CIE iGCSE Co-ordinated Sciences-B15.3 Sexual reproduction in plants - Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-B15.3 Sexual reproduction in plants – Study Notes
CIE iGCSE Co-ordinated Sciences-B15.3 Sexual reproduction in plants – Study Notes -CIE iGCSE Co-ordinated Sciences – 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 15.3.1
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
Identify in diagrams and images and describe the anthers and stigmas of a wind-pollinated flower
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Structure of an Insect-Pollinated Flower
📌 Introduction
Flowers are the reproductive organs of flowering plants. Insect-pollinated flowers have special structures to attract insects and ensure the transfer of pollen.
🌱 Main Parts to Identify
- Sepals → Small, green, leaf-like structures. Protect the flower bud before it opens.
- Petals → Large, brightly coloured. Attract insects with colour, scent, and nectar guides.
- Stamens (Male part)
- Filament → stalk holding anther.
- Anther → produces pollen grains (male gametes).
- Carpels (Female part)
- Stigma → sticky surface, traps pollen.
- Style → slender stalk, connects stigma to ovary.
- Ovary → contains ovules.
- Ovules → female gametes; after fertilisation → seeds.
📊 Summary Table
| Part | Function |
|---|---|
| Sepals | Protect unopened flower bud |
| Petals | Attract insects (colour, scent, nectar) |
| Filament | Holds anther in position |
| Anther | Produces pollen grains (male gametes) |
| Stigma | Receives pollen (sticky) |
| Style | Pathway for pollen tube |
| Ovary | Contains ovules |
| Ovules | Female gametes → develop into seeds |
⚡ Quick Recap
Sepals = protection
Petals = attraction
Stamen = male (filament + anther)
Carpel = female (stigma + style + ovary + ovules)
Memory tip: “Stamen = Sperm, Carpel = Child.”
Functions of Flower Structures
📌 Main Structures & Their Functions
- Sepals → Protect the unopened flower bud from drying, insects, or mechanical damage.
- Petals → Large, coloured, scented to attract insects. Sometimes have nectar guides to direct insects to nectar.
- Stamens (Male part)
- Filament → supports anther, positions it where insects will brush against.
- Anther → produces and releases pollen grains (male gametes).
- Carpel (Female part)
- Stigma → sticky surface to trap pollen.
- Style → holds stigma in position and provides pathway for pollen tube growth.
- Ovary → protects ovules; after fertilisation develops into fruit.
- Ovules → contain female gametes; after fertilisation develop into seeds.
📊 Summary Table
| Structure | Function |
|---|---|
| Sepals | Protect unopened bud |
| Petals | Attract insects (colour, scent, nectar guides) |
| Filament | Holds anther in position |
| Anther | Produces pollen grains |
| Stigma | Sticky → traps pollen |
| Style | Connects stigma to ovary; pollen tube grows through it |
| Ovary | Contains ovules; becomes fruit |
| Ovules | Female gametes; become seeds after fertilisation |
⚡ Quick Recap
Sepals = Safety
Petals = Attraction
Stamen (Filament + Anther) = Male gametes
Carpel (Stigma + Style + Ovary + Ovules) = Female gametes & fertilisation
Pollination
📌 Definition
Pollination is the transfer of pollen grains:
- From the anther (male part of the flower)
- To the stigma (female part of the flower).
🌱 Key Points
- First step in sexual reproduction of flowering plants.
- Allows male gametes (inside pollen) to reach female gametes (inside ovules).
- After pollination → fertilisation occurs when the male nucleus fuses with the female nucleus.
📊 Types of Pollination
| Type | Description | Example |
|---|---|---|
| Self-pollination | Pollen from anther of a flower → stigma of same flower/plant | Pea, Tomato |
| Cross-pollination | Pollen from anther of one flower → stigma of a different plant of same species | Apple, Sunflower |
⚡ Quick Recap
Pollination = Anther → Stigma
Two types: Self (same plant) vs Cross (different plant)
Leads to fertilisation
Memory tip: “Pollination = Pollen shift.”
Fertilisation in Plants
📌 Key Statement
Fertilisation occurs when a pollen nucleus (male gamete) fuses with a nucleus in an ovule (female gamete).
🌱 Key Points
- After pollination:
- Pollen grain lands on the stigma.
It grows a pollen tube down through the style into the ovary.
- Inside the ovary:
- Pollen tube enters the ovule.
- Pollen nucleus is released.
