NDA Biology · Free notes
Human Physiology — NDA Biology
Human Physiology is the largest chapter in NDA Biology — 55 PYQs across 2017–2026, almost all EASY or MODERATE, and almost all pure named-fact recall. The trick is not derivation; it is knowing the right table cold. The chapter teaches in nine movements, building from the body's raw materials up to whole organ systems: (1) Body tissues — the four tissue types and the connective-tissue family (blood, cartilage, tendon, ligament) that every later system is built from; (2) Digestion and enzymes — the enzyme-substrate-source-pH table and the gland chain that processes food; (3) Nutrition — the vitamin-deficiency table (the single highest-yield table in the chapter), balanced diet, and minerals; (4) Circulation — heart chambers and valves, arteries vs veins, blood, lymph and clotting; (5) Respiration — the airway, gas exchange in the alveoli, and lung volumes; (6) Excretion and reproduction — the nephron and spermatogenesis; (7) Nervous system and sense organs — the nerve impulse, the reflex arc and brain, and the eye; (8) Endocrine system — the hormone-gland-function table; (9) Immune system — which cells make antibodies. 23 concepts, every PYQ tagged. Most concepts are reference tables: memorise the table, win the marks.
The handout has every subtopic, worked example, formula and trap with answers shown. The formula sheet is the chapter’s formulas and traps alone, on one page.
Subtopic notes
Body Tissues — the Building Blocks
9 PYQsA tissue is a group of similar cells doing one job; the body builds every organ from four tissue types — epithelial (covering), connective (support), muscle (movement), and nervous (signalling).
Digestion and Enzymes
8 PYQsDigestion breaks food into absorbable molecules using enzymes — each enzyme acts on one substrate, comes from one gland, and works best at one pH.
Nutrition, Vitamins and Minerals
8 PYQsA balanced diet supplies seven components; vitamins and minerals are the micronutrients whose deficiency causes specific named diseases.
Circulation — Heart, Vessels and Blood
6 PYQsThe heart pumps blood through arteries and veins in a double circuit; blood is a connective tissue, lymph resembles plasma, and clotting seals wounds with fibrin.
The Respiratory System
5 PYQsAir travels down a branching airway to the alveoli, where gas exchange happens; the volumes of air moved are named, with tidal volume the smallest.
Excretion and Reproduction
3 PYQsThe nephron filters blood at Bowman's capsule to make urine; the kidney also releases renin to control blood pressure; sperm form through meiosis from the primary spermatocyte.
Nervous System and Sense Organs
9 PYQsNerve cells carry electrical signals using sodium and potassium ions; the reflex arc and brain coordinate responses; and the eye converts light into images.
The Endocrine System and Hormones
5 PYQsEndocrine glands release hormones into the blood; each hormone has a gland of origin and a specific job, and the menstrual cycle is run jointly by the ovary and pituitary.
The Immune System
2 PYQsWhite blood cells defend the body; lymphocytes are the cells that produce antibodies against foreign antigens.
Formula & revision sheet
0 formulas · 14 reference tables · 23 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
0 formulas · 14 reference tables · 23 gotchas across all subtopics — the exam-eve cheat-sheet
Reference tables (3)
The four types of animal tissue4 rows
| Tissue type | Function | Examples |
|---|---|---|
| Epithelial | Covering and lining of surfaces; protection, absorption, secretion | Skin surface, lining of mouth, oesophagus, intestine, glands |
| Connective | Support, binding, transport; cells in a matrix | Blood, bone, cartilage, tendon, ligament, adipose (fat) Blood is a CONNECTIVE tissue — fluid matrix (plasma) with cells (RBC, WBC, platelets) suspended in it. |
| Muscle | Contraction and movement; contains actin + myosin | Skeletal, smooth, cardiac muscle |
| Nervous | Conducting electrical signals | Neurons (brain, spinal cord, nerves) |
The connective-tissue family — tendon, ligament, cartilage, bone5 rows
| Tissue | Connects / role | Key fact |
|---|---|---|
| Tendon | Muscle to bone | Made of collagen; high tensile strength |
| Ligament | Bone to bone | Elastic; holds joints together |
