101. Assertion (A): All permanent plant cells can readily dedifferentiate whenever required. Reason (R): Dedifferentiation occurs only in some living differentiated cells under suitable conditions.
ⓐ. Both A and R are true, and R is the correct explanation of A
ⓑ. Both A and R are true, but R is not the correct explanation of A
ⓒ. A is true, but R is false
ⓓ. A is false, but R is true
Correct Answer: A is false, but R is true
Explanation: The assertion is incorrect because dedifferentiation is not a universal ability of all permanent cells. Only certain living differentiated cells can regain mitotic activity, and even then this happens under suitable developmental or physiological conditions. Many mature cells are too specialized or may even be dead at maturity, so they cannot dedifferentiate. The reason correctly states the limited and conditional nature of the process. Therefore, the assertion is false, while the reason is true.
102. A student says, “Once a plant cell becomes specialized, it can never again contribute to the formation of a new dividing tissue.” Which response is most accurate?
ⓐ. The statement is incorrect because some living differentiated cells can dedifferentiate
ⓑ. The statement is correct because specialization permanently destroys all cellular potential
ⓒ. The statement is correct because only zygotic cells are capable of division
ⓓ. The statement is incorrect because every mature plant cell divides continuously
Correct Answer: The statement is incorrect because some living differentiated cells can dedifferentiate
Explanation: Plants show a degree of developmental flexibility that allows some living differentiated cells to regain the capacity to divide. This process is called dedifferentiation and is seen in examples such as formation of interfascicular cambium or cork cambium. It does not mean that every mature cell can do this, but it clearly shows that specialization is not always an irreversible endpoint in plants. Because of this, the student’s statement is too absolute. Some specialized living cells can indeed contribute to new dividing tissues.
103. Which event best represents redifferentiation after the formation of a secondary meristem?
ⓐ. A mature parenchyma cell regains mitotic activity
ⓑ. A living permanent cell becomes cambial in nature
ⓒ. Cambial derivatives become specialized as secondary xylem and secondary phloem
ⓓ. A newly formed cell enlarges by vacuolar expansion only
Correct Answer: Cambial derivatives become specialized as secondary xylem and secondary phloem
Explanation: Redifferentiation refers to the stage in which cells produced from a dedifferentiated or meristematic tissue later mature into specialized permanent cells. Cambial derivatives becoming secondary xylem and secondary phloem fit this exactly. The cells are no longer merely dividing; they are now acquiring definite structure and function. In contrast, a mature cell regaining mitotic activity would be dedifferentiation, not redifferentiation. Therefore, specialization of cambial derivatives into permanent conducting tissues is a strong example of redifferentiation.
104. A plant organ increases in size because of cell division and enlargement, but the cells have not yet become specialized for particular functions. Which statement is most accurate?
ⓐ. Full differentiation has been completed, but growth has not started
ⓑ. Development is complete even without any specialization
ⓒ. Dedifferentiation must already have occurred in all cells
ⓓ. Growth is occurring, but development is not yet complete in the full sense
Correct Answer: Growth is occurring, but development is not yet complete in the full sense
Explanation: Growth refers mainly to an increase in size, number, or mass, while development includes growth together with differentiation and maturation. In this question, the organ is clearly increasing in size through cell division and enlargement, so growth is taking place. However, because specialization has not yet occurred, the full developmental process is still incomplete. This illustrates why development is broader than simple growth. Quantitative increase alone does not represent the whole developmental outcome.
105. In plant biology, plasticity refers to the ability of a plant to:
ⓐ. Remain genetically unchanged throughout life without any visible variation
ⓑ. Produce different structures or forms in response to different phases of life or environmental conditions
ⓒ. Stop growth completely when external conditions become unfavorable
ⓓ. Form only one fixed body pattern from seedling stage to maturity
Correct Answer: Produce different structures or forms in response to different phases of life or environmental conditions
Explanation: Plasticity is the capacity of plants to follow different developmental pathways and produce different forms under different conditions. A plant with the same genetic makeup may show different structures depending on age, habitat, or surrounding environment. This does not mean the genes themselves are changing; rather, the expression of developmental potential changes. Plasticity helps plants adjust their structure to suit their needs and conditions. It is therefore an important feature of plant development. The concept shows that plant form is often flexible rather than completely fixed.
