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Science MCQ, Class 9th, Chapter-14, Natural Resources
NCERT Based MCQ with Explanation:
1. What is the unique characteristic of plant growth?
(A) Plants grow in spurts.
(B) Growth is limited after flowering.
(C) Growth is indeterminate due to meristems.
(D) Growth is determined by seed size.
Explanation: Plants have meristems that enable continuous growth throughout their lifespan, making growth indeterminate.
2. Which type of meristem contributes to primary growth in plants?
(A) Lateral meristem
(B) Apical meristem
(C) Cork cambium
(D) Intercalary meristem
Explanation: Apical meristems are responsible for the elongation of roots and shoots, contributing to primary growth in plants.
3. What is the role of lateral meristems in plants?
(A) Increase the height of plants
(B) Increase the girth of plants
(C) Form leaves and flowers
(D) Develop seed structure
Explanation: Lateral meristems, such as vascular cambium and cork cambium, contribute to the secondary growth of plants, increasing their girth.
4. What does the term "dedifferentiation" refer to in plants?
(A) Loss of meristematic activity
(B) Reversion of mature cells to a meristematic state
(C) Specialization of cells for specific functions
(D) Elongation of cells in the root zone
Explanation: Dedifferentiation is the process where fully differentiated cells regain the ability to divide and become meristematic.
5. Which hormone is commonly known as the “stress hormone” in plants?
(A) Auxin
(B) Cytokinin
(C) Gibberellin
(D) Abscisic acid
Explanation: Abscisic acid helps plants cope with stress by inducing stomatal closure, promoting dormancy, and enhancing drought tolerance.
6. Which phase of growth involves cell enlargement and vacuolation?
(A) Meristematic phase
(B) Elongation phase
(C) Maturation phase
(D) Differentiation phase
Explanation: During the elongation phase, cells enlarge due to vacuolation, increased protoplasm, and new cell wall deposition.
7. What is the main characteristic of geometric growth in plants?
(A) Growth occurs at a constant rate.
(B) Only one daughter cell divides after mitosis.
(C) Growth follows a sigmoid curve.
(D) Growth stops during the stationary phase.
Explanation: In geometric growth, both daughter cells continue dividing, leading to exponential growth that eventually plateaus, forming a sigmoid curve.
8. What are plant growth regulators (PGRs)?
(A) Substances that solely promote growth
(B) Genetic factors influencing growth
(C) Chemical compounds controlling plant growth and development
(D) Nutrients required for plant growth
Explanation: PGRs are hormones like auxins, gibberellins, cytokinins, ethylene, and abscisic acid that regulate various aspects of plant growth and development.
9. Which PGR is responsible for inducing parthenocarpy in fruits?
(A) Auxins
(B) Gibberellins
(C) Cytokinins
(D) Ethylene
Explanation: Auxins promote parthenocarpy, leading to the development of seedless fruits such as tomatoes and bananas.
10. What is a sigmoid growth curve in plants?
(A) A linear increase in growth rate
(B) A curve representing geometric growth
(C) A curve showing lag, exponential, and stationary phases
(D) A curve representing seasonal growth
Explanation: A sigmoid growth curve illustrates the typical growth pattern in plants, starting with slow growth (lag phase), followed by rapid growth (exponential phase), and ending with a plateau (stationary phase).
11. What is the main role of auxins in plants?
(A) Delay senescence
(B) Promote cell division and elongation
(C) Induce seed dormancy
(D) Enhance fruit ripening
Explanation: Auxins stimulate cell elongation and division, especially in apical regions, and are involved in growth-related processes like phototropism.
12. Which PGR delays leaf senescence and promotes chloroplast development?
(A) Gibberellins
(B) Ethylene
(C) Cytokinins
(D) Abscisic acid
Explanation: Cytokinins help delay senescence by promoting nutrient mobilization and stimulating chloroplast development, keeping leaves green longer.
13. Which type of growth occurs when one daughter cell divides and the other matures?
(A) Arithmetic growth
(B) Geometric growth
(C) Sigmoid growth
(D) Determinate growth
Explanation: In arithmetic growth, one daughter cell continues to divide while the other differentiates and matures, leading to linear growth.
