CIE iGCSE Biology-16.3 Sexual reproduction in plants- Study Notes- New Syllabus
CIE iGCSE Biology-16.3 Sexual reproduction in plants- Study Notes – New syllabus
CIE iGCSE Biology-16.3 Sexual reproduction in plants- Study Notes -CIE iGCSE Biology – per latest Syllabus.
Key Concepts:
Core
- Identify in diagrams and images and draw the following parts of an insect-pollinated flower: sepals, petals, stamens, filaments, anthers, carpels, style, stigma, ovary and ovules
- State the functions of the structures listed in 16.3.1
- Identify in diagrams and images and describe the anthers and stigmas of a wind-pollinated flower
- Distinguish between the pollen grains of insect-pollinated and wind-pollinated flowers
- Describe pollination as the transfer of pollen grains from an anther to a stigma
- State that fertilisation occurs when a pollen nucleus fuses with a nucleus in an ovule
- Describe the structural adaptations of insect-pollinated and wind-pollinated flowers
- Investigate and describe the environmental conditions that affect germination of seeds, limited to the requirement for: water, oxygen and a suitable temperature
Supplement
- Describe self-pollination as the transfer of pollen grains from the anther of a flower to the stigma of the same flower or a different flower on the same plant
- Describe cross-pollination as the transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same species
- Discuss the potential effects of self-pollination and cross-pollination on a population, in terms of variation, capacity to respond to changes in the environment and reliance on pollinators
- Describe the growth of the pollen tube and its entry into the ovule followed by fertilisation (details of production of endosperm and development are not required)
Parts of an Insect-Pollinated Flower
✅ Main Flower Parts and Their Functions:
| Part | Location in Diagram | Function |
|---|---|---|
| Sepals | Green, leaf-like structures beneath the petals | Protect the unopened flower bud |
| Petals | Often brightly coloured, just inside sepals | Attract insects for pollination |
| Stamens | Male reproductive parts: made of anthers and filaments | Produce pollen |
| Filaments | Stalks that hold up the anthers | Support the anther |
| Anthers | Oval structures on top of filaments | Produce and release pollen grains |
| Carpels (Pistil) | Female reproductive parts: made of stigma, style, and ovary | Involved in fertilisation |
| Style | Stalk connecting stigma to ovary | Pollen tube grows down through it |
| Stigma | Top surface of the carpel | Sticky to catch pollen |
| Ovary | At the base of the carpel | Contains ovules; becomes fruit after fertilisation |
| Ovules | Inside the ovary | Female gametes; become seeds when fertilised |
Functions of the Main Parts of an Insect-Pollinated Flower
| Structure | Function |
|---|---|
| Sepals | Protect the developing flower bud before it opens. |
| Petals | Often brightly coloured and scented to attract insect pollinators. |
| Stamens | The male reproductive organ; made of filament + anther. |
| Filaments | Hold the anther in position to expose it to visiting insects. |
| Anthers | Produce and release pollen grains (male gametes). |
| Carpels (Pistil) | The female reproductive organ; includes stigma, style, ovary. |
| Style | Supports the stigma and allows pollen tubes to grow towards the ovary. |
| Stigma | Sticky surface that captures and holds pollen grains during pollination. |
| Ovary | Contains ovules and becomes the fruit after fertilisation. |
| Ovules | Contain the female gametes; become seeds after fertilisation. |
Male part = stamen → filament + anther
Female part = carpel → stigma + style + ovary
Anther = makes pollen
Ovary = holds ovules
Petals = attract insects
🍃 Anthers and Stigmas in Wind-Pollinated Flowers
✅ General Characteristics of Wind-Pollinated Flowers:
| Feature | Adaptation |
|---|---|
| Small, dull petals | No need to attract insects |
| No scent or nectar | Not needed |
| Exposed anthers and stigmas | To catch and release pollen easily |
| Very light pollen | So it can be carried by wind |
| Large feathery stigmas | To trap airborne pollen effectively |
🟡 Anther – Structure & Identification
| Position | Exposed outside the flower, often hanging loosely on long filaments |
| Function | Produces large amounts of light, smooth pollen for wind transport |
| Adaptation | Can sway freely in air to release pollen easily |
| Identification in Diagrams | Look for dangling, pollen-covered sacs outside the petals |
🟣 Stigma – Structure & Identification
| Shape & size | Large and feathery to increase surface area |
| Position | Exposed outside the flower to catch pollen in the wind |
| Function | Traps airborne pollen effectively |
| Identification in Diagrams | Look for feathery or branched structure at the flower’s top, outside the petals |
🔎 Quick Visual Clues in Diagrams & Images:
| Structure | What to Look For |
|---|---|
| Anther | Long filaments with loosely hanging sacs – often outside the petals |
| Stigma | Feathery or branched part above or outside the flower |
🧷 Wind-pollinated flowers:
→ Anthers = exposed + dangle freely to release pollen
→ Stigmas = large + feathery to catch wind-borne pollen
Comparison of Pollen Grains: Insect vs Wind Pollination
| Feature | Insect-Pollinated Flowers | Wind-Pollinated Flowers |
|---|---|---|
| Size | Larger | Smaller |
| Surface Texture | Sticky or spiky to cling to insects | Smooth and light to float easily in air |
| Quantity Produced | Moderate (not much is wasted — targeted transfer) | Very large quantity (most pollen is lost in the wind) |
| Shape | Often round or oval with surface features | Simple and round, aerodynamic |
| Weight | Heavier (won’t blow away) | Lighter (easily carried by air currents) |
Insect Pollination:
Wind Pollination:
🧠 Why the Differences?
