Biology · Excretory Products and Their Elimination · NEET
Human urine is a light yellow, watery fluid that is slightly acidic (pH about 6.0) and has a typical odour. An adult passes 1 to 1.5 litres per day, removing about 25-30 g of urea daily along with water, uric acid, creatinine, and ions like Na+, K+ and Cl-. Memory hook: think "1 to 1.5 litres, pH 6, 25-30 g urea" - these three exact numbers are what NEET asks.
Normal human urine: fixed NEET numbers (1-1.5 L/day, pH 6.0, 25-30 g urea), substances normally present, and abnormal substances whose presence signals disease.
Your doubts, answered
What is the exact composition of normal human urine according to NCERT?
NCERT states an adult excretes 1 to 1.5 litres of urine per day. It is a light yellow watery fluid, slightly acidic (pH about 6.0), with a characteristic odour. On average about 25-30 g of urea is removed per day. Along with water it carries nitrogenous wastes (urea, uric acid, creatinine) and ions (Na+, K+, Cl-, phosphate, sulphate). Learn these numbers exactly - NEET tests the values, not vague descriptions.
Why is urine yellow in colour?
The light yellow colour comes from a pigment called urochrome, which is formed from the breakdown of haemoglobin (old red blood cells). So urine colour is a byproduct of blood pigment breakdown, not of urea. When you are dehydrated, the pigment is more concentrated and urine looks darker yellow.
What is the pH of normal urine and is it acidic?
Normal urine is slightly acidic with a pH of about 6.0 (NCERT value). This is because the kidney removes extra H+ ions during tubular secretion to keep the blood pH steady. NEET often gives pH 6.0 as the correct option, so remember it is acidic, not neutral or basic.
Which substances are normally absent from urine, and what does their presence indicate?
Glucose, proteins, ketone bodies and blood cells are normally absent from urine. Their appearance signals disease: glucose in urine is glycosuria and ketone bodies in urine is ketonuria - both together indicate diabetes mellitus (NCERT). This is why urine analysis is used for clinical diagnosis.
How is urea in urine different from urea in blood?
Urea is made in the liver and carried by blood; the kidney filters and concentrates it into urine. Blood only holds a small amount (removing more would be toxic - a condition called uremia), while urine concentrates about 25-30 g of urea per day so the body clears it safely. Same molecule, different concentration and role.
⚠️ The NEET trap ✗ Urine is yellow because of urea and its pH is around 7 (neutral). ✓ Urine is yellow because of the pigment urochrome (from haemoglobin breakdown), and its pH is about 6.0 (slightly acidic). Urea is colourless. 🧠 Colour = urochrome, NOT urea. pH = 6.0 acidic, NOT 7 neutral. NCERT gives these exact facts.
Real NEET questions
2020
Presence of which of the following conditions in urine are indicative of diabetes mellitus?
A · Ketonuria and Glycosuria ✓
B · Renal calculi and Hyperglycaemia
C · Uremia and ketonuria
D · Uremia and Renal calculi
Solution: In diabetes mellitus blood glucose is high, so glucose spills into urine (Glycosuria), and poor glucose use makes the body produce ketone bodies that also appear in urine (Ketonuria). NCERT directly lists Glycosuria and Ketonuria as urine indicators of diabetes mellitus. Renal calculi, uremia and hyperglycaemia are not the urine-based diagnostic pair, so the other options are wrong.
Solved Excretory Products and Their Elimination NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
On average 1 to 1.5 litres per day, as stated in NCERT.
How much urea is excreted in urine per day?
About 25-30 grams of urea per day on average.
What gives urine its yellow colour?
The pigment urochrome, formed from the breakdown of haemoglobin, gives urine its light yellow colour.
Is normal urine acidic or basic?
Normal urine is slightly acidic, with a pH of about 6.0.
Why is urine analysis useful in medicine?
Because the presence of abnormal substances (like glucose in glycosuria or ketone bodies in ketonuria) helps diagnose metabolic disorders such as diabetes mellitus and kidney malfunction.
