Life Processes: Comprehensive University Study Notes

Fundamental Criteria of Life and Molecular Movement

Visible vs. Invisible Movement: * Common evidence for being alive often involves visible movement, such as a dog running, a cow chewing cud, or a human shouting. * Movement can be growth-related (in plants) or non-growth-related (animating activities). * Visible movement is not a comprehensive definitive characteristic of life because plants can be alive without visible growth, and animals can breathe without visible torso movement. * Molecular Movement: This refers to movements on very small scales, invisible to the naked eye. Professional biologists agree that molecular movement is essential for life.
The Case of Viruses: * Viruses do not show molecular movement within themselves until they infect a host cell. * This lack of independent molecular movement is the primary reason for the ongoing controversy regarding whether viruses are technically alive or non-living.
Necessity of Maintenance: * Living organisms are highly organized structures consisting of tissues, cells, and organelles. * The environment tends to break down this ordered nature over time. * If the organized structure breaks down, the organism dies. Therefore, living creatures must continuously repair and maintain their structures using molecular movement.

Concept of Life Processes

Definition: Life processes are the collective functions that perform the maintenance of a living organism, even when the organism is inactive (e.g., sitting still or sleeping).
Energy Requirement: Maintenance and prevention of breakdown require energy. Since this energy comes from external sources, it must be transferred into the body.
Nutrition: The process of transferring an energy source (food) from the outside to the inside of the organism is called nutrition. * Life on Earth is largely based on carbon molecules; hence, most food sources are carbon-based.
Respiration: Internal chemical reactions are required to break down or build up molecules from food into a uniform energy source for molecular maintenance. * Oxidizing-reducing reactions are the most common chemical means for this breakdown. * The process of acquiring oxygen from the environment to break down food for cellular needs is known as respiration.
Body Design and Transportation: * Single-celled Organisms: The entire surface is in contact with the environment. Simple diffusion is sufficient for oxygen intake, food intake, and waste removal. * Multi-cellular Organisms: Most cells are not in direct contact with the environment. Simple diffusion cannot meet the requirements of all cells. * Specialized tissues handle the uptake of food and oxygen and the removal of wastes. This necessitates a transportation system to move these substances between different parts of the body.
Excretion: Metabolic reactions produce by-products (e.g., nitrogenous wastes) that are useless or harmful. The removal of these wastes is called excretion. Specialized excretory tissues require the transportation system to deliver waste from the cells to the site of excretion.

Nutrition: Autotrophic and Heterotrophic

General Energy Needs: Every organism needs energy and materials to maintain order, grow, develop, and synthesize proteins.
Autotrophic Nutrition: * Organisms produce simple food from inorganic sources using $CO_{2}$ and $H_{2}O$ . * Examples: Green plants and some bacteria.
Heterotrophic Nutrition: * Organisms utilize complex substances prepared by other organisms. * These substances must be broken down by biological catalysts called enzymes for use by the body. * Examples: Animals and fungi. Their survival depends directly or indirectly on autotrophs.

Process of Photosynthesis

Definition: The process by which autotrophs take in $CO_{2}$ and $H_{2}O$ and convert them into stored carbohydrates in the presence of sunlight and chlorophyll.
The Chemical Reaction: * $6CO_{2} + 12H_{2}O \rightarrow C_{6}H_{12}O_{6} + 6O_{2} + 6H_{2}O$ * The reaction occurs in the presence of sunlight and chlorophyll.
Internal Energy Reserves: * Plants store unused carbohydrates as starch. * Humans store energy derived from food as glycogen.
Key Stages of Photosynthesis: 1. Absorption of light energy by chlorophyll. 2. Conversion of light energy to chemical energy and the splitting of water molecules into hydrogen and oxygen. 3. Reduction of carbon dioxide to carbohydrates. * Note: These steps don't always happen immediately. In desert plants, $CO_{2}$ is taken up at night to form an intermediate, which is processed by chlorophyll-absorbed energy during the day.
Chloroplasts: Cell organelles seen as green dots in a leaf cross-section. They contain chlorophyll, which is essential for photosynthesis.
Stomata and Gas Exchange: * Stomata are tiny pores on the leaf surface. Gaseous exchange for photosynthesis occurs through these, as well as through stems and roots. * Guard Cells: Control the opening and closing of the stomatal pore. They swell when water flows into them (opening the pore) and shrink (closing the pore) to prevent water loss.
Activity 5.2 (Potassium Hydroxide): Placing potassium hydroxide ( $KOH$ ) near a plant absorbs $CO_{2}$ , demonstrating that carbon dioxide is necessary for starch production.
Other Raw Materials for Plants: * Water: Taken up from the soil by roots. * Minerals: Nitrogen, phosphorus, iron, and magnesium. * Nitrogen: Essential for protein synthesis. Used as inorganic nitrates/nitrites or organic compounds prepared by atmospheric bacteria.

