Question

The fertilization in gymnosperms is
A. Porogamous
B. Chalazogamous
C. Mesogamous
D. None of the above

Answer 1

Hint: In gymnosperms, microsporangia (pollen grain) and megasporangia (potential ovules) together play a very important role in fertilization. Entry of pollen grain in the ovules decides which type of fertilization will take place. Pollen grains of gymnosperms pollinate through air and present in the lower part so their entry is governed by micropyle end. In gymnosperms, Male and female gametophyte structures are present on separate male and female cones.

Complete answer:
In gymnosperms, male and female cones generate from a leafy green sporophyte. Female cones are located up in the tree and they are bigger than male cones. Male gametophytes are produced by microsporophyll present in the male cone. Male cones are present in the lower region of the tree. Female gametophytes form the megaspore mother cell by meiosis. Meiosis is the reduction division, by this megaspore mother cell produces four haploid megaspores.
Pollen grains of gymnosperms shed and blown by the wind as they are light in weight, this arrangement makes self-pollination difficult. Microspore produces two nuclei by mitosis: generative and tube nucleus. After the maturation of male gametophyte (pollen grain) is released from the male cones and is carried by the wind to land on female cones. When the pollen lands on the female cone, tube cells develop and the cell migrates towards the ovule through the micropyle. This process is known as porogamy. After that fertilization takes place and diploid zygote is formed.
Mesogamy refers to the process where pollen grains enter through the middle part of the ovules while chalazogamy is the process in which pollen grains enter into the embryo sac through the chalazal end.
From the above information we can say that fertilization in gymnosperms is porogamous.

So, the correct answer is option A.

Note: In gymnosperms, the process of double fertilization does not occur because of separate male and female cones. In gymnosperms, the pollen tube takes approximately one year to grow and migrate to the female gametophyte. Fruit formation does not take place in gymnosperms as their seed does not have any covering. Pollen grains can reach the embryo sac by two modes either they swim directly to the egg inside the ovule or they move along the pollen tube to the egg. Conifers, Cycads, Ginkgo, Gnetophytes are the example of gymnosperms.