Q.61 The cell surface expands differently in different plant cells. Two common modes of expansion are
shown below ( X and Y ). Each rectangular box represents a cell marked with dots on its surface. The
spacing between the dots changes after the cell has undergone expansion as indicated by the arrow.
Which of the following statements is correct with respect to the growth of root hair and pollen tube?
X
Y
(A) Both grow as shown in X
(B) Both grow as shown in Y
(C) Pollen tube grows as shown in X , root hair grows as shown in Y
(D) Root hair grows as shown in X , pollen tube grows as shown in Y
Introduction
Plant cells expand in different ways depending on their function and structure. Two major modes of cell surface expansion are commonly discussed in cell biology:
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Tip growth
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Diffuse (uniform) growth
This question tests your understanding of these growth modes using a schematic representation (X and Y), where dots represent fixed points on the cell surface. The change in spacing between dots after expansion helps identify how growth occurs.
Such questions are frequently asked in CSIR NET, GATE, and MSc entrance exams, especially in plant physiology and cell biology.
Understanding the Diagrams (X and Y)
Mode X: Tip Growth
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Expansion occurs only at one end (the tip) of the cell.
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Dots near the growing tip become farther apart, while dots elsewhere remain relatively unchanged.
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Indicates localized cell wall loosening and membrane addition.
Mode Y: Diffuse Growth
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Expansion occurs uniformly along the entire cell surface.
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Spacing between all dots increases equally.
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Typical of cells that elongate evenly.
Growth Pattern of Root Hair and Pollen Tube
Root Hair
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Grows exclusively at the tip
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Requires focused vesicle delivery, actin cytoskeleton, and Ca²⁺ gradient
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Classic example of tip growth
Pollen Tube
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Also grows only at the apical tip
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Ensures directional growth toward the ovule
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Another textbook example of tip growth
👉 Both root hair and pollen tube exhibit tip growth, matching Mode X in the diagram.
Correct Answer
✅ (A) Both grow as shown in X
Explanation of All Options
Option (A): Both grow as shown in X — ✔ Correct
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Root hairs and pollen tubes elongate by tip growth
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Matches Mode X, where expansion is restricted to one end
Option (B): Both grow as shown in Y — ✘ Incorrect
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Mode Y represents diffuse growth
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This occurs in cells like stem internodes, not root hairs or pollen tubes
Option (C): Pollen tube grows as shown in X, root hair grows as shown in Y — ✘ Incorrect
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Root hairs do not grow diffusely
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Both structures show apical growth
Option (D): Root hair grows as shown in X, pollen tube grows as shown in Y — ✘ Incorrect
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Pollen tubes are the most classic examples of tip growth
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Diffuse growth does not apply here
Key Concept to Remember
| Cell Type | Mode of Growth | Diagram |
|---|---|---|
| Root hair | Tip growth | X |
| Pollen tube | Tip growth | X |
| Stem cells | Diffuse growth | Y |
Exam Tip (CSIR NET / GATE)
If you see keywords like:
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Pollen tube
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Root hair
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Fungal hyphae
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Apical Ca²⁺ gradient
👉 The answer is almost always TIP GROWTH.
Final Takeaway
Both root hairs and pollen tubes grow by localized expansion at the cell tip, corresponding to Mode X in the diagram.
✔ Correct Answer: (A) Both grow as shown in X
