Why this chapter matters for UPSC: The cardiovascular system (context for India's NCDs — cardiovascular disease is India's #1 killer), blood components (platelets for COVID-19 treatment, blood banks), and plant transportation (xylem/phloem — relevant to drought resistance, forest science) are GS3 science topics.

PART 1 — Quick Reference Tables

Components of Blood

Component Cell type Function
Red Blood Cells (RBC / Erythrocytes) No nucleus in mammals (includes humans) Carry oxygen using haemoglobin; also carry CO₂ back
White Blood Cells (WBC / Leucocytes) Have nucleus; several types Immune defence: fight bacteria, viruses, parasites
Platelets (Thrombocytes) Cell fragments; no nucleus Blood clotting (stop bleeding)
Plasma Liquid component (55% of blood) Transports nutrients, hormones, CO₂, waste products, clotting factors

Transport in Plants

System Tissue What it Transports Direction
Xylem Dead cells; thick walls; hollow tubes Water + dissolved minerals Root → stem → leaves (upward)
Phloem Living cells Sugars (glucose from photosynthesis) Leaves → rest of plant (bidirectional)

PART 2 — Detailed Notes

The Human Circulatory System

Key Term

Double circulation: Blood passes through the heart TWICE per complete circuit:

  1. Pulmonary circulation: Right heart → lungs (picks up O₂, drops CO₂) → left heart
  2. Systemic circulation: Left heart → body (delivers O₂, picks up CO₂) → right heart

Heart structure:

  • 4 chambers: Right atrium, Right ventricle, Left atrium, Left ventricle
  • Right side: Deoxygenated blood (from body → to lungs)
  • Left side: Oxygenated blood (from lungs → to body)
  • Valves: Prevent backflow; bicuspid (mitral) valve between left atrium and ventricle; tricuspid between right atrium and ventricle; semilunar valves at aorta and pulmonary artery openings
  • Heart rate: ~60–100 beats/minute (resting adult); each beat pumps ~70 mL blood

Blood vessels:

  • Arteries: Carry blood AWAY from heart; thick, elastic walls; blood under high pressure; no valves; carry oxygenated blood EXCEPT pulmonary artery (carries deoxygenated to lungs)
  • Veins: Carry blood TOWARD heart; thinner walls; lower pressure; have valves (prevent backflow); carry deoxygenated blood EXCEPT pulmonary vein (carries oxygenated from lungs)
  • Capillaries: Microscopic; single cell layer thick; site of gas/nutrient exchange between blood and cells

India's Cardiovascular Disease Burden

UPSC Connect

UPSC GS3 — NCDs and Cardiovascular health:

India's cardiovascular disease (CVD) statistics (2024):

  • CVD is the leading cause of death in India (~28% of all deaths)
  • ~4.77 million CVD deaths/year in India
  • India has the world's highest absolute burden of CVD deaths
  • Mean age of heart attack is younger in Indians (~53 years vs ~65 in Western countries)

Risk factors prominent in India:

  • Diabetes (~101 million diabetics — world's largest) — major CVD risk
  • Hypertension (~188 million with high blood pressure)
  • High salt diet, tobacco use (smoking + smokeless tobacco)
  • Sedentary lifestyle, urban stress, pollution

Government initiatives:

  • National Programme for Non-Communicable Diseases (NP-NCD): Screening for hypertension, diabetes, cancers at health and wellness centres (Ayushman Bharat HWCs)
  • Ayushman Bharat PM-JAY: Covers heart surgery (coronary artery bypass grafting is one of the covered procedures)
  • Pradhan Mantri Jan Aushadhi Pariyojana (PMJAP): Affordable generic medicines; aspirin, atenolol, statins available cheaply at Jan Aushadhi stores

Blood transfusion and safety:

  • India needs ~15 million units of blood/year; collects ~12–13 million
  • Voluntary blood donation drive: National Blood Donation Day (October 1)
  • National Blood Transfusion Council (NBTC): Apex body; standards for blood banks
  • HIV/Hepatitis screening: Mandatory before transfusion; significantly reduced transfusion-transmitted infections

Transportation in Plants

Explainer

Xylem and phloem:

Xylem (water transport):

  • Transport of water from roots to leaves (upward) through dead, hollow xylem cells
  • Why water goes up (against gravity):
    1. Root pressure: Roots actively absorb water from soil → pushes water up
    2. Transpiration pull (main mechanism): Water evaporates from leaf stomata → creates tension/suction that pulls water up the entire height of the tree
    3. Capillary action: Adhesion + cohesion of water molecules in narrow xylem vessels

A tall tree can transport water 100+ metres upward — entirely through passive mechanisms (no pump)

Phloem (food transport):

  • Transports sugars (sucrose produced by photosynthesis) from leaves to all other parts
  • Bidirectional: Can move sugars up (to growing shoot tips) or down (to roots, fruits)
  • Active transport (requires energy — ATP)

Transpiration:

  • Water loss from plant through stomata (leaves) and lenticels (stems)
  • Benefits: Creates the pull that moves water up xylem; cools the plant (like sweating)
  • 98% of water absorbed by roots is lost through transpiration (only 2% used in photosynthesis)
  • Transpiration is how forests create their own rain (water released → condenses → precipitation); deforestation disrupts this cycle → less rainfall in the area

Exam Strategy

Prelims traps:

  • Arteries carry blood AWAY from heart (NOT always oxygenated — pulmonary artery carries deoxygenated blood)
  • Veins carry blood TO heart (NOT always deoxygenated — pulmonary vein carries oxygenated blood from lungs)
  • Xylem = dead cells (thick walls, hollow tubes); Phloem = living cells — this distinction is asked
  • RBCs have NO NUCLEUS in mammals — they lose nuclei during development; can't divide; live ~120 days
  • CVD is India's leading cause of death (~28% deaths) — NOT cancer, NOT infectious disease
  • Transpiration pull = main mechanism for water going up tall trees (NOT root pressure alone)

Previous Year Questions

Prelims:

  1. Red blood cells (RBCs) in adult humans are unique in that they:
    (a) Contain two nuclei
    (b) Have no nucleus (enucleated) and cannot divide
    (c) Are the largest blood cells
    (d) Are produced in the spleen

  2. The main mechanism by which water rises to the top of a tall tree is:
    (a) Root pressure pushing water upward
    (b) Transpiration pull — evaporation of water from leaves creates suction that draws water up xylem
    (c) Active pumping by phloem cells
    (d) Osmotic pressure in leaf cells