Discussion
Which of the following seed plants have retained the flagellated type of sperm ? Choose the correct option :
(i) Cycas
(ii) Gnetum
(iii) Welwitschia
(iv) Casurina
(v) Ginkgo
Answer: C
The seed plants that retain flagellated sperm are Cycas and Ginkgo, so the answer is (i) and (v).
In cycads and Ginkgo the pollen tube is mainly a haustorial structure, and it releases large multiflagellate sperm that swim a short distance to the archegonium. This is a primitive feature that links them with the ferns, and the sperm of Cycas are among the largest in the plant kingdom.
Gnetum and Welwitschia are gymnosperms of the Gnetales, whose male gametes are non-motile and are carried to the egg by the pollen tube (siphonogamy). Casuarina (spelt Casurina in the paper) is a flowering plant, also with non-motile gametes. Every option containing (ii), (iii) or (iv) is therefore wrong.
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