Use the pathway to build a clear mental model. Open each node and answer the check question.
Food must be digested (broken down) into tiny molecules before the body can use it. These small molecules (nutrients) are absorbed into the blood through the walls of the small intestine.
Check: Why does food need to be digested before nutrients can enter the blood?
Nutrients dissolve in the liquid part of blood called plasma. Plasma carries glucose, amino acids, vitamins, and minerals around the body. The heart pumps blood to deliver these nutrients to every cell.
Check: What part of blood carries dissolved nutrients?
Capillaries have very thin walls (just one cell thick). Nutrients and oxygen pass through these walls from the blood into body cells. Carbon dioxide and waste pass from cells back into the blood.
Check: Why do capillaries need thin walls?
Water is essential for nutrient transport - nutrients dissolve in water, and plasma is mostly water. Water also enters cells and helps chemical reactions happen. Staying hydrated keeps nutrient transport working efficiently.
Check: Why is water important for nutrient transport?
Nutrient transport is how the body moves nutrients from where they enter (the digestive system) to where they're needed (every cell in your body). The circulatory system is the body's delivery network.
The food you eat contains large molecules that are too big to pass through cell membranes. The digestive system breaks these down:
These small molecules can then be absorbed through the walls of the small intestine.
The small intestine has millions of tiny finger-like projections called villi. These:
Nutrients pass through the villi walls into the capillaries and enter the bloodstream.
Once in the blood, nutrients dissolve in plasma (the liquid part of blood). The heart pumps blood around the body, delivering nutrients to all organs and tissues.
Capillaries reach every part of your body. At the capillaries:
Water is essential for nutrient transport because:
Every cell in your body needs nutrients to function. Without efficient nutrient transport, cells would starve even if you ate well. Understanding this system helps you see why eating a balanced diet and staying hydrated are so important - it's not just about what you eat, but about getting those nutrients to the trillions of cells that need them.
After eating a school lunch, your body digests the food over several hours. Glucose from the carbohydrates enters your bloodstream, causing a rise in blood sugar. The heart pumps this glucose-rich blood to your muscles and brain, giving you energy for afternoon lessons and PE.
Athletes drink water and sports drinks during exercise. Water keeps plasma volume up so blood flows easily. Some sports drinks contain dissolved glucose and salts that can be absorbed quickly, reaching muscles within minutes. However, the NHS recommends water for most activities - sports drinks are only needed for intense exercise lasting over an hour.
When someone cannot eat or drink (perhaps after surgery), NHS hospitals use intravenous (IV) drips to deliver nutrients directly into the bloodstream. This bypasses the digestive system entirely, putting nutrients straight into the blood plasma where they can be transported to cells immediately.
In 1822, American army surgeon William Beaumont studied a patient with a hole in his stomach (from a gunshot wound). He could observe digestion directly, watching food break down into smaller molecules. This helped scientists understand that digestion must happen before nutrients can enter the blood.
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Food cannot travel directly to cells - it must first be digested (broken down) in the digestive system, then absorbed into the blood, then transported to cells. Each step is necessary.
Digestion is BREAKING DOWN food into smaller molecules. Absorption is TAKING IN those molecules from the gut into the blood. They are two different processes - digestion must happen first.
Students often focus on red blood cells but forget that nutrients travel in plasma, not in red blood cells. Red cells carry oxygen; plasma carries dissolved nutrients, carbon dioxide, and waste products.
When asked why capillaries are important, don't just say "they have thin walls." Explain that thin walls allow substances to pass through easily - so nutrients can exit and waste can enter the blood.