Explanation 

(Option C) Polysaccharides: Polysaccharides are long chains of monosaccharide units (sugars). They are the chief components of cell walls in:

Plants: Cellulose is the primary polysaccharide, providing rigidity and strength.

Fungi: Chitin is a polysaccharide that forms the cell walls, giving them structure and protection.

Prokaryotes: Peptidoglycan, a complex polysaccharide, forms the cell wall in bacteria, providing shape and protection. Thus, polysaccharides are the main structural materials in the cell walls of these organisms.

(Option A) Proteins: Proteins are complex molecules made up of amino acids. They play a variety of crucial roles in cells, such as:

Enzymes: Catalysts that speed up chemical reactions.

Structural: Providing support and shape to cells (e.g., collagen in animals).

Transport: Moving substances across cell membranes (e.g., hemoglobin transporting oxygen in blood). However, proteins are not the main component of cell walls in plants, fungi, or prokaryotes.

(Option B) Lipids: Lipids are fatty molecules that are essential for forming cell membranes and storing energy. They include:

Phospholipids: Form the lipid bilayer of cell membranes.

Triglycerides: Store energy in fat cells. Lipids are important for cell membranes but are not the primary material in cell walls.

(Option D) Phospholipids: Phospholipids consist of two fatty acids and a phosphate group attached to a glycerol molecule. They are essential for:

Cell membranes: Forming a bilayer that serves as a barrier and matrix for membrane proteins. Phospholipids are crucial for membrane structure but not for cell walls.

Subject: Biology

Topic: Cell Structure & Function

Subtopic: Cell Wall

Difficulty Level: Moderate

Explanation

(Option D) Red Blood Cell: Red blood cells (RBCs), or erythrocytes, are unique among the listed cells because they do not have a nucleus when mature. During their development in the bone marrow, red blood cells lose their nucleus to maximize space for hemoglobin, the protein that carries oxygen. The absence of a nucleus allows RBCs to have more room for hemoglobin, increasing their oxygen-carrying capacity and flexibility to navigate through tiny blood vessels.

(Option A) Muscle Cell: Muscle cells, also known as muscle fibers, are specialized cells that make up muscle tissue. They have multiple nuclei, which are essential for the regulation of their large cell volumes and the high metabolic activity required for muscle contraction. These nuclei control the synthesis of proteins necessary for muscle function.

(Option B) Nerve Cell: Nerve cells, or neurons, are the fundamental units of the nervous system responsible for transmitting and processing information. Each neuron has a nucleus located in its cell body (soma), which contains the genetic material necessary for the cell's functions. The nucleus plays a critical role in regulating the activities of the neuron, including the production of neurotransmitters and maintenance of cellular health.

(Option C) White Blood Cell: White blood cells (WBCs) are a crucial component of the immune system, responsible for defending the body against infections and foreign invaders. They have a nucleus, which is essential for their various functions, including the production of antibodies, signaling to other immune cells, and regulating their own growth and response to pathogens.

Subject: Biology

Topic: Cells Structure & Function

Subtopic: Cytoplasm and cell organelles (Nucleus)

Difficulty Level: Easy

Smooth Muscle

Nerve Cell with Nucleus

Structure of WBC

Explanation

(Option C) Ethanol and CO2: Yeast carries out anaerobic respiration, also known as fermentation, when oxygen is not available. In this process, glucose is broken down into ethanol (alcohol) and carbon dioxide (CO2). This is a common process used in the production of bread, beer, and other alcoholic beverages.

(Option A) Ethanol and oxygen: In anaerobic respiration, organisms do not use oxygen. Instead, they produce energy through other pathways. Yeast, in anaerobic conditions, does not produce oxygen. This option is incorrect.

(Option B) Ethanol and water: Yeast produces ethanol and carbon dioxide (CO2) through a process called fermentation. While water is a byproduct of some chemical reactions, in this context, yeast does not produce significant amounts of water during anaerobic respiration. This option is incorrect.

(Option D) Lactic acid and CO2: Lactic acid is produced during a different type of anaerobic respiration called lactic acid fermentation. This process is common in some animals and bacteria, but yeast primarily produces ethanol and CO2 during anaerobic respiration.

Subject: Biology

Topic: Bio-energetics

Subtopic: Anaerobic respiration (respiration without oxygen)

Difficulty Level: Easy

Explanation

(Option A) Arachnoid Mater: The arachnoid mater is indeed the middle layer of the meninges. It is a thin, web-like membrane that lies between the dura mater (outer layer) and the pia mater (inner layer). It helps protect the brain and spinal cord by providing a cushioning effect.

