Chapter 15: Plant Growth and Development – Case-Based / Source-Based Questions with Answers

CBSE Class 11 Biology Chapter 15 – Plant Growth and Development | Case-Based / Source-Based Questions (NCERT)

Course & Examination Details

Course: CBSE Class 11 Biology
Unit: Unit IV – Plant Physiology
Chapter: Chapter 15 – Plant Growth and Development
Board: Central Board of Secondary Education (CBSE)
Question Type: Case-Based / Source-Based Questions
Syllabus: Strictly as per NCERT Biology Textbook

Section A: Growth in Plants (Case 1–8)

Case 1

A student observes that cells near the root tip of a plant divide actively, while cells away from the tip stop dividing and become specialized.

Q1. Identify the phase of growth occurring at the root tip.
Answer:
The meristematic phase of growth occurs at the root tip, where cells actively divide and possess thin cell walls, dense cytoplasm, and prominent nuclei.

Q2. Name the phase where cells stop dividing and become specialized.
Answer:
The maturation phase, where cells lose the ability to divide and differentiate into specialized tissues with specific structure and function.

Case 2

A plant shows a steady increase in length by a fixed amount every week.

Q3. Identify the type of growth pattern shown.
Answer:
The plant shows arithmetic growth, where increase in size occurs by a constant amount per unit time.

Q4. Name one plant part where this type of growth is commonly observed.
Answer:
Arithmetic growth is commonly observed in root elongation.

Case 3

Under laboratory conditions with unlimited nutrients, a plant shows rapid exponential increase in size initially but later the growth slows down.

Q5. Name the type of growth pattern initially observed.
Answer:
Initially, the plant shows geometric growth, where growth rate is proportional to the existing size.

Q6. Why does the growth slow down later?
Answer:
Growth slows due to environmental limitations such as space and nutrient availability, resulting in a sigmoid growth curve.

Case 4

A farmer notices stunted growth in crops during drought conditions.

Q7. Which essential factor for growth is limiting here?
Answer:
Water is the limiting factor affecting plant growth during drought conditions.

Q8. Explain one role of water in plant growth.
Answer:
Water maintains cell turgidity, enables cell elongation, and acts as a medium for metabolic and enzymatic reactions essential for growth.

Section B: Differentiation and Development (Case 9–14)

Case 5

Microscopic examination shows that some mature plant cells regain the ability to divide during secondary growth.

Q9. Name the process involved.
Answer:
The process is dedifferentiation, where mature cells regain the capacity to divide.

Q10. Give one example related to this process.
Answer:
Formation of cork cambium from cortical cells is an example of dedifferentiation.

Case 6

Cells formed after dedifferentiation later lose their dividing ability and form vascular tissues.

Q11. Identify the process involved.
Answer:
The process is redifferentiation, where cells specialize again after division.

Q12. Name the tissues formed by redifferentiation.
Answer:
Secondary xylem and secondary phloem are formed by redifferentiation.

Case 7

A plant species shows different leaf shapes when grown in water and on land.

Q13. What property of plants is demonstrated here?
Answer:
Developmental plasticity is demonstrated, showing the ability of plants to modify growth and form.

Q14. Why is this property advantageous?
Answer:
It allows plants to adapt to different environmental conditions, enhancing survival and efficient resource utilization.

Section C: Plant Hormones (Case 15–21)

Case 8

A gardener applies a hormone to stem cuttings and observes rapid root formation.

Q15. Identify the hormone responsible.
Answer:
Auxins are responsible for inducing root formation in stem cuttings.

Q16. Name a natural auxin.
Answer:
Indole-3-acetic acid (IAA) is a naturally occurring auxin.

Case 9

A rosette plant suddenly shows rapid stem elongation before flowering.

Q17. Which hormone causes this response?
Answer:
Gibberellins cause rapid stem elongation and bolting in rosette plants.

Q18. Name one additional function of this hormone.
Answer:
Gibberellins break seed dormancy and promote germination by activating enzymes.

Case 10

Leaves remain green for a longer time when treated with a specific hormone.

Q19. Identify the hormone.
Answer:
Cytokinins delay senescence and help maintain chlorophyll content.

Q20. Mention one more role of this hormone.
Answer:
Cytokinins promote lateral bud growth and cell division.

Case 11

A fruit ripening chamber contains a gaseous hormone to ensure uniform ripening.

Q21. Name the hormone used.
Answer:
Ethylene is the gaseous hormone used for fruit ripening.

Q22. Why is this hormone unique?
Answer:
Ethylene is unique because it is the only plant hormone that exists in gaseous form.

Case 12

During drought, a plant closes its stomata and shows reduced growth.

Q23. Which hormone is responsible for this response?
Answer:
Abscisic acid (ABA) is responsible for stomatal closure during drought.

Q24. Why is ABA called a stress hormone?
Answer:
ABA helps plants survive adverse conditions by inducing dormancy, reducing transpiration, and inhibiting growth.

Section D: Photoperiodism and Vernalisation (Case 22–25)

Case 13

A plant flowers only when nights are longer than a specific duration.

Q25. Identify the category of plant.
Answer:
It is a short-day plant, which requires longer nights to initiate flowering.

Case 14

A scientist interrupts the dark period of a flowering plant with a brief light exposure.

Q26. What effect will this have on short-day plants?
Answer:
Flowering will be inhibited because uninterrupted darkness is essential for short-day plants.

Case 15

A pigment exists in two interconvertible forms, responding to red and far-red light.

Q27. Name the pigment.
Answer:
The pigment is phytochrome.

Q28. Which form of phytochrome is biologically active?
Answer:
The Pfr form of phytochrome is biologically active.

Case 16

A biennial plant fails to flower when grown without exposure to cold.

Q29. Name the process required for flowering.
Answer:
Vernalisation is required for flowering in such plants.

Case 17

After cold treatment, plants are exposed to high temperature and fail to flower.

Q30. Name the phenomenon involved.
Answer:
The phenomenon is devernalisation, which reverses the effect of vernalisation.

Conclusion

These 25 Case-Based / Source-Based Questions with Answers are:

• Fully NCERT-aligned
• Designed as per CBSE Class 11 examination pattern
• Concept-based, analytical, and application-oriented
• Ideal for board exams, internal assessments, and concept revision