Life Processes

Nutrition in Animals

Nutrition is a vital life process through which animals obtain energy and nutrients necessary for growth, repair, and maintenance of their bodies. Animals consume a variety of foods depending on their habitat and physiology. For example, bees and sunbirds feed on nectar, infants feed on mother's milk, snakes swallow prey whole, and some aquatic animals filter tiny food particles from water. The food animals eat contains complex molecules like carbohydrates, proteins, and fats, which need to be broken down into simpler forms for absorption and use by the body. This breakdown occurs in a specialized long tube called the alimentary canal, which starts at the mouth and ends at the anus. Digestive juices secreted at various points in the canal chemically digest food, while mechanical processes like chewing physically break it down. The simpler nutrients are then absorbed through the walls of the alimentary canal and transported via blood to different body parts to perform various functions. This section introduces the concept of nutrition in animals, focusing on the human digestive system as a model to understand the digestion process.

• Animals consume diverse types of food depending on their species and habitat.
• Food contains complex components: carbohydrates, proteins, and fats.
• The alimentary canal is a long tube where digestion occurs, starting from mouth to anus.
• Mechanical digestion begins in the mouth via chewing.
• Chemical digestion involves digestive juices breaking down food into simpler forms.
• Absorption of nutrients occurs through the walls of the alimentary canal.
• 📌 Nutrition: The process by which living organisms obtain food and use it for energy and growth.
• 📌 Alimentary canal: The long tube in animals through which food passes and digestion occurs.
• 📌 Mechanical digestion: Physical breakdown of food into smaller pieces.

Digestion in human beings

Digestion in humans is a complex process involving both mechanical and chemical breakdown of food as it travels through the alimentary canal. The journey begins in the mouth where teeth crush and chew food into smaller pieces, a mechanical digestion process. Saliva, secreted by salivary glands, moistens food and contains an enzyme that starts chemical digestion by breaking down starch (a carbohydrate) into sugar. This is why starchy foods like chapati taste sweet when chewed for a long time. The tongue helps mix food with saliva and pushes it into the oesophagus or food pipe. The oesophagus moves food to the stomach by rhythmic contractions called peristalsis. In the stomach, food is churned and mixed with gastric juice containing digestive enzymes, acid, and mucus. The enzymes break down proteins into simpler forms, acid kills harmful bacteria and aids digestion, and mucus protects the stomach lining from acid damage. The partially digested food then moves into the small intestine, the longest part of the alimentary canal, which receives secretions from the liver (bile) and pancreas (pancreatic juice). Bile neutralizes stomach acid and emulsifies fats, while pancreatic juice digests carbohydrates, proteins, and fats further. The small intestine's inner lining has finger-like projections called villi that increase surface area for absorption of nutrients into the blood. The remaining undigested food passes into the large intestine, which absorbs water and salts, forming semi-solid waste called stool, stored in the rectum and expelled through the anus. This detailed process ensures that nutrients from food are efficiently digested and absorbed to sustain life.

• Mechanical digestion starts in the mouth by chewing and crushing food.
• Saliva contains enzymes that chemically break down starch into sugar.
• Food moves from mouth to stomach via oesophagus by peristalsis.
• Stomach secretes digestive juice to break down proteins and acid to kill bacteria.
• Small intestine receives bile and pancreatic juice to digest fats, proteins, and carbohydrates.
• Villi in small intestine absorb digested nutrients into the bloodstream.
• Large intestine absorbs water and salts, forming stool for egestion.
• 📌 Saliva: A digestive juice secreted in the mouth containing enzymes that begin starch digestion.
• 📌 Peristalsis: Wave-like muscle contractions that move food through the alimentary canal.
• 📌 Gastric juice: Digestive secretion in the stomach containing enzymes, acid, and mucus.