Correct Answer: Option B) Oxygen, carbon dioxide, food, waste products

Explanation:

Introduction:
Capillaries are tiny blood vessels that connect the arterioles (small arteries) and venules (small veins). They play a crucial role in the exchange of substances between the blood and the tissues. The substances that are exchanged include oxygen, carbon dioxide, nutrients (food), and waste products.

Exchange of Substances in Capillaries:
The capillaries enable the exchange of substances between the blood and the tissues through a process called diffusion. Diffusion occurs due to the concentration gradient between the blood and the tissues.

Oxygen:
Oxygen is required by the cells for cellular respiration, which is the process that produces energy. Oxygen is transported from the lungs to the cells through the bloodstream. In the capillaries, oxygen diffuses from the blood into the tissues where it is needed.

Carbon Dioxide:
Carbon dioxide is produced as a waste product during cellular respiration. It needs to be removed from the cells and transported back to the lungs to be exhaled. In the capillaries, carbon dioxide diffuses from the tissues into the blood, where it is carried back to the lungs for elimination.

Food:
Nutrients from the food we consume are absorbed into the bloodstream through the walls of the small intestine. These nutrients, including glucose, amino acids, and fatty acids, are transported by the blood to the tissues where they are needed for energy production, growth, and repair. In the capillaries, nutrients diffuse from the blood into the tissues.

Waste Products:
Metabolic waste products, such as urea and other nitrogenous compounds, are produced as a result of cellular metabolism. These waste products need to be removed from the tissues and transported to the excretory organs (such as the kidneys) for elimination. In the capillaries, waste products diffuse from the tissues into the blood, where they are carried away for excretion.

Conclusion:
In summary, the capillaries facilitate the exchange of oxygen, carbon dioxide, nutrients (food), and waste products between the blood and the tissues. This exchange occurs through the process of diffusion and is crucial for maintaining the proper functioning of the cells and organs in the body. Option B correctly represents the substances exchanged in the capillaries.