All living organisms carry out certain basic activities to survive and grow. In animals, these life processes include nutrition, respiration, transportation (circulation), excretion, and reproduction. Understanding these helps us appreciate how animal bodies function as integrated systems.
Key Concepts and Definitions
Nutrition is the process by which organisms obtain and use food. Animals are heterotrophs — they cannot make their own food and must eat plants or other animals. Digestion breaks food into small, soluble molecules that can be absorbed into the blood.
Digestion in humans involves the mouth (chewing, saliva containing amylase breaks starch), oesophagus (carries food by peristalsis), stomach (hydrochloric acid and enzymes digest proteins), small intestine (most digestion and absorption occur here; bile from the liver emulsifies fats), and large intestine (absorbs water; undigested matter is excreted).
- Respiration is the process by which food (glucose) is broken down to release energy. It occurs in two forms:
- Aerobic respiration: Glucose + Oxygen → Carbon dioxide + Water + Energy
- Anaerobic respiration (e.g., in yeast or during heavy exercise): Glucose → Lactic acid / Ethanol + Carbon dioxide + Energy (less energy released)
Breathing vs Respiration: Breathing is the physical act of inhaling and exhaling air. Respiration is the chemical process in cells that releases energy.
Transportation in animals involves the circulatory system. The human heart has four chambers: two atria and two ventricles. Arteries carry oxygenated blood away from the heart (except pulmonary artery). Veins carry deoxygenated blood to the heart (except pulmonary veins). Capillaries allow exchange of materials with cells.
Excretion is the removal of metabolic waste products. The kidneys filter blood and produce urine (water, urea, salts). Other organs of excretion include lungs (CO2, water vapour) and skin (sweat).
Worked Examples
Why does saliva contain the enzyme amylase?
Digestion of starch begins in the mouth. Amylase in saliva breaks large starch molecules into maltose (a simpler sugar) before the food reaches the stomach. This is an example of chemical digestion.
What is the role of hydrochloric acid in the stomach?
HCl creates an acidic environment (low pH) that activates pepsin (a protein-digesting enzyme) and kills most bacteria present in the food, protecting the body from infection.
Why does the small intestine have villi?
Villi are tiny finger-like projections that increase the surface area of the small intestine enormously, allowing faster and more efficient absorption of digested food molecules into the bloodstream.
Write the word equation for aerobic respiration.
Glucose + Oxygen → Carbon dioxide + Water + Energy
This process occurs in the mitochondria of cells and releases energy for all life activities.
Why do we breathe faster during exercise?
Muscles need more energy during exercise, so more glucose is oxidised. This requires more oxygen and produces more CO2. The breathing rate increases to supply extra oxygen and remove extra CO2 quickly.
What is the function of the kidneys?
The kidneys filter all the blood in the body about 300 times a day. They remove waste products like urea (formed from the breakdown of excess proteins), excess salts, and water, excreting them as urine. This maintains the chemical balance of the blood.
How does the four-chambered heart prevent mixing of oxygenated and deoxygenated blood?
The heart is divided into a left side (oxygenated blood from lungs, pumped to body) and a right side (deoxygenated blood from body, pumped to lungs). The septum (wall) between the two sides ensures these two blood streams never mix, making human circulation efficient.
- Key Facts
- The human body has about 5 litres of blood.
- The small intestine is about 6-7 metres long.
- Urea is formed in the liver from the breakdown of amino acids and is excreted by the kidneys.
Common mistakes
Students confuse arteries with veins. Remember: Arteries Away (carry blood away from the heart). Also, do not confuse breathing (physical) with respiration (chemical). Respiration occurs in every living cell, not just in the lungs.
Summary
Animals obtain nutrition by digesting food in a step-by-step process along the alimentary canal. Cells release energy through respiration (aerobic or anaerobic). The circulatory system transports materials; the excretory system removes wastes. All these life processes work together to keep the organism alive and healthy.