General Q&A for Class 12 · Page 255
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
Red tide causing organism belongs to which group of photosynthetic protists?
Solution:Dinoflagellates are responsible for red tide phenomena. Mechanism of Red Tide: Rapid multiplication (algal bloom) of dinoflagellates like Gonyaulax Release of saxitoxin and brevetoxin (neurotoxins) Water appears red/brown due to pigment concentration Causes mass mortality of fish and other marine organisms K
- GeneralClass 12All
Who classified animals into Anaima and Enaima?
Solution:Aristotle classified animals into two major groups: Category Meaning Characteristics Examples Enaima "With blood" <td w
- GeneralClass 12All
Who classified plants into herbs, shrubs, and trees?
Solution:Aristotle (384-322 BCE), the Greek philosopher and naturalist, developed this morphological classification system for plants. Aristotle's Plant Classification: Herbs: Small, non-woody plants (e.g., wheat, mustard) Shrubs: Medium-sized, woody plants with multiple stems (e.g., rose, hibiscus) Trees: Large, woody plants with single trunk (e.g.,
- GeneralClass 12All
Expand TMV.
Solution:TMV = Tobacco Mosaic Virus Structural Features: Shape: Rod-shaped (helical) Nucleic Acid: Single-stranded RNA (ssRNA) Protein Coat: 2,130 identical capsomere subunits Length: Approximately 300 nm Diameter: 18 nm Historical Significance: TMV was the first v
- GeneralClass 12All
Name the chemical substance present in the bacterial cell wall.
Solution: Peptidoglycan (also called murein) is the primary structural component of bacterial cell walls. Chemical Composition: N-acetylglucosamine (NAG) N-acetylmuramic acid (NAM) Peptide cross-links (typically containing D-amino acids) Bacterial Type
- GeneralClass 12All
Who coined the term virus?
Solution: Louis Pasteur coined the term "virus" (Latin for "poison" or "slimy liquid") in the late 19th century while studying infectious agents. Historical Timeline: 1892:J. Ivanowsky discovered tobacco mosaic disease agent 1898:W. Beijerinck termed it Contagium vivum fluidum 1935:M. Stanley crystallized Tobacco Mosaic Virus (TMV)
- GeneralClass 12All
Why are some fungi called 'fungi imperfecti'?
Solution: Certain fungi are designated as 'fungi imperfecti' or Deuteromycetes because they lack a known sexual (perfect) reproductive stage. Only their asexual and vegetative phases have been observed in laboratory conditions. Scientific Classification: Class: Deuteromycetes Reproduction: Asexual spores (conidia) Examples: Alternaria, Colletotrichum
- GeneralClass 12All
What are monerans?
Monerans are unicellular prokaryotic organisms lacking a well-defined nucleus and membrane-bound organelles. They possess a primitive nucleoid region containing naked DNA without histone proteins. Characteristics: Prokaryotic cell organization 70S ribosomes Cell wall composed of peptidoglycan (except Archaebacteria) Reproduce primarily through binary fission Pro Tip: Remember that monerans r
- GeneralClass 12All
Write a note on the kingdom Monera.
The kingdom Monera comprises all prokaryotic organisms—bacteria and cyanobacteria (blue-green algae)—characterized by the absence of a well-defined nucleus and membrane-bound organelles. These are the most primitive and ancient forms of life on Earth, with fossil evidence suggesting their existence over 3.5 billion years ago, long before any eukaryotic organisms evolved. Monerans are unicellular organisms with a simple cell structure: their genetic material (DNA) exists as a singl
- GeneralClass 12All
How are Pteridophytes different from Bryophytes?
Pteridophytes and bryophytes represent successive levels of evolutionary advancement in plant complexity, with pteridophytes being the first vascular land plants while bryophytes remain non-vascular. The most significant difference is that pteridophytes possess well-developed vascular tissue—xylem for water and mineral transport and phloem for food distribution—which allows them to grow much larger and inhabit drier environments than bryophytes, which lack these specialized conduc
- GeneralClass 12All
What are slime moulds? How are they different from protozoa?
Slime moulds are unique organisms classified within the kingdom Protista that exhibit characteristics of both fungi and animals at different stages of their life cycle, making them fascinating subjects for biological study. During their feeding stage, slime moulds exist as a plasmodium—a multinucleate, amoeba-like mass of protoplasm that creeps along decaying logs, leaf litter, or moist soil, engulfing bacteria, fungal spores, and organic particles through phagocytosis. When environment
- GeneralClass 12All
Give the differences between gymnosperms and angiosperms.
