In leaves, the small openings surrounded by guard cells that allow gas exchange are known as:
A. Lenticels
B. Hydathodes
C. Sclereids
D. Stomata
Answer: Option D
Solution (By JKExamLibrary)
Stomata are microscopic pores typically on the lower epidermis of leaves, bounded by two guard cells that regulate opening and closing for gas exchange (CO₂ in, O₂ out) and transpiration. Lenticels are on bark, hydathodes release water droplets (guttation), sclereids are thick-walled sclerenchyma cells. Stomatal density varies with environmental conditions.
Explanation:
The endocrine islets of Langerhans in the pancreas contain alpha cells that secrete glucagon and beta cells that secrete insulin, which regulate blood glucose. The liver stores and releases glucose, the spleen filters blood, the kidneys excrete waste. The pancreas also has exocrine functions secreting digestive enzymes.
Explanation:
Robert Brown, a Scottish botanist, discovered and named the nucleus in 1831 while studying orchid epidermal cells. Hooke coined 'cell', Schleiden and Schwann formulated cell theory. Brown's observation was pivotal.
Explanation:
Anabaena azollae lives in cavities of the water fern Azolla and fixes atmospheric nitrogen. It is used as a biofertilizer in rice paddies.
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