106. Which statement best defines heterophylly?
ⓐ. Formation of different flowers on the same plant
ⓑ. Production of different kinds of roots under soil and water
ⓒ. Presence of leaves of only one shape throughout the plant body
ⓓ. Occurrence of leaves of different shapes on the same plant
Correct Answer: Occurrence of leaves of different shapes on the same plant
Explanation: Heterophylly means that a single plant bears leaves of different forms. The difference may be seen between juvenile and mature leaves or between leaves growing under different environmental conditions. This makes heterophylly a clear example of developmental flexibility in plants. The plant is not producing random variation, but specific leaf forms suited to stage or surroundings. Because the variation involves leaf shape on the same plant, heterophylly is treated as a classic example of plasticity. It is therefore an important concept in plant growth and development.
107. Heterophylly in plants is considered an example of:
ⓐ. Plasticity
ⓑ. Senescence
ⓒ. Abscission
ⓓ. Dormancy
Correct Answer: Plasticity
Explanation: Heterophylly shows that the same plant can produce leaves of different forms under different developmental stages or environmental conditions. This demonstrates flexibility in the expression of form. Such flexibility is exactly what is meant by plasticity in plant development. The plant is not fixed to one permanent leaf pattern in all situations. Therefore, heterophylly is commonly used as a textbook example to explain plasticity. It helps students connect a visible structural feature with a broader developmental principle.
108. In buttercup, submerged leaves and aerial leaves differ in shape mainly due to:
ⓐ. Permanent loss of genetic material in water-grown parts
ⓑ. A disease affecting only the underwater leaves
ⓒ. Difference in environmental conditions acting on the same plant
ⓓ. Complete absence of development in the aerial region
Correct Answer: Difference in environmental conditions acting on the same plant
Explanation: In buttercup, leaf form changes according to whether the leaf develops in water or in air. This shows that the environment can influence the developmental pathway taken by the plant. The same plant body can therefore give rise to differently shaped leaves in different surroundings. This is a classic example of environmentally induced heterophylly. It does not occur because the submerged leaves lose genes or because the aerial region stops developing. The difference mainly reflects plastic response to contrasting conditions.
109. In cotton, coriander, and larkspur, heterophylly is mainly associated with:
ⓐ. The difference between reproductive and non-reproductive tissues only
ⓑ. Different developmental stages such as juvenile and mature phases
ⓒ. Only the effect of aquatic and terrestrial environments
ⓓ. Sudden mutation in the leaf primordia during adulthood
Correct Answer: Different developmental stages such as juvenile and mature phases
Explanation: In plants such as cotton, coriander, and larkspur, the leaves of young plants and mature plants differ in form. This type of heterophylly is linked mainly with developmental stage rather than with external habitat like water and air. As the plant moves from juvenile to mature growth, the developmental program changes and produces differently shaped leaves. This shows that internal phase-related factors can influence leaf form. Thus, heterophylly may arise from age or phase differences as well as from environment. These plants are standard examples of developmental heterophylly.
110. Which of the following is the best example of developmental heterophylly?
ⓐ. A buttercup producing narrow submerged leaves and broader aerial leaves
ⓑ. A plant showing temporary wilting at midday and recovery in the evening
ⓒ. A root producing root hairs in the maturation zone
ⓓ. A coriander plant showing different leaf forms in juvenile and mature stages
Correct Answer: A coriander plant showing different leaf forms in juvenile and mature stages
Explanation: Developmental heterophylly is caused mainly by differences in the phase of life of the plant rather than immediate external conditions like water or air. In coriander, the leaves of juvenile and mature plants differ in form, which reflects a stage-dependent developmental pattern. This makes it a classic example of heterophylly caused by internal developmental progression. By contrast, buttercup illustrates environmental heterophylly. Therefore, coriander is a suitable example when the question asks specifically about developmental heterophylly. It shows how age-related changes can alter plant form.
