3.2.5Unit 3: Practical Skills in Biology I
Fertilisation in Flowering Plants — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 4 parts Lesson 19 of 27 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 4From Pollination to the Ovule
Pollination and fertilisation are separate events that occur one after the other.
1
Pollen produced in the anther is transferred to the stigma of a flower, which is called pollination.
2
The pollen grain germinates on the stigma and a pollen tube grows down through the style towards the ovary.
3
Two haploid male nuclei travel in the tube: the tube nucleus and the generative nucleus.
4
The generative nucleus divides by mitosis to give two haploid male gametes, which move down the tube behind the tube nucleus.
5
When the tube reaches the ovule the tube nucleus breaks down and the two male nuclei are released into the ovule.
Section 2 of 4Double Fertilisation
Flowering plants are unusual because both male nuclei take part in fertilisation.
First fusion
- First fusion One haploid male nucleus fuses with the haploid nucleus of the egg cell to form a diploid zygote.
Second fusion
- Second fusion The other male nucleus fuses with the two polar nuclei in the ovule to form a triploid endosperm nucleus.
Zygote fate
- Zygote fate The zygote divides by mitosis and develops into the embryo plant inside the seed.
Endosperm fate
- Endosperm fate The triploid endosperm nucleus develops into endosperm tissue, a food store used by the embryo as the seed germinates.
Section 3 of 4Flower Structures Involved
Flower Structures Involved
Anther
- Anther The part of the male organ where pollen grains are produced and from which pollen is later released.
Stigma
- Stigma The receptive surface of the female organ that catches pollen grains from the air or from pollinators.
Style
- Style The tube-like part linking stigma and ovary, through which the pollen tube grows towards the ovule.
Ovary and ovule
- Ovary and ovule The ovary contains the ovules, and each ovule holds the egg cell and polar nuclei needed for double fertilisation.
Section 4 of 4Exam Checklist & Tips
3.2.5 – Key Points for the Exam
- Pollination Transfer of pollen from the anther to the stigma.
- Pollen tube A tube that grows from the germinating pollen grain through the style to the ovule.
- Double fertilisation Two separate fusions in one ovule, forming a diploid zygote and a triploid endosperm nucleus.
- Polar nuclei Two haploid nuclei in the ovule that fuse with a male nucleus to make the endosperm nucleus.
- Endosperm Nutrient-rich tissue that feeds the embryo plant during germination.
Common Mistakes
- Using the words pollination and fertilisation as if they mean the same thing;
- fertilisation is fusion of nuclei, after pollen has landed.
- Saying the endosperm nucleus is diploid; it is triploid because it forms from three haploid nuclei.
- Forgetting that the generative nucleus divides by mitosis to give two male gametes.
- Claiming the pollen tube grows from the ovule towards the stigma, when it grows from the stigma down the style.
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