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Living Organisms and Life Processes

Cell Structure and Organization​

1. Cell Theory​

Fundamental Principles:

  • All living organisms composed of cells
  • Cell is basic unit of life
  • All cells come from pre-existing cells
  • Cells can be unicellular or multicellular organizations

2. Prokaryotic Cells (प्रोकैरियोटिक कोशिका)​

Characteristics:

  • No membrane-bound nucleus
  • Simpler structure
  • Smaller (0.5-5 μm)
  • Example: Bacteria, archaea

Components:

  • Cell wall (peptidoglycan in bacteria)
  • Cell membrane
  • Cytoplasm
  • Ribosomes (70S)
  • Nucleoid (not nucleus, just DNA region)
  • No membrane-bound organelles

3. Eukaryotic Cells (यूकैरियोटिक कोशिका)​

Characteristics:

  • Membrane-bound nucleus
  • Complex structure
  • Larger (10-100 μm)
  • Examples: Animals, plants, fungi

Animal Cell Components:

Nucleus (केंद्रक):

  • Double membrane (nuclear envelope)
  • Contains genetic material (DNA)
  • Nuclear pores allow transport
  • Nucleolus for ribosome production

Mitochondria (माइटोकॉन्ड्रिया):

  • "Power house of cell"
  • Double membrane structure
  • Inner membrane folded (cristae)
  • Site of aerobic respiration
  • Produces ATP (energy)

Ribosomes:

  • 80S (eukaryotic)
  • Protein synthesis
  • Free or attached to ER

Endoplasmic Reticulum (ER):

  • Rough ER: With ribosomes, synthesizes proteins
  • Smooth ER: No ribosomes, synthesizes lipids, detoxification

Golgi Apparatus:

  • Modifies and packages proteins
  • Creates vesicles for transport

Lysosomes:

  • Contain digestive enzymes
  • Break down waste materials
  • Cellular digestion

Cytoplasm:

  • Gel-like substance
  • Contains organelles
  • Site of chemical reactions

Cell Membrane (कोशिका झिल्ली):

  • Phospholipid bilayer
  • Selectively permeable
  • Controls entry/exit of substances

Centrioles:

  • Organize spindle fibers during division
  • Absent in plant cells

Plant Cell Special Components:

Cell Wall:

  • Cellulose (not in animal cells)
  • Outside cell membrane
  • Protects and supports
  • Permits plasmolysis/deplasmolysis

Vacuole (बड़ी केंद्रीय रिक्तिका):

  • Large central vacuole
  • Stores water, minerals, waste
  • Maintains turgor pressure
  • Occupies 90% of cell volume

Chloroplasts (हरितलवक):

  • Double membrane
  • Inner membrane (thylakoids) and stroma
  • Contains chlorophyll (photosynthesis)
  • Produces glucose

Plasmodesmata:

  • Connections between plant cells
  • Allows cytoplasm to flow
  • Communication and transport

Life Processes​

1. Seven Life Processes (जीवन प्रक्रियाएं)​

Movement (गति):

  • Change in position
  • Locomotion in animals
  • Growth toward light in plants (phototropism)

Respiration (श्वसन):

  • Release of energy from food
  • Required for all life activities
  • Aerobic (with O₂) or anaerobic (without O₂)

Reproduction (प्रजनन):

  • Producing offspring
  • Sexual (two parents, variation) or asexual (one parent, clone)

Response/Sensitivity (संवेदनशीलता):

  • React to stimuli
  • Nerves in animals
  • Hormones in plants
  • Examples: Moving away from danger, plants growing toward light

Growth (वृद्धि):

  • Increase in size and complexity
  • Due to cell division and metabolic activity
  • Continues until maturity

Homeostasis (होमोस्टैसिस):

  • Maintain stable internal environment
  • Regulate temperature, pH, water
  • Negative feedback mechanisms

Excretion (उत्सर्जन):

  • Remove metabolic waste
  • CO₂, urea, water, salts
  • Kidneys, lungs, skin in animals

2. Types of Nutrition​

Autotrophic Nutrition (स्वपोषी):

  • Produce own nutrients
  • Use inorganic materials (CO₂, water) + energy
  • Photosynthesis: Plants use light energy
  • Chemosynthesis: Bacteria use chemical energy

Heterotrophic Nutrition (परपोषी):

  • Consume organic food produced by others
  • Holozoic: Ingest food (animals)
  • Saprophytic: Break down dead organic matter (fungi, decomposers)
  • Parasitic: Feed on living host

Respiration​

1. Aerobic Respiration (वायवीय श्वसन)​

Definition:

  • Breakdown of glucose using oxygen
  • Releases large amount of energy (36-38 ATP)
  • Occurs in mitochondria

Equation:

  • C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (2830 kJ)

Stages:

Glycolysis (in cytoplasm):

  • Glucose (6C) split into 2 pyruvate (3C)
  • Small energy release (2 ATP)
  • Produces NADH

Krebs Cycle (in mitochondrial matrix):

