Question

In a cucumber, pollen tube enters embryo sac through
(a)Integuments
(b)Micropyle
(c) Endosperm
(d)Chalaza

Answer 1

Hint: There are various ways by which the pollen tube can reach the embryo sac for pollination. Mesogamy is a type of fertilization observed in all Cucurbit plants, such as pumpkin, ridge gourds, bitter gourd, etc. In this type of fertilization, the pollen tube enters the ovule through its middle part.

Complete answer:
In a cucumber, a pollen tube enters the embryo sac through Integuments. The pollen tube pierces through the stigmatic papillae into the tissue of style. On reaching the ovary, the pollen tube grows towards the ovule and enters it. There are three methods of pollen tube entry into the ovule, namely porogamy, Chalazogamy, and mesogamy. The process of entry of pollen tube through integuments or funiculus is called Mesogamy. It is a kind of fertilization observed in Cucurbita, Populus, etc. Usually, the pollen tube enters the ovule along the side of the Integument, close to the placenta. After reaching the ovule, the pollen tube grows through the Micropylar end. Usually, only a single pollen tube enters the embryo sac. But in some instances, 3-5 pollen tubes may enter the same embryo sac. After entering the embryo sac, the tip of the pollen tube ruptures, discharging the whole contents to the embryo.

Additional Information: -Mesogamy is the kind of fertilization in which the pollen tube enters through the integuments. Example: cucumber
-Chalazogamy is the kind of fertilization in which the pollen tube enters through the chalazal tissues.
-When fertilization occurs through the Micropyle, then the process is known as porogamy
So, the correct answer is ‘Integuments’.

Note: -Inside the embryo sac one of the male gametes fuses with the egg and forms a diploid embryo zygote.
-The other one fuses with the diploid secondary nucleus and forms a triploid endosperm zygote or primary endosperm nucleus.
-Since fertilization involves two separate nuclear fusions it is called double fertilization.