116 previous year UPSC Prelims questions on zoology and human biology make this the largest Science chapter, from 1996 to 2025. UPSC asks about the classification of animals, genetics and genetic disorders, diseases and their vectors, the human body, and the biology of viruses and parasites. The explanations give the reasoning behind each fact.
Explanations state facts as of the year each question was asked; words like “recently” refer to that year.
Showing 21–30 of 116 questions
The fertilization of the ovum (egg) by the sperm typically occurs in the fallopian tube. Fertilization occurs in the ampullary region of the fallopian tube, where sperm meets the egg after ovulation. The fertilized egg (zygote) then travels down the fallopian tube to the uterus for implantation and further development.
The medulla oblongata, located in the brainstem, is responsible for regulating many autonomic functions, such as heart rate, breathing, blood pressure, and reflex actions like swallowing, vomiting, coughing, and sneezing. Options (a), (b), and (d) are incorrect:
The cerebellum is primarily responsible for coordinating voluntary movements, maintaining balance, and muscle tone. It ensures smooth and coordinated muscle actions, especially during complex movements. The cerebrum is the largest part of the brain, responsible for higher functions such as thought, reasoning, conscious movement, speech, and sensory processing. The pons is part of the brainstem, located above the medulla oblongata. It plays a key role in communication between the cerebellum and the cerebrum, as well as regulating sleep, respiratory rhythm, and facial movements.
The liver produces urea as a part of the urea cycle (also known as the ornithine cycle). Urea is a waste product formed when the liver breaks down amino acids during protein metabolism.Urea is then transported to the kidneys, where it is filtered out of the blood and excreted in urine. This process helps the body remove toxic ammonia, which is produced during the breakdown of proteins. Options (a), (c), and (d) are incorrect:
Lipase is an enzyme that breaks down fats into fatty acids and glycerol. It is produced by the pancreas, not the liver. Mucus is produced by various tissues in the body, especially in the respiratory and digestive systems. It is not produced by the liver. Mucus is secreted by the goblet cells in the mucosal lining of the gastrointestinal and respiratory tracts to protect and lubricate tissues. Hydrochloric acid (HCl) is produced by the parietal cells in the stomach, not the liver. It is essential for digesting food and killing harmful pathogens that may enter the stomach with food.
Gastrin is a hormone, not an enzyme. It is produced by G cells in the stomach lining. Gastrin stimulates the secretion of gastric acid (HCl) from parietal cells in the stomach, which aids in digestion. Options (a), (c) and (d) are incorrect:
Trypsin is a digestive enzyme produced by the pancreas and released into the small intestine. It plays a key role in breaking down proteins into smaller peptides, which are further digested into amino acids. It is part of the group of enzymes known as proteases and is essential for protein digestion. Ptyalin is also known as salivary amylase is a digestive enzyme produced in the salivary glands. It begins the process of digesting carbohydrates by breaking down starch into simpler sugars in the mouth. It is essential for the initial stage of carbohydrate digestion. Pepsin is a digestive enzyme secreted by the stomach in an inactive form (pepsinogen). It becomes active in the acidic environment of the stomach and breaks down proteins into smaller peptides.
The small intestine is an essential part of the human digestive system, responsible for digesting food and absorbing nutrients. It consists of three sections: the duodenum, jejunum, and ileum. The ileum is the longest part of the small intestine, measuring approximately 2.5 meters in length. It makes up the last part of the small intestine, connecting to the large intestine through the ileocecal valve. It is rich in villi (tiny finger-like projections) that increase the surface area for nutrient absorption. It absorbs essential nutrients like vitamins (B12), fat-soluble vitamins, and bile salts. The jejunum is about 2.5 meters long. While it is shorter than the ileum, it is thicker and has a more vascular structure. It is the primary site for the absorption of nutrients from digested food. It is specially adapted to absorb proteins, carbohydrates, and lipids. Its walls are lined with a large number of villi that aid in nutrient absorption. The rich blood supply to the jejunum allows for efficient nutrient transport to the rest of the body. The duodenum is the shortest section of the small intestine, measuring only about 25-30 cm (10-12 inches). It is the first part of the small intestine and connects to the stomach through the pyloric sphincter. The duodenum plays a crucial role in the chemical digestion of food. It receives digestive enzymes from the pancreas and bile from the liver and gallbladder. The duodenum is where most of the digestive action occurs before food moves into the jejunum and ileum for nutrient absorption. The duodenum’s role in digestion is so vital that it’s often called the "chemical reactor" of the body Thus, the correct sequence in decreasing order of length is:
Ileum > Jejunum > Duodenum.
Statement 1 is incorrect: The common bile duct transports bile from the liver and gallbladder and releases it into the duodenum, not the stomach. Bile aids in the emulsification of fats during digestion. The common bile duct is a vital component of the biliary system. It is formed by the union of the common hepatic duct and the cystic duct and its primary function is to carry bile from the liver and gallbladder.
Statement 2 is correct: The pancreatic duct carries digestive enzymes and bicarbonate from the pancreas into the duodenum. These enzymes play a crucial role in breaking down carbohydrates, proteins, and fats in the small intestine.
