Which of the following plant hormones delays leaf senescence (aging)?
A. Ethylene
B. Auxin
C. Abscisic acid
D. Cytokinin
Answer: Option D
Solution (By JKSSB Mock Tests)
Cytokinins are plant hormones that promote cell division, delay senescence by preventing chlorophyll degradation, and stimulate nutrient mobilization. Ethylene promotes ripening and senescence, abscisic acid promotes abscission and dormancy, auxin is involved in cell elongation. Cytokinins are synthesized in roots and transported upward. They are used to prolong the shelf life of leafy vegetables.
Explanation:
Andreas Schimper first described chloroplasts and coined the term in 1883. Hooke discovered cells, Leeuwenhoek observed live cells, Sachs showed starch is produced by photosynthesis.
Explanation:
Rhizopus stolonifer belongs to the class Phycomycetes (or Zygomycetes). These fungi are characterized by a coenocytic (multinucleate, aseptate) mycelium and reproduce asexually by forming motile or non-motile spores in sporangia. Ascomycetes (sac fungi) have septate hyphae and produce ascospores in asci. Basidiomycetes (club fungi) produce basidiospores on basidia. Deuteromycetes are imperfect fungi lacking a known sexual stage.
Explanation:
Lymphatic vessels collect interstitial fluid (lymph) and return it to the venous circulation (subclavian veins). This maintains fluid balance. Along the way, lymph nodes filter pathogens. The heart pumps blood, kidneys filter blood, lungs exchange gases. The lymphatic system is unidirectional.
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