Biology

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Human body — organs, blood, digestion, glands

⏱ 4 min read🧩 6 question types🎯 22 practice Q

The idea in one minute

This subtopic is a list of standard facts: body records, blood and heart, digestion, hormones and the brain. Learn each fact as a pair, such as bile and liver or insulin and pancreas. A few numbers (206 bones, 37 °C, 120/80) are asked again and again.

Body records

These records are asked in almost every paper.

Record	Answer
Largest organ	Skin
Largest gland / largest internal organ	Liver
Largest endocrine gland	Thyroid
Longest bone	Femur (thigh)
Smallest bone	Stapes (middle ear)
Smallest muscle	Stapedius (ear)
Strongest muscle (by force)	Jaw (masseter)
Bones in an adult	206
Bones in a newborn	about 300 (many fuse later)
Ribs	12 pairs = 24
Normal body temperature	37 °C (98.6 °F)

Watch: Largest gland is the liver. Largest endocrine gland is the thyroid. Do not mix the two.

Blood and circulation

An adult has about 5 litres of blood. It has four parts.

Part	Job
Plasma (55%)	The liquid part
RBC	Carries oxygen on haemoglobin
WBC	Defence
Platelets	Clotting

Blood groups: ABO plus Rh. O− is the universal donor. AB+ is the universal recipient.
The heart has 4 chambers: 2 atria and 2 ventricles.
Its natural pace-maker is the SA node.
Humans have double circulation. Blood passes through the heart twice per loop.
A sphygmomanometer measures blood pressure. Normal is about 120/80 mm Hg.
A resting heart beats about 72 times a minute.

Example: In one day the heart beats $72 \times 60 \times 24 = 103{,}680$ times. That is about 1 lakh beats.

Digestive system, organ by organ

Organ	What it does
Mouth	Salivary amylase starts starch digestion
Stomach	HCl and pepsin (protein). A mucous lining protects the stomach
Liver	Makes bile. The gall bladder stores it
Pancreas	Sends trypsin (protein) and lipase (fat)
Small intestine	Final digestion and absorption (villi)
Large intestine	Absorbs only water

Rule: Bile has no enzymes. It only emulsifies fat, which means it breaks fat into tiny drops.

Endocrine glands and hormones

A hormone is a chemical messenger made by a gland.

Gland	Hormone and effect
Pituitary	'Master gland'. Growth hormone. Too little gives dwarfism, too much gives gigantism
Thyroid	Thyroxine (contains iodine). Deficiency causes goitre
Pancreas	Insulin (from the islets of Langerhans) controls blood sugar. Failure is diabetes
Adrenal	Adrenaline, the 'fight-or-flight' hormone
Testes / ovaries	Testosterone / estrogen

Excretion and the brain

Kidneys filter the blood. Each has about a million nephrons.
Urine holds urea, water and salts. It reaches the bladder.
Cerebrum: thinking. It is the largest part of the brain.
Cerebellum: balance and posture.
Medulla oblongata: involuntary heartbeat and breathing. A spine injury there is fatal.
The spinal cord handles reflex actions without waiting for the brain.

Body numbers

Body mass index (BMI) tells if weight suits height.

\text{BMI} = \dfrac{\text{mass (kg)}}{\text{height (m)}^{2}}

The normal range is 18.5 to 24.9 (WHO). Take 54 kg and 1.5 m. Then $\dfrac{54}{1.5^{2}} = 24$ , which is normal.

Tip: Convert 37 °C to Fahrenheit with $F = \dfrac{9C}{5} + 32 = 66.6 + 32 = 98.6$ .

Question types you will see

Each type: how to recognise it, the method step by step, and one question to try.

Type 1very common4 practice Q

Body records (largest, smallest, number)

How to spot it:

'Largest gland / organ', 'longest bone', 'smallest bone', 'how many bones does an adult have'.

Method

Find the record word: largest, smallest or longest.
Recall it from the records table.
Test 'largest gland' (liver) against 'largest endocrine gland' (thyroid).

Why it works:

This is pure recall from one short list.

Try this

What is the smallest bone in the human body?

Show solution

It sits in the middle ear.
Its name is stapes.

Answer

Stapes

Type 2very common4 practice Q

Blood, groups and circulation

How to spot it:

'Universal donor / recipient', 'which blood cells fight infection', 'pace-maker of the heart', 'BP instrument'.

Method

RBC carries oxygen. WBC defends. Platelets clot.
O− gives to all. AB+ takes from all.
SA node is the pace-maker. Sphygmomanometer measures BP.

Why it works:

Each blood part and each blood group has one role.

Try this

Which blood group is the universal recipient?

