In a typical flower, germinating pollen grains pass through several parts of the gynoecium before they reach the ovule. A list of the parts of gynoecium is given below in different combinations. Choose the combination that represents the correct sequence of pollen tube pathway/journey:
- A.Style, Stigma, Ovary
- B.Stigma, Style, Ovary
- C.Pistil, Stigma, Ovary
- D.Ovary, Pistil, Style
Correct answer
Explanation
The correct answer is B, Stigma, Style, Ovary. A pollen grain lands on the stigma, grows a pollen tube that travels down through the style, and enters the ovary to reach an ovule, where fertilisation takes place. The gynoecium, or pistil, is the female part of a flower. Its tip, the stigma, is often sticky to catch pollen. The style is the long stalk below it, and the swollen base is the ovary, which holds the ovules. After pollination the pollen grain absorbs moisture and sugar on the stigma and puts out a tube. The tube grows through the style, enters the ovule usually through the micropyle and releases the male gametes; one fuses with the egg and the other with the polar nuclei, which is called double fertilisation. Option A is wrong because the style lies below the stigma, so the tube cannot meet the style first. Option C is wrong because the pistil is the whole gynoecium, not a stage on the way. Option D is wrong because it reverses the path, starting from the ovary, which is the destination. Exam tip: pollen tube path = stigma → style → ovary → ovule (micropyle).
Practice Questions
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1. Mg(HCO3)2
2. Ca(HCO3)2
3. CaCl2
4. MgSO4
Select the correct answer using the code given below.
- A.3 and 4
- B.2 and 3
- C.1 and 4
- D.1 and 2
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