Questions: Plant Growth and Development

Q1. Define growth and name four parameters used to measure it.

Answer (English): Growth is an increase in the size and mass of a living body, brought about by cell division and cell enlargement. It can be measured as an increase in cell number, cell size, length, area, volume, fresh weight or dry weight. No single parameter works for the whole life of a plant, so several are used together.

Hinglish: Growth size aur mass ka badhna hai jo cell division aur enlargement se hota hai. Isko cell number, length, area, volume, fresh weight ya dry weight se naap sakte hain, aur ek parameter poore jeevan ke liye kaafi nahi hota.

Q2. What is the difference between absolute and relative growth rate?

Answer (English): The absolute growth rate is the total increase in size per unit time, while the relative growth rate is that increase expressed per unit of initial size. A large tree may have a bigger absolute rate than a small seedling yet a much smaller relative rate, which is why the relative rate is the fairer comparison between plants of different sizes.

Hinglish: Absolute rate per unit time total badhotri batati hai, jabki relative rate usi badhotri ko starting size se divide karti hai. Isliye alag sizes ki tulna relative rate se karni chahiye.

Q3. Write the equations for arithmetic and geometric growth.

Answer (English): Arithmetic growth follows L_t = L_0 + r t, where L_t is the size at time t, L_0 is the initial size and r is the growth rate. Geometric growth follows W_1 = W_0 e raised to r t, where W_1 is the final size, W_0 the initial size, r the growth rate and t the time. Arithmetic growth plots as a straight line and geometric growth plots as an exponential curve.

Hinglish: Arithmetic growth ke liye L_t = L_0 + rt aur geometric growth ke liye W_1 = W_0 e^{rt} use hota hai. Pehla seedha line deta hai aur doosra exponential curve.

Q4. Name the three phases of growth seen in a root.

Answer (English): The three phases are the meristematic phase, the elongation phase and the maturation phase. The meristematic zone at the tip has actively dividing cells with thin walls and dense protoplasm. The elongation zone has cells that enlarge and develop vacuoles. The maturation zone has cells that finish enlarging and become specialised.

Hinglish: Root mein meristematic, elongation aur maturation phases hote hain. Meristematic zone mein cells divide karti hain, elongation zone mein badi hoti hain aur maturation zone mein specialise hoti hain.

Q5. Differentiate differentiation, dedifferentiation and redifferentiation.

Answer (English): Differentiation is the change of meristematic cells into specialised cells. Dedifferentiation is the loss of specialisation by mature living cells so that they divide again, as in the formation of interfascicular cambium or a callus. Redifferentiation is the formation of a new specialised structure from such undifferentiated cells, as when a callus gives rise to roots or shoots.

Hinglish: Differentiation mein cells specialise hoti hain, dedifferentiation mein mature cells dobara divide karti hain, aur redifferentiation mein un dividing cells se naya specialised tissue banta hai, jaise callus se root ya shoot.

Q6. Why is plant development called open and plastic?

Answer (English): Plant development is open because new organs are produced continuously from meristems through the life of the plant, unlike animals whose body plan is fixed at maturity. It is plastic because the form produced depends on the environment, so the same plant can make different leaf shapes or different growth forms in different conditions. Heterophylly in the buttercup is the standard example of this plasticity.

Hinglish: Plant development open isliye hai kyunki meristem se life bhar naye organs bante hain; plastic isliye hai kyunki environment ke hisaab se roop badal sakta hai, jaise buttercup ke different leaf shapes.

Q7. Name the five groups of plant growth regulators with one example each.

Answer (English): The five groups are auxins such as IAA, gibberellins such as GA3, cytokinins such as kinetin or zeatin, abscisic acid and ethylene. Auxin and gibberellin are mainly promoters of growth, cytokinin promotes cell division, abscisic acid inhibits growth and closes stomata under stress, and ethylene is a gaseous regulator of ripening and abscission.

Hinglish: Paanch groups hain auxin (IAA), gibberellin (GA3), cytokinin (kinetin/zeatin), abscisic acid aur ethylene. Auxin aur gibberellin growth promote karte hain, cytokinin division, ABA stress mein stomata band karta hai aur ethylene gas fruit ripening se juda hai.

Q8. What is apical dominance and how can it be overcome?

Answer (English): Apical dominance is the suppression of lateral bud growth by the growing apical bud. Auxin produced at the apex is responsible for it, as the experiment in which the coleoptile tip is removed shows. The condition can be overcome by removing the apical bud, by applying cytokinin to the lateral buds, or by applying a growth inhibitor that blocks the effect of auxin at the apex.

Hinglish: Apical dominance mein apical bud lateral buds ki growth ko dabata hai. Apex kaatne se ya lateral buds par cytokinin lagane se lateral buds grow karne lagte hain.

Q9. Why is abscisic acid called the stress hormone?

Answer (English): Abscisic acid is called the stress hormone because its level rises when the plant faces drought, salinity or cold. It closes the stomata, which limits water loss, and it promotes seed dormancy so that germination is delayed until conditions improve. Both responses help the plant survive a period of stress at the cost of growth.

Hinglish: ABA ka level drought, salinity aur cold mein badh jata hai. Yeh stomata band karke paani bachata hai aur seed dormancy badhata hai, isliye ise stress hormone kehte hain.

Q10. What is vernalisation and why is it used in agriculture?

Answer (English): Vernalisation is the promotion of flowering by a period of low temperature. It is used in agriculture because winter varieties of wheat need the cold of winter before they can flower; if they are sown in spring they do not flower within the season. Growers therefore sow winter wheat in autumn so that it gets the cold it needs, while spring wheat is sown in spring.

Hinglish: Vernalisation thandi ke period se flowering promote karta hai. Winter wheat ko phoolne ke liye winter ki thandi chahiye hoti hai, isliye use autumn mein boya jata hai; spring wheat spring mein boya ja sakta hai.

Quiz pointer. A five question chapter quiz follows this page. Attempt it without looking back, then read the explanation for every question you miss, because the quiz retests the growth equations and the regulator functions used above.