The iris in the human eye contracts and expands, controlling the amount of light that reaches the retina. what types of muscle control this? a. skeletal and voluntary b. smooth and cardiac c. skeletal and smooth d. smooth and involuntary

The iris is a pigmented muscular curtain found near the front of the eye and between the cornea and lens. It is perforated by an opening known as the pupil. The location of the iris is found in front of the eye lens and the ciliary body and posterior to the cornea. It is bathed in a fluid called as the aqueous humor.

The iris consists of two sheets of smooth muscles with opposing actions: dilation/expansion and contraction/constriction. The primary function of these muscles is tho control the size of the pupil and modulates how much light reaches the sensory tissue of the retina. The sphincter muscle of the iris is a rounded muscle that constricts the pupil whenever there is a bright light, whereas the dilator muscle expands the eye opening when it contracts.

Therefore, the answer is D. SMOOTH AND INVOLUNTARY because first of all the types of muscles that comprises the muscles in the iris are smooth and it is involuntary because they eyes auto-regulates the light that comes to it without our conscious effort.

before it leaves the nucleus of a eukaryotic cell, mrna is altered in the following ways: - a cap is added to the 5' end of the mrna molecule; - a poly a tail is added to the 3' end; - introns are removed and exons are spliced together.