Answer: Auxin accumulates on the lower side due to gravity. In stems, higher auxin concentration stimulates growth, causing the lower side to grow faster and bend the stem upwards.
Designing: Clinostat.
Answer: Rotate the plant slowly. Gravity acts on all sides equally, so the plant grows straight.
Analysis: Stem vs Root auxin.
Answer: Stems have a higher optimal concentration for growth than roots. The same concentration that stimulates a stem inhibits a root.
Differential growth name.
Answer: Tropism.
Case Study 2:
Gardener wants flowers out of season and to kill weeds.
6. Hormone for flowering?
Answer: Gibberellins.
Synthetic hormone as weedicide?
Answer: 2,4-D (2,4-Dichlorophenoxyacetic acid).
Creating: Schedule.
Answer: Apply 2,4-D in early spring to kill young weeds; apply Gibberellins when plant size is sufficient for flowering.
Critical Thinking: Why specific to broad-leaved?
Answer: Broad-leaved plants (dicots) have a higher absorption rate and different metabolic sensitivity to 2,4-D compared to narrow-leaved grasses (monocots).
Directions: (a) Both A/R true, R explains A; (b) Both true, R doesn't explain A; (c) A true, R false; (d) A false, R true.
Assertion (A): Decapitation promotes lateral growth.
Reason (R): Apical dominance is caused by Auxins.
Answer: (a) Both A and R are true and R is the correct explanation.
Assertion (A): ABA is "Stress Hormone".
Reason (R): It stimulates closure of stomata.
Answer: (a) Both A and R are true and R is the correct explanation.
Assertion (A): Ethylene is unique.
Reason (R): It is a gaseous hormone.
Answer: (a) Both A and R are true and R is the correct explanation.
Assertion (A): Roots show positive phototropism.
Reason (R): Roots grow towards light.
Answer: (d) A is false but R is true (in its definition, but roots actually show negative phototropism). Actually, A is false and R is false as a fact. Let's fix: (d) A is false. Roots are negatively phototropic.
Assertion (A): Thigmotropism in tendrils.
Reason (R): It is response to touch.
Answer: (a) Both A and R are true and R is the correct explanation.