Nutritional calcium is a vital mineral required for the growth and maintenance of strong bones and teeth. It also plays a crucial role in muscle function, nerve signaling, and blood clotting. Rice is not a significant source of calcium. While it provides carbohydrates and small nutrients it does not contain notable calcium levels. Fortified rice may contain added calcium but regular rice lacks this essential mineral for bone health. Options (b), (c), and (d) are incorrect:
Ragi or finger millet is an excellent plant-based source of calcium. It provides a good amount of calcium which is important for strong bones and teeth. Ragi is highly valued in regions where it is cultivated as a nutritious calcium-rich food. Skimmed milk is a good source of calcium and helps maintain bone health. Despite having reduced fat content skimmed milk retains high calcium levels. Dairy products like skimmed milk are among the best natural calcium sources. Eggs contain small amounts of calcium mainly found in the yolk. However they are not considered a major source of calcium compared to dairy products or fortified foods.
Statement 1 is correct: Caffeine, a constituent of tea and coffee is a diuretic. It means it increases urine production by promoting fluid loss from the body. It acts by inhibiting the reabsorption of sodium and water in the kidneys which leads to increased urination.
Statement 2 is correct: Citric acid is a common additive in soft drinks. It is used to add tartness and flavor, and it also helps to preserve the drinks. Citric acid occurs naturally in citrus fruits such as lemons and oranges, and its acidic nature helps balance the sweetness of soft drinks and prolong shelf life.
Statement 3 is correct: Ascorbic acid, commonly known as Vitamin C, plays a crucial role in the synthesis of collagen, a protein that is essential for the structure of bones, teeth, skin, blood vessels, and cartilage. Deficiency in Vitamin C can lead to scurvy, a condition characterized by weakened connective tissue, bleeding gums, and joint pain due to impaired collagen formation.
Statement 4 is incorrect: Citric acid primarily serves as a flavoring agent and preservative. While it has antioxidant properties, it does not provide the essential health benefits of Vitamin C. Ascorbic acid (Vitamin C) is crucial for collagen formation, immune function, and iron absorption, making it irreplaceable by citric acid in these vital bodily processes.
ELISA (Enzyme-Linked Immunosorbent Assay) is an immunological assay technique used to detect and quantify the presence of antibodies or antigens in a sample.
Statement 1 is incorrect: ELISA is not typically the first or most basic test for diagnosing cancer. Other tests, including imaging studies (X-rays, CT scans, MRIs), biopsies, and blood tests specific to cancer (e.g., PSA for prostate cancer, CA-125 for ovarian cancer) are usually used first. ELISA is used in a variety of diagnostic settings, such as for detecting infections (e.g., HIV, Hepatitis B) or monitoring immune responses.
Statement 2 is incorrect: Around 85% of humans have Rh+ (Rhesus positive) blood, meaning their red blood cells carry the Rh factor protein. Only 15% of humans have Rh- blood, lacking this protein. The presence or absence of the Rh factor is critical in blood transfusions and pregnancy.
Option (d) is correct: The hepatic portal vein is the blood vessel that carries nutrient-rich blood from the stomach and small intestine to the liver. This blood is rich in nutrients absorbed from digested food and it contains waste products that need to be processed by the liver. In the liver, these nutrients are processed, stored, or released into the bloodstream as needed. The liver also detoxifies harmful substances present in the blood before returning it to the general circulation. Options (a), (b), and (c) are incorrect:
Left Hepatic Artery supplies oxygenated blood to the liver but is not responsible for carrying nutrient-rich blood from the digestive system. Hepatic Vein carries deoxygenated blood from the liver to the inferior vena cava, which returns it to the heart. It does not carry blood from the stomach or intestine to the liver. Right Hepatic Artery also supplies oxygenated blood to the liver but does not carry nutrient-rich blood from the digestive system.
| Q | UPSC year | Correct answer |
|---|---|---|
| 21 | 2007 | (b) Fallopian tube |
| 22 | 2007 | (c) Medulla oblongata |
| 23 | 2007 | (b) Urea |
| 24 | 2007 | (b) Gastrin |
| 25 | 2007 | (d) Ileum - Jejunum - Duodenum |
| 26 | 2006 | (b) 2 only |
| 27 | 2006 | (a) Rice |
| 28 | 2006 | (b) 1, 2 and 3 only |
| 29 | 2006 | (d) Neither 1 nor 2 |
| 30 | 2006 | (d) Hepatic portal vein |
This page covers 116 previous year UPSC Prelims GS Paper-I questions on Biology: Zoology (Science and Technology), asked from 1996 to 2025. Each has the correct answer and an explanation.
A bat. The flying fox is a large fruit bat, a mammal that flies using wings of skin, not a bird, and it is found across India and South Asia.
The gene is on the X chromosome. A carrier mother can pass the gene to her son, who has only one X chromosome and no second copy to compensate, so he shows the condition.
A mammal. The Dugong is a marine mammal, a herbivore that feeds on seagrass, and it is vulnerable to extinction. It is found in the Gulf of Mannar and around the Andaman and Nicobar Islands.
