Reproduction and Inheritance · 7 question types
Past paper frequency (2018 to 2024)
This topic accounts for approximately 11% of your exam marks.
Sexual vs asexual reproduction comparisons appear frequently; IVF and cloning as application questions.
A flower is the reproductive organ of a flowering plant. It contains the male and female parts in one structure.
The main parts of a flower:
| Part | What it does |
|---|---|
| Sepal | A green leaf-like structure that protects the flower bud before it opens |
| Petals | Colourful (in insect-pollinated flowers) or small and dull (in wind-pollinated). Attract insects in the first case |
| Stamen (male part) | Made of an anther at the top, supported by a thin stalk called the filament |
| Anther | Produces and releases pollen grains, which contain the male gametes |
| Filament | The stalk that holds the anther in position |
| Carpel (female part) | Made of the stigma, style and ovary |
| Stigma | The top of the carpel, where pollen lands during pollination. May be sticky or feathery |
| Style | A tube connecting the stigma to the ovary |
| Ovary | Contains the ovules, which hold the female gametes |
| Ovule | The structure containing the female gamete; develops into a seed after fertilisation |
Pollination is the transfer of pollen from the anther of one flower to the stigma of another flower (or the same flower) of the same species
Pollination is not the same as fertilisation. Pollination is just the journey of the pollen grain to the stigma. Fertilisation is what happens later, when the male gamete inside the pollen fuses with the female gamete in the ovule.
There are two main methods of pollination: by insects and by wind. Flowers that use each method look quite different.
Insect-pollinated flowers are designed to attract insects (or birds, or bats) and to make sure pollen sticks to the visitor's body for the journey to the next flower.
Adaptations:
Examples: roses, sunflowers, snapdragons, orchids.
Wind-pollinated flowers are designed to release pollen into the air and catch pollen blowing past, with no help from animals.
Adaptations:
Examples: grasses, cereals (wheat, rice, maize), most trees (oak, birch, hazel).
| Feature | Insect-pollinated | Wind-pollinated |
|---|---|---|
| Petals | Large, brightly coloured | Small, dull (often green) |
| Scent and nectar | Strong scent, sweet nectar | None |
| Anthers | Inside the flower, stiff | Hang outside on long filaments |
| Stigmas | Sticky, inside the flower | Feathery, hang outside |
| Pollen grains | Large, few, sticky, often rough or spiky | Small, many, smooth, light |
Once a pollen grain lands on a compatible stigma, the male gamete still has to travel down to the ovule. The journey takes a few hours to a few days:
A new seedling that grows right next to its parent has to compete with the parent for light, water and nutrients. Plants therefore have many ways of dispersing their seeds so the next generation gets enough resources of its own:
Germination is the process by which a seed begins to grow into a new plant
A seed contains:
Three things are needed for germination:
A seed without any of these three things stays dormant and does not germinate. Light is not needed at the early stages, because the seedling uses its starch food store, not photosynthesis, until its first true leaves emerge.
Aim: to investigate which conditions (water, oxygen, warmth) are needed for seeds to germinate.
Method:
Expected results:
| Tube | Conditions removed | Outcome |
|---|---|---|
| A | Water absent | No germination |
| B | (control: all present) | Most seeds germinate |
| C | Oxygen absent | No germination |
| D | Warmth absent | No germination |
Conclusion: all three of water, oxygen and warmth are needed for germination. Removing any one of them stops the process.