Part 5 — Sequence of Developmental Processes in a Plant Cell; Cellular Events

Part 5 — Sequence of Developmental Processes in a Plant Cell; Cellular Events

96. Which is the correct chronological sequence in a cell becoming part of a differentiated tissue?
    A. Differentiation → Division → Expansion
    B. Division → Expansion (cell elongation) → Differentiation → Maturation
    C. Maturation → Dedifferentiation → Division
    D. Expansion → Division → Differentiation
    Answer: B
    Explanations:

• A: Incorrect. Cells usually divide before they differentiate.

• B: Correct. Cells divide (mitosis), then enlarge, then differentiate and mature.

• C: Incorrect. Maturation precedes dedifferentiation rarely; sequence wrong.

• D: Incorrect. Expansion normally follows division, not precede it.

97. Which cellular process provides new cells for plant growth?
    A. Meiosis only
    B. Mitosis in apical and lateral meristems
    C. Photosynthesis directly creating new cells
    D. Programmed cell death
    Answer: B
    Explanations:

• A: Incorrect. Meiosis produces gametes; not growth.

• B: Correct. Mitotic divisions in meristems produce new cells for growth and repair.

• C: Incorrect. Photosynthesis provides energy, not new cells directly.

• D: Incorrect. PCD removes cells.

98. Wall loosening required for cell expansion often involves:
    A. Cellulose synthase inhibition only
    B. Activity of expansins and acid-growth processes (H⁺-ATPase driven wall loosening) often promoted by auxin
    C. Complete removal of cell wall
    D. Disappearance of plasma membrane
    Answer: B
    Explanations:

• A: Incorrect. Cellulose synthase inhibition would reduce wall formation; expansion requires controlled loosening.

• B: Correct. Expansins and acid-growth hypothesis (proton pumping loosens bonds) facilitate cell wall extension.

• C: Incorrect. Walls aren’t removed; they’re loosened and extended.

• D: Incorrect. Plasma membrane remains.

99. The acid-growth hypothesis explains cell elongation by:
    A. Alkalinization of cell wall
    B. Acidification of cell wall space by H⁺ pumps, loosening wall polysaccharide bonds and enabling expansion
    C. Photosynthetic acid production only
    D. Immediate lignification of walls
    Answer: B
    Explanations:

• A: Incorrect. Acid-growth involves acidification, not alkalinization.

• B: Correct. Auxin activates proton pumps exporting H⁺, lowering pH and activating wall-loosening enzymes like expansins.

• C: Incorrect. Photosynthesis is separate.

• D: Incorrect. Lignification would restrict, not promote, expansion.

100. Which of the following is a hallmark of cell differentiation at molecular level?
     A. Random gene expression in all cells
     B. Differential gene expression (some genes upregulated, others downregulated) leading to specialization
     C. Chromosome number doubling only
     D. Permanent RNA degradation in all cells
     Answer: B
     Explanations:

• A: Incorrect. Differentiation is patterned, not random.

• B: Correct. Specialized expression profiles define cell identity and function.

• C: Incorrect. Polyploidy occurs sometimes but not hallmark of differentiation.

• D: Incorrect. Global RNA degradation would impair cell function.

101. Which organelle proliferation is commonly seen during differentiation of photosynthetic cells?
     A. Increased chloroplast number and development of thylakoids in mesophyll cells
     B. Disappearance of mitochondria entirely
     C. Conversion of nucleus into chloroplast
     D. Immediate lignification of plastids
     Answer: A
     Explanations:

• A: Correct. Mesophyll differentiation includes chloroplast development for photosynthesis.

• B: Incorrect. Mitochondria remain and cooperate with chloroplasts.

• C: Incorrect. Nucleus doesn’t convert into chloroplast; different organelles.

• D: Incorrect. Lignification concerns cell wall, not plastids.

102. Plasmodesmata are important during development because they:
     A. Block communication between cells
     B. Provide cytoplasmic continuity for transport of signals and molecules between cells
     C. Convert into xylem vessels directly
     D. Are only present in seeds
     Answer: B
     Explanations:

• A: Incorrect. They facilitate, not block, intercellular communication.

• B: Correct. Plasmodesmata allow symplastic transport of molecules and developmental signals.

• C: Incorrect. They don’t convert into vessels.

• D: Incorrect. They occur in many plant tissues, not only seeds.

103. Which process in development often requires targeted protein synthesis and localization?
     A. Cell expansion via uniform protein distribution only
     B. Polar localization of PIN proteins for directional auxin transport during organogenesis
     C. Random protein misfolding only
     D. Immediate DNA loss in differentiating cells
     Answer: B
     Explanations:

• A: Incorrect. Polarization often matters more than uniform distribution.

