During which phase of the cell cycle does DNA replication occur? MCQ with Answer and Explanation

During which phase of the cell cycle does DNA replication occur?
A. M phase
B. G2 phase
C. S phase
D. G1 phase
Answer: Option C
Solution (By JKExamLibrary)
The cell cycle consists of interphase (G1, S, G2) and M phase. DNA synthesis or replication occurs during the S (synthesis) phase, resulting in each chromosome having two sister chromatids. G1 is for cell growth and RNA/protein synthesis; G2 is for preparation for mitosis. M phase includes mitosis and cytokinesis. Accurate DNA replication in S phase is crucial for genetic continuity.

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Practice More Biology Questions

Question #1
The process by which plants lose water in the form of liquid droplets is:
A. Evaporation
B. Translocation
C. Transpiration
D. Guttation

Correct Answer: Option D


Explanation:
Guttation is the exudation of water droplets from hydathodes, driven by root pressure under high humidity and low transpiration conditions.

This question belongs to: Science Biology
Question #2
The 'Hormone Somatostatin' is a universal inhibitor. In the gastrointestinal tract, it inhibits the release of almost all other GI hormones. It is secreted by the:
A. Delta (D) cells of the pancreatic islets and the D cells of the GI mucosa
B. G cells of the stomach
C. I cells of the duodenum
D. S cells of the duodenum

Correct Answer: Option A


Explanation:
Somatostatin is a powerful, universal inhibitory peptide hormone. In the gastrointestinal tract and pancreas, it is secreted by the Delta (D) cells of the pancreatic islets and the D cells of the gastric and intestinal mucosa. Its primary role in the GI tract is to act as a paracrine inhibitor, suppressing the release of almost all other gastrointestinal hormones, including gastrin, secretin, cholecystokinin (CCK), vasoactive intestinal peptide (VIP), and gastric inhibitory peptide (GIP). It also inhibits gastric acid secretion, pancreatic enzyme secretion, and intestinal motility, acting as a 'brake' on the digestive system.

This question belongs to: Science Biology
Question #3
Which of the following hormones is secreted by the pineal gland and plays a key role in regulating the circadian rhythm (sleep-wake cycle)?
A. Calcitonin
B. Melatonin
C. Oxytocin
D. Thymosin

Correct Answer: Option B


Explanation:
Melatonin is a hormone secreted by the pineal gland, a small endocrine gland located in the brain. Its secretion is highly sensitive to light and dark cycles, being produced in higher amounts at night. Melatonin is crucial for regulating the circadian rhythm (sleep-wake cycle), maintaining biological clocks, and influencing seasonal reproductive functions in some animals. Thymosin is from the thymus, oxytocin from the posterior pituitary.

This question belongs to: Science Biology