1.The iris in the human eye is responsible for controlling the exposure of of light that reaches the retina. The movement of iris is controlled by a muscles called sphincter muscle and dilator muscle. sphincter muscle constricts the pupil in bright light while dilator muscle expands the pupil.
2. Sternum belongs to the axial skeleton, which is a long flat bone located in the central part of the chest. Axial skeleton consists of 80 bones and strenum is one of them. Axial skeleton functions to provide protection to vital organs such as brain, heart and lungs. Strenum functions to protect heart.
Answer: Directional selection occurs when individuals with traits on one side of the mean in their population survive better or reproduce more than those on the other. ... Directional selection does the “heavy lifting” of evolution by tending to move the trait mean toward the optimum for the environment.
