Living Organisms and Life Processes

Introduction to Living Organisms

1. Characteristics of Living Organisms

Key Features of Life:

Organization:

• Complex, orderly structure
• Cells as basic unit (all living things made of cells)
• Multicellular organisms organized into tissues, organs, systems
• Organization increases complexity from cells to organism

Response to Stimuli (निर्दय उत्तेजना - Responsiveness):

• React to environmental changes
• Detect temperature, light, touch, chemicals
• Nervous system mediates immediate responses
• Hormonal system provides longer-term responses

Metabolism (चयापचय - Metabolism):

• Chemical reactions maintaining life
• Breaking down nutrients for energy (catabolism)
• Building complex structures from simpler molecules (anabolism)
• Requires energy from sunlight (plants) or food (animals)

Movement:

• All organisms capable of movement
• Obvious in animals (locomotion, muscle movement)
• Less obvious in plants (growth, water movement, slow responses)
• Cells showing cytoplasmic streaming and organelle movement

Reproduction:

• Production of new organisms
• Asexual (one parent, genetically identical offspring)
• Sexual (two parents, genetically varied offspring)
• Ensures species continuation

Growth:

• Increase in size and mass
• Cell division and elongation primary mechanisms
• Humans continue growing (height, mass) through childhood/adolescence
• Some organisms continue growth throughout life

Homeostasis (होमियोस्टेसिस - Homeostasis):

• Maintenance of internal environment stability
• Temperature, pH, water content, glucose levels controlled
• Feedback mechanisms (negative feedback predominates)
• Crucial for survival in changing external environment

Excretion:

• Removal of waste products
• Metabolic waste (carbon dioxide, urea) eliminated
• Different from egestion (food waste elimination)
• Various routes: Lungs (CO₂), kidneys (urea), skin (sweat)

2. The Cell: Basic Unit of Life

Cell Theory:

1. All living organisms composed of cells
2. Cell is basic unit of life
3. All cells arise from pre-existing cells (cell division)
4. Smallest unit of life is cell

Prokaryotic vs. Eukaryotic Cells:

Prokaryotic Cells (bacteria):

• No membrane-bound nucleus
• DNA in nucleoid region (not enclosed)
• Smaller (typically 1-10 micrometers)
• Simpler structure
• Few organelles

Eukaryotic Cells (animal, plant, fungi):

• Membrane-bound nucleus containing DNA
• Larger (typically 10-100 micrometers)
• Complex structure
• Membrane-bound organelles
• More compartmentalization of functions

3. Animal Cell Structure and Function

Nucleus:

• Controls cell activities
• Contains chromosomes (DNA and proteins)
• Nuclear envelope (double membrane) surrounds it
• Nucleolus within nucleus produces ribosomes

Mitochondria (माइटोकॉन्ड्रिया):

• "Power house of cell"
• Site of aerobic respiration
• Produces ATP (adenosine triphosphate - energy currency)
• Double membrane structure
• Contains own DNA and ribosomes (suggests origin)

Ribosomes:

• Site of protein synthesis
• Read mRNA and translate to proteins
• Can be free in cytoplasm or bound (rough ER)
• Very small organelles

Endoplasmic Reticulum (ER):

• Network of membrane-bound channels throughout cytoplasm
• Rough ER: Associated with ribosomes, produces proteins
• Smooth ER: Lacks ribosomes, lipid synthesis and detoxification
• Extensive in secretory cells (digestive enzymes, hormones)

Golgi Apparatus (गोल्जी तंत्र):

• Modifies, packages, ships proteins from ER
• Stack of flattened membrane sacs
• Especially extensive in secretory cells
• Processing and packaging function

Lysosomes:

• Contain digestive enzymes (hydrolytic enzymes)
• Break down cellular waste and debris
• Single membrane-bound
• Remove dead organelles and materials

Cytoplasm:

• Gel-like substance filling cell
• Contains organelles and molecules
• Site of many metabolic reactions (glycolysis)
• Allows diffusion of molecules between organelles

Cell Membrane:

• Selectively permeable (semipermeable)
• Controls what enters/leaves cell
• Phospholipid bilayer with embedded/attached proteins
• Proteins involved in transport, recognition, signaling

4. Plant Cell Structure and Function

All Animal Cell Components Plus:

Cell Wall:

• Rigid outer layer outside cell membrane
• Composed of cellulose (in plants)
• Provides structural support and protection
• Allows plant cell to maintain shape without turgor pressure alone
• Plasmodesmata (small pores) allow communication between cells

Vacuole:

• Large, membrane-bound storage structure in plant cells
• Can occupy up to 90% of cell volume
• Stores water, ions, sugars, pigments
• Maintains turgor pressure (cell turgidity)
• Provides mechanical support to plants

Chloroplast (क्लोरोप्लास्ट):

• Site of photosynthesis
• Contains chlorophyll (green pigment)
• Double membrane with thylakoid membranes inside
• Stroma (fluid) surrounds thylakoids
• Own DNA and ribosomes (suggests origin)

Plasmodesmata:

• Channels through cell walls
• Allow cytoplasmic continuity between adjacent cells
• Transport molecules and signals
• Similar to animal cell gap junctions in function

Life Processes

1. Respiration (श्वसन)

Definition:

• Breaking down organic molecules to release energy
• Primarily glucose oxidation: C₆H₁₂O₆ + O₂ → CO₂ + H₂O + Energy