(Option B) Pia Mater: The pia mater is the innermost layer of the meninges. It is a thin and delicate membrane that directly covers the surface of the brain and spinal cord. It provides support and protection to these structures and also helps in the circulation of cerebrospinal fluid.

(Option C) Dura Mater: The dura mater is the outermost layer of the meninges. It is a tough and fibrous membrane that surrounds the brain and spinal cord. It provides a protective barrier and helps keep the central nervous system in place within the skull and vertebral canal.

(Option D) Cranium: The cranium is not a layer of the meninges. It is the bony structure that forms the skull, providing protection to the brain. While the cranium is essential for safeguarding the brain, it is not part of the meninges.

Subject: Biology

Topic: Coordination and Control/Nervous & Chemical Coordination

Subtopic: Transmission of action potential between cells–synapse

Difficulty Level: Moderate

The Three Layers of Meninges

Explanation

(Option D) Proteins: Proteins are the most abundant organic compounds in mammalian cells. They are large, complex molecules made up of amino acids, and they perform a vast array of functions within organisms, including catalyzing metabolic reactions (enzymes), DNA replication, responding to stimuli, transporting molecules, and providing structure (e.g., collagen in connective tissues). Proteins account for about 50% of the dry weight of cells, making them the most abundant organic molecules.

(Option A) Water: Water is indeed the most abundant substance in mammalian cells, but it is not an organic compound. Water (H₂O) is an inorganic molecule, essential for various cellular processes such as chemical reactions, nutrient transport, and temperature regulation. Although water is crucial and constitutes about 70-80% of the cell's total mass, it doesn't count as an organic compound.

(Option B) Lipids: Lipids are a diverse group of organic compounds that include fats, oils, waxes, and steroids. They play key roles in energy storage, cell membrane structure, and signaling. While lipids are abundant and essential in cells, they are not the most abundant organic compounds in terms of mass or number of molecules.

(Option C) Carbohydrates: Carbohydrates are organic compounds made of carbon, hydrogen, and oxygen, usually in a ratio of 1:2:1 (like glucose, C₆H₁₂O₆). They are crucial for energy storage and supply (e.g., glucose), structural components (e.g., cellulose in plants), and signaling. Although carbohydrates are vital and plentiful in cells, they are not the most abundant organic compounds in mammalian cells.

Subject: Biology

Topic: Biological Molecules

Subtopic: Introduction to biological molecules

Difficulty Level: Moderate

Explanation

(Option B) Chemosynthetic bacteria: Chemosynthetic bacteria are organisms that can synthesize organic compounds from inorganic molecules using energy derived from chemical reactions, rather than from sunlight. They are typically found in environments such as deep-sea hydrothermal vents, where sunlight is not available, but chemical energy sources like hydrogen sulfide are abundant.

Nitrifying bacteria, such as Nitrosomonas and Nitrobacter, are examples of chemosynthetic bacteria. They play a crucial role in the nitrogen cycle by converting ammonia (NH3) to nitrite (NO2-) and then to nitrate (NO3-).

(Option A) Heterotrophic bacteria: Heterotrophic bacteria are organisms that cannot synthesize their own food and rely on organic carbon sources for energy. They obtain their carbon from organic compounds produced by other organisms. Examples include many common bacteria that decompose organic matter, such as those involved in the decay of dead organisms.

(Option C) Saprophytic bacteria: Saprophytic bacteria are organisms that obtain their nutrition from dead and decaying organic matter. They decompose complex organic molecules into simpler forms, releasing nutrients back into the environment. Examples include bacteria involved in the decomposition of fallen leaves, dead animals, and other organic material in the soil.

(Option D) Parasitic bacteria: Parasitic bacteria are organisms that live on or inside another organism (the host) and obtain their nutrition from the host. They often cause harm to the host organism, either by consuming its tissues or by producing toxins. Examples include bacteria that cause diseases such as tuberculosis, cholera, and syphilis.

Subject: Biology

Topic:  Life Process in Animals & Plants

Subtopic:  Water and Mineral Uptake Mechanisms in Plants

Difficulty Level: Moderate

Explanation

(Option D) Heat: Heat is a significant factor in determining the resistance of microorganisms. Spores, particularly bacterial endospores, are renowned for their ability to withstand high temperatures, often much higher than those tolerated by cysts. This resistance to heat is a key feature of spores, allowing them to survive harsh conditions and germinate when conditions become favorable again.

(Option A) Light: Cysts and spores can both be affected by light, although some spores may have adaptations to resist UV radiation to some extent. However, light is not typically a primary factor in their resistance.

