Look — the Bihar Police Constable exam repeatedly pulls questions from two zones in biology: digestive system facts (enzymes, pH, organs) and basic human body structure (bones, processes). Both zones have a fixed pool of facts that examiners return to year after year. If you nail those facts, you pocket 2-3 marks with almost zero effort.
Here is the big picture. Your body runs on several systems, each with a specific job. The digestive system is the most exam-heavy of these. Its job is straightforward: break food down into molecules small enough to enter your blood and reach your cells. Think of it as a factory assembly line — raw material (food) enters, gets processed at multiple stations (mouth, stomach, small intestine), useful product (nutrients) is packed off into the bloodstream, and waste is expelled.
A useful analogy: imagine the digestive tract as a long tube — roughly 9 metres from mouth to anus — with specialized workers at each station. The mouth does mechanical work (chewing) and starts chemical work (salivary amylase on starch). The stomach is an acidic chamber (pH 1.2–3.0) that attacks proteins. The small intestine is where most chemical digestion is completed and almost all absorption happens. The large intestine mainly reclaims water.
Supporting this assembly line are accessory organs — the liver (produces bile, no enzymes), the pancreas (the star enzyme factory), and the salivary glands. These organs do not have food passing through them; they pour their secretions into the tube.
For the exam, three questions naturally arise from this picture:
Everything below is built to answer those three questions cleanly and quickly.
The body has roughly 206 bones in an adult (300+ at birth, because many fuse later). The skull is a specific exam target: it has 22 bones — 8 cranial bones that encase the brain and 14 facial bones. Do not confuse 22 with 20 or 29; examiners plant both as distractors.
Major body systems and their one-line functions:
| System | Primary Function | |---|---| | Digestive | Break down food; absorb nutrients | | Circulatory | Transport blood, oxygen, nutrients | | Respiratory | Gas exchange (O₂ in, CO₂ out) | | Skeletal | Support, protection, movement | | Nervous | Coordination, signal transmission | | Endocrine | Hormonal regulation | | Excretory | Remove metabolic waste |
Mouth (Buccal Cavity) Mechanical digestion (teeth) + chemical digestion begins. Saliva contains salivary amylase (ptyalin), which breaks starch into maltose. Saliva pH is slightly alkaline (6.5–7.5).
Oesophagus A muscular tube — no digestion happens here. Food moves down by peristalsis (wave-like muscle contractions).
Stomach Gastric glands in the stomach wall secrete gastric juice, which contains:
The acidic environment also kills most bacteria ingested with food. The semi-liquid food mass leaving the stomach is called chyme.
Small Intestine: Three Parts This is the most-tested structural fact. The small intestine has exactly three parts:
Pancreas: The Enzyme Powerhouse The pancreas secretes pancreatic juice containing:
Key point: the pancreas secretes trypsinogen (inactive), not trypsin directly. Activation happens in the small intestine. Examiners sometimes ask "which gland secretes trypsin" — answer is still Pancreas (as the source of trypsinogen that becomes trypsin).
Liver The largest gland in the body. It produces bile — a greenish-yellow fluid stored in the gall bladder. Bile contains no enzymes. It emulsifies fats (breaks large fat globules into smaller ones so lipase can work efficiently). The liver also:
Large Intestine Main function: absorb water and electrolytes from undigested material. No significant digestion of food happens here. The remaining solid waste (faeces) is expelled via the rectum and anus.
During dehydration, the body loses water along with electrolytes. The dominant electrolyte lost is sodium chloride (NaCl — common salt). This is why ORS (Oral Rehydration Solution) contains salt + sugar + water. Potassium is also lost but sodium chloride is the primary answer for this exam context.
The process by which a larva transforms into an adult through a series of developmental changes is called metamorphosis. This appears in biology questions about life cycles — frog, butterfly, and silkworm are classic examples. Complete metamorphosis (holometabolism) has four stages: egg → larva → pupa → adult. Incomplete metamorphosis has three: egg → nymph → adult.
Remember the three parts as D-J-I (Duodenum, Jejunum, Ileum) using the phrase "Digestion Jumps In" — Digestion (chemical) completes in the Duodenum, absorption Jumps into action in the Jejunum, and the Ileum finishes the job. Without this hook, students confuse "three" with "four" or mix up the order. With this, you answer the "how many parts" question in under 5 seconds vs. searching your memory for 20-25 seconds.
Memorise a simple ladder: Saliva (6.5–7.5, near neutral) → Stomach/Gastric juice (1.2, very acidic) → Small intestine (7–8, slightly alkaline, because pancreatic juice neutralises). The pattern is: neutral → very acidic → back to alkaline. When the question gives pH options like 1.2, 2.2, 7.4, and 10.0, this ladder eliminates 7.4 (blood pH) and 10.0 (too alkaline) immediately. You circle 1.2 in under 8 seconds vs. 30+ seconds if you try to recall without the pattern.
Use the acronym PSLS: Pancreas (trypsin, amylase, lipase) → Stomach (pepsin, HCl) → Liver (bile, no enzyme) → Salivary gland (salivary amylase only). When a question asks "which gland secretes enzyme X", slot X into PSLS. Liver is the classic trap — it makes bile but zero enzymes. This eliminates the "Liver" distractor in under 3 seconds. Standard approach (recalling each organ separately): 20-30 seconds. With PSLS: 5 seconds.
