Chapter 22: Life Processes - Vardaan Class Notes

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1. Fundamentals of Life Processes

The 4 Vital Life Processes

Nutrition: Process of intake and utilization of nutrients to obtain energy and raw materials for body repair.
Respiration: Biochemical catabolism of glucose inside cells to liberate energy in the form of ATP.
Transportation: Internal transit of oxygen, nutrients, water, and metabolic wastes between organs.
Excretion: Removal of toxic nitrogenous metabolic wastes (urea, uric acid) from the body.

2. Nutrition: Modes and Mechanisms

Feature	Autotrophic Nutrition	Heterotrophic Nutrition
Carbon Source	Inorganic $\mathrm{CO_2}$ and $\mathrm{H_2O}$.	Complex organic food from other organisms.
Chlorophyll	Present (essential for trapping sunlight).	Absent.
Examples	Green plants, Cyanobacteria (blue-green algae).	Animals, Fungi (moulds, yeasts), Protozoa.

A. Photosynthesis & Stomatal Mechanism

Photosynthesis Balanced Equation:

$$6\mathrm{CO_2} + 12\mathrm{H_2O} \;\underset{\text{Sunlight}}{\overset{\text{Chlorophyll}}{\longrightarrow}}\; \mathrm{C_6H_{12}O_6} + 6\mathrm{O_2} + 6\mathrm{H_2O}$$

3 Sequential Events of Photosynthesis

Absorption: Chlorophyll traps solar light energy in chloroplasts.
Photolysis of Water: Water is split into protons, electrons, and oxygen ($2\mathrm{H_2O} \rightarrow 4\mathrm{H^+} + 4\mathrm{e^-} + \mathrm{O_2}\uparrow$). All oxygen liberated originates from water, NOT carbon dioxide.
Reduction: Hydrogen reduces $\mathrm{CO_2}$ to form glucose ($\mathrm{C_6H_{12}O_6}$), stored as starch in plants.

Figure 22.1: Stomatal Pore — Open (Turgid Guard Cells) vs Closed (Flaccid Guard Cells)

Stomatal Guard Cell Mechanism

Opening (Turgid State): Water enters guard cells $\rightarrow$ cells swell $\rightarrow$ thin outer walls bulge outward $\rightarrow$ thick inner walls pull apart $\rightarrow$ pore opens.
Closing (Flaccid State): Water leaves guard cells $\rightarrow$ cells shrink $\rightarrow$ thick inner walls straighten back $\rightarrow$ pore closes.
Desert Plants: Stomata open at night to absorb $\mathrm{CO_2}$ (stored as malic acid) to prevent water loss during the day.

B. Nutrition in Amoeba

Figure 22.2: Stages of Phagocytosis and Intracellular Digestion in Amoeba

5 Stages of Holozoic Nutrition in Amoeba

Ingestion: Amoeba projects finger-like pseudopodia around the food particle to form a food vacuole.
Digestion: Lysosomal digestive enzymes break complex food into soluble substances inside the vacuole.
Absorption: Digested nutrients diffuse directly from the food vacuole into the cytoplasm.
Assimilation: Absorbed food is utilized for energy release and growth.
Egestion: The undigested residue is moved to the cell membrane surface, which ruptures to cast it outside.

C. Human Digestive System

Figure 22.3: Anatomical Layout of the Human Alimentary Canal and Glands

Organ / Gland	Enzyme / Secretion	Direct Biochemical Action
Mouth	Salivary Amylase (Ptyalin)	Starch $\rightarrow$ Maltose ($\text{pH} \approx 6.8$).
Stomach	$\mathrm{HCl}$	Acidifies chyme ($\text{pH} 1.5-2.5$), activates pepsinogen to pepsin, kills microbes.
	Pepsin	Proteins $\rightarrow$ Peptones (active in acidic medium).
	Mucus	Shields stomach wall from excoriation by $\mathrm{HCl}$.
Liver	Bile Juice (No enzymes)	Emulsification: Breaks large fat globules into tiny droplets; provides alkaline medium.
Pancreas	Trypsin	Proteins/peptones $\rightarrow$ Peptides (active in alkaline medium).
Pancreas	Pancreatic Lipase	Emulsified fats $\rightarrow$ Fatty Acids + Glycerol.
Small Intestine	Villi & Intestinal Enzymes	Villi maximize absorptive surface area; blood capillaries absorb glucose and amino acids; lacteals absorb fats.

