21000+ Important MCQs for UPSC

Ptyalin, also known as salivary amylase, is the enzyme present in saliva.

• It helps in the digestion of carbohydrates by breaking down starch into maltose (a simpler sugar).
• It is the first step in the digestion process, occurring in the mouth before food enters the stomach.

Why not the others?

• (A) Lipase – Breaks down fats (lipids), mainly found in the stomach and pancreas.
• (B) Trypsin – Helps in protein digestion, secreted by the pancreas into the small intestine.
• (D) Invertase – Breaks down sucrose into glucose and fructose, mainly found in yeast, not in saliva.

Frogs have multiple respiratory surfaces and can breathe through more than one organ depending on their life stage and environment:

1. Lungs – Used for breathing on land.
2. Skin (Cutaneous Respiration) – Frogs can absorb oxygen directly through their moist skin, especially when underwater.
3. Buccal Cavity (Buccopharyngeal Respiration) – They can also exchange gases through the lining of their mouth.

This adaptation helps them survive in both aquatic and terrestrial environments.

Why not the others?

• (A) Pleura – It is a membrane around human lungs, not an animal.
• (B) Human – Humans rely only on lungs for respiration.
• (C) Fish – Fish use gills exclusively for breathing underwater.

Operculum is a bony flap that covers and protects the gills in bony fish (Osteichthyes), including most sea fish. It helps in respiration by allowing water to flow over the gills.

Why not the others?

• (A) Birds – Birds do not have gills or operculum; they have lungs for respiration.
• (C) Cartilaginous fish – Sharks and rays (cartilaginous fish) lack an operculum. Instead, they have gill slits for respiration.
• (D) None of these – Incorrect, as operculum is present in bony fish.

Birds have beaks instead of teeth. Their jaws are adapted for different feeding habits, but they do not have teeth like mammals, reptiles, or fish.

Why not the others?

• (B) Reptiles – Most reptiles, like snakes and lizards, have teeth.
• (C) Fish – Many fish species have teeth, including sharks and bony fish.
• (D) None of these – Incorrect, as birds do have jaws without teeth.

Lymph is a fluid that is similar to plasma but has a different composition. It contains:

• Proteins: Lymph has some proteins, though in lower amounts than blood plasma.
• Water: Lymph is mostly water, but it is not the defining component.
• Lipids: Lymph absorbs fats from the intestines, but lipids are not the most abundant component.
• Oxygen: Lymph is not primarily involved in oxygen transport.

Thus, proteins are the most abundant among the given options.

Plants do not have a nervous system like animals. Instead, they coordinate their functions through plant hormones (also called phytohormones). These hormones regulate growth, development, and responses to environmental stimuli.

Some key plant hormones include:

• Auxins – Control cell elongation and phototropism.
• Gibberellins – Promote stem elongation and seed germination.
• Cytokinins – Promote cell division.
• Abscisic Acid (ABA) – Helps in stress responses and stomatal closure.
• Ethylene – Involved in fruit ripening.

Thus, hormones are responsible for coordination in plants.