Double Fertilisation
Syngamy and triple fusion and the origin of the endosperm. (Biology › Sexual Reproduction in Flowering Plants, NEET UG syllabus.)
What is Double Fertilisation?
The unique process in flowering plants involving two fusion events: syngamy (fusion of male gamete with egg cell) and triple fusion (fusion of another male gamete with the central cell's polar nuclei).
Key formula / rule: Ploidy of Zygote
Key points
- Define double fertilisation and explain its significance.
- Describe the sequence of events leading to double fertilisation.
- Identify the structures involved in syngamy and triple fusion.
- State the products of syngamy and triple fusion and their ploidy levels.
Common exam trap
Confusing syngamy with triple fusion.
Definitions
- Term
Double Fertilisation
- Meaning
The unique process in flowering plants involving two fusion events: syngamy (fusion of male gamete with egg cell) and triple fusion (fusion of another male gamete with the central cell's polar nuclei).
- Term
Syngamy
- Meaning
The fusion of one male gamete (n) with the egg cell (n) to form a diploid (2n) zygote.
- Term
Triple Fusion
- Meaning
The fusion of the second male gamete (n) with the two polar nuclei (n+n, or 2n after fusion) of the central cell to form a triploid (3n) Primary Endosperm Nucleus (PEN).
- Term
Zygote
- Meaning
The diploid (2n) cell formed by the fusion of a male gamete and an egg cell during syngamy, which develops into the embryo.
- Term
Primary Endosperm Nucleus (PEN)
- Meaning
The triploid (3n) nucleus formed by triple fusion, which develops into the endosperm.
- Term
Endosperm
- Meaning
A nutritive tissue, typically triploid, that develops from the Primary Endosperm Nucleus and provides nourishment to the developing embryo in angiosperms.
Learning objectives
Define double fertilisation and explain its significance.
Describe the sequence of events leading to double fertilisation.
Identify the structures involved in syngamy and triple fusion.
State the products of syngamy and triple fusion and their ploidy levels.
Explain the fate of the zygote and primary endosperm nucleus.
Formulae
- Name
Ploidy of Zygote
- Note
Zygote develops into embryo.
- Expression
n (male gamete) + n (egg cell) = 2n
- Name
Ploidy of Primary Endosperm Nucleus (PEN)
- Note
PEN develops into endosperm.
- Expression
n (male gamete) + 2n (secondary nucleus formed from 2 polar nuclei) = 3n
Prerequisites
Basic knowledge of flower structure (stigma, style, ovary, ovule).
Understanding of microsporogenesis and megasporogenesis.
Knowledge of male gametophyte (pollen grain) and female gametophyte (embryo sac) development.
Concept of haploidy (n) and diploidy (2n).
Common mistakes
Confusing syngamy with triple fusion.
Incorrectly identifying the ploidy levels of the zygote (2n) and PEN (3n).
Believing that both male gametes fuse with the egg cell.
Not understanding the role of the central cell and polar nuclei.
Forgetting that double fertilisation is exclusive to angiosperms.
Keywords
Angiosperms
Pollen tube
Embryo sac
Egg cell
Central cell
Polar nuclei
Male gamete
Syngamy
Triple fusion
Zygote
Primary Endosperm Nucleus (PEN)
Endosperm
Embryo
Seed
Fertilisation
Practice preview
Which of the following are the direct products of double fertilisation in angiosperms?…
medium
Which of the following statements about double fertilisation in angiosperms is INCORRECT?…
hard
What is the ploidy level of the primary endosperm nucleus (PEN) in a typical angiosperm?…
easy