The pulmonary semilunar valve guards the entrance to the

Explanation:

The pulmonary valve is an important semilunar valve and found in the heart between the pulmonary artery and the right ventricle. This valve contains three cups that are responsible for the guarding of the pulmonary trunk. The pulmonary trunk is an important vessel of the heart that arises from the right ventricle and plays an important role in the circulation of the deoxygenated blood. The pulmonary trunk is called the main pulmonary artery.

1) gene flow

- it is described as the transfer of genes from one population to another population so that frequency of gene is increased.

-a zebra migrates to join a different herd of zebras.

2) natural selection

- a mechanism of evolutionary change in which individuals with advantageous traits survive and reproduce whereas the others ( those that can not adapt) eliminate from the population.

-competition for sunlight leads to taller trees.

3) mutation

- permanent change in the nucleotide sequence of dna ( genetic material) that could have harmful or useful consequences.

-the dna of a snake changes to make its venom stronger.

4) genetic drift - it is a random phenomenon ( that occurs by chance such as fire) that results in change in the gene frequency in a small population.    

-a grassfire randomly sweeps through a population of buffalo and kills most of the animals.

explanation: