Q4. What happens to a seed when favourable conditions for growth are absent?
It does not germinate and goes into a period of suspended growth or rest; if viable and non-dormant, it resumes germination once suitable conditions return (NCERT Class 11, page 166).
Q5. Assertion: abscisic acid helps seeds survive unfavourable periods. Reason: abscisic acid induces dormancy, which helps seeds withstand desiccation. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion (NCERT pages 177–178).
Q6. In a maize grain, which sheath protects (a) the plumule and (b) the radicle?
(a) The coleoptile; (b) the coleorhiza (NCERT Class 11, page 67).
Q7. What makes the apical hook form in a dicot seedling, and when does the hook straighten?
Ethylene causes apical hook formation in dicot seedlings (NCERT page 177). Beyond the NCERT text, the hook is typical of seedlings growing in darkness, and it straightens once the seedling is exposed to light (Armarego-Marriott and colleagues, Journal of Experimental Botany, 2020).