Heterotrophic Strategies and Unicellular Nutrition

Nutritive Strategies: * External Breakdown: Fungi (bread moulds, yeast, mushrooms) break down food outside the body and then absorb it. * Internal Breakdown: Animals take in whole materials and digest them internally. * Parasitism: Organisms like Cuscuta (amar-bel), ticks, lice, leeches, and tapeworms derive nutrition without killing the host.
Nutrition in Amoeba: 1. Uses temporary finger-like extensions (pseudopodia) to engulf food. 2. Fuses extensions to form a food-vacuole. 3. Complex food is broken down into simple substances inside the vacuole and diffuses into the cytoplasm. 4. Undigested material is moved to the cell surface and expelled.
Nutrition in Paramoecium: * A unicellular organism with a definite shape. * Food is moved to a specific spot by the movement of cilia that cover the entire cell surface.

Human Digestive System

Alimentary Canal: A long tube from the mouth to the anus.
The Mouth: * Food is crushed by teeth. * Saliva: Produced by salivary glands. It wets food for smooth passage. * Salivary Amylase: An enzyme in saliva that breaks down starch (complex molecule) into simple sugar.
Oesophagus: Transports food to the stomach via peristaltic movements (rhythmic muscle contractions).
The Stomach: * A large muscular organ that expands upon entry of food. * Gastric Glands: Secrete Hydrochloric acid ( $HCl$ ), Pepsin (protein-digesting enzyme), and Mucus. * $HCl$ : Creates an acidic medium to activate pepsin. * Mucus: Protects the stomach lining from acid action. * Sphincter Muscle: Regulates the exit of food from the stomach to the small intestine.
The Small Intestine: * The longest part of the canal, extensively coiled. * Length varies: Herbivores (longer for cellulose digestion), Carnivores (shorter for meat digestion). * Bile Juice (from Liver): Makes food alkaline and emulsifies fats (breaks large globules into smaller ones). * Pancreatic Juice: Contains Trypsin (digests proteins) and Lipase (breaks down emulsified fats). * Intestinal Juice: Final conversion of proteins to amino acids, complex carbohydrates to glucose, and fats to fatty acids and glycerol. * Absorption: The inner lining has villi (finger-like projections) which increase surface area. Villi are richly supplied with blood vessels.
The Large Intestine: Absorbs water from unabsorbed food. The remaining waste is expelled via the anus, regulated by the anal sphincter.
Clinical Note: Dental Caries: Tooth decay caused by bacteria producing acids from sugar. Plaque covers teeth, preventing saliva from neutralizing acid. Brushing removes plaque.

Respiration: Pathways and Mechanism

Glucose Breakdown Pathways: 1. Cytoplasm: Glucose ( $6$ -carbon) $\rightarrow$ Pyruvate ( $3$ -carbon). Common to all pathways. 2. Anaerobic (Yeast): Pyruvate $\rightarrow$ Ethanol + $CO_{2}$ + Energy (takes place in the absence of oxygen). 3. Lack of Oxygen (Human Muscle): Pyruvate $\rightarrow$ Lactic acid + Energy. Build-up causes cramps during sudden activity. 4. Aerobic (Mitochondria): Pyruvate $\rightarrow$ $CO_{2}$ + $H_{2}O$ + Energy (takes place in presence of oxygen). Releases much more energy.
ATP (Adenosine Triphosphate): * The energy currency of the cell. * $ADP + \text{Inorganic Phosphate} + \text{Energy} \rightarrow ATP$ * Breaking the terminal phosphate linkage using water releases $30.5\,kJ/mol$ of energy.
Plant Respiration: * Gas exchange via stomata by diffusion. * Night: No photosynthesis; $CO_{2}$ elimination is the major exchange. * Day: $CO_{2}$ from respiration is used for photosynthesis; $O_{2}$ release is the major event.
Aquatic vs. Terrestrial Animals: * Aquatic: Use dissolved oxygen. Since the concentration of dissolved oxygen is low, the breathing rate is much faster than in terrestrial animals (e.g., fish). * Terrestrial: Breathe atmospheric oxygen. Lungs/respiratory surfaces must be fine and delicate, protected inside the body.
Human Respiratory System: * Nostrils: Air is filtered by fine hairs and mucus. * Throat/Trachea: Contains rings of cartilage to prevent the airway from collapsing. * Alveoli: Balloon-like structures at the end of bronchioles. They provide a massive surface area (approx. $80\,m^{2}$ ) for gas exchange. * Hemoglobin: Respiratory pigment in RBCs with a high affinity for oxygen. Oxygen is carried by hemoglobin; $CO_{2}$ is carried mostly in dissolved form in plasma. * Residual Volume: Air remaining in lungs after exhalation to ensure continuous gas exchange.
Clinical Note: Tobacco and Smoking: Smoking destroys lung cilia, leading to infections and lung cancer. Tobacco chewing is a major cause of oral cancer.

