Science and Technology: UPSC Previous Year Questions (Prelims)

Explanation

Plant chlorophyll absorbs light most efficiently in the blue (around 430-450 nm) and red (around 640-680 nm) regions of the spectrum. These wavelengths drive the light-dependent reactions of photosynthesis, converting light energy into chemical energy. This energy is then used to convert carbon dioxide and water into glucose and oxygen. The absorption of blue light helps in the energy conversion, while red light plays a key role in the process of creating sugars. The green light is mostly reflected bach which is why plants appear green to us.

Explanation

Robert Webster is renowned for his research on the influenza virus. His studies have been instrumental in understanding the genetics and epidemiology of influenza viruses. He has worked extensively on avian influenza, focusing on how the virus mutates and its ability to infect humans, especially during the H5N1 and H1N1 outbreaks. Webster has helped shape our understanding of how influenza viruses evolve and spread, helping to develop vaccines and antiviral strategies.

Explanation

The appendix is a small, tube-like structure that is attached to the large intestine. It is located at the junction where the small intestine (specifically the ileum) meets the large intestine. This area is known as the cecal junction, and the appendix is attached to the cecum, which is a pouch-like structure in the lower right abdomen. The appendix is thought to be a vestigial organ, meaning it may have once had a more significant function in digestion but is now largely considered to be without a clear, vital role.

Explanation

Parathyroid Hormone (PTH) is crucial for regulating the levels of calcium and phosphate in the blood. It increases blood calcium levels by stimulating the release of calcium from bones, increasing calcium absorption in the intestines, and reducing calcium excretion through the kidneys. It decreases blood phosphate levels by increasing phosphate excretion in the urine through the kidneys. The parathyroid hormone is secreted by the parathyroid glands, which are small glands located behind the thyroid gland.

Explanation

Insects primarily breathe through the tracheal system, a highly specialized network of tubes that deliver oxygen directly to their tissues and remove carbon dioxide. The tracheal system consists of tubes (tracheae) that branch out from the insect’s spiracles (small openings on the body surface) to deliver oxygen directly to the cells. Air enters through the spiracles and travels through the tracheae, which are connected to smaller branches called tracheoles that penetrate the tissues of the insect. This allows for efficient gas exchange at the cellular level. air sac dorsal tracheal trunk Thoracic spiracles First abdominal spiracle Spiracular branch Ventral branch Ventral tracheal truck Eight abdominal spiracle Visceral branch

Explanation

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.

Explanation

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.

Explanation

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.

Explanation

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.

Explanation

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.