Question

which explanation best describes why lipid - soluble hormones like t₃ and t₄ requ carrier proteins in the bloodstream?
lipid - soluble hormones chemically convert into water - soluble forms in the live so carrier proteins only function to prevent premature excretion.
endocrine glands secrete t₃ and t₄ already bound to carrier proteins because plasma is nonpolar and would otherwise break down the hormones before they reach endocrine targets.
waters polarity allows it to directly dissolve all endocrine hormones, so carrier proteins are used only to increase hormone half - life, not for transport.
water in plasma cannot dissolve lipid - soluble molecules such as thyroid hormones, fat - soluble vitamins (a, d, e, k), and dissolved gases like o₂; therefore, these molecules must bind to transport proteins to remain suspended and travel to target tissues.

Explanation:

1. Analyze the first option: Lipid - soluble hormones don't convert to water - soluble in the liver for this purpose. Carrier proteins are for transport, not just preventing excretion. So this is incorrect.
2. Analyze the second option: Plasma is mostly water (polar), not non - polar. And endocrine glands don't secrete T₃/T₄ already bound; they bind in the blood. So this is incorrect.
3. Analyze the third option: Water (plasma) can't dissolve lipid - soluble hormones. Carrier proteins are needed for transport, not just increasing half - life. So this is incorrect.
4. Analyze the fourth option: Plasma is aqueous (water - based, polar). Lipid - soluble molecules (like T₃, T₄, fat - soluble vitamins, some gases) can't dissolve in polar water. So they need carrier proteins to stay suspended and reach target tissues. This matches the principles of solubility (like dissolves like: polar dissolves polar, non - polar dissolves non - polar) and hormone transport.

Answer:

The option: "Water in plasma cannot dissolve lipid - soluble molecules such as thyroid hormones, fat - soluble vitamins (A, D, E, K), and dissolved gases like O₂; therefore, these molecules must bind to transport proteins to remain suspended and travel to target tissues."