  • Pyruvate converted to Acetyl-CoA
  • Complete oxidation of glucose
  • Releases CO₂
  • Produces NADH and FADH₂

Electron Transport Chain (in inner mitochondrial membrane):

  • NADH and FADH₂ oxidized
  • Large ATP production (34 ATP)
  • Oxygen is final electron acceptor
  • Water produced

2. Anaerobic Respiration (अवायवीय श्वसन)​

Definition:

  • Breakdown of glucose without oxygen
  • Small energy release (2 ATP)
  • In cytoplasm

Products:

  • Animals/Muscles: Glucose → Lactate (lactic acid)

    • During intense exercise
    • Lactate causes muscle fatigue/soreness

  • Yeast/Plants: Glucose → Ethanol + CO₂

    • Fermentation
    • Used in bread making, brewing

Equation (Animals):

  • C₆H₁₂O₆ → 2C₃H₆O₃ (lactic acid) + Energy (120 kJ)

Equation (Yeast):

  • C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + Energy (120 kJ)

3. Respiration vs. Photosynthesis​

FeatureRespirationPhotosynthesis
EnergyReleaseAbsorb
EquationC₆H₁₂O₆ + O₂ → CO₂ + H₂O6CO₂ + 6H₂O → C₆H₁₂O₆ + O₂
LocationMitochondriaChloroplasts
TypeCatabolicAnabolic
All organismsYesOnly autotrophs

Photosynthesis​

1. Definition and Importance​

Photosynthesis:

  • Plants convert light energy to chemical energy
  • Produces glucose and oxygen
  • Foundation of most food chains

Equation:

  • 6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ + 6O₂

2. Light-Dependent Reactions (प्रकाश-आश्रित अभिक्रिया)​

Location: Thylakoid membranes

Process:

  • Chlorophyll absorbs light energy
  • Water molecules split (photolysis): 2H₂O → 4H⁺ + O₂ + 4e⁻
  • Electrons energized
  • Electron transport chain pumps H⁺
  • Energy produces ATP
  • NADP⁺ reduced to NADPH

Products:

  • ATP (energy)
  • NADPH (reducing agent)
  • Oxygen (by-product)

3. Light-Independent (Dark) Reactions (प्रकाश-स्वतंत्र अभिक्रिया)​

Location: Stroma

Calvin Cycle:

  1. Carbon Fixation: CO₂ + RuBP → 3-PGA (uses RuBisCO enzyme)
  2. Reduction: 3-PGA → G3P (uses ATP and NADPH)
  3. RuBP Regeneration: G3P → RuBP (uses ATP)
  4. Glucose Synthesis: Some G3P exits cycle to form glucose

Requirements:

  • ATP from light reactions
  • NADPH from light reactions
  • Can occur in darkness (but needs products from light reactions)

4. Factors Affecting Photosynthesis​

Light Intensity:

  • Increases up to saturation point
  • Beyond that, other factors limiting
  • At 0 light: No photosynthesis (compensation point lower)

Temperature:

  • Optimal around 25°C
  • Enzyme dependent
  • Too high: Enzymes denature
  • Too low: Reactions slow

Carbon Dioxide Concentration:

  • Limiting factor at normal atmosphere levels
  • More CO₂ increases photosynthesis (until saturated)
  • Below compensation point: Cellular respiration > photosynthesis

Compensation Point:

  • Light intensity where photosynthesis = respiration
  • No net gas exchange
  • Varies with plant species and temperature

Gas Exchange​

1. Respiration and Gas Exchange​

Oxygen Uptake, CO₂ Release:

  • Required for aerobic respiration
  • Gas exchange surfaces provide area

2. Photosynthesis and Gas Exchange​

CO₂ Uptake, Oxygen Release:

  • Needed for photosynthesis
  • Stomata control gas exchange

3. Gas Exchange Surfaces​

Plants:

  • Stomata: Small pores on leaves

    • Guard cells control opening/closing
    • Opened by day (photosynthesis, transpiration)
    • Closed at night (reduce water loss)
    • CO₂ enters, O₂ exits

  • Mesophyll: Spongy tissue with air spaces

    • Large surface area
    • All cells in contact with air
    • Diffusion over short distances

Insects:

  • Tracheal System: Tubes (tracheae)
    • Bring air directly to cells
    • ≥Tracheal fluid for diffusion
    • No blood transport of gases

Fish:

  • Gills: Thin membranes
    • Counter-current flow with water
    • Oxygen extracted from water
    • Very efficient

Mammals:

  • Lungs: Large surface area
    • Alveoli (tiny air sacs)
    • Thin epithelium (1 cell thick)
    • Capillaries for blood transport
    • Diaphragm aids ventilation

Summary​

Living organisms characterized by:

  • Cell Structure: Basic unit of life
  • Life Processes: Movement, respiration, growth, reproduction, etc.
  • Nutrition: Autotrophic (produce own) or heterotrophic (consume food)
  • Respiration: Release energy from food
  • Photosynthesis: Convert light to chemical energy
  • Gas Exchange: Obtain O₂ and release CO₂

These processes fundamental to all life on Earth.