Final answer:
Each cell receives food and oxygen via diffusion through its plasma membrane, allowing substances to move from higher to lower concentrations, facilitated by transport molecules for water-soluble nutrients.
Step-by-step explanation:
The cells receive nutrients and oxygen through a process similar to a crowd spreading out in a public space. The substances move from an area of higher concentration to one of lower concentration across cell membranes, a concept known as diffusion. In our body, this means nutrients like glucose, amino acids, and oxygen pass through the cell's plasma membrane from the bloodstream, which contains a higher concentration of these substances, into the interior of cells that have a lower concentration. The plasma membrane is selectively permeable, allowing certain molecules to pass through while keeping others out.
Nutrients are first absorbed into the bloodstream via the digestive tract and are transported to the liver. From there, they are delivered to body cells. Oxygen is diffused into the blood from the lungs and transported through the body by the circulatory system. Similarly, hormones are released by endocrine glands into the bloodstream and reach target cells. The blood also carries cellular wastes and byproducts to various organs for excretion. Cells are separated from the surrounding interstitial fluid (IF) by a selectively permeable cell membrane, which regulates material passage. Specifically, water-soluble nutrients must use transport molecules to pass through the hydrophobic phospholipid bilayer of the cell membrane.