Aerobic Respiration (वायुजीवी श्वसन):

• Requires oxygen
• Occurs in mitochondria
• Much more efficient (30-32 ATP per glucose)
• Stages:
  1. Glycolysis: Glucose → 2 pyruvate (cytoplasm, 2 ATP net)
  2. Krebs Cycle: Pyruvate broken down (mitochondrial matrix, CO₂ released)
  3. Electron Transport Chain: Electrons move, ATP synthesis (inner membrane, uses O₂)

Anaerobic Respiration (अवायुजीवी श्वसन):

• Occurs without oxygen
• Much less efficient (2 ATP per glucose)
• Products: Ethanol + CO₂ (yeast), Lactate (muscle)
• Occurs in cytoplasm
• Temporary energy source when oxygen unavailable

Energy from Respiration:

• ATP (adenosine triphosphate) primary energy molecule
• Hydrolysis of ATP → ADP + Pi + Energy
• Immediate energy for cellular work
• Recharged by respiration

2. Photosynthesis (प्रकाश संश्लेषण)

Definition:

• Light energy converted to chemical energy
• Glucose synthesized from CO₂ and H₂O
• General equation: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂

Location:

• Occurs in chloroplasts
• Light reactions occur in thylakoids
• Dark reactions (Calvin cycle) occur in stroma

Light-Dependent Reactions (प्रकाश-आश्रित अभिक्रिया):

• Require light
• Occur in thylakoid membranes
• Water split: 2H₂O → O₂ + 4H⁺ + 4e⁻
• Electrons moved through electron transport chain
• ATP and NADPH produced
• Oxygen released as byproduct

Light-Independent Reactions (Calvin Cycle):

• Can occur without immediate light (dark reactions)
• Occur in stroma
• CO₂ fixed into 3-phosphoglycerate
• ATP and NADPH from light reactions used
• Glucose synthesized via Calvin cycle

Factors Affecting Photosynthesis:

• Light intensity (increases rate up to saturation)
• CO₂ concentration (increases rate up to maximum)
• Temperature (increases rate to optimum, then decreases)
• Chlorophyll concentration (more absorption)

3. Nutrition (पोषण)

Types:

Autotrophic Nutrition:

• Organisms synthesize own food
• Green plants (photosynthesis)
• Some bacteria (chemosynthesis)

Heterotrophic Nutrition:

• Must ingest pre-made organic molecules
• Holozoic: Ingest whole organisms/food particles
  • Birds, mammals, most animals
• Saprophytic: Absorb organic molecules from dead matter
  • Many bacteria and fungi
• Parasitic: Obtain nutrients from living host
  • Tapeworms, some bacteria

Human Digestive System:

• Mouth: Mechanical digestion (teeth), chemical (amylase enzyme)
• Stomach: Acidic, mechanical churning, pepsin enzyme
• Small intestine: Main digestion and absorption site, many enzymes, bile
• Large intestine: Water absorption, fecal matter formation

Nutrient Categories:

Carbohydrates:

• Energy source (4 calories/gram)
• Glucose primary energy molecule
• Glycogen storage in animals
• Starch storage in plants

Proteins:

• Building structures (muscles, enzymes, antibodies)
• Contain nitrogen
• Made of amino acids
• Digested to amino acids for absorption

Lipids:

• Energy source (9 calories/gram)
• Storage (fat in animals)
• Insulation and cushioning
• Cell membranes

Vitamins:

• Organic compounds essential in small amounts
• Vitamin A (vision), B (energy metabolism), C (immunity), D (calcium absorption)
• Cannot be synthesized; must be obtained from food

Minerals:

• Inorganic substances required
• Iron (oxygen transport), calcium (bones), sodium (nerve)
• Often cofactors for enzymes

Fiber:

• Indigestible carbohydrates
• Aids digestion and bowel health
• Not absorbed but important for GI function

4. Gas Exchange (गैस विनिमय)

in Plants:

• Stomata (small pores on leaves) for CO₂ uptake and O₂ release
• Lenticels (pores in bark) for gas exchange
• Guard cells regulate stomate opening
• Transpiration (water loss) accompanies gas exchange

in Animals:

Simple Organisms:

• Diffusion across entire surface
• Body small enough or thin-walled enough
• Amoeba, cnidarians

Fish:

• Gills extract dissolved O₂ from water
• Counter-current flow increases efficiency
• Water flows over gill filaments backward
• Blood flows through opposite direction

Amphibians:

• Skin (moist, vascular) important for gas exchange
• Lungs less developed
• Some aquatic species rely primarily on skin

Mammals:

• Lungs primary respiratory organ
• Trachea, bronchi, bronchioles, alveoli
• Alveoli site of gas exchange (large surface area, thin walls)
• Diaphragm and intercostal muscles enable ventilation

Summary

Combined science foundations include:

• Cell Structure: Understanding cellular organization and compartmentalization
• Life Processes: Respiration, photosynthesis, nutrition providing energy and building materials
• Gas Exchange: Oxygen uptake and carbon dioxide removal across body surfaces
• Energy Conversion: Light to chemical energy (photosynthesis), chemical to ATP (respiration)
• Organisms: From cells to integrated systems performing life functions

These concepts form foundation for understanding ecology, human biology, and biochemistry across both biology and integrated science.