Germination Flashcards
D3.1.8; D3.1.9; D3.1.10; D3.1.11; D3.1.12 (31 cards)
What are the three stages of the reproductive cycle of flowering plants?
- Gamete production - the production of gametes in flowering plants involves two critical phases – sporogenesis and gametogenesis
- Pollination - the transfer of the male gamete (stored in pollen) to the female reproductive centre (ovule)
- Fertilisation - once a pollen grain has been transferred to the ovule, the sperm and egg will fuse (fertilisation) to produce a diploid zygote
What is the main advantage of sexual reproduction in flowering plants?
It ensures genetic variation and adaptability.
What are the two stages in gamette production in flowering plants?
Sporogenesis is the process of producing haploid spores via meiosis – males produce microspores, while females produce megaspores.
Gametogenesis involves the differentiate of the undeveloped spores into mature gametes – either sperm (males) or ova (females).
Describe the process of pollination in flowering plants.
The transfer of the male gamete (stored in pollen) to the female reproductive centre (ovule) is called pollination.
To support the survival of the gamete during pollen transfer, pollen grains typically enter a metabolically inactive state upon dispersal.
Exposure to environmental conditions (heat, drought, cold, humidity) causes the pollen grains to lose water and enter a state of partial desiccation.
Changing climactic conditions may impact this development, threatening overall pollen production and viability.
Describe the process of fertilisation in flowering plants.
Once a pollen grain has been transferred to the ovule, the sperm and egg will fuse (fertilisation) to produce a diploid zygote.
The growing embryo continues to develop within a seed casing, before eventually sprouting to produce a new plant (germination).
Germination may not occur spontaneously – some seeds will remain dormant until exposed to certain external triggers.
What happens to the ovule after fertilization?
The ovule becomes a seed, containing the embryo, endosperm, and a protective seed coat.
Describe the male reproductive parts of flowers.
Male Reproductive Parts (Stamen)
Anther: Produces pollen grains containing male gametes.
Filament: Supports the anther and positions it for effective pollination.
Describe the female reproductive parts of flowers.
Female Reproductive Parts (Carpel/Pistil)
Stigma: Receives pollen during pollination.
Style: A tube connecting the stigma to the ovary.
Ovary: Contains ovules where female gametes develop.
Describe the male contributions to gamete production.
Male Gametes Develop Pollen, inside the Anther:
* Diploid cells undergo meiosis, producing haploid cells.
* Each haploid cell develops into a pollen grain, which contains:
a. Two male gametes (sperm cells).
b. A tube nucleus to guide pollen tube growth.
Describe the female contributions to gamete production.
Female Gametes Develop The Ovule, inside the Ovary:
a. Diploid cells undergo meiosis, producing haploid nuclei.
b. One nucleus becomes the egg cell (female gamete), while others assist in fertilization or embryonic development.
In addition to these reproductive structures, flowers possess a number of other support structures, what are they?
Petals – brightly coloured modified leaves, which function to attract pollinators
Sepal – Outer covering which protects the flower when in bud
Peduncle – Stalk of the flower
What is the difference between pollination and fertilization?
Pollination is the movement of pollen, while fertilization is the fusion of gametes.
What are the two key methods of pollination?
Wind Pollination: Grasses and conifers rely on lightweight pollen carried by the wind.
Animal Pollination: Insects, birds, and mammals transfer pollen as they feed on nectar.
Explain self-pollination in flowering plants.
Hermaphrodite plants have both male and female reproductive structures on their flowers and are capable of self-pollination.
These plants can either transfer pollen grains to the stigma of the same flower, or alternatively to a different flower of the same plant.
Self-pollination leads to inbreeding, which decreases genetic diversity and increases the proportion of deleterious alleles within a population.
Explain cross-pollination in flowering plants.
Dioecious plants possess only one type of reproductive structure (male or female) and must produce offspring via cross-pollination.
Because plants are immobile, cross-pollination requires either an environmental agent or biological vector to transfer the pollen.
Terrestrial plants may rely on wind to disperse pollen, while aquatic plants may distribute pollen within the water.
Animals (such as insects and birds) can also transfer pollen, and flowers possess specific features (bright petals and nectar) to recruit these pollinators.
Describe the process of fertilisation.
Once pollen lands on a compatible stigma:
1. Pollen Tube Formation:
* The pollen grain germinates, forming a pollen tube that grows down the style toward the ovule.
* The tube nucleus directs this growth.
2. Fusion of Gametes:
* One male gamete fuses with the egg cell, forming a diploid zygote.
* The second male gamete fuses with additional nuclei in the ovule, forming a triploid endosperm to nourish the developing embryo.
Describe the process of embryo development in flowering plants.
- After fertilization, the zygote undergoes mitosis, leading to:
a) Embryo Formation: Develops structures like roots, shoots, and cotyledons.
b) Seed Maturation:
* The ovule becomes a seed, containing:
* The embryo.
* The endosperm, a nutrient source.
* A protective seed coat.
2.The ovary develops into a fruit, aiding seed dispersal.
What mechanisms do plants have to prevent self-pollination and promote cross-pollination?
Physical Separation: Male and female organs are positioned apart.
Self-Incompatibility: A genetic mechanism prevents pollen from fertilizing ovules of the same plant.
Flowers produce specific proteins that are present on both the pollen and the stigma.
The stigma will reject any pollen that possess identical proteins – preventing self-fertilization.
Only pollen with different proteins can fertilise the stigma – promoting cross-pollination between plants.
Name the function and adaptation of Anthers and Filaments (Stamen).
Anthers:
* Function: Produce and release pollen grains containing male gametes.
* Adaptation: Positioned to brush against visiting insects.
Filaments:
* Function: Support the anthers.
* Adaptation: Hold anthers in a position accessible to pollinators.
Name the function and adaptation of petals.
Function: Attract pollinators with their bright colors and patterns.
Adaptation: Often large and vividly colored to act as a visual signal for insects.
Name the function and adaptation of Stigma, Style, and Ovary (Carpel).
Stigma:
* Function: Capture pollen from insects.
* Adaptation: Sticky or feathery surface to ensure pollen adherence.
Style:
* Function: Connects the stigma to the ovary.
* Adaptation: Provides a pathway for the pollen tube to grow toward the ovary.
Ovary:
* Function: Contains ovules, which develop into seeds after fertilization.
* Adaptation: Protects ovules and later develops into fruit to aid seed dispersal.
Name the function and adaptation of pollen grains.
Function: Carry male gametes to the stigma.
Adaptation: Large, sticky, or spiky to adhere to insects.
Why is cross-pollination important?
Genetic Variation: Cross-pollination mixes genetic material, leading to offspring with diverse traits.
Adaptability: Greater genetic diversity enhances a plant population’s ability to adapt to changing environments.
Hybrid Vigor: Offspring from cross-pollination often grow stronger and healthier than those from self-pollination.
What is a challenge plants face in cross-pollination and a solution to it?
Challenge: Pollen may not reach a compatible plant.
Solution: Produce large amounts of pollen or rely on specialized pollinators.
