NEET Biology — Human Physiology Complete Chapter Guide

Chapter Overview & Weightage

Human Physiology is the single highest-weightage unit in NEET Biology. Across the seven sub-chapters — Digestion, Breathing, Circulation, Excretion, Locomotion, Neural Control, and Chemical Coordination — NEET consistently asks 18–22 questions. That’s roughly 25% of your Biology score sitting in one unit.

Weightage Data (NEET, 2019–2024)

Year	Questions from Human Physiology	Marks
2019	21	84
2020	19	76
2021	20	80
2022	22	88
2023	18	72
2024	21	84

Average: 20.2 questions per year. No other unit comes close.

Sub-chapter-wise distribution matters more than the total. Neural Control and Chemical Coordination together account for 6–8 questions. Digestion and Breathing are 4–5 each. Many students spend equal time on all seven — a costly mistake.

Key Concepts You Must Know

Ranked by how frequently they appear — spend your time proportionally.

Tier 1 — High Frequency (appears almost every year)

Resting membrane potential and action potential — the exact ion movements (Na⁺ in during depolarisation, K⁺ out during repolarisation), the role of Na⁺/K⁺ ATPase pump
Nephron structure and urine formation — filtration, reabsorption, secretion, and concentration by the loop of Henle; JGA and renin-angiotensin system
Cardiac cycle — systole/diastole timing, heart sounds (lub-dub), stroke volume, cardiac output = SV × HR
Hormones and their target organs — especially ADH, PTH, insulin/glucagon, ACTH, FSH/LH, oxytocin; distinguish hypothalamic vs pituitary vs target gland hormones
Digestive enzymes — which enzyme, which substrate, which product, secreted by which gland, optimal pH

Tier 2 — Medium Frequency (every 2–3 years)

Breathing mechanics — pressure changes during inspiration/expiration, tidal volume, IRV, ERV, residual volume, vital capacity = TV + IRV + ERV
Oxygen-haemoglobin dissociation curve — factors shifting it left/right (Bohr effect: CO₂, H⁺ shift right)
Synaptic transmission — neurotransmitter release, reuptake, EPSP vs IPSP
Muscle contraction — sliding filament theory, role of Ca²⁺, troponin-tropomyosin system, ATP hydrolysis steps
Blood groups and Rh factor — agglutinins vs agglutinogens, universal donor/recipient, erythroblastosis foetalis

Tier 3 — Lower Frequency (but don’t skip)

Counter-current mechanism in loop of Henle
ECG waves (P, QRS, T) and what each represents
Types of joints (fibrous, cartilaginous, synovial) with examples
Reflex arc components — receptor → afferent nerve → nerve centre → efferent nerve → effector

Important Formulas

Cardiac Output (CO) = Stroke Volume (SV) × Heart Rate (HR)

Normal: 70 mL × 72 beats/min ≈ 5040 mL/min ≈ 5 L/min

When to use: Questions asking about factors affecting cardiac output, or comparing values under exercise vs rest. Exercise increases both SV and HR, so CO can reach 20–25 L/min.

Vital Capacity (VC) = TV + IRV + ERV

Total Lung Capacity (TLC) = VC + Residual Volume (RV)

Standard values: TV = 500 mL, IRV = 2500 mL, ERV = 1100 mL, RV = 1200 mL → VC = 4100 mL, TLC = 5300 mL

When to use: Any question on spirometry, pulmonary function values, or the difference between obstructive vs restrictive lung disease.

Filtration Fraction = GFR / Renal Plasma Flow

Normal GFR ≈ 125 mL/min (180 L/day filtered, ~1.5 L urine formed)

When to use: Questions on kidney efficiency, or comparing what is filtered vs what is excreted. Remember: glucose is fully reabsorbed up to plasma concentration of ~180 mg/dL (renal threshold).

Resting Membrane Potential ≈ −70 mV (inside negative)

During action potential: depolarises to +30 mV, then repolarises back to −70 mV (briefly overshoots to −90 mV = hyperpolarisation).

When to use: Questions on which ions are responsible for which phase, or what happens during refractory period.

Solved Previous Year Questions

PYQ 1 — NEET 2022 (Neural Control)

Q: Which of the following is correct about the resting membrane potential of a neuron?

(A) Outside is negative, inside is positive (B) Outside is positive, inside is negative (C) Both outside and inside are positive (D) K⁺ concentration is higher outside the cell

Solution:

The neuron is not conducting any impulse. The membrane is polarised — there’s a charge difference across it.

At rest: K⁺ is higher inside, Na⁺ is higher outside. The K⁺ leak channels allow K⁺ to diffuse out, leaving behind negatively charged proteins inside. This makes the inside negative (−70 mV).

Option A is reversed. Option C is impossible at rest. Option D is wrong — K⁺ is higher inside. Answer: (B).

PYQ 2 — NEET 2023 (Excretion)

Q: The counter-current mechanism in the human kidney involves:

(A) Bowman’s capsule and PCT (B) Loop of Henle and vasa recta (C) DCT and collecting duct (D) PCT and loop of Henle

Solution:

Counter-current means two flows running in opposite directions alongside each other. This creates a gradient that helps concentrate urine.

The loop of Henle (descending + ascending limbs, fluid flowing in opposite directions) and the vasa recta (capillaries running parallel, blood flowing in opposite direction to tubular fluid) together maintain the medullary osmotic gradient.

