Which of the following is incorrect?
Mutations do not always result in beneficial changes; they can also be harmful or neutral.
Ref: NCERT Class 12 Biology Chapter 6: Evolution Darwinism Lamarckism and Modern Synthetic Theory
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Which of the following is incorrect?
Lamarck's theory of use and disuse is not widely accepted; Darwin's theory of natural selection is the accepted mechanism of evolution.
Ref: NCERT Class 12 Biology Chapter 6: Evolution Darwinism Lamarckism and Modern Synthetic Theory
Which of the following statements about oxytocin is correct?
Oxytocin, secreted by the posterior pituitary, stimulates uterine contractions and helps in milk ejection during breastfeeding.
Ref: NCERT Class 11 Biology Chapter 19: Chemical Coordination and Integration Endocrine System and Hypothalamus Pituitary Axis
Which group is classified as nonvascular plants?
Tracheophytes including pteridophytes, gymnosperms and angiosperms all contain lignified xylem tracheary elements with bordered pits facilitating efficient long-distance water transport under negative pressure and structural support enabling tall upright growth independent of turgor. Nonvascular plants lack true lignified xylem and phloem, instead possess hydroids lacking lignin and leptoids for conduction plus external capillary action, limiting size to few centimeters. Bryophytes constitute sole recognized extant group occupying nonvascular grade. Classifying bryophytes as nonvascular aligns with morphology, life cycle dominance, and molecular phylogeny distinguishing basal land plants.
Ref: Vanderpoorten & Goffinet Bryophyte Biology 2nd ed.; Campbell Ch 29: Nonvascular
Thick spore walls in land plants mainly protect against
Land plant spores possess complex wall stratification including innermost intine cellulosic, middle exine rich in chemically inert sporopollenin highly resistant polymer derived from lipid metabolism, and outer perispore. Primary adaptive value involves preventing desiccation during prolonged airborne dispersal across dry air, fluctuating humidity and high temperatures, maintaining protoplast viability until germination on moist substrate. While sporopollenin confers resistance against pathogens, chemical degradation and UV, desiccation resistance drives major selection. Herbivory and mechanical damage affect larger vegetative organs, but microscopic spores chiefly face abiotic drying stress during colonization.
Ref: Wellman et al. Sporopollenin wall, J Micropalaeontology; Campbell Ch 29: Spore
Embryos retained within maternal tissue are a feature of
Embryophyte name derived by Bower directly refers to retention and nutritional support of diploid embryo within maternal thallus after fertilization. Unlike algal zygote often released free-living and dormant, land plant zygote divides mitotically developing into multicellular embryo inside archegonium venter receiving nutrients via specialized placental transfer cells with labyrinthine walls, ensuring early development protected from drying and UV. Fungi produce dikaryotic mycelium after plasmogamy, cyanobacteria lack embryonic development completely, most algae lack maternal retention. Matrotrophy represents crucial adaptation allowing offspring survival in variable terrestrial conditions.
Ref: Kenrick 2000 Embryophyte embryo evolution; Campbell Ch 29; Bower Archegoniate
Gametangia in plants are important because they
Plants evolved multicellular gametangia termed antheridia and archegonia enclosing gametes within one or more layers of sterile jacket cells protecting against environmental stress. This architecture protects developing spermatozoids and eggs from desiccation, mechanical abrasion, UV and microbial attack during terrestrial reproduction when exposed to air. Unlike unicellular gametangia of algae releasing gametes directly into ambient water film, jacket cells retain internal moisture and facilitate internal fertilization by chemotaxis. Spore or seed dispersal and food storage involve sporophytic structures like sporangia and endosperm, not gametangial function.
Ref: Graham Biology of Embryophytes; Campbell Ch 29: Gametangia; NCERT Ch 3
The waxy cuticle in plants primarily functions to
Cuticle comprises cutin polyester matrix impregnated and covered by epicuticular waxes deposited on outer epidermal wall of aerial organs of embryophytes. Ultrastructurally it forms continuous hydrophobic barrier dramatically reducing non-stomatal water loss rate by orders of magnitude, preventing tissue desiccation under fluctuating humidity and allowing survival away from water films. Additional functions include UV screening, mechanical defense, prevention of pathogen entry and self-cleaning, but primary selective pressure during terrestrialization was water retention. CO2 absorption occurs via stomata whose opening regulated; cuticle actually impedes gas exchange.
Ref: Raven et al. Cuticle chemistry; Campbell Ch 29: Adaptations to land; Taiz Plant Physiology
The earliest land plants appeared approximately
Molecular clocks calibrated with fossils, cryptospore fossils and early macrofossils place earliest embryophytes in mid Ordovician to early Silurian, approximately 470 million years ago, long after Cyanobacteria origin. Evidence includes tetrahedral cryptospore tetrads and dyads with sporopollenin walls from Oman, Argentina and China deposits, plus liverwort-like cuticle fragments and thalloid compressions. Vascular plants appeared later near 430 million years ago. This timeframe predates Devonian forests and far exceeds 100 million years which corresponds to angiosperm radiation. Three point two billion and one billion correspond to prokaryotic and early eukaryotic algal evolution.
Ref: Wellman & Gray 2000 Cryptospores 470 Ma, Nature; Edwards et al. Early land plants