperature, pH, light, salt concentration