Describe the sequence of cellular events from pollen tube arrival at the ovule to the formation of the zygote and the endosperm in a flowering plant. Include the roles of the two sperm cells and the significance of each step for seed development.
Answer
Pollen tube delivers two sperm; one fuses with the egg forming the zygote and the other fuses with the central cell forming endosperm; this double fertilisation ensures coordinated development of embryo and endosperm.
Step-by-step solution
- Pollen grain lands on stigma and germinates, forming a pollen tube.
- The pollen tube grows through the style and reaches the ovule, guided by chemical signals.
- At the micropyle, the tube bursts, releasing two sperm cells into the female gametophyte.
- One sperm cell fuses with the egg cell, forming the zygote (future embryo).
- The second sperm fuses with the two polar nuclei of the central cell, forming the triploid endosperm.
- Endosperm develops to provide nutrition for the growing embryo.
- Thus, the two sperm cells perform distinct but coordinated roles that are essential for successful seed development.
Common mistake: mixing up the order of sperm fusion events or omitting the role of the central cell
Concept tested: Double fertilisation sequence
Published · How this solution was prepared and checked
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