General Q&A for Class 12 · Page 62
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
What kind of appendages are present in coelenterates?
Coelenterates (phylum Cnidaria) possess tentacles as their primary appendages. These specialized structures surround the mouth and serve multiple functions: Prey capture: Tentacles are armed with specialized stinging cells called cnidocytes or nematocysts that inject toxins to paralyze prey Defense: Protection against predators through stinging capabilities Food mani
- GeneralClass 12All
Ingestion of solid food occurs in which type of nutrition?
Ingestion of solid food particles occurs in holozoic nutrition (also called heterotrophic nutrition). This feeding method involves: Ingestion: Taking in solid or liquid food Digestion: Breaking down complex food molecules into simpler, absorbable forms Absorption: Taking up digested nutrients into cells Assimilation: Using absorbed nutrients for energy and growth</
- GeneralClass 12All
Corals belong to which phylum of animals?
Corals belong to phylum Cnidaria (also called Coelenterata), specifically to class Anthozoa. Characteristics of corals include: Colonial or solitary: Most reef-building corals are colonial polyps Calcium carbonate skeleton: Secrete hard external skeletons forming coral reefs Symbiotic relationship: Harbor photosynthetic algae called zooxanthellae in their tissues <
- GeneralClass 12All
Which phylum does Octopus belong to?
The octopus belongs to phylum Mollusca (or Mollusks), specifically to class Cephalopoda. Mollusca is the second-largest animal phylum, characterized by soft bodies, and many species have shells (though octopuses have lost theirs through evolution). Cephalopods, including octopuses, squids, and cuttlefish, represent the most intelligent and advanced mollusks, featuring complex nervous systems, excellent vision, tentacles with suckers, and remarkable camouflage
- GeneralClass 12All
What is the other name of Cyanobacteria?
Cyanobacteria are commonly called blue-green algae due to their characteristic blue-green coloration from photosynthetic pigments. However, this common name is scientifically misleading because cyanobacteria are prokaryotic bacteria, not true algae (which are eukaryotic). Other names include: Cyanophyta (in older classification systems) Blue-green bacteria These photosynthetic microorg
- GeneralClass 12All
Vascular bundles are scattered and closed in which group of angiosperms?
Monocotyledonous plants (monocots) have scattered and closed vascular bundles. Key characteristics include: Scattered arrangement: Vascular bundles are randomly distributed throughout the stem's ground tissue rather than arranged in a ring, as seen in dicots. Closed vascular bundles: They lack cambium (lateral meristematic tissue) between xylem and phloem, preventing secondary growth. This means monocot stems
- GeneralClass 12All
Name an annelid that sucks blood from its host.
Leech (genus Hirudo, particularly Hirudo medicinalis—the medicinal leech) is an annelid that feeds on blood. Leeches belong to class Hirudinea within phylum Annelida. Key characteristics include: Ectoparasitic: Attach externally to hosts Specialized suckers: Anterior and posterior suckers for attachment Anticoagulant secretion: Produce hirudin, preven
- GeneralClass 12All
What are the two main ways oxygen is consumed and carbon dioxide is produced?
The two primary processes that consume oxygen and produce carbon dioxide are cellular respiration and combustion. Cellular respiration is a biological process occurring in living organisms, where cells break down glucose and other organic molecules using oxygen to release energy, producing CO₂ and water as byproducts. This process is essential for life, providing the energy needed for all cellular activities. Combustion, or burning, is a chemical reaction whe
- GeneralClass 12All
What are natural resources?
Natural resources are materials and substances occurring in nature that can be exploited for economic gain or used to support life. These include both renewable resources like sunlight, wind, forests, and freshwater, which can regenerate or replenish themselves over time, and non-renewable resources like fossil fuels, minerals, and metals, which exist in finite quantities and take millions of years to form. Natural resources provide the raw materials for human civilization&md
- GeneralClass 12All
What are the two main processes that contribute to soil formation?
Weathering and biological activity are the two fundamental processes driving soil formation. Weathering (both physical and chemical) breaks down parent rock material into smaller mineral particles that form the inorganic component of soil. Physical weathering creates fragments, while chemical weathering alters the minerals' composition, making nutrients more available to plants. Biological activity introduces the organic component—decomposing plant and
- GeneralClass 12All
Why is air called the "breath of life"?
