The structure that connects the fetus to the uterine wall and allows nutrient exchange is the: MCQ with Answer and Explanation

Explanation:
About 70% CO₂ is carried as bicarbonate. The main stimulus is high CO₂; external respiration is in lungs; diaphragm moves downward (contracts) during inhalation.

Explanation:
Iodine is incorporated into thyroxine (T₄) and triiodothyronine (T₃) synthesized by the thyroid gland. Deficiency leads to goiter and hypothyroidism. Iron is in hemoglobin, zinc in insulin and enzymes, cobalt in B₁₂.

Explanation:
Vitamin A (retinol) is essential for the synthesis of rhodopsin, the visual pigment in rod cells responsible for low-light vision. Deficiency leads to night blindness (nyctalopia) and, if severe, xerophthalmia and permanent blindness. Vitamin B₁ deficiency causes beriberi, C scurvy, D rickets.