Key Points

Life processes are the essential functions performed by living organisms to survive, including nutrition, respiration, excretion, and reproduction.

The human digestive system consists of a long tube called the alimentary canal, which includes the mouth, oesophagus, stomach, small intestine, large intestine, and anus.

Digestion begins in the mouth where teeth perform mechanical digestion (chewing) and saliva begins chemical digestion by breaking down starch into sugars.

The oesophagus, or food pipe, pushes softened food from the mouth down into the stomach through wave-like muscular contractions.

The stomach churns food and secretes digestive juices, acid to kill bacteria, and mucus to protect its lining. It primarily digests proteins.

The small intestine is the longest part of the alimentary canal where the final digestion of carbohydrates, proteins, and fats occurs and nutrients are absorbed.

The liver secretes bile, which helps break down fats. The pancreas secretes pancreatic juice that acts on carbohydrates, proteins, and fats.

The inner walls of the small intestine have thousands of finger-like projections that increase the surface area for efficient absorption of digested nutrients into the blood.

The large intestine absorbs water and some salts from undigested food. The remaining semi-solid waste, called stool, is stored in the rectum before egestion.

Grass-eating animals like cows are called ruminants. They quickly swallow partially chewed food and later bring it back to the mouth for thorough chewing in a process called rumination.

Breathing is a physical process of inhaling and exhaling air. Respiration is a chemical process inside cells that uses oxygen to break down food and release energy.

Air is inhaled through the nostrils, passes through the nasal passages and windpipe, and enters the lungs, which are protected by the rib cage.

During inhalation, the diaphragm moves down and the rib cage moves up and out, increasing chest space. During exhalation, the diaphragm and ribs return to their original positions.

In the lungs, exchange of gases occurs in tiny balloon-like sacs called alveoli. Oxygen ($\text{O}_2$) from inhaled air passes into the blood, and carbon dioxide ($\text{CO}_2$) from the blood is exhaled.

Respiration breaks down glucose with oxygen to produce energy, carbon dioxide, and water. The equation is: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy}$.

Different animals have adapted different breathing mechanisms. Fish use gills, earthworms use their moist skin, and adult frogs use lungs on land and moist skin in water.