Plant Growth AND Development flash cards

1. 1.Define growth in plants.

   Growth is an irreversible permanent increase in size of an organ or its parts or even of an individual cell.

   Hint: Irreversible + permanent increase in size

2. 2.On what basis is plant growth said to be measurable?

   Growth is accompanied by metabolic processes (both anabolic and catabolic) that occur at the expense of energy; it can be measured by increase in size, area, length, height, volume, cell number, etc.

   Hint: Needs energy; many parameters

3. 3.Why is plant growth described as indeterminate?

   Plants retain the capacity for unlimited growth throughout life because of meristems (regions with the ability to divide and self-perpetuate) at certain locations.

   Hint: Meristems allow open/unlimited growth

4. 4.What is the basis of the open form of growth in plants?

   The presence of meristematic tissues that can divide indefinitely (e.g. root and shoot apical meristems produce new cells continuously).

   Hint: Meristem = open growth

5. 5.Name the meristem responsible for primary growth (increase in length).

   Apical meristems (root apical meristem and shoot apical meristem).

   Hint: At the tips; elongation

6. 6.Which meristems bring about secondary growth (increase in girth)?

   Lateral meristems — vascular cambium and cork cambium (phellogen).

   Hint: Cambium = girth

7. 7.What is the intercalary meristem and where is it found?

   Meristem present between mature tissues, e.g. at the base of internodes/leaves in grasses; along with apical meristem it constitutes primary meristem.

   Hint: Between mature tissues; grasses

8. 8.Name the two phases of a plant cell's life during growth described in NCERT.

   The formative (meristematic/cell division) phase and later the phase of cell enlargement (elongation) followed by maturation/differentiation.

   Hint: Division then enlargement

9. 9.What are the three phases of growth?

   Meristematic phase (cell division), phase of elongation (cell enlargement), and phase of maturation (differentiation).

   Hint: Division, elongation, maturation

10. 10.Describe the meristematic phase of growth.

    Cells in root and shoot apex are constantly dividing; they are rich in protoplasm, have large conspicuous nuclei, thin primary cellulosic walls and abundant plasmodesmatal connections.

    Hint: Apical/root tip cells, thin walls, dense cytoplasm

11. 11.Describe the phase of elongation.

    Cells proximal (just next) to the meristematic zone show increased vacuolation, cell enlargement, and new cell wall deposition.

    Hint: Vacuolation + enlargement, next to meristem

12. 12.Describe the maturation phase of growth.

    Cells further from the apex, i.e. beyond the elongation zone, attain their maximal size in terms of wall thickening and protoplasmic modifications — they differentiate.

    Hint: Farthest from tip; wall thickening

13. 13.By how much can a maize root apical meristem add to the root, illustrating growth rate?

    A maize root apical meristem can give rise to more than 17,500 new cells per hour.

    Hint: Maize root; per hour figure

14. 14.Give the NCERT example of cell size increase in watermelon.

    Cells in a watermelon may increase in size by up to 350,000 times.

    Hint: Watermelon; huge multiplier

15. 15.Define growth rate.

    Growth rate is the increased growth per unit time; it can be expressed mathematically.

    Hint: Increase per unit time

16. 16.What is arithmetic growth?

    Growth in which following mitotic cell division only one daughter cell continues to divide while the other differentiates and matures; the rate of growth is constant.

    Hint: One cell keeps dividing; constant rate

17. 17.Give an example of arithmetic growth.

    Elongation of a root at a constant rate.

    Hint: Root elongating steadily

18. 18.Write the mathematical expression for arithmetic growth.

    $L_t = L_0 + rt$, where $L_t$ = length at time t, $L_0$ = length at time zero, r = growth rate (elongation per unit time).

    Hint: Linear equation, constant r

19. 19.What shape of curve does arithmetic growth give when plotted against time?

    A linear curve (straight line).

    Hint: Straight line

20. 20.What is geometric growth?

    Growth in which both daughter cells following mitosis retain the ability to divide and continue to do so; characteristic of many higher plants especially in early stages.

    Hint: Both daughter cells divide

21. 21.What is the typical shape of the geometric growth curve?

    A sigmoid (S-shaped) curve.

    Hint: S-shaped

22. 22.Name the three phases of a sigmoid growth curve.

    Lag phase, log (exponential) phase, and stationary phase (steady/decline phase where growth slows and stops due to limited nutrients).

    Hint: Lag, log, stationary

23. 23.Why does geometric growth slow down after the log phase?

    Because limited nutrient supply (and other factors) leads to slowing of growth, giving the stationary phase and hence the sigmoid shape.

    Hint: Limited nutrients cause plateau

24. 24.Write the exponential growth equation.

    $W_1 = W_0 e^{rt}$, where $W_1$ = final size, $W_0$ = initial size, r = growth rate, t = time of growth, e = base of natural logarithms.

    Hint: W1 = W0 e^{rt}

25. 25.In the exponential equation, what does 'r' represent and why is it important?

    'r' is the relative growth rate and is also the measure of the ability of the plant to produce new plant material (efficiency index).

    Hint: Relative growth rate / efficiency index

26. 26.Differentiate absolute and relative growth rates.

    Absolute growth rate = measurement and comparison of total growth per unit time. Relative growth rate = growth per unit time expressed on a common basis, e.g. per unit initial parameter.

    Hint: Total vs per-unit-initial

27. 27.QUESTION: Two leaves A and B differ in initial size; A is larger. Both increase area by 5 cm² in a day. Which has greater relative growth rate?

    Leaf B (the smaller one) has the greater relative growth rate, because the same absolute increase (5 cm²) is a larger fraction of its smaller initial area; their absolute growth rates are equal.

    Hint: Same absolute increase, smaller initial base

28. 28.What conditions are necessary for plant growth?

    Water, oxygen and nutrients (essential elements). Also optimum temperature and, for some phases, light and gravity.

    Hint: Water, O2, nutrients

29. 29.Why is water essential for growth (especially cell enlargement)?

    Turgidity of cells due to water helps in extension growth; water provides the medium for enzymatic activities needed for growth.

    Hint: Turgor drives cell extension

30. 30.Define differentiation.

    The process in which cells derived from root and shoot apical meristems and cambium differentiate and mature to perform specific functions.

    Hint: Cells mature to specific functions

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