Question
The light micrograph shows a cross section of seminiferous tubules.
Concerns have been raised about the effect of rising pollution levels on sperm production in men. To investigate the possible effects of pollution on spermatogenesis, sperm samples from men of similar ages were collected in Kolkata in the 1980s and 2000s. The box plot represents the mean and range of sperm counts in the 1980s and 2000s.
a. A hypothesis has been suggested that pollution may have a negative effect on spermatogenesis. Evaluate whether the data support this hypothesis. [3]
b.i. Calculate the actual size of the seminiferous tubule in the area indicated by the line across it, giving the units. [1]
b.ii. Identify the type of cell labelled Z. [1]
▶️Answer/Explanation
Markscheme
a. hypothesis not supported as there is a «slight» increase/not much difference in sperm count between the 1980s and the 2000s
OR
hypothesis not supported as similar means/values for both groups
b. no information on sample size
c. no information/data provided on pollution levels/types of pollution
d. other factors affecting sperm count not considered
OR
other elements than sperm count could be affected
e. data limited to Kolkata/one country/one city
OR
pollution may affect spermatogenesis elsewhere
[Max 3 Marks]
62 mm Υ400 = 0.155 mm/155 μm/micrometers/10-6 m
OR
61 mm Υ400 = 0.153 mm/153 μm/micrometers/10–6 m
Calculation and units required. Accept correct answers expressed in cm
spermatogonium
OR
primary spermatocyte
Question
The drawing shows part of a Thunbergia grandiflora plant. It has been widely cultivated as an ornamental garden plant.
The drawing shows a section through a T. grandiflora flower, which contains a honeybee (Apis mellifera).
a. Using the drawing, deduce which plant phylum T. grandiflora belongs to, giving one visible recognition feature of this phylum. [1]
b.i. Identify the structure labelled X. [1]
b.ii. Outline the relationship the bee has with the T. grandiflora flower. [2]
c. After fertilization, seeds of T. grandiflora form in a small pod. If you were provided with Petri dishes, absorbent cotton balls and seeds, suggest how one variable affecting germination of these seeds could be investigated.
[3]
▶️Answer/Explanation
Markscheme
Angiospermophyta/Angiosperms
AND
flowers «as reproductive organs» ✔
Both required.
ovule ✔
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» ✔
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