Plant Growth and Development

13 NEET-UG practice questions on Plant Growth and Development, part of Botany. The first 13 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Easy

   A root elongates at a constant rate, with only one daughter cell of each division continuing to divide. Which equation describes this growth?

   1. ALₜ = L₀ × rt
   2. BLₜ = L₀ + rt
   3. CW₁ = W₀e^(rt)
   4. DLₜ = L₀ − rt

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   Answer: B · Lₜ = L₀ + rt

   When only one daughter cell keeps dividing, length rises at a constant rate. This is arithmetic growth, and it gives a straight line on a graph of length against time.

   • A: Multiplying gives zero length at time zero, which is not arithmetic growth.
   • C: This exponential form describes geometric growth, with both daughter cells dividing.
   • D: A minus sign would mean the root shortens with time.

   Remember this

   Arithmetic growth gives a straight line with Lₜ = L₀ + rt; geometric growth gives a sigmoid curve with W₁ = W₀e^(rt).

2. Question 2 · Medium

   In one day, leaf P grows from 8 cm² to 12 cm², while leaf Q grows from 40 cm² to 44 cm². Which comparison is correct?

   1. ASame absolute growth and same relative growth
   2. BSame relative growth, and the absolute growth of Q is five times that of P
   3. CSame absolute growth, and the relative growth of P is five times that of Q
   4. DSame absolute growth, and the relative growth of Q is five times that of P

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   Answer: C · Same absolute growth, and the relative growth of P is five times that of Q

   Both leaves gain 4 cm², so absolute growth is equal. Relative growth is P = 4/8 = 50% and Q = 4/40 = 10%, and 50/10 = 5.

   • A: Relative growth differs, at 50% and 10%.
   • B: Absolute gain is equal, at 4 cm² each.
   • D: This divides by size wrongly, as the smaller leaf has the higher relative rate.

   Remember this

   Relative growth divides the gain by the previous size, so a small leaf with the same gain has the higher rate.

3. Question 3 · Medium

   Match List-I with List-II. List-I (regulator) A. IBA B. GA₃ C. Cytokinin D. Ethephon List-II (use or effect) I. Hastens ripening of tomatoes and apples II. Initiates rooting in stem cuttings III. Elongates grape stalks IV. Helps overcome apical dominance

   1. AA-II, B-III, C-IV, D-I
   2. BA-III, B-II, C-IV, D-I
   3. CA-I, B-III, C-IV, D-II
   4. DA-II, B-IV, C-III, D-I

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   Answer: A · A-II, B-III, C-IV, D-I

   IBA is an auxin used for rooting of cuttings. Gibberellins lengthen grape stalks. Cytokinins promote lateral shoot growth and so overcome apical dominance. Ethephon releases ethylene, which hastens fruit ripening.

   • B: This swaps the uses of auxin and gibberellin.
   • C: This swaps the uses of auxin and ethephon.
   • D: This swaps the uses of gibberellin and cytokinin.

   Remember this

   Ethephon is the main ethylene source in agriculture because it is absorbed and transported, then releases ethylene slowly.

4. Question 4 · Hard

   A seedling grows geometrically with r = 0.07 per day. How long does its dry weight take to rise from 5 g to 20 g? Take ln 2 = 0.7.

   1. A20 days
   2. B214 days
   3. C30 days
   4. D10 days

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   Answer: A · 20 days

   W₁ = W₀e^(rt), so rt = ln(20/5) = ln 4 = 2 × 0.7 = 1.4, and t = 1.4/0.07 = 20 days. Check by doublings: one doubling takes 0.7/0.07 = 10 days, and 5 g to 10 g to 20 g is two doublings, which is 20 days.

   • B: This uses arithmetic growth, 15/0.07, instead of the exponential form.
   • C: This counts three doublings, which would reach 40 g.
   • D: This counts only one doubling.

   Remember this

   In geometric growth, doubling time is ln 2 divided by r, and it stays constant during the log phase.