(Option B) Desiccation: Desiccation refers to the process of drying out. While both cysts and spores can withstand desiccation to some degree, spores are generally more resistant due to their specialized structures, such as tough outer coats.

(Option C) pH: Both cysts and spores can exhibit resistance to changes in pH to some extent, but neither of them is solely resistant or vulnerable to pH changes compared to the other factors listed.

Subject: Biology

Topic: Prokaryotes Reproduction

Subtopic: Cellular Structure of bacteria (Fission and spore formation)

Difficulty Level: Moderate

Explanation

A hinge joint is a type of synovial joint that operates like a door hinge, allowing movement primarily in one plane, like the opening and closing of a door. Here's an explanation of each option:

(Option A) Humerus and radio-ulna: This option refers to the elbow joint. The humerus is the bone of the upper arm, while the radius and ulna are the bones of the forearm. The hinge joint between the humerus and the ulna allows for flexion and extension of the forearm.

(Option B) Femur and pectoral girdle: The femur is the thigh bone, and the pectoral girdle consists of the bones that connect the upper limbs to the axial skeleton. There is no direct hinge joint between the femur and the pectoral girdle.

(Option C) Femur and acetabulum: The acetabulum is a part of the pelvis where the femur forms the hip joint. While the hip joint does allow for movement in multiple directions, including some degree of rotation, it is not considered a hinge joint.

(Option D) Humerus and pectoral girdle: There is no direct hinge joint between the humerus and the pectoral girdle. The shoulder joint, which involves the humerus and the scapula (a bone of the pectoral girdle), is a ball-and-socket joint, allowing for a wide range of motion.

Subject: Biology

Topic:  Support & movement

Subtopic: Types of Joints

Difficulty Level: Hard

Types of Joints

Explanation

(Option C) A different conformation but fit into the active site: Non-competitive inhibitors bind to a site on the enzyme that is distinct from the active site, called the allosteric site. When they bind, they induce a conformational change in the enzyme, which reduces the enzyme's activity by either inhibiting substrate binding or hindering the catalytic function. Despite having a different conformation, they still fit into the allosteric site.

(Option A) A similar structure to the normal substrate molecule: Non-competitive inhibitors typically do not have a similar structure to the substrate molecule. If they did, they would compete with the substrate for binding to the active site, making them competitive inhibitors, not non-competitive.

(Option B) A quite different structure from the substrate molecule: This is partially correct, but it doesn't fully capture the concept. Non-competitive inhibitors indeed have a different structure from the substrate molecule, but the crucial point is that they don't necessarily bind to the active site. Instead, they typically bind to an allosteric site on the enzyme.

(Option D) A similar conformation but does not fit into the active site: If the inhibitor had a similar conformation but did not fit into the active site, it might still be able to bind competitively, which would make it a competitive inhibitor rather than a non-competitive one.

Subject: Biology

Topic: Enzymes

Subtopic: Enzyme Inhibition

Difficulty Level: Hard

Non-competitive inhibition

This occurs when:

• an inhibitor does not bind to the active site but binds to a different part of the enzyme
• this changes the active site shape
• this stops the substrate binding to the enzyme and decreases the reaction rate
• Non-competitive inhibition cannot be reversed by increasing the substrate concentration.
• Examples of non-competitive inhibitors include cyanide, mercury and silver.

Explanation

(Option A) Maternal-foetal incompatibility: Maternal-foetal incompatibility, also known as Rh incompatibility, occurs when a Rh-negative mother carries a Rh-positive fetus. During childbirth or other instances where the mother's and baby's blood may mix, the mother's immune system may produce antibodies against the Rh-positive blood cells in the fetus. This can lead to various complications for the baby, including hemolytic disease of the newborn (HDN), which can result in jaundice, anemia, and even neurological damage if severe.

(Option B) Paternal-foetal incompatibility: While there can be blood type incompatibility between father and fetus, it's less concerning than Rh incompatibility. The mother's immune system is the primary concern in this scenario.

(Option C) Cancer of fetus: There is no direct correlation between the Rh factor difference and cancer of the fetus. Rh incompatibility primarily affects the blood and can lead to hemolytic disease of the newborn but not cancer.

(Option D) Death of mother: While Rh incompatibility can cause complications for the baby, such as hemolytic disease of the newborn, it does not directly result in the death of the mother. However, if the complications arising from Rh incompatibility are severe and left untreated, they could indirectly contribute to maternal mortality, but this is not a direct consequence of the Rh factor difference.

Subject: Biology

Topic:  Variation & genetics/inheritance

Subtopic: Rh blood group system

Difficulty Level: Hard

ABO blood group system