Life Processes

Overview of Life Processes

Life processes are the fundamental metabolic maintenance functions performed by living organisms to sustain biological integrity, repair tissues, and prevent bodily breakdown even when resting. Core processes include: Nutrition, Respiration, Transportation, and Excretion.

1. Nutrition

Autotrophic Nutrition (Photosynthesis):

Green plants synthesize glucose from inorganic carbon dioxide and water in the presence of solar energy and chlorophyll:

$$6\text{CO}_2 + 12\text{H}_2\text{O} \xrightarrow[\text{Chlorophyll}]{\text{Sunlight}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 + 6\text{H}_2\text{O}$$

Key Sequential Events of Photosynthesis:

1. Absorption of light energy by chlorophyll pigments.
2. Conversion of light energy into chemical energy and photolysis of water: $2\text{H}_2\text{O} \rightarrow 4\text{H}^+ + 4e^- + \text{O}_2 \uparrow$.
3. Reduction of carbon dioxide to carbohydrates by chemical assimilatory power ($NADPH$ and $ATP$).

Heterotrophic Nutrition:

• Holozoic: Ingestion and internal breakdown of complex food (Humans, Amoeba).
• Saprophytic: Digestion of dead organic matter outside the body, absorbing nutrients (Fungi, Yeast, Bread mold).
• Parasitic: Deriving nutrition without killing host (Cuscuta/Amarbel, Tapeworms, Ticks).

Human Digestive System:

• Mouth / Buccal Cavity: Salivary amylase breaks starch into maltose sugars ($\text{pH} \approx 6.8$).
• Stomach: Gastric glands secrete:

1. Hydrochloric Acid ($HCl$): Creates acidic medium ($\text{pH} \approx 1.5$) for enzyme activation and destroys ingested microbes.
2. Pepsin: Protein-digesting enzyme active only in acidic medium.
3. Mucus: Coats and shields stomach walls from corrosive acid.

• Small Intestine (Site of Complete Digestion):
• Bile (from Liver): Emulsifies large fat globules into micro-droplets and alkalinizes chime.
• Pancreatic Juice: Trypsin (proteins $\rightarrow$ peptides), Pancreatic Amylase, Pancreatic Lipase (emulsified fats $\rightarrow$ fatty acids + glycerol).
• Villi: Millions of microscopic, finger-like projections richly supplied with blood capillaries and lymph vessels (lacteals) that maximize surface absorption area.

2. Respiration: Energy Release

Breakdown Pathways of Glucose:

                     Glucose (6-Carbon)
                            │
               (In Cytoplasm - Glycolysis)
                            ↓
                     Pyruvate (3-Carbon) + Energy
             ┌──────────────┼───────────────────────┐
             ↓              ↓                       ↓
    [Absence of O2]   [Lack of O2]           [Presence of O2]
      (Yeast)       (Human Muscle)            (Mitochondria)
         ↓                  ↓                       ↓
     Ethanol +         Lactic Acid +          CO2 + H2O +
     CO2 + 2 ATP          2 ATP                 38 ATP
  (Fermentation)     (Muscle Cramps)      (Aerobic Respiration)

3. Transportation in Humans

Structure of Human Heart & Double Circulation:

The human heart is a muscular four-chambered pump designed to keep oxygenated and deoxygenated blood completely separated.

Deoxygenated Blood from Body ---> Vena Cava ---> Right Atrium 
---> Tricuspid Valve ---> Right Ventricle ---> Pulmonary Artery ---> Lungs (Oxygenation)
Oxygenated Blood from Lungs ---> Pulmonary Veins ---> Left Atrium 
---> Bicuspid/Mitral Valve ---> Left Ventricle ---> Aorta ---> Systemic Circulation to Body

• Double Circulation: Blood passes through the heart twice during each complete cardiac cycle.

1. Pulmonary Circulation: Heart $\rightarrow$ Lungs $\rightarrow$ Heart.
2. Systemic Circulation: Heart $\rightarrow$ Body tissues $\rightarrow$ Heart.

4. Excretion in Humans

Excretion is the biological process by which organisms eliminate toxic nitrogenous metabolic wastes (primarily urea and uric acid).

Structure and Working of a Nephron:

A nephron is the basic structural and functional filtration unit of the kidney (~$1.2$ million per kidney).

1. Bowman's Capsule & Glomerulus: Cluster of high-pressure capillaries where ultrafiltration takes place under hydrostatic pressure. Large proteins and blood cells are retained; water, glucose, amino acids, urea, and salts pass into renal tubule.
2. Selective Tubular Reabsorption: In the Proximal Convoluted Tubule (PCT) and Loop of Henle, essential nutrients (glucose, amino acids, water) are actively reabsorbed into surrounding peritubular capillaries.
3. Tubular Secretion & Collection: Excess potassium and hydrogen ions are secreted into filtrate, which enters the Collecting Duct as concentrated urine.