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Human Body Systems - The Digestive System

Grade 7IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The Digestive System is responsible for breaking down large, insoluble food molecules into small, water-soluble molecules like glucose (C6H12O6C_6H_{12}O_6) that can be absorbed into the bloodstream.

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Mechanical digestion involves the physical breakdown of food (e.g., chewing in the mouth, churning in the stomach), while chemical digestion uses enzymes and substances like Hydrochloric Acid (HClHCl) to break chemical bonds.

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Enzymes are biological catalysts that speed up reactions. For example, Amylase breaks down starch into maltose, and Protease breaks down proteins into amino acids.

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The stomach maintains a low pHpH (approx. 1.51.5 to 3.53.5) due to the presence of HClHCl, which provides the optimum environment for the enzyme pepsin to function.

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The small intestine contains villi, which are finger-like projections that significantly increase the surface area-to-volume ratio (SA:VSA:V) to maximize the rate of nutrient absorption.

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The liver produces bile, which is stored in the gallbladder; bile emulsifies fats (increasing surface area) and neutralizes the acidic chyme coming from the stomach using sodium bicarbonate (NaHCO3NaHCO_3).

📐Formulae

Starch→AmylaseMaltose\text{Starch} \xrightarrow{\text{Amylase}} \text{Maltose}

Proteins+H2O→Protease/PepsinAmino Acids\text{Proteins} + H_2O \xrightarrow{\text{Protease/Pepsin}} \text{Amino Acids}

Lipids+H2O→LipaseGlycerol+3×Fatty Acids\text{Lipids} + H_2O \xrightarrow{\text{Lipase}} \text{Glycerol} + 3 \times \text{Fatty Acids}

HCl+NaHCO3→NaCl+H2O+CO2HCl + NaHCO_3 \rightarrow NaCl + H_2O + CO_2

💡Examples

Problem 1:

A student is studying the effect of pHpH on the enzyme Pepsin. If the pHpH in the test tube is increased from 22 to 99 by adding a base, what will happen to the rate of protein digestion?

Solution:

The rate of protein digestion will decrease significantly or stop entirely.

Explanation:

Pepsin is a protease that functions optimally in the acidic environment of the stomach (pH≈2pH \approx 2). At pHpH 99, the enzyme becomes denatured, meaning its active site changes shape and can no longer bind to the protein substrate.

Problem 2:

Explain the chemical importance of the reaction between HClHCl and NaHCO3NaHCO_3 in the duodenum.

Solution:

The reaction HCl+NaHCO3→NaCl+H2O+CO2HCl + NaHCO_3 \rightarrow NaCl + H_2O + CO_2 neutralizes the acid.

Explanation:

Food leaving the stomach is highly acidic due to HClHCl. Enzymes in the small intestine (like pancreatic lipase) require a slightly alkaline pHpH to function. The NaHCO3NaHCO_3 in pancreatic juice neutralizes the acid, protecting the intestinal lining and providing the correct environment for chemical digestion.