Chapter 15: Plant Growth and Development – Very Short Answer Type Questions
CBSE Class 11 Biology Chapter 15 – Plant Growth and Development | Very Short Answer Questions (NCERT)
Course & Examination Details
Course: CBSE Class 11 Biology
Unit: Unit IV – Plant Physiology
Chapter: Chapter 15 – Plant Growth and Development
Board: CBSE (Central Board of Secondary Education)
Question Type: Very Short Answer Questions
Syllabus: Strictly as per NCERT Biology
Section A: Growth in Plants (Q1–Q12)
Q1. What is growth in plants?
Answer: Growth in plants is a permanent and irreversible increase in size, mass, volume, or number of cells, resulting from metabolic activities.
Q2. Why is plant growth described as indeterminate?
Answer: Plant growth is indeterminate because meristematic tissues remain active throughout life, allowing continuous growth at roots and shoots.
Q3. Name the three phases of plant growth.
Answer: The three phases of plant growth are meristematic phase, elongation phase, and maturation phase, occurring sequentially in growing plant parts.
Q4. What characterizes the meristematic phase of growth?
Answer: The meristematic phase is characterized by active cell division, thin cell walls, dense cytoplasm, prominent nuclei, and absence of vacuoles.
Q5. What happens during the elongation phase?
Answer: During the elongation phase, cells enlarge rapidly due to wall loosening, vacuole expansion, and increased synthesis of proteins and carbohydrates.
Q6. Define maturation phase in plant growth.
Answer: The maturation phase involves differentiation of cells into specialized tissues, where growth rate decreases and cells attain permanent shape and function.
Q7. What is arithmetic growth?
Answer: Arithmetic growth is a growth pattern where an organism increases by a constant amount per unit time, forming a linear growth curve.
Q8. What is geometric growth?
Answer: Geometric growth occurs when growth rate is proportional to the existing size, leading to exponential increase and formation of a sigmoid growth curve.
Q9. What is growth rate?
Answer: Growth rate is the increase in size, length, area, volume, or mass of a plant or organ per unit time.
Q10. Mention two internal factors affecting plant growth.
Answer: Internal factors affecting plant growth include genetic makeup of the plant and the concentration and interaction of plant hormones.
Q11. Name two external factors necessary for plant growth.
Answer: External factors essential for plant growth include light and temperature, which influence photosynthesis, enzyme activity, and overall metabolic processes.
Q12. Why is water essential for plant growth?
Answer: Water is essential for plant growth as it maintains cell turgidity, acts as a solvent, and facilitates biochemical reactions and nutrient transport.
Section B: Differentiation and Development (Q13–Q20)
Q13. What is differentiation in plants?
Answer: Differentiation is the process by which meristematic cells develop specific structural and functional features to form specialized tissues.
Q14. Give one example of differentiation.
Answer: Differentiation of meristematic cells into xylem and phloem tissues is an example of structural and functional specialization in plants.
Q15. Define dedifferentiation.
Answer: Dedifferentiation is the process by which mature, differentiated cells regain the ability to divide under certain conditions.
Q16. Give an example of dedifferentiation.
Answer: Formation of cork cambium from cortical cells is an example of dedifferentiation in plants.
Q17. What is redifferentiation?
Answer: Redifferentiation is the process where dedifferentiated cells lose the capacity to divide and specialize again to perform specific functions.
Q18. Define development in plants.
Answer: Development in plants is the sum total of growth and differentiation, leading to the formation of various organs and completion of the life cycle.
Q19. What factors regulate plant development?
Answer: Plant development is regulated by internal factors like hormones and genes, and external factors such as light, temperature, and nutrients.
Q20. Why are plants considered developmentally plastic?
Answer: Plants are developmentally plastic because they can modify their growth and development patterns in response to environmental conditions.
Section C: Plant Hormones (Q21–Q35)
Q21. What are plant hormones?
Answer: Plant hormones are small organic substances synthesized in plants that regulate growth, development, and physiological responses at low concentrations.
Q22. Name any two growth-promoting plant hormones.
Answer: Auxins and gibberellins are growth-promoting plant hormones that stimulate cell elongation, stem growth, and various developmental processes.
