Entrance Exams
Govt. Exams
Mesophyll tissue consists of palisade and spongy parenchyma and is located between the two epidermal layers.
Guard cells are specialized epidermal cells that change shape to open or close the stomatal pore.
Stomata are pores in the leaf epidermis that regulate gas exchange (CO2 intake, O2 release) and transpiration.
Monocot stems have scattered vascular bundles throughout the ground tissue, unlike dicots which have ring-arranged bundles.
Cork tissue (phellem) is produced outward by the cork cambium (phellogen), which is a lateral meristem.
Xylem is a vascular tissue that transports water and mineral nutrients from roots to aerial parts of the plant.
In early vascular plants like Rhyniophytes, the evolution of true leaves with expanded surface area was critical for maximizing photosynthesis in terrestrial environments. Though roots evolved to access underground water, the immediate advantage for terrestrial survival was increased photosynthetic capability. True leaves with organized vascular tissue provided both structural support and efficient light capture, giving competitive advantage over earlier bryophytes.
Gymnosperms are characterized by naked ovules that are not enclosed within an ovary wall. This distinguishes them from angiosperms (which have ovules in ovaries) and pteridophytes (which lack seeds). The term 'gymnosperm' literally means 'naked seed'.
The shift from gametophytic to sporophytic dominance in pteridophytes is advantageous because: (1) Sporophytes with indeterminate growth can produce more spores, increasing reproductive success, and (2) Spores with thick protective walls (sporopollenin) can survive in drier environments, reducing dependence on moisture. This represents a major evolutionary transition.
In gymnosperms like Pinus, the mature male gametophyte (pollen grain) at the time of pollination contains 2 vegetative cells (tube cell and prothallial cell) and 1 generative cell that later divides to form sperm cells.