Gymnosperms and angiosperms represent two major evolutionary groups of seed plants with fundamental differences in their reproductive structures and strategies. The most obvious distinction is that gymnosperms produce naked seeds exposed on cone scales or similar structures, while angiosperms produce seeds enclosed within fruits that develop from the ovary wall after fertilization. Gymnosperms lack flowers and instead produce pollen and ovules in separate male and female cones, relying primar
- GeneralClass 12All
Name any two liverworts.
Marchantia and Riccia are two common and widely studied examples of liverworts, representing the diversity within this group of bryophytes. Marchantia is perhaps the most familiar liverwort, easily recognized by its flat, ribbon-like green thallus with a distinctive pattern of polygonal markings on the upper surface, often found growing on moist soil, rocks, or near water bodies. It reproduces both sexually through specialized umbrella-like structures (archegoniophores and antheridiophores) a
- GeneralClass 12All
Name the group of plants which produce seeds but not fruits.
Gymnosperms are the group of plants that produce seeds but not fruits, with their seeds developing exposed on the surface of cone scales or similar structures rather than being enclosed within a protective fruit wall. The name "gymnosperm" derives from Greek words meaning "naked seed," directly referring to this characteristic feature that distinguishes them from flowering plants. Common examples include conifers like pine, fir, spruce, and cedar trees, as well as cycads, ginkgo, and gnetophy
- GeneralClass 12All
What are saprophytes? Saprotrophism is the characteristic feature of which group?
Saprophytes, more accurately termed saprotrophs, are organisms that obtain their nutrition by feeding on dead and decaying organic matter, playing a vital role as nature's decomposers. These organisms secrete powerful digestive enzymes onto dead plant and animal material, breaking down complex organic compounds into simpler substances that they then absorb for nutrition. This mode of nutrition is called saprotrophism or saprophytic nutrition, and it's essential for nutrient recycling in ecosy
- GeneralClass 12All
Name the three groups of the kingdom Protista.
The kingdom Protista is traditionally divided into three main groups based on their modes of nutrition and locomotion: Chrysophytes (golden algae and diatoms), Dinoflagellates, and Euglenoids among the plant-like protists; Slime moulds and Protozoans representing fungus-like and animal-like forms respectively. More specifically, the three major groups commonly referenced are Chrysophytes, which are primarily photosynthetic organisms with silica cell walls; Dinoflagellates, which are mostly ma
- GeneralClass 12All
Give one characteristic feature of the division Bryophyta.
The most distinctive characteristic feature of Bryophyta is the absence of vascular tissue (xylem and phloem), making them non-vascular plants that rely on diffusion and osmosis for water and nutrient transport. This fundamental limitation restricts bryophytes to small sizes and moist environments, as they cannot efficiently transport water and minerals over long distances like vascular plants. Without specialized conducting tissues, water moves slowly from cell to cell, which is why mosses,
- GeneralClass 12All
What are cotyledons?
Cotyledons are the embryonic seed leaves present in the seed of a plant, serving as the first leaves to appear during germination and playing a crucial role in early seedling nutrition. These specialized structures store food reserves—primarily proteins, carbohydrates, and lipids—that nourish the developing embryo until the seedling can produce its own food through photosynthesis. In some plants, cotyledons emerge above ground and turn green to photosynthesize (epigeal germination
- GeneralClass 12All
Cycas and Pinus belong to which group of plant kingdom?
Cycas and Pinus both belong to the group Gymnosperms, which are seed-bearing vascular plants characterized by having "naked seeds" that are not enclosed within a fruit. The term gymnosperm literally means "naked seed" in Greek, referring to the fact that their seeds develop on the surface of cone scales or specialized structures rather than being protected inside an ovary. Cycas represents the cycads, an ancient group with palm-like appearance and large compound leaves, while Pinus (pine tree
- GeneralClass 12All
Give two examples of algae.
Spirogyra and Chlamydomonas are two common examples of algae that demonstrate the diversity within this group of photosynthetic organisms. Spirogyra is a filamentous green alga often found in freshwater ponds and slow-moving streams, recognizable by its ribbon-like spiral chloroplasts that give it a distinctive appearance under the microscope. Chlamydomonas, on the other hand, is a unicellular green alga that moves using two flagella and is widely studied in laboratory settings to understand