Fertilisation, Seed and Fruit

Lesson

Part 1 — what happens after the pollen tube reaches the embryo sac.

In this lesson you will

Explain double fertilisation and triple fusion and their significance
Distinguish cellular, nuclear and helobial endosperm and define perisperm
Describe embryo development in dicots and monocots

Diagram

Double fertilisation

The pollen tube releases two male gametes into a synergid. One fuses with the egg (syngamy) to form the diploid zygote. The other fuses with the two polar nuclei (triple fusion) to form the triploid primary endosperm nucleus (PEN). Two fusions in one embryo sac make double fertilisation, unique to flowering plants.

Concept

Significance of double fertilisation

Double fertilisation links the formation of food tissue to successful fertilisation.

Table of the significance of syngamy and triple fusion
Event	Significance
Syngamy	Restores the diploid number in the zygote; combines characters of two parents
Triple fusion	Forms the triploid endosperm, a nutritive tissue for the developing embryo
Both together	Food tissue is made only when an egg is fertilised, so the plant does not waste food on ovules that fail

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