111. Which of the following best explains why plasticity is important in plants?
ⓐ. It allows plants to respond by producing forms suited to different conditions or stages
ⓑ. It prevents all structural variation within a single plant species
ⓒ. It ensures that every plant organ remains identical throughout life
ⓓ. It makes environmental factors more important than genes in all cases
Correct Answer: It allows plants to respond by producing forms suited to different conditions or stages
Explanation: Plasticity is important because it gives plants developmental flexibility. A plant can adjust its form according to environmental conditions or according to its phase of growth and maturity. This helps the plant function more effectively in changing situations. The idea does not mean that genes are unimportant, but that the same genetic system can give rise to different visible outcomes. Plasticity therefore supports survival and proper adaptation of form. It is one reason why plant development often appears dynamic and responsive rather than rigid.
112. Which statement correctly compares plasticity and heterophylly?
ⓐ. Plasticity is a special case of heterophylly seen only in aquatic plants
ⓑ. Heterophylly is broader, whereas plasticity refers only to leaf characters
ⓒ. Plasticity and heterophylly are unrelated because one concerns roots and the other leaves
ⓓ. Plasticity is a broad developmental ability, whereas heterophylly is one visible expression of it
Correct Answer: Plasticity is a broad developmental ability, whereas heterophylly is one visible expression of it
Explanation: Plasticity is the broader concept describing the ability of plants to produce different forms in response to developmental stage or environment. Heterophylly is one specific manifestation of this ability, involving variation in leaf shape on the same plant. So heterophylly helps demonstrate plasticity in an easily visible way. The two ideas are therefore closely related but not identical in scope. Plasticity includes a wider principle, while heterophylly is a particular example within that principle. This distinction is important for conceptual clarity.
113. Which statement about heterophylly is correct?
ⓐ. It always results from mutation and cannot be a normal developmental feature
ⓑ. It is always caused only by external environmental factors
ⓒ. It may arise due to developmental stage or due to environmental condition
ⓓ. It is found only in leaves of submerged aquatic plants
Correct Answer: It may arise due to developmental stage or due to environmental condition
Explanation: Heterophylly is not limited to a single cause. In some plants, it appears because juvenile and mature phases produce different kinds of leaves. In other plants, the environment, such as aquatic versus aerial conditions, influences leaf form. This means heterophylly can arise from internal developmental factors or from external environmental conditions. The phenomenon is therefore broader than one narrow cause. Understanding both possibilities is essential to understanding why heterophylly is treated as an expression of plasticity.
114. A botanist grows genetically similar shoots of an aquatic plant under two conditions: one submerged in water and the other exposed to air. The leaves that develop later differ markedly in shape. This result most directly demonstrates:
ⓐ. Mutation occurring separately in each shoot
ⓑ. Environmental plasticity expressed through heterophylly
ⓒ. Permanent chromosome loss in submerged tissues
ⓓ. Failure of normal leaf development in the aerial shoot
Correct Answer: Environmental plasticity expressed through heterophylly
Explanation: When genetically similar shoots produce different leaf forms under different surroundings, the difference is best explained by environmental plasticity. The plant has the ability to follow more than one developmental pathway depending on external conditions. Because the visible difference appears in leaf form, the phenomenon is also heterophylly. This does not require mutation or chromosome loss. Instead, it shows that the same genetic system can produce different leaf shapes in response to the environment.
115. Which observation would be the best non-example of heterophylly?
ⓐ. A coriander plant bearing different leaf forms in juvenile and mature stages
ⓑ. A buttercup bearing finely divided submerged leaves and broader aerial leaves
ⓒ. A mango plant producing leaves of the same general shape throughout its vegetative life
ⓓ. A single plant showing different leaf shapes in different parts under different conditions
Correct Answer: A mango plant producing leaves of the same general shape throughout its vegetative life
Explanation: Heterophylly means the occurrence of different leaf forms on the same plant. If a plant maintains essentially the same leaf shape throughout its vegetative life, that condition does not illustrate heterophylly. The other options all involve clear variation in leaf form within one plant due to developmental stage or environmental differences. Therefore, a plant with one consistent leaf pattern is the best non-example. This helps distinguish true heterophylly from ordinary leaf production.
