Question

In Casuarina, fertilization occurs by:
A) Chalazogamy
B) Mesogamy
C) Porogamy
D) Apogamy

Answer 1

The process of fusion of the female gamete, the ovum or egg and the male gamete produced in the pollen tube by the pollen grain is called fertilization.

Complete answer:
The ovule is a multicellular oval-shaped structure which originates from the placenta and lies inside the chamber of the ovary. Each chamber may consist of one or more number of ovules. A fully mature ovule consists of the stalk or funicle and the body. Based on the entry of pollen tube through various region of ovule, the fertilization is classified as:
Types of fertilization:
Option A: The entry of pollen tube in the ovule through the chalazal tissues. Example: Casuarina. Hence, in Casuarina fertilization takes place through Chalaza, as the pollen tube enters the ovule from Chalaza to release the male gametes which will fuse with the egg cell and central cell, resulting in fertilization. Therefore, this is the correct option.

Option B: The most common form of fertilization in which the entry of pollen tube in the ovule through the micropyle. It occurs in most of the angiosperms and Lilly. Therefore, this is the incorrect option.

Option C: The entry of pollen tube in the ovule through the integuments (e.g. Cucurbita) or through funiculus (e.g. Pistacia). Therefore, this is the incorrect option.

Option D: It is a type of reproduction in which sporophyte develops directly from the gametophyte without the fusion of gametes. Therefore, this is the incorrect option.

Thus, the correct option is (A) Chalazogamy.

Note: Double fertilization most commonly occurs in angiosperm, during which a single female gamete undergoes fusion with two male gametes. Here, one of the sperm cells undergoes fusion with the zygote while the other fuses with the two nuclei to produce endosperm.