As far as I know, the adrenal glands, when submitted under pressure such as the one described in the example, secrete a substance known as epinephrine which has the tendency of increasing the affected person's heart rate and breathing.
Answer:

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Answer:
Population density of horse
Explanation:
Population density refers to the number of people (or any other living species) existing in a particular area. This reflects the quantity of a particular type of living species that exist over an area of about 1 km².
Population density is obtained mathematically by, dividing the total population of the area by the total size of the area.
In the given question, it describes the quantity (number) of wild horses that are present per square kilometer in the prairie lands. This refers to the population density of horses.
Answer:
The percentage (%) of the alleles that code for this trait in the population will increase, as more individuals are born with the trait.
Explanation:
The more individuals get born expressing the trait, the higher its frequency gets in the population. By generation, there are more individuals carrying the allele for the advantageous trait. These individuals reproduce and increase the probabilities of the progeny to inherit the mentioned allele. When this sequence keeps occurring in the population over many generations, the allele percentage will increase. On the other hand, the other allele or alleles will decrease. Probably, if there are no changes that might influence or affect this pattern, the alleles for the advantageous trait will fixate, while the other allele might get lost.