Question

Ephedra and Gnetum are exceptions to gymnosperms as they show
A. Double fertilization
B. Siphonogamy
C. Aggregation of sporophylls
D. Presence of ovules

Answer 1

Gnetum and Ephedra are a non-flowering seed plant, genus of gymnosperm shrubs. The word gymnosperm comes from Greek word which means naked seeds.

Complete Answer:
- Ephedra is produced by plant Ephedra sinica for medicinal preparation. It belongs to genus Ephedra which is used for medicines. Gnetum is a Taxonomic rank of gymnosperms, the genus of Gnetaceae and order Gnetales family.
- Gnetum and Ephedra express a rudimentary pattern of double fertilization that results in the formation of two zygotes per pollen tube. The process of double fertilization in G. gnemon was examined with light and fluorescence microscopy and the DNA content of various nuclei involved in sexual reproduction was quantified.
- Male and female gamete nuclei pass through the synthesis phase of the cell cycle and increase their DNA content from 1C to 2C before fertilization. Each of the two zygotes found in association with a pollen tube is diploid and contains the 4C quantity of DNA at inception.
- Based on these results as well as previous studies of nuclear DNA content in plant sperm, eggs, and zygotes, three fundamental and distinct patterns of gamete karyogamy among seed plants can be circumscribed:

(1) G1 karyogamy, in which male and female gametes contain the 1C quantity of DNA throughout karyogamy and the zygote undergoes DNA replication
(2) S-phase karyogamy, in which gamete nuclei initiate fusion at 1C but pass through the S phase of the cell cycle before completely fusing
(3) G2 karyogamy, in which male and female gamete nuclei pass through the S phase of the cell cycle before the onset of fertilization.
Thus, from the above information we can conclude that Ephedra and Gnetum are exceptions to gymnosperms as they show double fertilization.

Hence, the correct answer is option A.

Note: Double fertilization is a process that occurs in flowering plants. The process starts with one female gametes united with two female gametes and then one of the male gametes fertilizes the egg resulting in the formation of zygote which will later form an embryo.