SSC CGL 2025 Tier-I · 15 September 2025, Shift 3 · General Awareness · Question 13 of 100

We transcribed this text from the pictures on a candidate's response sheet for this shift; the answer is the key SSC colour-marked on that sheet. Solution last reviewed 11 September 2026.

Where this paper and its answers come from

SSC does not publish CGL question papers or a public answer key. From 2025 the candidate response sheet prints every question and option as a picture, so the text here is transcribed from those pictures for this shift and checked against them independently; where the layout carries meaning, the picture is shown as well. Each answer is the key SSC colour-marked on that sheet. SSC released a tentative key for challenge and later its final one, both only to candidates behind a login, and the sheet does not say which of the two it carries. The solutions are written by UnlockIAS.

Which part of the human brain regulates the circadian rhythm?

(a)Cerebellum
(b)Hypothalamus
(c)Medulla oblongata
(d)Thalamus

Answer

Why

Correct — B. The body's master clock is the suprachiasmatic nucleus (SCN), and NINDS places the SCN within the hypothalamus.

The SCN takes light information directly from the eyes and controls the sleep–wake rhythm. It signals the pineal gland to make more melatonin in the evening, causing sleepiness → option (b).

Why the others are wrong

(a)
Cerebellum — The cerebellum is hindbrain. NCERT has it integrating information from the ear's semicircular canals and the auditory system: balance, not the daily clock.
(c)
Medulla oblongata — The medulla oblongata holds centres for respiration, cardiovascular reflexes and gastric secretions (NCERT). It does not house the master clock.
(d)
Thalamus — The thalamus relays sensory and motor signals and goes quiet in most sleep stages. The master clock, the SCN, lies in the hypothalamus at its base.

Concept

Circadian rhythms are physical, mental and behavioural changes that follow a roughly 24-hour cycle. A master clock keeps the body's many clocks in step.

In humans that clock is the suprachiasmatic nucleus, a group of nerve cells in the hypothalamus. It reads light through the eyes, drives melatonin release from the pineal gland, and synchronises rhythms in organs across the body.

NCERT adds that the hypothalamus controls body temperature and the urge to eat and drink.

NCERT credits melatonin from the pineal gland with regulating the 24-hour rhythm. That fits: the pineal makes melatonin on the SCN's signal, so the hypothalamus holds the clock and the pineal carries its message.

Key facts

The suprachiasmatic nucleus (SCN), the human master clock, lies within the hypothalamus.
The pineal gland receives signals from the SCN and increases melatonin production.
NCERT: the medulla contains centres for respiration, cardiovascular reflexes and gastric secretions.
NCERT: the thalamus is a major coordinating centre for sensory and motor signalling.

Study next

Hypothalamic hormones and the pituitary glandThe pineal gland and melatoninForebrain, midbrain and hindbrain: parts and functions

Common traps

Choosing the thalamus because the names look alike. The SCN is in the hypothalamus, at the thalamus's base.
Mixing up the clock and its messenger: the pineal releases melatonin on the SCN's signal.

Here a brain part is asked by function. NCERT Class 11 Biology asks the same thing in its exercises: "Which part of our central neural system acts as a master clock?"

Related PYQs

No directly related past PYQ was found.

Topic: Scientific Research — all 178 SSC CGL questions on it, every solved shift.