
To review:
The events took place inside the body of a female koala and the possible cause of ovulation that could be removed through the given experiment.
Introduction:
In most of the female mammals, including humans, the ovulation takes place in a cyclical pattern. These females ovulate spontaneously and require no stimulus from outside to release their eggs. On the other hand, there are certain female mammals that require external stimulus to release their eggs and are called as reflex ovulators. Reflex ovulators include female mammals, such as rabbit, koala, and camels, and they ovulate only after copulation.
It is already given:
Experiment: The following two groups, each including four female koalas, were formed.
Group A: Pairing and mating of females with males on the 2nd day of the estrus cycle.
Group B: Shifting of koala females next to males without any physical contact.
The blood samples from both the groups provided the following results:
Group A: 25 ng/mL (nanogram per milliliter) of LH during the duration of 24 to 32 hours after mating and birth of baby koalas after 35 days postcoitus.
Group B: No change in the levels of LH hormone and no birth of any baby koala.

Explanation of Solution
In humans, the ovulation cycle takes place after every 24 to 28 days in a cyclical fashion. The eggs are released whether mating has taken place or not. Mammals, such as koalas, enter into the estrus cycle but do not release their eggs until the mating has taken place. The luteinizing hormone is released only during ovulation; hence, in the given experiment, LH is taken as an indicator.
In a female koala, the mating provides an external stimulus, which leads to the release of LH. The mature follicles get triggered by LH and the eggs get released. Mating provides the sperms from a male, which fertilize the eggs as a result of which female koalas give birth, 35 days after the mating.
Thus, it can be concluded that the female koalas produce LH and release their eggs only when the external stimuli, which is mating with the male, is provided. Contact with the male could be removed from the given experiment to avoid ovulation.
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Chapter 42 Solutions
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