Comprehensive Study Guide: Life Processes (Science Class X)

Definition and Identification of Life

Criteria for Being Alive: * Common indicators include visible movements such as a dog running, a cow chewing cud, or a human shouting. * Organisms are still considered alive even when asleep; evidence includes the process of breathing or growth over time. * Visible movement alone is insufficient as a defining characteristic. For example, plants may not show visible growth but are still alive, and some animals breathe without noticeable body movement.
Molecular Movement: * Life requires movements on a very small scale, specifically invisible molecular movements. * Professional biologists consider these invisible movements necessary for life. * The Virus Controversy: Viruses do not exhibit molecular movement until they infect a cell, leading to a debate over whether they are truly alive.
Biological Organization and Maintenance: * Living organisms are well-organized structures consisting of tissues, cells, and smaller cellular components. * Environmental effects tend to break down this ordered nature over time. * If biological order breaks down, the organism dies; therefore, organisms must constantly perform repair and maintenance. * Maintenance requires moving molecules because all biological structures are molecule-based.

Overview of Life Processes

Definition: Life processes are the collective functions that perform the job of maintaining the organism's body, even when the organism is inactive or asleep.
Energy Requirements: * Maintenance requires energy to prevent damage and breakdown. * Energy must come from outside the body in the form of a source called food. * Nutrition: The process of transferring an external energy source (food) to the inside of the organism.
Chemical Complexity and Carbon Basis: * Life on Earth is dependent on carbon-based molecules. Most food sources are carbon-based. * External energy sources are varied and must be broken down or built up into a uniform energy source for molecular maintenance and growth. * Oxidizing-Reducing Reactions: These are common chemical means to break down molecules.
Respiration: The process of acquiring oxygen from outside the body to break down food sources for cellular needs.
Body Design and Complexity: * Single-celled Organisms: No specific organs are needed for food intake, gas exchange, or waste removal because the entire surface is in contact with the environment. * Multi-cellular Organisms: Simple diffusion is insufficient because not all cells are in contact with the environment. This necessitates specialized tissues for nutrition, oxygen uptake, and transportation systems.
Excretion: The process of removing harmful or useless chemical by-products (generated from carbon and oxygen use) from the body. Specialized tissues and transportation systems are developed for this purpose in complex organisms.

Nutrition

General Needs: Energy is required to maintain a state of order and to provide raw materials for growth, development, and the synthesis of proteins.
Modes of Nutrition: * Autotrophs: Organisms that utilize simple food material from inorganic sources like carbon dioxide ( $CO_2$ ) and water ( $H_2O$ ). Examples include green plants and some bacteria. * Heterotrophs: Organisms that utilize complex substances which must be broken down by bio-catalysts called enzymes. Their survival depends directly or indirectly on autotrophs. Examples include animals and fungi.

Autotrophic Nutrition and Photosynthesis

Process of Photosynthesis: Autotrophs take in external substances and convert them into stored energy. $CO_2$ and $H_2O$ are converted into carbohydrates in the presence of sunlight and chlorophyll.
Energy Storage: * Carbohydrates provide immediate energy. * Unused carbohydrates are stored as starch in plants. * In humans, energy is stored in the form of glycogen.
Steps of 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. * Note: These steps may not happen sequentially. Desert plants take up $CO_2$ at night to form an intermediate that is acted upon by light energy during the day.
Organelles: Chloroplasts are the green dot-like cell organelles containing chlorophyll.
Gas Exchange and Stomata: * Stomata are tiny pores on leaf surfaces for gas exchange. * Gases also exchange across stems, roots, and leaves. * Guard Cells: Regulate the opening and closing of stomatal pores. They swell when water flows in (opening the pore) and shrink (closing the pore) to prevent water loss.
Raw Materials for Building the Body: * Water: Taken from soil by roots. * Nitrogen: Essential for protein synthesis; taken as inorganic nitrates, nitrites, or organic compounds prepared by bacteria. * Other Minerals: Phosphorus ( $P$ ), Iron ( $Fe$ ), and Magnesium ( $Mg$ ).

Heterotrophic Nutrition Strategies

External Breakdown: Fungi (bread moulds, yeast, mushrooms) break down food outside the body before absorption.
Internal Breakdown: Animals take in whole material and break it down inside.
Parasitic Strategy: Deriving nutrition from a host without killing it. Examples: Cuscuta (amar-bel), ticks, lice, leeches, and tape-worms.
Unicellular Digestion: * Amoeba: Uses temporary finger-like extensions (pseudopodia) to form a food-vacuole. Complex substances are broken down and diffuse into the cytoplasm; results are thrown out of the cell surface. * Paramoecium: Has a definite shape; food is moved to a specific spot by cilia.

