Which structure in the eye is responsible for focusing light on the retina?
Lens
Pupil
Iris
Cornea
The Correct Answer is A
A. Lens: The lens is a transparent, flexible structure located behind the iris. By changing its shape (accommodation), it fine-tunes the focus of light onto the retina to allow clear vision at various distances.
B. Pupil: The pupil is simply the opening (hole) in the center of the iris that allows light to enter the eye. It does not focus light itself.
C. Iris: The iris is the colored muscle that controls the size of the pupil, regulating the amount of light entering, but not the focus.
D. Cornea: The cornea is the clear outer layer that provides the initial and strongest refraction (bending) of light. However, the lens is the structure responsible for the variable focusing adjustment required to see clearly.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is D
Explanation
A. Ribosomes:Ribosomes are the sites of protein synthesis. They read RNA sequences to assemble amino acids into proteins, but they do not produce energy.
B. Golgi apparatus:The Golgi apparatus functions as the cell's "post office." It modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.
C. Nucleus:The nucleus is the control center of the cell, housing the genetic material (DNA). While it directs cellular activities, it does not directly generate ATP.
D. Mitochondria:Often called the "powerhouse" of the cell, mitochondria are the site of cellular respiration. They break down nutrients (glucose and fatty acids) in the presence of oxygen to produce Adenosine Triphosphate (ATP), the primary energy currency of the cell.
Correct Answer is C
Explanation
A. The release of oxytocin during childbirth:This is the classic example of positivefeedback. Uterine contractions stimulate the release of oxytocin, which causes stronger contractions, which stimulates more oxytocin, continuing until delivery is complete.
B. The activation of the sympathetic nervous system during stress:This is a neurological "fight or flight" response. While it involves hormones (epinephrine), the mechanism of rapidly ramping up the body's alert state is not a homeostatic negative feedback loop (which aims to reverse a change).
C. The regulation of blood glucose levels by insulin and glucagon:Negative feedback works to reverse a deviation from the set point. If blood glucose rises, insulin is released to lower it. If blood glucose drops, glucagon is released to raise it. The system works to negate the stimulus (high or low sugar) to maintain balance.
D. The release of adrenaline during exercise:Similar to choice B, this is a response to increased demand (feed-forward) rather than a loop designed to keep adrenaline levels constant.
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