| Cartilage | Flexible support | In nose, ear, larynx, trachea, knee NOT in the urinary bladder or the bronchioles. |
| Bone | Rigid framework | Calcified; the skeleton |
| Blood | Transport | Fluid matrix (plasma) + cells |
Epithelium and skin4 rows
| Feature | Detail |
|---|---|
| Squamous epithelium | Flat cells; lines the oesophagus, alveoli, blood vessels |
| Columnar epithelium | Tall cells; lines the intestine and stomach (absorption/secretion) |
| Skin pigment | Melanin — gives colour to skin, hair, iris |
| Melanin's role | Absorbs ultraviolet (UV) radiation — not infrared, X-ray or radio NDA 2017 — melanin protects against ULTRAVIOLET radiation specifically. |
Watch out for (4)
- Blood is connective tissue, not 'a fluid' of its own→ The four types of animal tissue
- Tendon ↔ ligament — the direction is the answer→ The connective-tissue family — tendon, ligament, cartilage, bone
- 'Cartilage is NOT found in ___' — know the exceptions→ The connective-tissue family — tendon, ligament, cartilage, bone
- Melanin blocks UV, not infrared or X-rays→ Epithelium and skin
Reference tables (2)
Digestive enzymes — substrate, source, and pH4 rows
| Enzyme | Substrate | Source | Optimum pH |
|---|---|---|---|
| Pepsin | Protein | Stomach wall | ~2 (acidic) NDA 2025 — pepsin works at pH ~2, trypsin at pH ~7.9. Opposite ends. |
| Trypsin | Protein | Pancreas | ~8 (alkaline) |
| Amylase | Starch / carbohydrate | Saliva, pancreas | Slightly alkaline / neutral |
| Lipase | Fat (after bile emulsifies it) | Pancreas | Alkaline |
The ruminant (four-chambered) stomach4 rows
| Chamber | Role |
|---|---|
| Rumen | Largest; microbial fermentation of cellulose |
| Reticulum | Forms the cud; traps foreign objects |
| Omasum | Absorbs water and minerals |
| Abomasum | The 'true' stomach — acid + enzymes |
Watch out for (3)
- Pepsin = acid, trypsin = alkaline→ Digestive enzymes — substrate, source, and pH
- Bile is not an enzyme→ Digestive enzymes — substrate, source, and pH
- The pancreas is an enzyme factory, not a bile store→ Digestive glands and their secretions
Reference tables (3)
Vitamins — chemical name, deficiency, and source6 rows
| Vitamin | Chemical name | Deficiency disease | Source |
|---|---|---|---|
| A | Retinol | Night blindness | Carrots, liver |
| B1 | Thiamin | Beriberi | Whole grains |
| B12 | Cobalamin | Anaemia | Intestinal bacteria, animal foods |
| C | Ascorbic acid | Scurvy | Citrus fruits NDA 2019 — Vitamin C deficiency = scurvy (NOT rickets, which is Vitamin D). |
| D | Calciferol | Rickets | Sunlight |
| K | Phylloquinone | Poor blood clotting | Leafy greens, gut bacteria |
Balanced diet and macronutrients6 rows
| Component | Main role |
|---|---|
| Carbohydrates | Main energy source (glucose) |
| Proteins | Growth and repair |
| Fats | Energy store (most energy per gram) |
| Vitamins + Minerals | Micronutrients (from fruits and vegetables) |
| Fibre (roughage) | Aids bowel movement |
| Water | Medium for all reactions |
Minerals and metabolic waste4 rows
| Mineral / waste | Linked to |
|---|---|
| Iodine | Thyroxine synthesis (deficiency → goitre) |
| Iron | Haemoglobin (deficiency → anaemia) |
| Calcium | Bones, teeth, clotting |
| Uric acid | From nucleic acids → high levels cause gout NDA 2017 — gout patients should minimise NUCLEIC-ACID-rich foods (uric acid comes from purines). |
Watch out for (3)
- Not every disease in the options is a deficiency disease→ Vitamins — chemical name, deficiency, and source
- Don't confuse the chemical names→ Vitamins — chemical name, deficiency, and source
- Fibre and water count as diet components→ Balanced diet and macronutrients
Reference tables (1)
Arteries vs veins4 rows
| Feature | Artery | Vein |
|---|---|---|
| Direction | Away from heart | Towards heart |
| Wall | Thick, elastic | Thinner |
| Valves | Absent | Present |
| Usual blood | Oxygenated | Deoxygenated EXCEPTION: pulmonary artery = deoxygenated; pulmonary vein = oxygenated. |
Watch out for (3)
- Bicuspid = left, tricuspid = right→ Heart chambers, valves, and blood flow
- 'Arteries carry oxygenated blood' is only USUALLY true→ Arteries vs veins
- Fibrinogen vs fibrin→ Blood, lymph, and clotting
Reference tables (1)
Lung volumes and capacities5 rows
| Volume | Meaning | Approx. |
|---|---|---|
| Tidal volume | Normal quiet breath | ~500 mL (lowest) NDA 2025/2026 — tidal volume is the air of a normal breath AND the smallest named volume. |