3. Respiration: Pathways and Human Respiratory Tract

Breakdown of Glucose by Various Pathways

Figure 22.4: The Three Major Metabolic Fates of Pyruvate

Summary of Pyruvate Breakdown

Initial Step (in Cytoplasm): 1 Glucose (6-C) $\xrightarrow{\text{Glycolysis}}$ 2 Pyruvate (3-C) + 2 ATP.

1. Yeast (Fermentation): Absence of $\mathrm{O_2} \rightarrow$ Ethanol + $\mathrm{CO_2}$ + 2 ATP.
2. Human Muscle Cells: Lack of $\mathrm{O_2}$ during vigorous sprint $\rightarrow$ Lactic Acid + 2 ATP. (Lactic acid accumulation causes muscle cramps!)
3. Mitochondria (Aerobic): Presence of $\mathrm{O_2} \rightarrow$ $6\mathrm{CO_2} + 6\mathrm{H_2O} + 36-38\text{ ATP}$.

Figure 22.5: Structural Anatomy of the Human Respiratory Tract and Alveoli

Respiratory Tract Features & Breathing Mechanics

Tracheal C-Rings: C-shaped hyaline cartilage rings keep the windpipe permanently open and prevent airway collapse under negative thoracic pressure.
Alveoli: Thin-walled balloon sacs wrapped in capillaries. Vast surface area ($\approx 80\,\text{m}^2$) allows rapid diffusion of $\mathrm{O_2}$ and $\mathrm{CO_2}$.
Inhalation: Diaphragm contracts and flattens; rib cage moves upward and outward $\rightarrow$ Thoracic volume increases $\rightarrow$ Air pressure drops $\rightarrow$ Air rushes into lungs.
Exhalation: Diaphragm relaxes into its upward dome shape; rib cage moves downward and inward $\rightarrow$ Thoracic volume decreases $\rightarrow$ Air forced out.
Hemoglobin ($\mathrm{Hb}$): Respiratory pigment in RBCs with high chemical affinity for $\mathrm{O_2}$. $\mathrm{CO_2}$ is transported mainly dissolved in plasma as bicarbonate ions.

4. Transportation in Animals and Plants

Figure 22.6: Sectional View and Four-Chambered Anatomy of the Human Heart

Cardiac Anatomy & Mechanics

Four Chambers: Right Atrium and Right Ventricle handle deoxygenated blood; Left Atrium and Left Ventricle handle oxygenated blood.
Interventricular Septum: Completely separates oxygenated and deoxygenated blood, preventing mixing and maintaining the high metabolic efficiency needed for warm-blooded homeothermy ($37^\circ\text{C}$).
Ventricular Wall Thickness: Ventricles have significantly thicker muscular walls than atria because they must pump blood under high pressure across distant systemic organs and lungs.
Valves: Tricuspid and Bicuspid/Mitral valves prevent backflow of blood into atria during ventricular contraction.

Schematic Representation of Transport Double Circulation

Figure 22.7: Complete Circuit of Double Circulation in Humans

Double Circulation Pathways

Pulmonary Circuit: Right Ventricle $\rightarrow$ Pulmonary Artery $\rightarrow$ Lungs (Oxygenated) $\rightarrow$ Pulmonary Veins $\rightarrow$ Left Atrium.
Systemic Circuit: Left Ventricle $\rightarrow$ Aorta $\rightarrow$ Body Tissues $\rightarrow$ Vena Cava $\rightarrow$ Right Atrium.

Feature	Arteries	Veins
Direction of Flow	Carry blood away from heart.	Carry blood towards heart.
Nature of Blood	Oxygenated (Except Pulmonary Artery).	Deoxygenated (Except Pulmonary Vein).
Walls & Valves	Thick, elastic walls; No valves.	Thin walls; Valves present to prevent backflow.