8 cranial + 14 facial = 22. Think: "8 to protect the brain, 14 for the face — total 22 bones in the skull's case." Distractors 20, 16, and 29 are all wrong. Once you fix 8 + 14 = 22, the distractor 29 (total spinal vertebrae in another context) and 20 (deciduous teeth count) cannot confuse you. Answering time: under 5 seconds vs. 25 seconds without the split.
Dehydration question options always include calcium phosphate, potassium chloride, sugar, and sodium chloride. Eliminate by logic: calcium phosphate is a bone mineral (not in sweat/fluids at significant levels), sugar is not an electrolyte lost in sweat, potassium is lost but not the primary loss. Sodium chloride is the answer every time this question type appears. Elimination gets you there in 10 seconds vs. 30+ seconds of recall.
When you see a digestive system question in the exam, run this decision tree:
Step 1 — Is it an enzyme/secretion question? → Yes: Apply PSLS. Match the enzyme to the organ. Done. → No: Go to Step 2.
Step 2 — Is it a structural/number question? → Small intestine parts: answer is Three (D-J-I). → Skull bones: answer is 22 (8+14). → No: Go to Step 3.
Step 3 — Is it a pH/chemical environment question? → Gastric juice: 1.2 (strongly acidic, HCl). Not 7.4 (that is blood). → No: Go to Step 4.
Step 4 — Is it an electrolyte/dehydration question? → Primary loss: Sodium chloride. Always.
Step 5 — Is it a process/terminology question? → Larva to adult transformation: Metamorphosis (कायान्तरण). → Other processes: use the station-by-station knowledge.
Spend no more than 20 seconds per question in this chapter. These are fact-based — either you know it or you eliminate down to two options and pick the one that fits the framework.
Why this question: Trypsin is a top-3 recurring enzyme question across UP Police and Bihar Police exams. Examiners use "Liver" as the trap because it is the largest gland.
Solving path: Apply PSLS. Trypsin (as trypsinogen) → Pancreas. Liver makes bile, no enzyme. Salivary gland makes only salivary amylase. Gastric gland makes pepsin. Circle Pancreas. Time: 8 seconds.
Why this question: "How many parts" questions on the small intestine appear almost every cycle. The wrong options (Ten, Eight, Four) are completely arbitrary — knowing D-J-I makes this instant.
Solving path: D-J-I = Duodenum, Jejunum, Ileum = Three parts. Options include "Four" as the close distractor (students confuse with four chambers of heart or four parts of large intestine). Lock in Three. Time: 5 seconds.
Why this question: pH of gastric juice appears repeatedly. The trap options are 7.4 (blood pH) and 2.2 (close but not the accepted answer — the commonly cited figure is 1.2).
Solving path: Gastric juice = HCl + pepsin = very acidic = pH approximately 1.2. Option 7.4 is blood pH (neutral territory). Option 10.0 is strongly alkaline — impossible for stomach. Option 2.2 is close but 1.2 is the standard exam answer. Circle 1.2. Time: 8 seconds.
Why this question: Dehydration electrolyte loss is a nutrition-meets-physiology question. It bridges digestive system knowledge with basic chemistry, which is why it resurfaces across years.
Solving path: Eliminate Calcium Phosphate (bone mineral), Sugar (not an electrolyte lost in sweat), Potassium Chloride (lost but not primary). Sodium Chloride is the dominant electrolyte in extracellular fluid — its loss drives dehydration. Circle Sodium Chloride. Time: 10 seconds.
Why this question: Skull bone count is a classic body-structure fact. The 22-bone answer trips up students who remember only that "adults have 206 bones" without knowing the skull breakdown.
Solving path: 8 cranial + 14 facial = 22. Option 29 is a distractor (vertebral column has 33 vertebrae in early life, 26 in adults — unrelated). Option 20 matches deciduous teeth (also unrelated). Fix 22. Time: 5 seconds.
Why this question: Metamorphosis (कायान्तरण) is a recurring biology process question. Students who do not know the Hindi term get confused, especially when options include "वृद्धि" (growth) as a near-correct sounding distractor.
Solving path: The question asks for the process of larva transforming into adult. Growth (वृद्धि) is general increase in size — not a transformation process involving structural change. Metamorphosis (कायान्तरण) is the specific term. Circle कायान्तरण. Time: 8 seconds.
Saying liver produces trypsin or pepsin. The liver produces only bile — a digestive fluid with no enzymes at all. This is the single most common wrong answer in enzyme questions. Lock in: Liver = Bile = No Enzyme.
Confusing four parts of the large intestine with three parts of the small intestine. The small intestine has three parts (D-J-I). Students who vaguely remember "intestine → four parts" are thinking of the large intestine (caecum, colon, rectum, anal canal). Keep the two separate.
Writing gastric juice pH as 2.2 instead of 1.2. Both look similar and examiners exploit this. The standard accepted answer for gastric juice pH is 1.2. If 2.2 appears as an option alongside 1.2, always go with 1.2.
Confusing potassium chloride with sodium chloride in dehydration questions. Both are salts. The primary electrolyte lost is sodium chloride because it is the dominant ion in extracellular fluid. Potassium is mostly intracellular. Do not second-guess this.
Mixing up skull bones (22) with total adult bones (206) or spinal vertebrae (26/33). The question will specify "skull" (खोपड़ी) — read the question carefully. 22 is only for the skull.
Treating trypsinogen and trypsin as different answers. The pancreas secretes trypsinogen (inactive form). It becomes active trypsin in the small intestine. When the question asks "which gland secretes trypsin enzyme", the answer is still Pancreas — because that is the organ of origin. Do not mark "small intestine" because that is only where activation occurs.