- It fuses with the ovule nucleus → zygote formed.
- Zygote divides by mitosis → develops into an embryo (young plant).
📊 Summary Table
| Step | Event |
|---|---|
| Pollination | Pollen lands on stigma |
| Pollen tube growth | Tube grows down style into ovary |
| Fertilisation | Pollen nucleus + ovule nucleus fuse → zygote |
| After fertilisation | Zygote → embryo, ovule → seed, ovary → fruit |
⚡ Quick Recap
Fertilisation = Male nucleus + Female nucleus → Zygote
Zygote → Embryo (seed inside fruit)
Memory tip: “Fusion forms the future plant.”
Adaptations of Pollinated Flowers
📌 Introduction
Flowers show special adaptations depending on their mode of pollination:
- Insect-pollinated flowers → attract and use insects.
- Wind-pollinated flowers → rely on wind to carry pollen.
🐝 Insect-Pollinated Flowers (Entomophilous)
- Petals: Large, brightly coloured → attract insects.
- Scent & Nectar: Present → lure insects.
- Anthers: Inside the flower, firm → ensure pollen sticks to insect body.
- Pollen grains: Fewer in number, larger, sticky/spiky → attach to insects.
- Stigma: Inside flower, sticky → receives pollen from insects.
💨 Wind-Pollinated Flowers (Anemophilous)
- Petals: Small, dull, often green → no need to attract insects.
- Scent & Nectar: Absent → not required.
- Anthers: Large, outside flower, loosely attached → easy pollen release.
- Pollen grains: Produced in very large numbers, small, light, smooth → carried by wind.
- Stigma: Large, feathery, hanging outside → traps pollen from air.
📊 Summary Table
| Feature | Insect-Pollinated | Wind-Pollinated |
|---|---|---|
| Petals | Large, bright, scented | Small, dull, green |
| Nectar/Scent | Present | Absent |
| Anthers | Firm, inside flower | Loose, outside flower |
| Pollen | Few, large, sticky | Many, small, light |
| Stigma | Sticky, inside flower | Large, feathery, outside flower |
⚡ Quick Recap
Insect = Attractive (bright, scented, sticky pollen)
Wind = Simple (dull, light pollen, feathery stigma)
Memory tip: “Insects like showy flowers, wind likes simple ones.”
Germination of Seeds
📌 Definition
Germination = the process by which a seed develops into a young plant (seedling).
It needs specific environmental conditions to start growth.
Conditions Required
- Water 💧
Softens seed coat → allows embryo to swell.
Activates enzymes → convert stored starch into glucose for respiration. - Oxygen 🌬️
Needed for aerobic respiration.
Provides energy (ATP) for cell division and growth. - Suitable Temperature 🌡️
Must be optimal for enzyme activity.
Too low → enzymes inactive, growth very slow.
Too high → enzymes denature, seed dies.
📊 Summary Table
| Condition | Role in Germination |
|---|---|
| Water | Activates enzymes, softens seed coat, allows transport of food |
| Oxygen | Enables aerobic respiration → energy release |
| Suitable temperature | Ensures enzymes work properly → growth |
⚡ Quick Recap
Water → activates enzymes
Oxygen → respiration energy
Temperature → enzyme function
Memory tip: “WOT = Water, Oxygen, Temperature → seeds WOT they need to grow.”
Anthers & Stigmas of Wind-Pollinated Flowers
📌 Introduction
Wind-pollinated flowers are adapted for pollen transfer by air currents, not insects. Their anthers and stigmas have special structures for this role.
🌱 Anthers (Male part)
- Large and exposed → hang outside the flower.
- Loosely attached filaments → swing freely in the wind.
- Produce large quantities of pollen → increases chance of some reaching a stigma.
- Pollen grains = small, smooth, light → easily carried by air.
🌸 Stigmas (Female part)
- Large, feathery, branched → big surface area.
- Hang outside the flower → directly exposed to moving air.
- Designed to trap floating pollen grains from the air.
📊 Summary Table
| Structure | Adaptation | Function |
|---|---|---|
| Anthers | Large, exposed, loose | Release pollen easily into air |
| Stigmas | Large, feathery, outside | Trap pollen efficiently |
⚡ Quick Recap
Anthers = Outside, loose, pollen shower.
Stigmas = Feathery nets catching pollen.
Memory tip: “Wind needs wide nets (stigmas) and swinging dusters (anthers).”