Question

Through which route, the pollen tube enters the ovule?
(a)Chalaza
(b)Micropyle
(c)Funiculus
(d)All of the above

Answer 1

Hint: Once the pollen lands on the stigma of the carpel, it germinates to give rise to a pollen tube that grows inside the style up to the ovary of the carpel. This pollen tube is responsible for carrying the male gametes up to the ovule because they are non-motile.

Complete Answer:
Pollen germinates on the stigma to give rise to the pollen tube and it is part of the pollen-pistil interaction. Once the pollen tube reaches the ovary it can enter the ovule in the following ways:
Porogamy: In this type of entry, the pollen tube enters the ovule through the micropyle end where the egg apparatus is present.
Chalazogamy: The pollen tube enters the ovule through the chalazal end which is the opposite to the micropyle end.
Mesogamy: The pollen tube enters the ovule through the integuments or funiculus which is the stalk of the ovule.
Once the pollen tube enters the ovule, the male gametes are released for double fertilization to occur.

Additional information:
Let us look at the process of double fertilization in detail.
-Two male gametes are released into the cytoplasm of the synergid present in the ovule by the pollen tube.
-One male gamete fuses with the egg resulting in a diploid cell called the zygote. This process is known as fertilization or syngamy.
-The other male gamete is involved in triple fusion in which it fuses with the two polar nuclei of the central cell.
Since, there are two types of fusion taking place, syngamy and triple fusion, this entire process is known as double fertilization.
-The central cell develops further to give rise to endosperm whereas the zygote gives rise to the embryo.

So, the correct option is ‘All of the above’.

Note:
-Once the pollen tube enters the ovule, the filiform apparatus of the synergids guide its entry towards the egg.
-Pollen tube germinates from one of the germ pores of the pollen grain. Germ pore is the region where there is only a thin layer of the exine.
-Once the pollen tube germinates, pollen grains at the two-celled stage become three-celled because the generative cell divides to give rise to 2 male gametes.