Q4. Assertion: removing the shoot tip makes a plant bushy. Reason: the growing apical bud inhibits the growth of the lateral buds. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion: decapitation ends apical dominance, so the lateral buds grow (NCERT page 175).
Q5. Name two natural and two synthetic auxins.
Natural: IAA and IBA, isolated from plants; synthetic: NAA and 2,4-D (NCERT page 175).
Q6. From which sources was the natural cytokinin zeatin isolated?
Corn kernels and coconut milk (NCERT page 176).
Q7. Which PGR promotes rapid internode elongation in deep water rice, and why does this help?
Ethylene; it keeps the leaves and upper parts of the shoot above water (NCERT page 177).
Q8. Name four events in a plant’s life that are affected by more than one PGR.
Dormancy in seeds and buds, abscission, senescence and apical dominance (NCERT page 178).
Q9. What disease led to the discovery of gibberellins, and which organism caused it?
The ‘bakanae’ (foolish seedling) disease of rice seedlings, caused by the fungus Gibberella fujikuroi (NCERT page 175).