Vascular Transport in Plants: Xylem vs. Phloem

Xylem: Transports water and minerals unidirectionally (roots $\rightarrow$ leaves) through dead tracheids and vessels. Driven by physical forces: Root Pressure (dominant at night) and Transpiration Pull (dominant daytime suction). Consumes NO ATP.
Phloem: Transports synthesized sucrose and amino acids bidirectionally from source leaves to sinks through living sieve tubes and companion cells (Translocation). Driven actively using ATP to build osmotic pressure.

5. Excretion and Osmoregulation

Figure 22.8: Gross Anatomical Architecture of the Human Excretory System

Organs of Excretion

Kidneys: Pair of bean-shaped organs in the abdomen that filter nitrogenous wastes from blood.
Ureters: Pair of tubes conducting urine from kidneys to the urinary bladder.
Urinary Bladder: Muscular reservoir storing urine until micturition.
Urethra: Terminal canal expelling urine out of the body.

Figure 22.9: Microscopic Functional Structure of a Nephron

The 3 Steps of Urine Formation in Nephrons

Glomerular Ultrafiltration: High pressure forces water, glucose, amino acids, urea, and salts from the Glomerulus into Bowman's Capsule. Initial filtrate = $180\,\text{L/day}$!
Selective Tubular Reabsorption: Along PCT and Henle's Loop, all glucose, amino acids, and $99\%$ of water are reabsorbed into surrounding capillaries. Excreted urine volume = only $1.5 - 2\,\text{L/day}$!
Tubular Secretion: Surplus $\mathrm{H^+}$, $\mathrm{K^+}$, and ammonium ions are actively secreted into the tubule to regulate blood $\text{pH}$ and electrolyte balance.

Hemodialysis (Artificial Kidney): Removes toxic urea across semi-permeable cellophane tubes into dialyzing fluid by diffusion. Unlike natural kidneys, hemodialysis performs NO selective reabsorption.

Excretion in Plants

Gaseous Wastes: Excess $\mathrm{O_2}$ and $\mathrm{CO_2}$ diffuse through stomata and lenticels.
Excess Water: Eliminated via transpiration.
Solid & Soluble Wastes: Stored in cellular vacuoles, shedding aging leaves, dead bark, and as gums and resins in old non-functional xylem.

6. Important Review Questions & Model Answers

Question 1: Why is the breathing rate of aquatic animals much faster than terrestrial animals?

Model Answer: Terrestrial organisms breathe atmospheric air containing approximately $21\%$ oxygen. Aquatic organisms extract dissolved oxygen from water, where solubility of oxygen is very low. To acquire enough oxygen for cellular metabolism, aquatic organisms (like fish) must pump water across their gills much more rapidly, resulting in a significantly faster breathing rate.

Question 2: Why do ventricles have thicker muscular walls than atria?

Model Answer: Atria only receive blood and push it down into adjacent ventricles under low pressure. Ventricles must contract with high force to pump blood across great distances against high resistance: the right ventricle to the lungs, and the left ventricle to the entire systemic body. The thicker muscular myocardium prevents ventricular rupture under high hydrostatic pressure.

Question 3: What causes muscle cramps during severe sprinting?

Model Answer: During sudden vigorous exercise, cellular oxygen demand exceeds cardiovascular delivery. Muscle cells switch temporarily to anaerobic glycolysis, converting pyruvate into lactic acid. Accumulation of lactic acid in muscle fibers produces acute fatigue and cramps.

Question 4: What is the role of Bile Juice if it contains no digestive enzymes?

Model Answer: (1) Emulsification of Fats: Bile salts mechanically break large fat globules into minute droplets, vastly multiplying the surface area for pancreatic lipase to act. (2) Alkaline Medium: Contains sodium bicarbonates that neutralize acidic gastric chyme, creating the alkaline $\text{pH}$ ($\approx 7.8-8.4$) required for pancreatic enzymes (trypsin and lipase) to function.

Question 5: How do plants excrete their waste products?

Model Answer: (1) Gaseous wastes ($\mathrm{O_2, CO_2}$) diffuse through stomata and lenticels. (2) Excess water is eliminated through transpiration. (3) Wastes are stored in central vacuoles of cells. (4) Wastes accumulate in aging leaves and dead bark that are periodically shed. (5) Insoluble gums and resins are sequestered inside old, non-conducting xylem vessels.