The respiratory systems of birds are very efficient at providing oxygen to the blood, which is necessary for birds to expend the energy necessary to fly. What feature of the bird respiratory system makes it more efficient than the respiratory systems of other animals?

A. a one-way air flow through the lungs and airways
B. a two-way air flow through the lungs and airways
C. bubble-like alveoli for gas exchange in the lungs
D. many tracheal tubes that connect the lungs to the skin

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:

      n