Answer: (B). The PCT is for reabsorption, not counter-current concentration.

PYQ 3 — NEET 2024 (Chemical Coordination)

Q: Which hormone is responsible for the ‘fight or flight’ response and is secreted by the adrenal medulla?

(A) Cortisol (B) Aldosterone (C) Adrenaline (Epinephrine) (D) Thyroxine

Solution:

This is a direct factual question but the trap is in confusing adrenal cortex vs medulla products.

Adrenal cortex (outer) → steroid hormones: Cortisol (glucocorticoid), Aldosterone (mineralocorticoid), sex hormones
Adrenal medulla (inner) → catecholamines: Adrenaline and Noradrenaline

Adrenaline prepares the body for emergency — increases heart rate, dilates pupils, raises blood glucose, diverts blood to muscles. This is the classic fight-or-flight response.

Answer: (C). Cortisol is stress hormone but from the cortex, not medulla.

Difficulty Distribution

NEET Human Physiology — Typical Difficulty Split

Level	% of Questions	Type
Easy	35%	Direct recall — enzyme names, hormone-organ pairs, normal values
Medium	50%	Application — interpreting a graph, identifying disorder from symptoms, comparing two processes
Hard	15%	Integration — linking two sub-chapters, exception-based questions, clinical reasoning

The 50% medium-level questions are where rank is decided. Easy questions everyone gets right. Hard questions separate 680+ scorers. Your target: perfect the medium tier.

Digestion and Locomotion lean easier. Neural Control and Chemical Coordination have more medium-to-hard questions. Excretion has the most graph-based questions (GFR vs plasma concentration curves).

Expert Strategy

How toppers approach this chapter is different from how average students approach it.

The 3-Pass Method for Human Physiology

Pass 1 (Week 1): Read NCERT line by line. Mark every number, every ion, every enzyme. Don’t summarise — NEET asks from the exact NCERT sentence.
Pass 2 (Week 2): Solve last 10 years of PYQs chapter-wise. You’ll find that 60–70% of questions are either direct repeats or slight variations. Pattern recognition is the skill here.
Pass 3 (Week 3+): Make a one-page formula and fact sheet per sub-chapter. Test yourself by covering answers. This is active recall — far more effective than re-reading.

Sub-chapter priority order (based on marks per hour of study):

Neural Control & Chemical Coordination — highest weightage, conceptual, rewarding once you understand it
Digestion & Absorption — most straightforward, lots of direct recall questions
Excretion — medium difficulty, graph questions are very learnable with practice
Circulation — cardiac cycle and ECG questions repeat almost every year
Breathing — calculation-based lung volumes are mechanical once you know the formulas
Locomotion — lowest weightage, just learn muscle contraction steps and types of joints

For Chemical Coordination specifically: Make a table with columns — Gland | Hormone | Target | Effect | Excess disorder | Deficiency disorder. This single table covers 80% of questions from this sub-chapter. NEET loves asking about disorders: acromegaly, cretinism, diabetes insipidus, Addison’s disease, Cushing’s syndrome.

Common Traps

These are patterns where students who’ve studied the chapter still lose marks.

Trap 1 — Adrenal Cortex vs Medulla

Cortisol and Aldosterone come from the cortex (remember: cortex → corticosteroids). Adrenaline and Noradrenaline come from the medulla. Questions often pair cortisol with “emergency/stress” to mislead you into picking medulla. Cortisol is a stress hormone, yes, but it’s a slow, sustained response. Adrenaline is the immediate fight-or-flight response.

Trap 2 — Lung Volumes and Capacities

Students confuse volumes (single measurements) with capacities (sums of volumes). Residual Volume (RV) cannot be measured by spirometry — this appears as an MCQ option regularly. Also: Vital Capacity does NOT include RV. Total Lung Capacity = VC + RV. Draw this diagram once, memorise it.

Trap 3 — The Bohr Effect Direction

Increased CO₂ (or decreased pH, or increased temperature) shifts the O₂-Hb dissociation curve to the right — meaning haemoglobin releases O₂ more easily at tissues. Students often get the direction wrong under pressure. Remember: at tissues where CO₂ is high, you WANT Hb to release O₂. The rightward shift makes biological sense.

Trap 4 — JGA vs DCT in Kidney Regulation

The Juxtaglomerular Apparatus (JGA) secretes renin in response to low blood pressure/low sodium. Renin → Angiotensin I → Angiotensin II → triggers Aldosterone release from adrenal cortex → Na⁺ reabsorption in DCT → water follows → blood pressure rises. Questions mix up where each hormone is secreted vs where it acts. Aldosterone is secreted by adrenal cortex but acts on DCT collecting duct.

Trap 5 — Smooth vs Skeletal vs Cardiac Muscle

Smooth muscle: involuntary, non-striated, spindle-shaped, no troponin (uses calmodulin). Skeletal: voluntary, striated, multinucleated. Cardiac: involuntary, striated, uninucleated with intercalated discs. A question in NEET 2021 asked which muscle type is non-striated but involuntary — many students marked cardiac muscle. Cardiac is striated. Answer is smooth muscle.

With 20+ questions every year and a clear pattern across the last decade, Human Physiology is where serious NEET rank improvement happens. The chapter rewards consistent revision over cramming — the concepts connect across sub-chapters (hormones affect kidney function, nervous system controls breathing rate), and that integration is exactly what the harder 15% of questions test.