Q23. What is the primary function of auxins?
Answer: Auxins primarily promote cell elongation, maintain apical dominance, induce root formation, and regulate tropic movements.
Q24. Name the natural auxin found in plants.
Answer: Indole-3-acetic acid (IAA) is the most common naturally occurring auxin found in plants.
Q25. What role do gibberellins play in plants?
Answer: Gibberellins promote stem elongation, bolting, seed germination, flowering in some plants, and breaking of seed dormancy.
Q26. Name one commercial use of gibberellins.
Answer: Gibberellins are used to increase fruit size, induce malting in barley, and enhance yield in some agricultural crops.
Q27. What are cytokinins?
Answer: Cytokinins are plant hormones that promote cell division, delay senescence, stimulate lateral bud growth, and enhance nutrient mobilization.
Q28. Name one naturally occurring cytokinin.
Answer: Zeatin is a naturally occurring cytokinin commonly found in developing fruits and seeds.
Q29. Which hormone is responsible for fruit ripening?
Answer: Ethylene is the plant hormone responsible for fruit ripening, senescence, and abscission processes.
Q30. Why is ethylene unique among plant hormones?
Answer: Ethylene is unique because it is the only plant hormone that exists in gaseous form and acts rapidly.
Q31. What is the triple response of ethylene?
Answer: The triple response includes reduced stem elongation, increased lateral swelling, and horizontal growth of seedlings.
Q32. What is abscisic acid (ABA)?
Answer: Abscisic acid is a growth-inhibiting plant hormone that induces dormancy, promotes stomatal closure, and helps plants tolerate stress.
Q33. Why is ABA called a stress hormone?
Answer: ABA is called a stress hormone because it helps plants respond to adverse conditions like drought by closing stomata and reducing growth.
Q34. Which hormones delay senescence?
Answer: Cytokinins delay senescence by promoting nutrient mobilization and maintaining protein and chlorophyll content in plant tissues.
Q35. Name one growth inhibitor in plants.
Answer: Abscisic acid is a major growth inhibitor that suppresses growth and promotes dormancy and senescence.
Section D: Photoperiodism and Vernalisation (Q36–Q50)
Q36. What is photoperiodism?
Answer: Photoperiodism is the response of plants to the relative length of day and night, especially affecting flowering time.
Q37. What is the critical photoperiod?
Answer: Critical photoperiod is the specific duration of light or darkness required by a plant to induce flowering.
Q38. Define short-day plants.
Answer: Short-day plants flower when the day length is shorter than the critical photoperiod, requiring longer nights.
Q39. Give one example of a short-day plant.
Answer: Rice is an example of a short-day plant that flowers under shorter daylight conditions.
Q40. Define long-day plants.
Answer: Long-day plants flower when the day length exceeds the critical photoperiod, requiring shorter nights.
Q41. Give one example of a long-day plant.
Answer: Wheat is a long-day plant that requires extended daylight periods to initiate flowering.
Q42. What are day-neutral plants?
Answer: Day-neutral plants flower irrespective of day length and are not influenced by photoperiod.
Q43. Name one day-neutral plant.
Answer: Tomato is a day-neutral plant whose flowering is independent of photoperiod length.
Q44. What is phytochrome?
Answer: Phytochrome is a photoreceptor pigment that regulates flowering and other light-dependent responses in plants.
Q45. In how many forms does phytochrome exist?
Answer: Phytochrome exists in two interconvertible forms: Pr (inactive) and Pfr (active).
Q46. Define vernalisation.
Answer: Vernalisation is the process by which exposure to low temperature stimulates flowering in certain plants.
Q47. Why is vernalisation important?
Answer: Vernalisation ensures flowering occurs at a favorable time, shortening the vegetative phase and improving reproductive success.
Q48. Which plants require vernalisation?
Answer: Biennial plants and winter annuals commonly require vernalisation to initiate flowering.
Q49. What is devernalisation?
Answer: Devernalisation is the reversal of the vernalisation effect by exposure to high temperature after cold treatment.
Q50. How are photoperiodism and vernalisation related?
Answer: Both photoperiodism and vernalisation regulate flowering time by integrating environmental signals with plant hormonal responses.