Part 4 — Differentiation, Dedifferentiation, Redifferentiation; Totipotency

Part 4 — Differentiation, Dedifferentiation, Redifferentiation; Totipotency

76. Differentiation in plant cells refers to:
    A. Reversion of specialized cells to meristematic state
    B. Acquisition of specialized structure and function by cells
    C. Permanent cell death
    D. Only increase in cell size without function change
    Answer: B
    Explanations:

• A: Incorrect. That’s dedifferentiation.

• B: Correct. Differentiation = specialization (e.g., xylem, phloem).

• C: Incorrect. Not about death.

• D: Incorrect. Differentiation involves structural & functional specialization, not just size change.

77. Dedifferentiation is best described as:
    A. Differentiated cells becoming more specialized
    B. Differentiated cells reverting to a less specialized, meristematic state
    C. Death of meristematic cells
    D. Differentiated cells immediately producing seeds
    Answer: B
    Explanations:

• A: Incorrect. That’s further differentiation.

• B: Correct. Dedifferentiation allows a cell to regain division potential (e.g., callus formation).

• C: Incorrect. Dedifferentiation is reversion, not death.

• D: Incorrect. Seed production is unrelated.

78. Redifferentiation refers to:
    A. Dedifferentiated cells becoming specialized again into new types (e.g., organogenesis from callus)
    B. Cells losing genetic information
    C. Permanent inactivity of tissue
    D. Only root hair formation always
    Answer: A
    Explanations:

• A: Correct. After dedifferentiation, cells can redifferentiate to form organs/tissues (organogenesis).

• B: Incorrect. Genetic information is retained generally.

• C: Incorrect. Redifferentiation implies renewed activity, not inactivity.

• D: Incorrect. Root hair formation is one example, not the definition.

79. Plant cell totipotency means:
    A. Only meristematic cells can divide
    B. Many mature plant cells can give rise to a whole plant under suitable conditions
    C. Only zygote is capable of totipotency
    D. Cells permanently lose nucleus during differentiation
    Answer: B
    Explanations:

• A: Incorrect. Totipotency extends beyond meristematic cells under culture conditions.

• B: Correct. Many plant cells retain potential to form whole plants when provided hormones and conditions.

• C: Incorrect. Zygote is totipotent, but so are many somatic plant cells in appropriate conditions.

• D: Incorrect. Losing nucleus would prevent development; not true.

80. A callus is:
    A. A meristematic mass formed during dedifferentiation in tissue culture
    B. A fruit type
    C. Only found in animal cells
    D. A vascular tissue type
    Answer: A
    Explanations:

• A: Correct. Callus is an unorganized proliferating mass of dedifferentiated plant cells used in in vitro propagation.

• B: Incorrect. Callus is not a fruit.

• C: Incorrect. Callus is a plant tissue phenomenon.

• D: Incorrect. It’s not specialized vascular tissue.

81. Which combination of plant hormones typically induces shoot organogenesis from callus?
    A. High auxin : low cytokinin
    B. Low auxin : high cytokinin
    C. ABA only
    D. Ethylene only
    Answer: B
    Explanations:

• A: Incorrect. High auxin with low cytokinin favors root formation.

• B: Correct. Low auxin and high cytokinin favors shoot induction (organogenesis).

• C: Incorrect. ABA generally induces dormancy/suppresses organogenesis.

• D: Incorrect. Ethylene is not the primary organogenesis inducer.

82. To induce root formation from a cutting, which hormonal balance is commonly applied?
    A. High cytokinin : low auxin
    B. High auxin : low cytokinin
    C. ABA only
    D. High ethylene only
    Answer: B
    Explanations:

• A: Incorrect. That balance favors shoots.

• B: Correct. Root formation is stimulated by higher auxin relative to cytokinin.

• C: Incorrect. ABA inhibits growth in many contexts.

• D: Incorrect. Ethylene is not primary rooting hormone.

