Final answer:
Needed substances are carried to the body cells by blood, which transports oxygen, hormones, nutrients, and carries away wastes. Nutrients that provide energy, like glucose, and essential vitamins and electrolytes are dissolved in blood and delivered to cells.
Step-by-step explanation:
The substances that are needed by body cells are carried to the cells primarily by blood. This includes oxygen from the air we breathe, which diffuses into the blood and moves from the lungs to the heart, hormones released by the endocrine glands, and nourishment from the digested food such as glucose, which is a form of energy for the cells. Blood also transports cellular wastes to different parts of the body for removal. For example, it carries carbon dioxide to the lungs for exhalation and waste products to the kidneys and liver for excretion.
Nutrients like carbohydrates, proteins, and fats are broken down into smaller molecules, such as glucose, which provides energy in the form of ATP through metabolic pathways. Vitamins and electrolytes, which are also essential nutrients, dissolve in blood to be transported to where they are needed in the body. The transportation of these substances is facilitated by the plasma within blood via a range of mechanisms, including active transport, passive diffusion, and facilitated diffusion.