Show solution

Universal recipient means it can take from all groups.
AB+ has no anti-A or anti-B antibodies.

Answer

AB+

Type 3very common4 practice Q

Organ and its secretion or function

How to spot it:

'Insulin is secreted by', 'bile is produced in', 'which organ filters the blood', 'HCl is secreted in'.

Method

Split the question: made where, stored where.
Use the digestive table for enzymes.
Use the brain list for cerebrum, cerebellum and medulla.

Why it works:

Making and storing are different: the liver makes bile, the gall bladder stores it.

Try this

Bile, which helps digest fats, is produced by which organ?

Show solution

Bile is made in the largest gland.
The gall bladder only stores it.

Answer

Liver

Type 4very common3 practice Q

Hormone, gland and deficiency

How to spot it:

'Insulin / thyroxine / adrenaline is secreted by', 'master gland', 'which hormone controls blood sugar'.

Method

Match hormone to gland: thyroxine to thyroid, insulin to pancreas.
Link the hormone to its problem: goitre, diabetes, dwarfism.
Any corner of gland, hormone and disease can be asked.

Why it works:

Gland, hormone and disease form a fixed triangle.

Try this

Which gland is called the master gland?

Show solution

Its hormones steer the other glands.
Growth hormone comes from it.

Answer

Pituitary

Type 5common2 practice Q

Digestion steps and enzymes

How to spot it:

'Which enzyme digests protein / starch / fat', 'where is food absorbed', 'function of bile'.

Method

Amylase acts on starch. Pepsin and trypsin act on protein. Lipase acts on fat.
The small intestine does final digestion and absorption.
The large intestine takes only water.

Why it works:

Each enzyme works on one food type.

Try this

Digested food is absorbed mainly in which organ?

Show solution

Villi increase the surface area.
They line the small intestine.

Answer

Small intestine

Type 6common2 practice Q

Body numbers (computed)

How to spot it:

'How many times does the heart beat in a day', 'normal body temperature in °F', 'how much blood does an adult have'.

Method

Write the given rate, such as 72 a minute.
Multiply by 60 and by 24 for a day.
For temperature use F = 9C/5 + 32.

Why it works:

Split the multiplication into easy steps.

Try this

At 72 beats per minute, about how many times does the heart beat in a day?

Show solution

72 × 60 = 4,320 beats an hour.
4,320 × 24 = 103,680.

Answer

103,680 (about 1 lakh)

Formula sheet

Body mass index

\text{BMI} = \frac{\text{mass (kg)}}{\text{height (m)}^{2}}

Mass in kilograms divided by height in metres squared. 18.5–24.9 is the normal range (WHO)

Shortcuts that save time

⚡ Blood group giving: O gives, AB takes

O has no A or B antigens, so it can give to all. AB has no anti-A or anti-B antibodies, so it can take from all.

Example

The universal recipient blood group is?

Show solution

AB has no anti-A or anti-B antibodies.
So it accepts blood from all groups.

Answer

⚡ Brain parts: Cerebrum thinks, Cerebellum balances, Medulla keeps you alive

Thinking and memory: cerebrum. Balance and posture: cerebellum. Heartbeat and breathing: medulla oblongata.

Mistakes to avoid

Where most students lose marks on this subtopic.

Mistake 01

Saying bile contains digestive enzymes.

Bile has no enzymes. It only emulsifies fats.

Mistake 02

Answering thyroid for the master gland.

The master gland is the pituitary.

Mistake 03

Naming the heart or liver as the largest organ.

Skin is the largest organ. The liver is the largest gland and internal organ.

Mistake 04

Answering liver for the largest endocrine gland.

The largest endocrine gland is the thyroid.

Mistake 05

Saying bile is made in the gall bladder.

The liver makes bile. The gall bladder only stores it.

Quick revision

Read this the night before the exam.

206 adult bones. Stapes smallest. Femur longest. Skin largest organ. Liver largest gland.
O− universal donor. AB+ universal recipient. SA node is the pace-maker.
BP 120/80 mm Hg (sphygmomanometer). Heart about 72 beats a minute.
Bile: no enzymes, emulsifies fat. Stomach: HCl and pepsin. Villi absorb in the small intestine.
Pituitary: master gland. Thyroxine needs iodine. Insulin from pancreas. Adrenaline: fight-or-flight.
Cerebrum thinks, cerebellum balances, medulla keeps the heart beating.
Body temperature 37 °C = 98.6 °F.

Practice: 22 questions

Sets of 10, mixed across the question types above. Every answer has a step-by-step explanation.

Topic test · 10 questions

Suggested time 3 min · wrong answers go to your mistake notebook automatically.

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