Edexcel A Level (IAL) Biology -3.13 Fertilization: Flowering Plants- Study Notes- New Syllabus
Edexcel A Level (IAL) Biology -3.13 Fertilization: Flowering Plants- Study Notes- New syllabus
Edexcel A Level (IAL) Biology -3.13 Fertilization: Flowering Plants- Study Notes -Edexcel A level Biology – per latest Syllabus.
Key Concepts:
- 3.13 know the process of fertilisation in flowering plants, starting with the growth of a pollen tube and ending with the fusion of nuclei
Fertilisation in Flowering Plants
🌱 Introduction
Fertilisation in flowering plants involves fusion of male and female gametes. It ensures genetic variation and forms a diploid zygote → develops into a seed.
1. Pollination & Pollen Tube Growth
- Pollination: Transfer of pollen from anther (male) → stigma (female).
- Pollen grain germination: Absorbs water from stigma → forms pollen tube growing through style toward ovule.
- Nuclei in pollen grain:
- Generative nucleus → divides into two male gametes.
- Vegetative nucleus → controls pollen tube growth.
- Key Point: Pollen tube acts as a delivery system for male gametes.
2. Entry into the Ovule
- Pollen tube enters micropyle (small opening in ovule) → grows toward embryo sac (female gametophyte).
3. Double Fertilisation
- Unique to flowering plants → involves two fusion events:
- First fusion: one male gamete + egg nucleus → diploid zygote (2n) → develops into embryo.
- Second fusion: other male gamete + two polar nuclei → triploid endosperm (3n) → food storage for embryo.
- Key Point: Double fertilisation ensures zygote and nutritive tissue develop together.
4. Summary of Steps
- Pollen grain lands on stigma → absorbs water.
- Pollen tube grows through style toward ovule.
- Generative nucleus divides → forms two male gametes.
- Pollen tube enters micropyle → reaches embryo sac.
- First fusion: male gamete + egg → diploid zygote.
- Second fusion: male gamete + two polar nuclei → triploid endosperm.
📊 Summary Table
| Step | Location / Structure | Outcome |
|---|---|---|
| Pollen grain germination | Stigma | Pollen tube formation |
| Pollen tube growth | Style | Male gametes move toward ovule |
| Entry into ovule | Micropyle | Reaches embryo sac |
| Fusion with egg | Egg cell nucleus | Diploid zygote → embryo |
| Fusion with polar nuclei | Central cell | Triploid endosperm → nutritive tissue |
⚡ Quick Recap
Double fertilisation → unique to flowering plants.
Pollen tube delivers male gametes to ovule.
1st male gamete + egg → diploid zygote → embryo.
2nd male gamete + 2 polar nuclei → triploid endosperm → food storage.
Endosperm nourishes developing embryo in seed.
RECOMMENDED ADDITIONAL PRACTICAL
Investigating Factors Affecting Pollen Tube Growth
🌱 Introduction
Pollen tube growth delivers male gametes to the egg in flowering plants. This practical investigates how environmental and chemical factors influence pollen tube elongation.
Aim
To investigate how different factors (temperature, pH, sucrose concentration, humidity) affect pollen tube growth.
Materials Needed
- Fresh pollen grains (lily, hibiscus, etc.)
- Microscope slides & cover slips
- Germination medium (agar + sucrose + calcium nitrate + boric acid)
- pH buffers, sucrose solutions, temperature-controlled incubator
- Light microscope
- Ruler or eyepiece graticule for measuring pollen tube length
Method (Step-by-Step)
- Prepare germination medium: Dissolve sucrose, calcium nitrate, boric acid in agar. Adjust pH if testing pH effects.
- Place pollen on medium: Sprinkle fresh pollen grains; cover gently with cover slip.
- Apply test conditions:
- Temperature: 15°C, 25°C, 35°C
- pH: 5, 7, 9
- Sucrose: 5%, 10%, 15%
- Incubation: Allow pollen tubes to grow for 1–2 hours.
- Observation under microscope: Locate pollen tubes under low magnification → measure length under higher magnification.
- Measurement: Use eyepiece graticule; measure at least 10 pollen tubes per condition.
- Record results: Average lengths; compare growth under different conditions.
Factors Affecting Pollen Tube Growth
| Factor | Effect on Growth | Explanation |
|---|---|---|
| Temperature | Optimal → fastest growth; too low/high → slow or no growth | Enzyme activity is temperature-dependent |
| pH | Optimal pH promotes growth | Extreme acidity/alkalinity denatures enzymes & proteins |
| Sucrose concentration | Optimal concentration → maximum growth | Too low → insufficient energy; too high → osmotic stress |
| Humidity / Water availability | High humidity → better growth | Pollen tube elongation requires water |
Key Points for Success
- Use fresh pollen for best results.
- Handle slides gently to avoid breaking pollen tubes.
- Maintain consistent incubation times for fair comparison.
- Take multiple measurements to reduce errors.
⚡ Quick Recap
Pollen tubes deliver male gametes to egg.
Growth influenced by temperature, pH, sucrose, and water availability.
Measure tube length using microscope & eyepiece graticule.
Optimal conditions → longer, healthier pollen tubes.