Life Processes | Class 10 Science Notes

Nutrition in Human Beings

The human digestive system is a complex organ system designed to break down food into absorbable nutrients. It consists of the alimentary canal, a long tube extending from the mouth to the anus, and associated glands. The alimentary canal includes the mouth, oesophagus, stomach, small intestine, and large intestine. Food is first crushed by teeth and mixed with saliva in the mouth. Saliva contains the enzyme salivary amylase which begins the digestion of starch into simple sugars. The tongue helps in mixing and swallowing the food. Peristaltic movements of muscles in the alimentary canal push the food forward. The food passes through the oesophagus to the stomach, where gastric glands secrete hydrochloric acid, pepsin (a protein-digesting enzyme), and mucus. The acid creates an acidic medium facilitating pepsin action and kills bacteria, while mucus protects the stomach lining. The stomach churns food into a semi-liquid form. Food then enters the small intestine, the longest part of the canal, where complete digestion occurs with the help of pancreatic juice and bile from the liver. Bile emulsifies fats, increasing the efficiency of lipase enzymes. Pancreatic enzymes digest proteins and fats, while intestinal glands secrete enzymes to convert carbohydrates, proteins, and fats into absorbable forms. The inner lining of the small intestine has villi, finger-like projections that increase surface area for absorption. Nutrients absorbed enter the bloodstream to be transported to body cells. The large intestine absorbs water and forms feces, which are expelled through the anus. Dental caries or tooth decay is discussed as a common problem caused by bacterial action on sugars producing acids that damage teeth. This section provides a detailed overview of human nutrition and digestion.

📊 Diagram: Figure 5.6 Human alimentary canal

🧪 Activity: Activity 5.3: Testing starch digestion by saliva using iodine solution in test tubes.

🔗 Connection: This section connects to the next topic of respiration, explaining how digested food is used to release energy.