83. Which of the following observations indicates dedifferentiation in a plant tissue culture?
    A. Formation of organized xylem strands only
    B. Formation of an unorganized, proliferating cell mass (callus) from explant tissue
    C. Immediate flowering in culture
    D. No cell division and only aging
    Answer: B
    Explanations:

• A: Incorrect. Organized tissue formation is redifferentiation.

• B: Correct. Callus formation shows cells reverting to meristematic state (dedifferentiation).

• C: Incorrect. Flowering is advanced differentiation.

• D: Incorrect. Dedifferentiation involves active division.

84. Which tissue is most characteristically derived from redifferentiation after dedifferentiation?
    A. New shoot or root meristems (organogenesis)
    B. Permanent epidermis only
    C. Secondary xylem exclusively
    D. Soil bacteria
    Answer: A
    Explanations:

• A: Correct. Callus cells redifferentiate into organ primordia forming shoots/roots.

• B: Incorrect. Epidermis is specialized but organogenesis typically yields meristems.

• C: Incorrect. Secondary xylem is specialized tissue often from cambial activity.

• D: Incorrect. Bacteria are non-plant.

85. Which experimental technique demonstrates a plant cell’s totipotency?
    A. Growing a whole plant from a single cultured somatic cell or small explant (micropropagation)
    B. Observing leaf fall in autumn only
    C. Measuring transpiration rate
    D. Counting stomata per mm²
    Answer: A
    Explanations:

• A: Correct. Regeneration of a whole plant from a somatic cell proves totipotency.

• B: Incorrect. Leaf fall is unrelated.

• C: Incorrect. Transpiration measurement is physiological, not proof of totipotency.

• D: Incorrect. Stomatal counts aren’t relevant to totipotency.

86. Which cellular changes accompany differentiation?
    A. Changes in gene expression patterns and formation of specialized organelles/cell wall modifications
    B. Loss of nucleus in all cells
    C. Creation of new chromosomes unique to cell type
    D. Immediate cell death
    Answer: A
    Explanations:

• A: Correct. Differentiation involves activation/suppression of gene sets, organelle development and structural specialization.

• B: Incorrect. Most differentiated plant cells retain nuclei unless they are specific terminally enucleate cells (rare).

• C: Incorrect. Chromosomes remain the same; expression changes, not genome structure.

• D: Incorrect. Differentiation is not cell death.

87. Which is an example of redifferentiation in natural plant repair?
    A. Formation of callus-like tissue at wound site and regeneration of new tissue/organs
    B. Permanent scab formation without regeneration
    C. Death of tissue following infection only
    D. Formation of seeds in damaged tissue
    Answer: A
    Explanations:

• A: Correct. Wounded tissues may dedifferentiate and then redifferentiate to repair damage.

• B: Incorrect. Scab without regeneration isn’t redifferentiation.

• C: Incorrect. Death is not regeneration.

• D: Incorrect. Seeds are reproductive, not direct repair.

88. Which hormone combination favors callus induction in many tissue culture protocols?
    A. Balanced auxin and cytokinin (ratio often equal or auxin slightly higher) depending on species
    B. Only ethylene and ABA exclusively
    C. Only gibberellin alone
    D. No hormones; callus will form spontaneously always
    Answer: A
    Explanations:

• A: Correct. Callus induction commonly uses auxin + cytokinin; exact ratio varies with species and explant.

• B: Incorrect. Ethylene/ABA are not typical callus-inducing hormones.

• C: Incorrect. GA primarily promotes elongation, not callus formation alone.

• D: Incorrect. Some explants may produce callus without hormones, but generally exogenous hormones facilitate it.

89. Which of these statements about plant cell differentiation is TRUE?
    A. Differentiation is irreversible in all plant cells.
    B. Many plant cells retain the capacity to dedifferentiate under appropriate conditions (unlike many animal cells).
    C. Differentiation always involves loss of DNA.
    D. Differentiated cells never perform specialized functions.
    Answer: B
    Explanations:

• A: Incorrect. Many plant cells can dedifferentiate (e.g., callus formation).

