Life Processes

The One Thing

Life depends on four coordinated processes: nutrition supplies materials, respiration releases usable energy, transportation distributes substances, and excretion removes metabolic wastes. Together, these processes enable organisms to grow, function and maintain stable internal conditions.

Reactions, Processes and Experiments

Key Terms

• Life processes: Basic activities necessary for the survival and maintenance of living organisms.
• Nutrition: The process of obtaining and using food for energy, growth, repair and body functions.
• Autotrophic nutrition: Nutrition in which organisms make their own food from carbon dioxide and water using light energy and chlorophyll.
• Photosynthesis: The process by which green plants prepare glucose using carbon dioxide, water, sunlight and chlorophyll.
• Heterotrophic nutrition: Nutrition in which organisms obtain food from other organisms.
• Human digestive system: A group of organs that ingests food, digests it, absorbs nutrients and removes undigested material.
• Digestion: The breakdown of complex, insoluble food into simpler, soluble substances that can be absorbed.
• Respiration: The process of breaking down food to release energy for cellular activities.
• Aerobic respiration: Respiration using oxygen, producing carbon dioxide, water and a large amount of energy.
• Anaerobic respiration: Respiration without oxygen, producing less energy and different end products.
• ATP: Adenosine triphosphate, the energy-carrying molecule used by cells for immediate activities.
• Transportation: The movement of nutrients, gases, water, hormones and wastes within an organism.
• Xylem: Plant tissue that transports water and minerals mainly from roots to other parts.
• Phloem: Plant tissue that transports food from leaves to growing and storage regions.
• Transpiration: Loss of water vapour from the aerial parts of a plant, mainly through stomata.
• Human circulatory system: The heart, blood and blood vessels that transport substances throughout the body.
• Double circulation: A system in which blood passes through the heart twice during one complete circuit of the body.
• Excretion: The removal of harmful metabolic wastes from the body.
• Nephron: The structural and functional unit of the kidney that filters blood and forms urine.
• Urine formation: The processes of filtration, selective reabsorption and secretion that produce urine in nephrons.
• Homeostasis: The maintenance of stable internal conditions despite changes outside the organism.
• Stomata: Tiny pores, mainly on leaves, that allow exchange of gases and loss of water vapour.
• Villi: Structures in the small intestine that increase its surface area for absorption.
• Alveoli: Respiratory surfaces adapted for efficient gas exchange; a respiratory surface should be thin, moist and sufficiently large.
• Haemoglobin: The substance in red blood cells that transports oxygen.
• Plasma: The liquid component of blood that carries dissolved substances.
• Capillaries: Small blood vessels that allow exchange of substances with tissues.
• Blood pressure: The pressure of blood in the circulatory system, commonly represented as systolic pressure over diastolic pressure and measured in mm Hg.
• Ureters: Tubes that carry urine from the kidneys to the urinary bladder.
• Urinary bladder: The organ that stores urine before it leaves the body.
• Urethra: The tube through which urine leaves the body.
• Egestion: Removal of undigested food from the digestive tract.
• Metabolic wastes: Harmful substances produced by cellular activities and removed through excretion.

Easily Confused

• Respiration and breathing: Respiration is the cellular breakdown of food to release energy; breathing is the exchange of gases with the environment.
• Excretion and egestion: Excretion removes metabolic wastes, whereas egestion removes undigested food from the digestive tract.
• Autotrophic and heterotrophic nutrition: Autotrophic organisms make their own food; heterotrophic organisms obtain food from other organisms.
• Aerobic and anaerobic respiration: Aerobic respiration uses oxygen and releases a large amount of energy; anaerobic respiration occurs without oxygen and releases less energy.
• Xylem and phloem: Xylem transports water and minerals mainly upward from roots; phloem transports food from leaves to storage and growing regions and requires energy.
• Arteries and veins: Arteries generally carry blood away from the heart; veins generally carry blood toward the heart.
• Bile and digestive enzymes: Bile emulsifies fats and helps create an alkaline medium but does not contain a digestive enzyme; digestive enzymes chemically break down food.
• Filtration and selective reabsorption: Filtration removes substances from blood into the nephron; selective reabsorption returns useful substances to the blood.
• Nutrition and respiration: Nutrition obtains food and materials; respiration releases usable energy from food.
• Excretion in plants and animals: Plants remove wastes by diffusion, transpiration, storage and release of substances such as resins and gums; animals use specialised organs such as kidneys.

What Gets Asked

• Write the equation for photosynthesis. Marks depend on reproducing 6CO2 + 6H2O --sunlight and chlorophyll--> C6H12O6 + 6O2. accurately, including sunlight and chlorophyll.
• Compare aerobic and anaerobic respiration. The required distinction is that aerobic respiration uses oxygen and produces carbon dioxide, water and a large amount of energy, whereas anaerobic respiration produces less energy and different end products.
• Explain digestion in the human digestive system. Specific points include salivary amylase in the mouth, hydrochloric acid and pepsin in the stomach, bile emulsification without digestive enzymes, and the role of villi in the small intestine.
• Describe transport in plants and animals. Questions may require the functions of xylem, phloem, arteries, veins and capillaries; omitting the energy requirement of phloem translocation or the transpiration pull loses the relevant distinction.
• Describe the human circulatory system and double circulation. The four heart chambers and the fact that blood passes through the heart twice in one complete circuit must be identified.
• Explain excretion and urine formation. A complete answer distinguishes excretion from egestion and includes nephron filtration, selective reabsorption and secretion, followed by movement of urine through the ureters, urinary bladder and urethra.