Human Alimentary Canal and Digestion

Mouth: * Teeth crush food to a uniform texture. * Saliva: Secreted by salivary glands; wets food and contains salivary amylase, which breaks down starch into simple sugar. * Tongue: Moves food for thorough mixing.
Oesophagus: Moves food to the stomach via peristaltic movements (rhythmic muscle contractions).
Stomach: * A large muscular organ that expands when food enters. * Gastric Glands: Release Hydrochloric acid ( $HCl$ ), pepsin (protein-digesting enzyme), and mucus. * $HCl$ creates an acidic medium for pepsin. * Mucus: Protects the stomach lining from acid. * Sphincter Muscle: Regulates the release of small amounts of food into the small intestine.
Small Intestine: * Longest part of the canal, extensively coiled. * Length varies: Herbivores (longer for cellulose digestion) vs. Carnivores (shorter for meat). * Liver: Secretes bile juice (makes food alkaline, salts emulsify fat globules). * Pancreas: Secretes pancreatic juice containing trypsin (protein digestion) and lipase (breaks down emulsified fats). * Intestinal Juice: Converts proteins to amino acids, complex carbohydrates to glucose, and fats to fatty acids and glycerol. * Villi: Finger-like projections that increase surface area for absorption; rich in blood vessels to transport food to cells.
Large Intestine and Anus: * Absorbs water from unabsorbed food. * Waste is removed via the anus, regulated by the anal sphincter.

Dental Caries (Tooth Decay)

Softening of enamel and dentine caused by bacterial acid production from sugars.
Dental Plaque: Bacterial masses and food particles that cover teeth, preventing saliva from neutralizing acid.
If untreated, bacteria can invade the pulp, causing infection.

Respiration Pathways

Cellular Respiration: Use of food to provide energy in cells.
Glycolysis: The first step in all cases; breakdown of glucose (6-carbon) into pyruvate (3-carbon) in the cytoplasm.
Anaerobic Respiration (No Oxygen): * In yeast (Fermentation): Pyruvate converts to ethanol and carbon dioxide. * In Muscle Cells (Lack of oxygen): Pyruvate converts to lactic acid (3-carbon), which causes cramps during sudden activity.
Aerobic Respiration (With Oxygen): * Occurs in the mitochondria. Pyruvate breaks down into three molecules of carbon dioxide and water. * Releases significantly more energy than anaerobic respiration.
ATP (Adenosine Triphosphate): * The energy currency for cellular processes. * Synthesized from $ADP$ and inorganic phosphate. * Energy release: Breaking the terminal phosphate linkage using water releases $30.5\,kJ\,mol^{-1}$ .

Human Respiratory System

Anatomy: * Nostrils: Filter air with fine hairs and mucus. * Throat: Contains rings of cartilage to keep the air passage from collapsing. * Lungs: Passages divide into smaller tubes terminating in alveoli (balloon-like structures).
Gas Exchange Mechanism: * Alveoli provide an extensive surface for gas exchange and are covered in blood vessels. * Inhalation: Ribs lift, diaphragm flattens, chest cavity expands, and air is sucked into lungs. * Residual Volume: Lungs always retain some air to ensure time for oxygen absorption and carbon dioxide release.
Respiratory Pigment: * Haemoglobin: Found in red blood corpuscles; has a high affinity for oxygen. * Carbon dioxide is more water-soluble and is mostly transported in dissolved form in the blood.
Interests and Hazards: * Smoking destroys cilia in the upper respiratory tract, leading to infection and lung cancer. * Alveolar surface area is approximately $80\,m^2$ . * Without haemoglobin, it would take 3 years for oxygen to diffuse from lungs to toes.

Respiration in Other Organisms

Plants: Exchange gases via stomata and diffusion. At night, $CO_2$ elimination is the major activity. During the day, $CO_2$ is reused for photosynthesis, and $O_2$ release is the major event.
Aquatic Organisms: Use dissolved oxygen. Because dissolved $O_2$ is lower than atmospheric $O_2$ , the breathing rate in fish is much faster than in terrestrial animals. Fish force water past gills for oxygen uptake.
Terrestrial Organisms: Use atmospheric oxygen through specialized organs with high surface area.

Human Transportation: The Circulatory System

Blood: A fluid connective tissue consisting of plasma (transports food, $CO_2$ , nitrogenous wastes, salts) and red blood corpuscles (transport Oxygen).
The Heart: * A muscular organ the size of a fist. * Four chambers: To separate oxygenated and de-oxygenated blood. * Path of Blood: 1. Oxygen-rich blood from lungs $\rightarrow$ Left Atrium (relaxes) $\rightarrow$ Left Ventricle (contracts) $\rightarrow$ Body. 2. De-oxygenated blood from body $\rightarrow$ Right Atrium (relaxes) $\rightarrow$ Right Ventricle (contracts) $\rightarrow$ Lungs. * Ventricles: Have thicker muscular walls than atria because they pump blood to organs. * Valves: Prevent backflow of blood.
Double Circulation: Blood goes through the heart twice during one cycle passage through the body (present in mammals/birds).
Circulation in Other Vertebrates: * Amphibians/Reptiles: 3-chambered hearts; tolerate some mixing of blood; body temperature varies with environment. * Fishes: 2-chambered hearts; single circulation (heart $\rightarrow$ gills $\rightarrow$ body).

