Question

question 20
which of the following minerals is essential for the formation of thyroid hormone?
calcium
iron
copper
lodine
question 21
transparent structure of the eye containing regularly aligned collagen fibers.
choroid
ciliary body
sclera
cornea
lens
question 22
hormone that inhibits osteoclast activity in children.
calcitonin
thyroxine
oxytocin
parathyroid hormone
catecholamines

Explanation:

• Question 20: Thyroid hormones (such as thyroxine) are iodinated amino acids. Iodine is actively taken up by the thyroid gland and incorporated into the hormone structure. Calcium is important for bone health and muscle function, iron for hemoglobin (involved in oxygen transport), and copper for various enzymatic reactions (e.g., in electron - transfer processes), but not directly for thyroid hormone synthesis.
• Question 21: The cornea is the clear front - part of the eye. It is composed of regularly arranged collagen fibers, which give it its transparency. The choroid is a vascular layer between the retina and sclera, the ciliary body is involved in accommodation (changing lens shape), the sclera is the tough white outer layer of the eye, and the lens is a biconvex structure (not primarily defined by regularly aligned collagen fibers for transparency like the cornea).
• Question 22: Calcitonin is a hormone produced by the parafollicular cells (C cells) of the thyroid gland. In children (and adults), it inhibits osteoclast activity. Osteoclasts break down bone. Thyroxine is a thyroid hormone involved in metabolism, oxytocin is involved in childbirth and lactation, parathyroid hormone increases osteoclast activity (opposite of what the question asks), and catecholamines (e.g., epinephrine, norepinephrine) are involved in the body's stress response.

Answer:

• Question 20: Iodine
• Question 21: Cornea
• Question 22: Calcitonin