Transportation: Heart and Blood

Blood Composition: * Plasma: Fluid medium; carries food, $CO_{2}$ , and nitrogenous wastes. * Red Blood Corpuscles (RBCs): Carry oxygen. * Platelets: Responsible for blood clotting at injury sites to prevent pressure loss and bleeding.
The Heart: * A muscular organ about the size of a fist. * Chambers: 4 chambers (Left Atrium, Left Ventricle, Right Atrium, Right Ventricle). * Separation: Keeps oxygenated and deoxygenated blood separate, essential for high energy efficiency (needed by birds and mammals for temperature regulation). * Blood Flow: Lungs $\rightarrow$ Left Atrium $\rightarrow$ Left Ventricle $\rightarrow$ Body $\rightarrow$ Right Atrium $\rightarrow$ Right Ventricle $\rightarrow$ Lungs. * Double Circulation: Blood passes through the heart twice per cycle in vertebrates. * Comparison: Fish have a 2-chambered heart; amphibians and reptiles usually have 3-chambered hearts (can tolerate some mixing).
Blood Vessels: * Arteries: Thick, elastic walls. Carry blood away from the heart under high pressure. * Veins: Thin walls, contain valves to prevent backflow. Bring blood back to the heart. * Capillaries: Smallest vessels, one-cell thick, where material exchange between blood and cells occurs.
Blood Pressure: * Systolic Pressure: Pressure during ventricular contraction ( $120\,mm\,Hg$ ). * Diastolic Pressure: Pressure during ventricular relaxation ( $80\,mm\,Hg$ ). * Hypertension: High blood pressure caused by arteriole constriction.
Lymph: Also called tissue fluid. Plasma/proteins/cells escape from capillaries. It is colorless, has less protein, carries digested fat, and drains excess fluid back to the blood.

Transportation in Plants

Need for System: Required when distance between roots (minerals) and leaves (energy) is too large for simple diffusion.
Energy Consumption: Plants have low energy needs due to large amounts of dead tissue and lack of movement.
Xylem (Water Transport): * Consists of vessels and tracheids. * Root Pressure: Active uptake of ions by roots creates a concentration gradient, pushing water into the xylem. Significant at night. * Transpiration Pull: Evaporation of water from leaf stomata creates a suction that pulls water from roots through the xylem. Major driving force during the day.
Phloem (Food Transport): * Translocation: Movement of soluble products of photosynthesis. * Occurs in sieve tubes with companion cells. * Sucrose Transfer: Active process utilizing energy from ATP. * Osmotic Pressure: High osmotic pressure moves material to tissues with lower pressure (e.g., sugar moving to buds in spring).

Excretion: Human and Plant Systems

Human Excretory System: * Organs: Pair of kidneys (in abdomen), pair of ureters, urinary bladder, urethra. * Nephron: Basic filtration unit. * Mechanism: 1. Blood enters capillary clusters in Bowman's capsule. 2. Initial Filtrate: Contains glucose, amino acids, salts, and large volume of water (approx. $180\,L$ daily). 3. Selective Re-absorption: Essential materials and most water are re-absorbed as filtrate moves through the tubule. 4. Urine Formation: Only $1$ to $2\,L$ is actually excreted daily. 5. Regulation: Re-absorption depends on body water levels and waste concentration. * Hemodialysis (Artificial Kidney): Used in kidney failure. Blood passes through semi-permeable tubes in dialysing fluid to remove nitrogenous waste. Unlike natural kidneys, there is no re-absorption step.
Excretion in Plants: * Oxygen: Released during photosynthesis. * Transpiration: Removes excess water. * Storage: Wastes stored in cell vacuoles, leaves (which fall off), or as resins/gums in old xylem. * Direct Excretion: Some wastes are excreted into the soil around the roots.

Questions & Discussion

Q: Why is diffusion insufficient for oxygen in humans? * A: In multi-cellular organisms, most cells are far from the environment. Diffusion is too slow; oxygen would take 3 years to reach the toes from the lungs without hemoglobin.
Q: What materials are used from the outside? * A: Food (carbon sources), Oxygen, Water, and Minerals (Nitrogen, Phosphorus, etc.).
Q: How are lungs designed for gas exchange? * A: Lungs contain alveoli which provide a large, thin, blood-vessel-rich surface area for efficient diffusion.
Q: Why separate oxygenated and deoxygenated blood? * A: It provides a highly efficient oxygen supply, necessary for maintaining constant body temperature in mammals and birds.
Q: What is organ donation? * A: A generous act of donating organs (kidneys, liver, heart, etc.) from a living or deceased (often brain-dead) donor to a recipient in need.