NDA & CDS 1 2026 Exam Biology – Human Body Class 2

Introduction

The human body performs numerous metabolic activities every second, producing useful as well as waste materials. To maintain internal balance (homeostasis), the body must remove metabolic wastes and coordinate all functions efficiently.
The Excretory System helps in the removal of nitrogenous wastes, while the Nervous System controls and coordinates all body activities through impulses. Together, they maintain the body’s stability, efficiency, and survival.

Part I – The Excretory System

1. Introduction to Excretion

• Definition: Process of removal of metabolic waste from the body.
• Major excretory products: Urea, uric acid, CO₂, ammonia, salts, water.
• Organs of excretion: Kidneys, lungs, skin, liver.

2. Structure of the Human Excretory System

• Kidneys – Bean-shaped organs located on either side of the backbone.
• Ureters – Tubes carrying urine from kidneys to urinary bladder.
• Urinary bladder – Muscular sac for urine storage.
• Urethra – Passage for urine elimination.

3. Nephron – The Functional Unit

• Parts: Bowman’s capsule, glomerulus, proximal tubule, loop of Henle, distal tubule, collecting duct.
• Functions:
  • Filtration (in glomerulus)
  • Reabsorption (in tubules)
  • Secretion (of wastes into tubules)

4. Formation of Urine

• Steps: Filtration → Reabsorption → Secretion → Excretion.
• Hormonal control: ADH (Antidiuretic Hormone) regulates water reabsorption.

5. Other Organs of Excretion

• Lungs – Remove CO₂ and water vapor.
• Skin – Excretes sweat containing water and salts.
• Liver – Converts ammonia to urea.

Part II – The Nervous System

1. Introduction

• Definition: System responsible for control, coordination, and communication within the body.
• Types of control systems:
  • Nervous control (fast, via impulses)
  • Endocrine control (slow, via hormones)

2. Divisions of the Nervous System

1. Central Nervous System (CNS) – Brain and spinal cord.
2. Peripheral Nervous System (PNS) – Cranial and spinal nerves.
3. Autonomic Nervous System (ANS) – Controls involuntary activities (sympathetic and parasympathetic systems).

3. Structure and Function of a Neuron

• Parts: Dendrites, cell body, axon.
• Function: Transmission of nerve impulse through electrical and chemical signals.
• Synapse: Junction between two neurons where impulse transfer occurs.

4. The Brain

• Forebrain: Cerebrum – Controls intelligence, memory, reasoning.
• Midbrain: Controls reflexes related to sight and sound.
• Hindbrain: Cerebellum (balance), Pons, Medulla oblongata (involuntary actions like heartbeat, breathing).

5. The Spinal Cord

• Connects brain to peripheral nerves.
• Controls reflex actions and transmits impulses to and from the brain.

6. Reflex Action and Reflex Arc

• Reflex action: Automatic, quick response to a stimulus (e.g., pulling hand away from flame).
• Reflex arc: Pathway of reflex (Receptor → Sensory neuron → Spinal cord → Motor neuron → Effector).

Conclusion

The Excretory System ensures internal chemical stability by removing waste, while the Nervous System maintains coordination and control, enabling the body to respond to internal and external changes. Together, they are vital for maintaining homeostasis, efficiency, and survival — key aspects of human physiology crucial for NDA/CDS biology understanding.