Blood Vessels and Pressure

Arteries: Carry blood away from the heart; thick, elastic walls; high pressure.
Veins: Collect blood and bring it back to the heart; thin walls; contain valves to ensure one-way flow.
Capillaries: Smallest vessels, walls are one-cell thick; site of material exchange.
Blood Pressure: * Force exerted against vessel walls; measured with a sphygmomanometer. * Systolic Pressure: Contraction phase ( $\sim 120\,mm \text{ of Hg}$ ). * Diastolic Pressure: Relaxation phase ( $\sim 80\,mm \text{ of Hg}$ ). * Hypertension: High blood pressure caused by constriction of arterioles.
Platelets: Cells that circulate in the blood to plug leaks and clot blood at injury sites.
Lymph (Tissue Fluid): * Formed from plasma, proteins, and cells escaping capillaries into intercellular spaces. * Colourless, contains less protein than plasma. * Carries digested fat and drains excess fluid back into the blood.

Transportation in Plants

Energy Needs: Plants have low energy needs because they do not move and have many dead cells.
Xylem: Moves water and minerals from soil (roots) to the rest of the plant. * Root Pressure: Result of active ion uptake in roots creating a concentration difference. * Transpiration: The loss of water as vapour from aerial parts. It creates a suction (transpiration pull) that moves water upward during the day and helps in temperature regulation.
Phloem: Transports products of photosynthesis (translocation) from leaves to storage organs (roots, fruits, seeds) and growing organs. * Translocation involves sieve tubes and companion cells. * It requires energy (ATP). * Materials like sucrose are transferred using energy, which increases osmotic pressure and moves material to lower pressure tissues.

Excretion in Human Beings

Excretory System: Consists of a pair of kidneys, a pair of ureters, a urinary bladder, and a urethra.
Kidneys: Located in the abdomen on either side of the backbone. Filters nitrogenous waste (urea, uric acid) from blood.
Nephron: The basic filtration unit. * Bowman’s Capsule: Cup-shaped end of a coiled tube that collects filtrate from capillary clusters (glomerulus). * Selective Re-absorption: Glucose, amino acids, salts, and water are re-absorbed as filtrate flows through the tube. * Initial filtrate volume: Roughly $180\,L$ daily; actual urine excreted: $1\text{--}2\,L$ daily.
Urinary Bladder: Muscular organ under nervous control that stores urine.

Artificial Kidney and Organ Donation

Hemodialysis: Using an artificial kidney to remove nitrogenous waste when kidneys fail. It uses semi-permeable tubes in dialysing fluid. Unlike real kidneys, there is no re-absorption.
Organ Donation: A generous act to help persons with organ failure. Can involve corneas, kidneys, heart, liver, pancreas, lungs, intestines, and bone marrow. Donors can be living or deceased (brain dead).

Excretion in Plants

Oxygen: Released as a waste product of photosynthesis.
Water: Excess water removed via transpiration.
Tissue Usage: Plants use dead cells; some wastes are stored in leaves that fall off.
Storage: Waste products are stored in cellular vacuoles, or as resins and gums in old xylem.
Soil: Some waste products are excreted into the soil surrounding the roots.

Questions & Discussion

Why is diffusion insufficient for multi-cellular organisms? In large organisms like humans, not all cells are in direct contact with the environment; diffusion is too slow to reach all parts (e.g., oxygen reaching the toes).
What criteria decide if something is alive? Various types of movement, including growth-related and invisible molecular movements.
What are outside raw materials used for? Energy (food), growth (carbon-based sources), and building body structures (minerals like nitrogen).
Essential life processes? Nutrition, respiration, transportation, and excretion.
Role of acid in stomach? Creates an acidic medium for pepsin action and potentially kills microbes.
Function of digestive enzymes? Act as bio-catalysts to break complex food molecules into simpler, absorbable ones.
Small intestine design for absorption? Extensive coiling for length and villi to increase surface area for maximum absorption.
Difference between autotrophic and heterotrophic nutrition? Autotrophs synthesize food from inorganic sources; heterotrophs consume food produced by others.
Where do plants get raw materials? $CO_2$ from air; water and minerals ( $N, P, Fe, Mg$ ) from soil.
Ways glucose is oxidized? Aerobically (with $O_2$ in mitochondria) and anaerobically (without $O_2$ in cytoplasm/yeast or muscles).
Haemoglobin deficiency consequences? Reduced oxygen-carrying capacity leading to fatigue and inefficient energy production.
Comparison of Alveoli and Nephrons? Alveoli provide surface area for gas exchange in lungs; nephrons provide surface area for filtration and re-absorption in kidneys.