Air is called the "breath of life" because it contains oxygen, which is essential for cellular respiration in most living organisms. Animals, plants (during non-photosynthetic periods), fungi, and many microorganisms require oxygen to convert nutrients into usable energy through aerobic respiration. This process is far more efficient than anaerobic metabolism, producing approximately 18 times more energy from glucose. Without a continuous supply of oxygen from the air, comple
- GeneralClass 12All
Why is life not possible on Venus and Mars?
Life as we know it cannot exist on Venus and Mars due to their extreme atmospheric conditions and lack of liquid water. Venus has a runaway greenhouse effect with surface temperatures around 450°C (850°F)—hot enough to melt lead—and crushing atmospheric pressure 90 times greater than Earth's. Its thick carbon dioxide atmosphere traps heat so effectively that Venus is actually hotter than Mercury, despite being farther from the sun. Mars fa
- GeneralClass 12All
Why do Earth and two other planets have atmospheres?
Earth, Venus, and Mars all possess atmospheres, though of vastly different compositions and densities. Planets can retain atmospheres when their gravitational pull is strong enough to prevent atmospheric gases from escaping into space and when they receive sufficient volcanic activity or other outgassing processes to create and replenish atmospheric gases. Earth's atmosphere formed from volcanic outgassing early in its history and was later transformed by bio
- GeneralClass 12All
Which organisms carry out denitrification in the nitrogen cycle?
Denitrifying bacteria, including species from genera like Pseudomonas, Thiobacillus, and Clostridium, perform denitrification in the nitrogen cycle. These specialized microorganisms convert nitrates (NO₃⁻) and nitrites (NO₂⁻) in soil back into atmospheric nitrogen gas (N₂), completing the nitrogen cycle. Denitrification primarily occurs in oxygen-poor (anaerobic) conditions, such as waterlogged soils, wetlands, and aquatic sediments. While this proc
- GeneralClass 12All
What are three physical agents that cause weathering of rocks?
The three primary physical weathering agents are temperature changes, water (freeze-thaw action), and wind. Temperature fluctuations cause rocks to expand when heated and contract when cooled; repeated cycles create stress that eventually cracks rocks apart, particularly in desert environments with extreme day-night temperature variations. Water is perhaps the most powerful weathering agent—when it enters rock cracks and freezes, it exp
- GeneralClass 12All
What are two significant effects of soil erosion?
Soil erosion causes loss of fertile topsoil and water pollution. The removal of nutrient-rich topsoil severely reduces agricultural productivity, as this layer contains the organic matter and minerals essential for plant growth. It can take hundreds to thousands of years to naturally form just one inch of topsoil, but intensive erosion can remove it in mere decades. This loss forces farmers to use more fertilizers, increasing costs and environmental impacts.
- GeneralClass 12All
What does smog indicate about air quality?
Smog is a visible indicator of severe air pollution, signaling the presence of harmful concentrations of ground-level pollutants. The term combines "smoke" and "fog," and modern smog typically forms when nitrogen oxides and volatile organic compounds from vehicles and industry react with sunlight to create photochemical smog. The presence of smog indicates elevated levels of ozone, particulate matter, and other pollutants that pose serious health risks, particularly for child
- GeneralClass 12All
What compound in marble reacts with acids in acid rain?
Calcium carbonate (CaCO₃) is the primary compound in marble that reacts with acids in acid rain. When sulfuric or nitric acid from acid rain contacts marble, a chemical reaction occurs: the acid dissolves the calcium carbonate, forming soluble calcium sulfate or calcium nitrate, water, and carbon dioxide gas. This reaction gradually erodes the marble surface, causing irreversible damage to historic monuments, sculptures, and buildings. Famous structures like the Taj Mahal, th
- GeneralClass 12All
What is the composition of acid rain and how does it form?
Acid rain primarily consists of sulfuric acid (H₂SO₄) and nitric acid (HNO₃) dissolved in precipitation. It forms when sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) are released into the atmosphere, mainly from burning fossil fuels in power plants, industrial facilities, and vehicles. These pollutants react with water vapor, oxygen, and other atmospheric chemicals to form acidic compounds. When precipitation occurs, these acids fall to Earth in rain, snow, f
- GeneralClass 12All
Can you provide an example of bacteria that converts nitrites into nitrates?
Nitrobacter is a key genus of bacteria that oxidizes nitrites (NO₂⁻) into nitrates (NO₃⁻) through a process called nitrification. These chemolithotrophic bacteria obtain energy by oxidizing nitrites and play a critical role in the second step of the nitrification process. The complete nitrification process involves two stages: first, Nitrosomonas bacteria convert ammonia (NH₃) to nitrites, then Nitrobacter completes the transformation by converting