• B: Correct. Plant cells commonly retain plasticity enabling dedifferentiation and regeneration.

• C: Incorrect. DNA is retained; expression patterns change.

• D: Incorrect. Differentiated cells do perform specialized functions.

90. Which of the following best describes organogenesis in vitro?
    A. Development of whole plants from seed only
    B. Formation of organized structures (roots/shoots) from callus or explant under hormonal control
    C. Formation of bacterial colonies on agar
    D. Only production of secondary metabolites
    Answer: B
    Explanations:

• A: Incorrect. Organogenesis refers to organ formation in tissue culture, not only from seed.

• B: Correct. Hormone balance directs callus or explant to form shoots/roots in vitro.

• C: Incorrect. Bacterial growth is unrelated.

• D: Incorrect. Secondary metabolite production can occur but is not organogenesis.

91. During dedifferentiation, which molecular event is likely?
    A. Repressing cell cycle genes permanently
    B. Reactivation of cell cycle genes and chromatin remodeling to permit division
    C. Copying mitochondrial DNA to nucleus only
    D. Sudden loss of cellular organelles
    Answer: B
    Explanations:

• A: Incorrect. Dedifferentiation involves reactivating, not repressing, cell cycle genes.

• B: Correct. Cells activate mitotic programs and alter chromatin to become meristematic.

• C: Incorrect. That specific transfer is not the hallmark event.

• D: Incorrect. Organelles are generally retained; some modifications may occur.

92. Which explant is commonly used for plant tissue culture due to high regenerative potential?
    A. Young meristematic tissue or young leaf/petiole explants
    B. Fully senescent leaves only
    C. Mature wood with heavy lignification only
    D. Root hairs exclusively
    Answer: A
    Explanations:

• A: Correct. Young, actively dividing tissues often regenerate efficiently in culture.

• B: Incorrect. Senescent tissue has low regeneration potential.

• C: Incorrect. Lignified mature wood is less responsive.

• D: Incorrect. Root hairs are tiny and challenging as explants.

93. Which of the following is a consequence of redifferentiation of callus in tissue culture?
    A. Development of shoots or roots depending on hormone ratio
    B. Permanent loss of totipotency
    C. Formation of rock-like tissue only
    D. Conversion into fungal mycelium
    Answer: A
    Explanations:

• A: Correct. Redifferentiation yields organized organs under suitable hormonal signals.

• B: Incorrect. Totipotency is manifested by the ability to regenerate, not lost by redifferentiation.

• C: Incorrect. Teratoma-like tissues may form sometimes, but organogenesis is typical desired outcome.

• D: Incorrect. Plant tissue does not convert into fungi.

94. Which technique would most directly demonstrate dedifferentiation and redifferentiation potential?
    A. Plant regeneration from leaf explant on medium with specific auxin/cytokinin balance
    B. Counting stomata size under microscope only
    C. Testing soil pH only
    D. Measuring transpiration in candles
    Answer: A
    Explanations:

• A: Correct. Regeneration experiments from explants show dedifferentiation to callus and subsequent organogenesis.

• B: Incorrect. Stomatal counts don’t test cellular plasticity.

• C: Incorrect. Soil pH is unrelated.

• D: Incorrect. Nonsensical.

95. A cell that has redifferentiated into xylem will likely show:
    A. Lignified secondary walls and programmed cell death characteristics (for vessel elements)
    B. Increased chloroplast number only
    C. Loss of vacuole function only
    D. Immediate flowering induction
    Answer: A
    Explanations:

• A: Correct. Xylem cells develop thick lignified walls and may undergo PCD to form functional vessels.

• B: Incorrect. Xylem cells are non-photosynthetic, not enriched in chloroplasts.

• C: Incorrect. Vacuole changes occur but main feature is wall lignification.

• D: Incorrect. Flowering is unrelated.

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