Insect-pollinated flowers rely on animals (like bees) to carry pollen directly to another flower – so the grains are sticky and designed to attach to their bodies.
Wind-pollinated flowers rely on air currents — so the pollen needs to be light, smooth, and produced in huge numbers.
Insect → sticky, large, fewer pollen grains
Wind → smooth, light, many pollen grains
Shape & surface match the pollination method
Pollination
✅ Definition:
Pollination is the transfer of pollen grains from the anther (male part) to the stigma (female part) of a flower.
📘 Key Details:
| Feature | Description |
|---|---|
| Pollen grains | Contain the male gametes (sperm cells) |
| Anther | Part of the stamen that produces and releases pollen |
| Stigma | Part of the carpel that receives pollen for fertilisation |
🔁 Types of Pollination:
| Type | Description |
|---|---|
| Self-pollination | Pollen is transferred within the same flower or to another flower on the same plant |
| Cross-pollination | Pollen is transferred to a flower on a different plant of the same species |
🧠 Importance of Pollination:
- It is the first step in sexual reproduction in flowering plants.
- Leads to fertilisation and the formation of seeds and fruit.
Fertilisation in Flowering Plants
✅ Key Statement:
Fertilisation occurs when a pollen nucleus fuses with a nucleus in an ovule.
📘 Explanation:
- Pollen grains land on the stigma during pollination.
- A pollen tube grows down the style to reach the ovary.
- The male nucleus travels through the tube to the ovary.
- It fuses with the female nucleus inside an ovule.
🔁 Result of Fertilisation:
- A zygote is formed.
- The zygote develops into an embryo.
- The ovule becomes a seed, and the ovary becomes a fruit.
Fertilisation = Fusion of nuclei
Happens inside ovule
Forms zygote → seed
Ovary turns into fruit
Structural Adaptations of Flowers for Pollination
🔶 Insect-Pollinated Flowers
| Feature | Adaptation |
|---|---|
| Petals | Large, bright, and often scented to attract insects |
| Nectar | Present to reward insect pollinators |
| Pollen grains | Sticky or spiky so they attach to insect bodies |
| Anthers | Firmly attached inside the flower to brush pollen onto insects |
| Stigma | Sticky and positioned inside the flower to collect pollen from insects |
| Flower position | Often upright or slightly open for insect landing |
🌾 Wind-Pollinated Flowers
| Feature | Adaptation |
|---|---|
| Petals | Small, dull, and not scented (no need to attract insects) |
| Nectar | Absent |
| Pollen grains | Light, smooth, and small — easily carried by wind |
| Anthers | Exposed and hang outside the flower — pollen released freely into air |
| Stigma | Large, feathery, and exposed — traps airborne pollen effectively |
| Flower position | Often hangs or dangles for easy pollen release and capture |
🗒️ Note:
- Insect-pollinated: bright, sticky, scented, targeted
- Wind-pollinated: dull, light pollen, open to air, mass release
- Key = position of anthers and stigmas + type of pollen
Germination of Seeds – Environmental Conditions
✅ Definition of Germination:
Germination is the process by which a seed begins to grow and develop into a new plant.
🔍 Requirements for Germination:
| Condition | Why It’s Needed |
|---|---|
| Water | Activates enzymes that break down food reserves in the seed and allows the embryo to grow. |
| Oxygen | Required for aerobic respiration to release energy for cell division and growth. |
| Suitable Temperature | Enables enzyme activity; too cold or too hot will slow or stop germination. |
🧪 Investigation (Practical Idea):
Aim:
To show the effect of water, oxygen, and temperature on seed germination.
Method Overview:
Prepare four test tubes or petri dishes with cotton wool and seeds:
| Set-Up | Condition Tested |
|---|---|
| A – water + air + warmth | Control (all conditions present – should germinate) |
| B – dry cotton wool + air + warmth | Lacks water |
| C – boiled (deoxygenated) water + oil layer + warmth | Lacks oxygen |
| D – water + air + kept in fridge | Low temperature |
Observation:
Only Set-Up A shows full germination.