116. Assertion (A): Heterophylly always proves that different genes are present in different leaves of the same plant. Reason (R): Different leaf forms may arise from different developmental or environmental conditions acting on the same plant body.
ⓐ. Both A and R are true, and R is the correct explanation of A
ⓑ. Both A and R are true, but R is not the correct explanation of A
ⓒ. A is false, but R is true
ⓓ. A is true, but R is false
Correct Answer: A is false, but R is true
Explanation: The assertion is incorrect because heterophylly does not mean that different leaves necessarily have different genes. In most cases, the same plant genome is present, but leaf form varies because developmental stage or environmental conditions influence which developmental pathway is followed. The reason correctly states this principle. Thus, the variation is largely due to differential expression of developmental potential rather than different genetic sets in different leaves. So the assertion is false while the reason is true.
117. A student says, “If one plant shows two kinds of leaves, it must belong to two different species joined together.” Which response is most accurate?
ⓐ. The statement is incorrect because one plant may normally show heterophylly
ⓑ. The statement is correct because one species can produce only one leaf shape
ⓒ. The statement is correct because leaf form never changes with development
ⓓ. The statement is incorrect only when flowers are absent
Correct Answer: The statement is incorrect because one plant may normally show heterophylly
Explanation: A single plant can naturally produce different leaf forms, and this phenomenon is called heterophylly. It may arise due to differences in developmental stage, such as juvenile versus mature leaves, or due to environmental conditions, such as submerged versus aerial growth. Therefore, the presence of two leaf forms does not mean that two species are joined together. Leaf shape in plants can be flexible and developmentally regulated. The student’s conclusion is therefore based on a misconception.
118. Which statement best distinguishes plasticity from mutation in the context of leaf form?
ⓐ. Plasticity always creates new genes, whereas mutation only changes growth conditions
ⓑ. Mutation is always reversible, whereas plasticity is always permanent
ⓒ. Plasticity changes phenotype in response to conditions, whereas mutation involves change in genetic material
ⓓ. Plasticity occurs only in reproductive organs, whereas mutation occurs only in leaves
Correct Answer: Plasticity changes phenotype in response to conditions, whereas mutation involves change in genetic material
Explanation: Plasticity refers to the ability of the same genotype to produce different visible forms under different developmental or environmental situations. Mutation, in contrast, involves a change in the genetic material itself. In heterophylly caused by plasticity, the leaf form changes without requiring a new mutation in every case. This is why plants can show different leaf types under different conditions while remaining the same species. The distinction between phenotype flexibility and gene change is the key point here.
119. A terrestrial branch of a plant bears broad leaves, while a submerged branch of the same plant bears narrow dissected leaves. Which comparison is correct?
ⓐ. This is developmental heterophylly because only age determines the difference
ⓑ. This is environmental heterophylly because habitat conditions differ around the branches
ⓒ. This is not heterophylly because both branches belong to the same plant
ⓓ. This is evidence that submerged leaves are not true leaves
Correct Answer: This is environmental heterophylly because habitat conditions differ around the branches
Explanation: In this case, the leaf differences arise because one branch develops in air and the other in water. The contrasting habitat conditions influence the developmental pathway and lead to different leaf forms. Since the difference depends mainly on surrounding environment rather than on age or phase of the plant, it is classified as environmental heterophylly. The fact that both branches belong to the same plant actually supports the concept of heterophylly. Thus, the correct classification is environmental heterophylly.
120. Which statement about developmental heterophylly is most appropriate?
ⓐ. It depends primarily on changes in life stage rather than immediate external habitat
ⓑ. It can occur only in plants that live partly in water and partly on land
ⓒ. It always disappears when the plant reaches maturity
ⓓ. It means that all leaves on the mature plant become identical to juvenile leaves
Correct Answer: It depends primarily on changes in life stage rather than immediate external habitat
Explanation: Developmental heterophylly is linked mainly with internal developmental progression, such as juvenile and mature phases of the same plant. The leaf form changes because the stage of growth changes, not necessarily because the plant shifts from one habitat to another. This is why plants like coriander or cotton are used as examples. The phenomenon is therefore phase-related rather than directly habitat-driven. It highlights how internal developmental timing can influence plant form.
