Comprehensive theory, key formulas, diagrams, and memory aids for Life Processes.
What distinguishes living things from non-living things? If we see a dog running, a cow chewing cud, or a human shouting, we know they are alive. But what about a plant? We know it's alive because it grows over time. Living organisms possess certain basic functions that must be continuously performed to maintain their life, even when they are sleeping or sitting idly. The basic functions performed by living organisms to maintain their life on Earth are called life processes.
The fundamental life processes include nutrition, respiration, transportation, and excretion.
When we walk or ride a bicycle, we use energy. Even when not engaged in apparent activity, our body requires energy to maintain its state of order and prevent damage or breakdown. This energy comes from outside the body in the form of food. The process of acquiring this food and utilizing it is called nutrition.
This type of nutrition is seen in green plants and some bacteria. They can synthesize their own organic food (like carbohydrates) from simple inorganic substances like carbon dioxide and water in the presence of sunlight. * Photosynthesis: The complex process by which autotrophs take in substances from the outside and convert them into stored forms of energy. * Equation: 6CO₂ + 12H₂O + Sunlight + Chlorophyll → C₆H₁₂O₆ (Glucose) + 6O₂ + 6H₂O * Events in Photosynthesis: 1. Absorption of light energy by chlorophyll. 2. Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen. 3. Reduction of carbon dioxide to carbohydrates. * Stomata: Tiny pores present on the surface of leaves through which massive amounts of gaseous exchange take place for photosynthesis. Guard cells regulate the opening and closing of these pores.
Animals and fungi cannot make their own food; they depend on autotrophs or other heterotrophs for their nutritional requirements. * Holozoic Nutrition: Taking in solid food and digesting it internally (e.g., humans, amoeba). * Saprophytic Nutrition: Organisms feed on dead and decaying organic matter by breaking down the food material outside the body and then absorbing it (e.g., bread moulds, yeast, mushrooms). * Parasitic Nutrition: Obtaining nutrients from a host organism without killing it (e.g., cuscuta, ticks, lice, leeches, tapeworms).
The human digestive system is basically a long tube (alimentary canal) extending from the mouth to the anus, accompanied by various glands. 1. Mouth: Digestion begins here. Teeth crush food, and saliva (containing the enzyme salivary amylase) breaks down complex starch into simpler sugar. 2. Stomach: The muscular walls of the stomach help in churning the food with gastric juices. The gastric glands release hydrochloric acid (creates an acidic medium), pepsin (enzyme for protein digestion), and mucus (protects the inner lining of the stomach). 3. Small Intestine: The site of complete digestion of carbohydrates, proteins, and fats. It receives secretions from: * Liver: Secretes bile juice, which makes the acidic food alkaline and breaks down large fat globules into smaller ones (emulsification). * Pancreas: Secretes pancreatic juice containing enzymes like trypsin (for digesting proteins) and lipase (for breaking down emulsified fats). * Absorption: The inner walls have finger-like projections called villi, which increase the surface area for the rapid absorption of digested food into the blood. 4. Large Intestine: Absorbs water from the undigested food. The remaining solid waste is removed via the anus.
The food material taken in during nutrition is used by cells to provide energy for various life processes. The process of breaking down food (glucose) to release energy is called respiration.
The Respiratory System in Humans: Air is taken into the body through the nostrils, filtered by fine hairs, and passes down the trachea (which has rings of cartilage so it doesn't collapse). Within the lungs, the passage divides into smaller tubes (bronchi, bronchioles) which finally terminate in balloon-like structures called alveoli. The alveoli provide a vast surface area for the exchange of gases (oxygen and carbon dioxide) with the surrounding blood capillaries.
Once food is digested and oxygen is absorbed, these materials need to be transported to every single cell in the body. Conversely, metabolic wastes must be transported away from the cells.
Our circulatory system consists of a pumping organ (the heart), a network of tubes (blood vessels), and a circulatory medium (blood and lymph). * Blood: A fluid connective tissue consisting of a fluid medium called plasma (transports food, CO₂, nitrogenous wastes) and cells (Red Blood Cells transport oxygen; White Blood Cells fight infection; Platelets help in blood clotting). * The Heart: A muscular organ with four chambers. The right side handles deoxygenated blood (sending it to the lungs), while the left side handles oxygenated blood (receiving it from the lungs and pumping it to the rest of the body). This prevents the mixing of oxygen-rich and oxygen-poor blood. * Double Circulation: Blood passes through the heart twice during one complete cycle through the body (pulmonary circulation to lungs, systemic circulation to body). * Blood Vessels: Arteries (carry blood away from the heart, thick-walled), Veins (carry blood towards the heart, have valves), and Capillaries (extremely thin vessels where exchange of materials occurs).
Plants need a transport system to move water from the roots to the leaves, and food from the leaves to other parts. * Xylem: Transports water and dissolved minerals upwards from roots to stems and leaves. This upward movement is primarily driven by transpiration pull (the suction force created by the evaporation of water from the stomata of leaves). * Phloem: Transports the soluble products of photosynthesis (food) from the leaves to all other parts of the plant. This process is called translocation and requires energy (ATP).
The biological process involved in the removal of harmful metabolic wastes from the body is called excretion.
The excretory system of human beings includes a pair of kidneys, a pair of ureters, a urinary bladder, and a urethra. * Kidneys: Located in the abdomen. Their purpose is to filter out poisonous nitrogenous waste (urea, uric acid) from the blood. * Nephrons: The basic filtration unit in the kidneys. Each kidney has millions of these. They filter the blood, and then selectively reabsorb useful substances (like glucose, amino acids, salts, and a major amount of water) back into the blood. * The liquid waste left behind is urine, which travels through the ureters to be stored in the urinary bladder until it is passed out through the urethra.
Plants use completely different strategies for excretion. * Oxygen itself can be considered a waste product generated during photosynthesis! * They get rid of excess water by transpiration. * Waste products may be stored in leaves that eventually fall off. * Other waste products are stored as resins and gums, especially in old xylem. * Plants also excrete some waste substances into the soil around them.
Life processes are the essential maintenance jobs of living organisms. Nutrition provides the raw materials (food) and oxygen required for energy. Respiration is the chemical breakdown of that food to release energy (ATP) for cellular work. Transportation systems ensure that oxygen, water, and nutrients reach every cell, while picking up waste products. Finally, the excretory system acts as the body's filtration plant, removing toxic metabolic byproducts to maintain a healthy internal environment. Together, these beautifully coordinated systems keep the flame of life burning.