5. Question 5 · Medium

   Consider these statements on ethylene. A. It promotes apical hook formation in dicot seedlings. B. It promotes root hair formation. C. It delays fruit ripening. D. It promotes male flowers in cucumbers. Which of these are correct?

   1. AA and B only
   2. BB, C and D only
   3. CA, B and C only
   4. DC and D only

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   Answer: A · A and B only

   Ethylene gives apical hooks in dicot seedlings and raises root hair formation. It hastens fruit ripening, and in cucumbers it promotes female flowers and so raises yield. Hence only A and B hold.

   • B: C and D are false, and A has been left out.
   • C: C is false, because ethylene hastens ripening.
   • D: Both C and D reverse the true effects.

   Remember this

   Ethylene hastens ripening, abscission and senescence; in cucumbers it promotes female flowers.

6. Question 6 · Easy

   Which sequence of phases does a sigmoid growth curve show?

   1. AStationary, log, lag
   2. BLog, lag, stationary
   3. CLag, stationary, log
   4. DLag, log, stationary

   Answer and explanation in LearnFree account

7. Question 7 · Medium

   Given below are two statements: Statement I: Interfascicular cambium and cork cambium arise when differentiated parenchyma cells regain the power to divide. Statement II: Cells formed by such dedifferentiated meristems may lose the capacity to divide and mature again, which is called redifferentiation. Choose the correct answer.

   1. ABoth Statement I and Statement II are incorrect
   2. BBoth Statement I and Statement II are correct
   3. CStatement I is incorrect but Statement II is correct
   4. DStatement I is correct but Statement II is incorrect

   Answer and explanation in LearnFree account

8. Question 8 · Medium

   Arrange these regions in the order met when moving upward from the very tip of a root. A. Region of elongation B. Root cap C. Region of maturation D. Meristematic region

   1. AD, B, A, C
   2. BB, D, A, C
   3. CB, A, D, C
   4. DB, D, C, A

   Answer and explanation in LearnFree account

9. Question 9 · Easy

   Which synthetic auxin is widely used to kill dicotyledonous weeds?

   1. A2,4-D
   2. BGA₃
   3. CZeatin
   4. DIAA

   Answer and explanation in LearnFree account

10. Question 10 · Hard

    Assertion A: Abscisic acid stimulates the closure of stomata during water stress. Reason R: Abscisic acid helps seeds to withstand desiccation and enter dormancy. Choose the correct answer.

    1. ABoth A and R are correct but R is not the correct explanation of A
    2. BA is correct but R is not correct
    3. CA is not correct but R is correct
    4. DBoth A and R are correct and R is the correct explanation of A

    Answer and explanation in LearnFree account

11. Question 11 · Hard

    Three similar shoots are treated as follows. P: the shoot tip is removed. Q: the shoot tip is removed and auxin paste is applied to the cut end. R: the tip is left on, and cytokinin is applied to a lateral bud. In which shoots do the lateral buds grow out?

    1. AP and R only
    2. BQ and R only
    3. CP, Q and R
    4. DP only

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12. Question 12 · Medium

    Pea shoots received the four treatments named under the bars, and lateral bud length was measured after a week. Paste S carries the hormone normally produced at the shoot apex. Going by the result, which hormone is it?

    

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    1. AAuxin
    2. BGibberellin
    3. CAbscisic acid
    4. DCytokinin

    Answer and explanation in LearnFree account

13. Question 13 · Medium

    Assertion A: The figure shows that leaf X has a higher relative growth rate than leaf Y even though leaf X gains less area. Reason R: Relative growth rate is the growth per unit time expressed per unit initial parameter. Choose the correct answer.

    

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    1. ABoth A and R are correct but R is not the correct explanation of A
    2. BBoth A and R are correct and R is the correct explanation of A
    3. CA is correct but R is not correct
    4. DA is not correct but R is correct

    Answer and explanation in LearnFree account