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Date May 2017 Marks available 8 Reference code 17M.2.HL.TZ2.7
Level Higher level Paper Paper 2 Time zone Time zone 2
Command term Explain Question number 7 Adapted from N/A

Question

Outline how reproductive isolation can occur in an animal population.

[3]
a.

Describe the different cell types in the seminiferous tubules that are involved in the process of spermatogenesis.

[4]
b.

Explain the roles of specific hormones in the menstrual cycle, including positive and negative feedback mechanisms.

[8]
c.

Markscheme

a. can be sympatric or allopatric 

b. temporal isolation by members of difference populations reproducing at different times  OWTTE

c. behavioural isolation by difference in courtship behaviours  OWTTE

d. geographic isolation by a population being separated by river/mountain/barrier to contact  
An example of a geographic barrier is required.

e. polyploidy

a.

a. spermatogonia «2n» are undifferentiated germ cells  OWTTE

b. spermatogonia mature and divide «by mitosis» into primary spermatocytes «2n» 

c. primary spermatocytes divide by meiosis I into secondary spermatocytes «1n» 

d. secondary spermatocytes divide by meiosis II into spermatids «1n» 

e. spermatids differentiate/mature into spermatozoa/sperm 

f. Sertoli/nurse cells provide nourishment/support to these developing cells 

g. Leydig/interstitial cells produce testosterone

b.

a. anterior pituitary/hypophysis secretes FSH which stimulates ovary for follicles to develop 

b. follicles secrete estrogen 

c. estrogen stimulates more FSH receptors on follicle cells so respond more to FSH 

d. increased estrogen results in positive feedback on «anterior» pituitary 

e. estrogen stimulates LH secretion 

f. estrogen promotes development of endometrium/uterine lining 

g. LH levels increase and cause ovulation 

h. LH results in negative feedback on follicle cells/estrogen production 

i. LH causes follicle to develop into corpus luteum
OR
follicle cells produce more progesterone 

j. progesterone thickens the uterus lining 

k. high progesterone results in negative feedback on pituitary/prevents FSH/LH secretion 

l. progesterone levels drop and allow FSH secretion 

m. falling progesterone leads to menstruation/degradation of uterine lining

Award [5 max] if no reference to feedback is made.

c.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.

Syllabus sections

Core » Topic 6: Human physiology » 6.6 Hormones, homeostasis and reproduction
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