Which of these substances is transported by the blood plasma?

The correct option is All of the above.

Blood plasma is the straw-colored, liquid component of blood in which the blood cells are suspended. It makes up about 55% of the total blood volume and is composed of approximately 90% water, along with dissolved proteins, glucose, mineral ions, hormones, carbon dioxide, and waste products. It serves as a key transport medium for various substances throughout the body:
1. Carbon dioxide: A significant portion of carbon dioxide generated by cellular respiration is dissolved in the plasma (mainly as bicarbonate ions) to be carried to the lungs for excretion.
2. Nitrogenous waste: Metabolic waste products, such as urea and uric acid, are dissolved in the plasma and transported to the kidneys, where they are filtered out and excreted in urine.
3. Food: Digested nutrients (such as glucose, amino acids, vitamins, and lipids) are absorbed from the digestive tract into the bloodstream and carried by the plasma to various cells and tissues for energy and growth.

Since carbon dioxide, nitrogenous waste, and digested food (nutrients) are all transported by the blood plasma, "All of the above" is the correct choice.