🧠 Conclusion:
Seeds require water, oxygen, and a suitable temperature to germinate. Without any one of these, germination either fails or is delayed.
Germination = water + oxygen + warmth
Water = enzyme activation
Oxygen = respiration
Temperature = enzyme speed
Self-Pollination
✅ Definition:
Self-pollination is the transfer of pollen grains from the anther of a flower to the stigma of the same flower or another flower on the same plant.
📘 Key Features:
| Feature | Description |
|---|---|
| Involves one plant | Both pollen and ovule come from the same individual |
| Gametes involved | Male and female gametes of the same plant |
| No need for pollinators | Does not rely on insects or wind for transfer |
| More likely in plants with | Bisexual flowers (having both stamens and carpels in one flower) |
✅ Advantages of Self-Pollination:
| Advantage | Explanation |
|---|---|
| Reliable | Occurs even when pollinators or other plants are absent |
| Fast and energy-saving | No special adaptations needed to attract pollinators |
| Preserves successful traits | Offspring are genetically similar to parent |
❌ Disadvantages of Self-Pollination:
| Disadvantage | Explanation |
|---|---|
| Lack of genetic variation | All offspring are similar; less adaptable to change |
| Increased risk of disease | If parent is susceptible, offspring likely are too |
| Reduced evolutionary potential | Limits natural selection and adaptability |
Self-pollination = same plant
Fast, reliable — but no genetic variation
Common in plants with both male & female parts
Cross-Pollination
✅ Definition:
Cross-pollination is the transfer of pollen grains from the anther of one flower to the stigma of a flower on a different plant of the same species.
📘 Key Points:
| Aspect | Description |
|---|---|
| Plants involved | Two different plants of the same species |
| Pollen transfer | Carried by insects, wind, water, or animals |
| Genetic effect | Produces genetically varied offspring |
| Common in | Plants that promote cross-pollination by structural adaptations (e.g. stigma and anthers maturing at different times) |
✅ Advantages of Cross-Pollination:
| Advantage | Benefit |
|---|---|
| Increased genetic variation | Leads to greater adaptability and survival |
| Healthier plants | Less chance of inheriting harmful traits |
| Better fruit and seed quality | Due to mixing of genes |
❌ Disadvantages:
| Disadvantage | Limitation |
|---|---|
| Requires pollinators | Depends on insects, wind, etc. |
| Less reliable | May not occur if pollinators are absent |
| More energy used | Producing attractants like nectar and petals |
Cross-pollination = anther → stigma of another plant
Promotes genetic diversity
Requires pollination agents (insects/wind)
Self-Pollination vs Cross-Pollination – Effects on Populations
| Aspect | Self-Pollination | Cross-Pollination |
|---|---|---|
| Genetic Variation | Low – offspring are genetically similar to the parent | High – offspring show more genetic diversity |
| Ability to Adapt to Environment | Limited – poor adaptability to environmental changes | Better – wider variation means higher chance of survival |
| Risk of Harmful Traits | Higher – harmful recessive traits may accumulate | Lower – mixing genes reduces risk of genetic disorders |
| Dependence on Pollinators | Low – no need for insects or wind | High – requires agents like insects, wind, birds, etc. |
| Reproductive Reliability | More reliable – even in isolated areas | Less reliable – pollinators must be available |
| Speed and Energy Efficiency | Faster and energy-saving – fewer resources needed | Slower – needs energy to attract pollinators (e.g. nectar) |
📘 Summary:
- Self-Pollination ensures reproduction even when isolated, but may reduce genetic health and adaptability.
- Cross-Pollination increases variation and adaptability, helping plants survive in changing environments, but it depends on external pollinators.
Self = reliable but low variation
Cross = diverse, adaptable but needs help
Both affect survival and evolution
Pollen Tube Growth and Fertilisation in Flowering Plants
✅ Step-by-Step Description:
1. Pollination Occurs
A pollen grain lands on the stigma of a flower (either by wind, insect, etc.).
2. Pollen Tube Formation
The pollen grain germinates on the stigma and grows a pollen tube down through the style.
3. Pollen Tube Navigation
The tube grows towards the ovary, following chemical signals, and eventually reaches the ovule inside the ovary.
4. Entry into Ovule
The pollen tube enters the ovule through a small opening called the micropyle.
5. Nucleus Fusion (Fertilisation)
The male nucleus from the pollen grain travels down the pollen tube.
It fuses with the female nucleus (egg cell) inside the ovule.
This fusion of nuclei is called fertilisation and results in the formation of a zygote.
🧠 Key Terms:
| Term | Definition |
|---|---|
| Pollen tube | A slender tube that carries the male nucleus to the ovule |
| Micropyle | A tiny opening in the ovule through which the pollen tube enters |
| Fertilisation | The fusion of male and female nuclei to form a zygote |
Pollen tube grows from stigma → ovary
Micropyle = ovule entry point
Fertilisation = male + female nuclei → zygote