| Expiratory reserve | Extra forced out | ~1100 mL |
| Residual volume | Always remains | ~1200 mL |
| Inspiratory reserve | Extra forced in | ~3000 mL |
| Vital capacity | TV + IRV + ERV | ~4600 mL |
Watch out for (2)
- Bowman's capsule is NOT a breathing structure→ The airway and gas exchange in the alveoli
- Tidal volume is the smallest — not residual→ Lung volumes and capacities
Watch out for (1)
- Bowman's capsule filters; it doesn't carry urine away→ The nephron — filtration and renin
Reference tables (1)
The eye — parts and photoreceptors5 rows
| Part | Role |
|---|---|
| Cornea | Transparent front; light ENTERS here; avascular, proteins + cells NDA 2021 — the cornea is composed of proteins and cells; it is NOT light-sensitive and has NO blood vessels. |
| Iris / Pupil | Iris controls the pupil — the light aperture |
| Lens | Focuses light onto the retina |
| Retina | Light-sensitive screen; IMAGE forms here |
| Cones / Rods | Cones = colour vision; rods = dim-light vision |
Watch out for (4)
- Both ions — not just sodium→ The nerve impulse — sodium and potassium
- A reflex does not go through the brain→ The reflex arc and brain regions
- Cornea vs retina — entry vs image→ The eye — parts and photoreceptors
- Rods vs cones→ The eye — parts and photoreceptors
Reference tables (2)
Hormones — gland and function5 rows
| Hormone | Gland | Function |
|---|---|---|
| Thyroxine | Thyroid | Controls metabolic rate (needs iodine) Iodised salt supplies the iodine the thyroid needs to make thyroxine. |
| Insulin | Pancreas | Lowers blood glucose |
| Adrenaline | Adrenal medulla | Increases heartbeat (fight/flight) |
| Estrogen | Ovary | Female sexual characters |
| FSH / LH | Pituitary | Drive the menstrual cycle / reproduction |
Reproductive hormones and the menstrual cycle2 rows
| Gland | Hormones | Role |
|---|---|---|
| Pituitary | FSH, LH | Trigger follicle growth and ovulation |
| Ovary | Estrogen, Progesterone | Build and maintain the uterus lining |
Watch out for (2)
- Match the hormone to the RIGHT gland→ Hormones — gland and function
- Two glands, not one→ Reproductive hormones and the menstrual cycle
Reference tables (1)
White blood cells and antibody production4 rows
| Cell | Main role |
|---|---|
| Lymphocytes | Produce ANTIBODIES (B-cells → plasma cells) NDA 2024/2025 — the antibody-producing cells are LYMPHOCYTES. |
| Neutrophils | Phagocytosis of bacteria |
| Eosinophils | Parasites, allergy |
| Monocytes | Become macrophages |
Watch out for (1)
- Antibodies = lymphocytes, not other WBCs→ White blood cells and antibody production
PYQ weightage by concept
23 concepts · 55 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
23 concepts · 55 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| The connective-tissue family — tendon, ligament, cartilage, bone | 5 | 9% |
| The four types of animal tissue | 2 | 4% |
| Epithelium and skin | 2 | 4% |
| Levels of organization — cells to organ systemsfoundation | — | — |
| Concept | PYQs | Share |
|---|---|---|
| Digestive enzymes — substrate, source, and pH | 3 | 5% |
| Digestive glands and their secretions | 3 | 5% |
| The ruminant (four-chambered) stomach | 1 | 2% |
| Concept | PYQs | Share |
|---|---|---|
| Vitamins — chemical name, deficiency, and source | 4 | 7% |
| Balanced diet and macronutrients | 3 | 5% |
| Minerals and metabolic waste | 1 | 2% |
| Concept | PYQs | Share |
|---|---|---|
| Blood, lymph, and clotting | 3 | 5% |
| Heart chambers, valves, and blood flow | 2 | 4% |
| Arteries vs veins | 1 | 2% |
| Concept | PYQs | Share |
|---|---|---|
| The airway and gas exchange in the alveoli | 3 | 5% |
| Lung volumes and capacities | 2 | 4% |
| Concept | PYQs | Share |
|---|---|---|
| The nephron — filtration and renin | 2 | 4% |
| Spermatogenesis — where meiosis happens | 1 | 2% |
| Concept | PYQs | Share |
|---|---|---|
| The eye — parts and photoreceptors | 4 | 7% |
| The reflex arc and brain regions | 3 | 5% |
| The nerve impulse — sodium and potassium | 2 | 4% |
| Concept | PYQs | Share |
|---|---|---|
| Hormones — gland and function | 4 | 7% |
| Reproductive hormones and the menstrual cycle | 1 | 2% |
Test yourself on Human Physiology
15 past NDA questions from this chapter, timed at 15 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.