• B: Correct. PIN auxin efflux carriers polarize on membranes to create directional auxin flows guiding development.

• C: Incorrect. Misfolding is pathological, not developmental.

• D: Incorrect. DNA is retained.

104. Which developmental process involves programmed cell death (PCD) as a normal step?
     A. Formation of vessel elements and tracheids (xylem) where PCD creates hollow conducting elements
     B. Root hair formation that requires cell death always
     C. Chloroplast development via cell death
     D. Seed maturation without any cell death
     Answer: A
     Explanations:

• A: Correct. Xylem differentiation often includes PCD to form hollow vessels for water conduction.

• B: Incorrect. Root hair cells remain alive; they don’t typically undergo PCD to form hairs.

• C: Incorrect. Chloroplasts develop in living cells.

• D: Incorrect. Some PCD events may occur during seed development in certain tissues.

105. Which molecular signal is often mobile and acts as a positional cue during pattern formation?
     A. mRNA and small peptides/hormones that move through plasmodesmata or apoplast
     B. DNA migration between cells regularly
     C. Permanent root-to-shoot DNA transport only
     D. Static cell walls without communication
     Answer: A
     Explanations:

• A: Correct. Mobile RNAs, peptides, and hormones serve as signals for positional information during development.

• B: Incorrect. DNA movements between cells are not typical intercellular signals.

• C: Incorrect. DNA transport is rare and not a routine signaling mechanism.

• D: Incorrect. Plants actively communicate via plasmodesmata and hormones.

106. During leaf development, adaxial–abaxial polarity is established by:
     A. Gravity only
     B. Differential gene expression and signaling (e.g., HD-ZIP genes adaxial, KANADI abaxial)
     C. Random cell division only
     D. Immediate conversion of epidermis to xylem
     Answer: B
     Explanations:

• A: Incorrect. Gravity affects other tropisms but not polarity gene networks mainly.

• B: Correct. Specific transcription factors determine dorsal/ventral leaf identity.

• C: Incorrect. It’s not random; gene-regulated patterning occurs.

• D: Incorrect. Cell fate conversion to xylem is unrelated to surface polarity.

107. Which factor often determines whether a plant cell will undergo division or enter differentiation?
     A. Local concentration of hormones (auxin, cytokinin) and positional signals
     B. External color of container only
     C. Presence of insects only
     D. Random chance every time
     Answer: A
     Explanations:

• A: Correct. Hormone ratios and positional cues decide cell fate: division vs differentiation.

• B: Incorrect. Container color rarely determines cell fate.

• C: Incorrect. Insects may induce defense responses but not basic division/differentiation decisions generally.

• D: Incorrect. Decisions are regulated, not random.

108. Which cytoskeletal element plays a major role in orienting cellulose microfibril deposition during cell wall formation?
     A. Intermediate filaments only
     B. Cortical microtubules guiding cellulose synthase trajectories
     C. Flagella only
     D. Myosin motors externally
     Answer: B
     Explanations:

• A: Incorrect. Plants lack classical intermediate filaments as in animals.

• B: Correct. Cortical microtubules guide cellulose synthase complexes to orient microfibril deposition.

• C: Incorrect. Flagella are unrelated to wall orientation (present in some algae/gametes).

• D: Incorrect. Myosins act with actin, but microtubules are primary for orientation.

109. Which developmental stage involves prominent vacuolation in plant cells leading to cell enlargement?
     A. Differentiation into stomata only
     B. Expansion phase where central vacuole enlarges, contributing to cell size increase
     C. DNA replication exclusively
     D. Immediate lignification only
     Answer: B
     Explanations:

• A: Incorrect. Stomatal differentiation involves specialized processes; vacuolation is general.

• B: Correct. Vacuole enlargement is a key driver of cell enlargement, storing water and solutes for turgor.

• C: Incorrect. DNA replication occurs during S-phase before mitosis, not vacuolation.

• D: Incorrect. Lignification restricts expansion.

110. During xylem differentiation, lignin deposition occurs in cell walls to:
     A. Make walls flexible for expansion
     B. Strengthen walls and render them impermeable and rigid for conduction
     C. Convert xylem into phloem
     D. Remove plasmodesmata permanently in all plant cells
     Answer: B
     Explanations:

• A: Incorrect. Lignification rigidifies walls, reducing flexibility.

• B: Correct. Lignin provides mechanical strength and water impermeability needed in xylem.

• C: Incorrect. Lignification doesn’t convert tissues to phloem.

• D: Incorrect. Lignification is not equivalent to universal plasmodesmata removal.

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