14. What is the effect of gibberellins on rosette plants?
(A) Induces flowering
(B) Promotes bolting
(C) Enhances lateral growth
(D) Increases seed dormancy
Explanation: Gibberellins induce bolting, which is the elongation of internodes, in plants like cabbages and beets before flowering.
15. Which phase of growth is characterized by the attainment of maximum size by cells?
(A) Meristematic phase
(B) Elongation phase
(C) Maturation phase
(D) Lag phase
Explanation: In the maturation phase, cells undergo structural modifications, including wall thickening, and attain their maximum functional size.
Biology MCQ, Class-12, Chapter-10, Biotechnology and Its Applications16. How is abscisic acid antagonistic to gibberellins?
(A) It promotes seed germination while gibberellins inhibit it.
(B) It induces dormancy, opposing gibberellins' role in promoting growth.
(C) It enhances cell elongation while gibberellins retard it.
(D) It encourages bolting in rosette plants.
Explanation: Abscisic acid promotes dormancy in seeds and buds, counteracting gibberellins, which stimulate germination and growth.
17. What role does ethylene play in ripening fruits?
(A) Induces seed dormancy
(B) Enhances the respiratory climactic
(C) Promotes apical dominance
(D) Delays senescence
Explanation: Ethylene increases the respiration rate during fruit ripening, a process termed the respiratory climactic, hastening ripening.
18. What is the function of intercalary meristems?
(A) Increase the girth of plants
(B) Enable elongation of internodes
(C) Differentiate into secondary tissues
(D) Develop root hairs
Explanation: Intercalary meristems, found in grass nodes, allow elongation between mature tissues, facilitating growth in length.
19. What is the significance of plasticity in plant development?
(A) It allows plants to grow in specific directions only.
(B) It ensures uniform leaf shapes.
(C) It enables plants to develop differently based on environmental conditions.
(D) It restricts changes in cellular differentiation.
Explanation: Plasticity allows plants to adapt to environmental cues by altering their structure, such as heterophylly in buttercup leaves.
20. What is the role of cytokinin in tissue culture?
(A) Stimulates root growth
(B) Inhibits cell division
(C) Promotes shoot differentiation
(D) Induces senescence
Explanation: Cytokinins are crucial in tissue culture for inducing shoot development, especially in callus cultures, by stimulating cell division.
21. Which hormone promotes apical dominance?
(A) Cytokinin
(B) Auxin
(C) Gibberellin
(D) Abscisic acid
22. Which phase of the sigmoid growth curve is exponential?
(A) Lag phase
(B) Log phase
(C) Stationary phase
(D) Maturation phase
23. What is the primary site of auxin synthesis in plants?
(A) Root tips
(B) Shoot apices
(C) Vascular cambium
(D) Leaf mesophyll
24. Which PGR is widely used to promote fruit set in pineapples?
(A) Ethylene
(B) Gibberellins
(C) Cytokinins
(D) Abscisic acid
25. How is relative growth rate defined?
(A) Increase in growth per unit time.
(B) Growth per unit time relative to the initial parameter.
(C) Overall increase in growth across the lifespan.
(D) Difference between exponential and arithmetic growth.
26. What is the main factor that affects the direction of plant growth?
(A) Nutrient availability
(B) Light and gravity
(C) Water content in the soil
(D) Size of the seed
27. What is the typical shape of a geometric growth curve?
(A) Linear
(B) Bell-shaped
(C) S-shaped or sigmoid
(D) Parabolic
28. Which of the following is a growth-promoting PGR?
(A) Abscisic acid
(B) Ethylene
(C) Gibberellins
(D) None of the above
29. Which cells in a plant actively divide and form new tissues?
(A) Parenchyma cells
(B) Sclerenchyma cells
(C) Meristematic cells
(D) Collenchyma cells
30. Which PGR is used to increase sugarcane yield?
(A) Auxins
(B) Gibberellins
(C) Cytokinins
(D) Ethylene