krit.club logo

Human Nutrition - Alimentary canal

Grade 12IGCSEBiology

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

🔑Concepts

•

The Alimentary Canal is a continuous tube from the mouth to the anus where food is processed through five main stages: Ingestion, Digestion, Absorption, Assimilation, and Egestion.

•

Mechanical Digestion involves the physical breakdown of food into smaller pieces without changing its chemical nature (e.g., chewing by teeth and emulsification of fats by bile). This increases the surface area for enzyme action.

•

Chemical Digestion involves the breakdown of large, insoluble molecules into small, soluble molecules through the action of enzymes and water (hydrolysis).

•

The stomach secretes Gastric Juice containing Hydrochloric Acid (HClHCl), which provides an acidic environment (around pH 2.0pH\ 2.0) to kill bacteria and provide the optimum pHpH for the protease enzyme, pepsin.

•

Bile is produced in the liver, stored in the gallbladder, and released into the duodenum. It serves two functions: neutralizing the acidic chyme from the stomach and emulsifying fats into small droplets to increase the surface area for LipaseLipase action.

•

The small intestine (specifically the ileum) is adapted for absorption through structures called villi. Villi increase surface area and contain a network of blood capillaries for absorbing glucose and amino acids, and a lacteal for absorbing fatty acids and glycerol.

•

Assimilation is the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells.

📐Formulae

Starch+nH2O→AmylaseMaltose\text{Starch} + nH_{2}O \xrightarrow{\text{Amylase}} \text{Maltose}

Maltose+H2O→MaltaseGlucose\text{Maltose} + H_{2}O \xrightarrow{\text{Maltase}} \text{Glucose}

Proteins+nH2O→ProteaseAmino Acids\text{Proteins} + nH_{2}O \xrightarrow{\text{Protease}} \text{Amino Acids}

Lipids+3H2O→LipaseGlycerol+3Fatty Acids\text{Lipids} + 3H_{2}O \xrightarrow{\text{Lipase}} \text{Glycerol} + 3\text{Fatty Acids}

Neutralization: HCl+NaHCO3→NaCl+H2O+CO2\text{Neutralization: } HCl + NaHCO_{3} \rightarrow NaCl + H_{2}O + CO_{2}

💡Examples

Problem 1:

Calculate the theoretical increase in surface area if a flat membrane of 1 cm21\text{ cm}^2 is covered in 10410^4 villi, where each villus is a cylinder with a radius (rr) of 0.05 mm0.05\text{ mm} and a height (hh) of 0.5 mm0.5\text{ mm}.

Solution:

The surface area of one villus (excluding the base) is 2πrh2\pi rh. Given r=0.005 cmr = 0.005\text{ cm} and h=0.05 cmh = 0.05\text{ cm}, SA=2×π×0.005×0.05≈0.00157 cm2SA = 2 \times \pi \times 0.005 \times 0.05 \approx 0.00157\text{ cm}^2. Total area for 10410^4 villi ≈15.7 cm2\approx 15.7\text{ cm}^2.

Explanation:

This demonstrates how the presence of villi significantly increases the surface area available for the absorption of nutrients like C6H12O6C_6H_{12}O_6 and amino acids.

Problem 2:

A student adds AmylaseAmylase to a starch solution at pH 2.0pH\ 2.0 and pH 7.0pH\ 7.0. In which test tube will the Benedict's test be positive?

Solution:

The test tube at pH 7.0pH\ 7.0.

Explanation:

Salivary AmylaseAmylase has an optimum pHpH near neutral (pH 7.0pH\ 7.0). At pH 2.0pH\ 2.0 (highly acidic), the enzyme denatures, preventing the hydrolysis of starch into reducing sugars like maltose, which are required for a positive Benedict's test.

Alimentary canal - Revision Notes & Key Diagrams | IGCSE Grade 12 Biology