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What type of pollination brings genetically different types of pollen grains to the stigma?
What type of pollination brings genetically different types of pollen grains to the stigma?
Majority of plants use abiotic agents for pollination.
Majority of plants use abiotic agents for pollination.
False
What are the two types of abiotic agents used for pollination?
What are the two types of abiotic agents used for pollination?
Wind and water
Wind-pollinated flowers often have a ______ ovule in each ovary.
Wind-pollinated flowers often have a ______ ovule in each ovary.
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Match the following types of pollination with their characteristics:
Match the following types of pollination with their characteristics:
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Which of the following plants is a familiar example of wind-pollination?
Which of the following plants is a familiar example of wind-pollination?
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Pollination by water is more common than pollination by wind.
Pollination by water is more common than pollination by wind.
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What type of flowers produce an enormous amount of pollen compared to the number of ovules?
What type of flowers produce an enormous amount of pollen compared to the number of ovules?
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What is the process of formation of microspores from a pollen mother cell called?
What is the process of formation of microspores from a pollen mother cell called?
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Pollen grains have a soft outer layer that protects them from environmental factors.
Pollen grains have a soft outer layer that protects them from environmental factors.
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What are the two cells found in a mature pollen grain?
What are the two cells found in a mature pollen grain?
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The outer layer of the pollen grain, made up of sporopollenin, is called the ______.
The outer layer of the pollen grain, made up of sporopollenin, is called the ______.
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Match the parts of the pollen grain with their descriptions:
Match the parts of the pollen grain with their descriptions:
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What happens to microspores as the anthers mature?
What happens to microspores as the anthers mature?
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Pollen grains are always uniformly shaped across species.
Pollen grains are always uniformly shaped across species.
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Pollen grains typically measure about ______ micrometers in diameter.
Pollen grains typically measure about ______ micrometers in diameter.
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Which of the following are characteristics of pollen/nectar robbers?
Which of the following are characteristics of pollen/nectar robbers?
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Self-incompatibility is a mechanism that promotes self-pollination.
Self-incompatibility is a mechanism that promotes self-pollination.
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What is the primary effect of inbreeding depression in flowering plants?
What is the primary effect of inbreeding depression in flowering plants?
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Pollen is released before the stigma becomes receptive or the stigma becomes receptive much before the release of pollen is known as __________.
Pollen is released before the stigma becomes receptive or the stigma becomes receptive much before the release of pollen is known as __________.
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Match the following devices to their function in preventing self-pollination:
Match the following devices to their function in preventing self-pollination:
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What method do some flowering plants use to prevent autogamy by placing anthers and stigma at different positions?
What method do some flowering plants use to prevent autogamy by placing anthers and stigma at different positions?
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In monoecious plants, male and female flowers are present on separate plants.
In monoecious plants, male and female flowers are present on separate plants.
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Describe the role of the pistil in pollen-pistil interaction.
Describe the role of the pistil in pollen-pistil interaction.
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What is the process called when both syngamy and triple fusion occur in flowering plants?
What is the process called when both syngamy and triple fusion occur in flowering plants?
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The development of the embryo occurs before the development of the endosperm.
The development of the embryo occurs before the development of the endosperm.
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What happens to the central cell after triple fusion?
What happens to the central cell after triple fusion?
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The term for the fusion of one male gamete with the egg cell nucleus is __________.
The term for the fusion of one male gamete with the egg cell nucleus is __________.
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What is bagged before the flowers open during the pollination process?
What is bagged before the flowers open during the pollination process?
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Match the following processes to their descriptions:
Match the following processes to their descriptions:
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Emasculation is necessary when the female parent produces unisexual flowers.
Emasculation is necessary when the female parent produces unisexual flowers.
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What is the main role of the primary endosperm nucleus (PEN)?
What is the main role of the primary endosperm nucleus (PEN)?
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What is polyembryony?
What is polyembryony?
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Hybrid seeds maintain their characteristics when grown from collected seeds.
Hybrid seeds maintain their characteristics when grown from collected seeds.
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What is the primary function of the androecium in flowers?
What is the primary function of the androecium in flowers?
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The __________ develops inside the microsporangia and matures into pollen grains.
The __________ develops inside the microsporangia and matures into pollen grains.
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Match the following parts of the flower with their functions:
Match the following parts of the flower with their functions:
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What is a significant benefit of apomixis in hybrid seed production?
What is a significant benefit of apomixis in hybrid seed production?
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Pollen grains consist of a single-layered wall.
Pollen grains consist of a single-layered wall.
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What surrounds the microsporangium in a typical anther?
What surrounds the microsporangium in a typical anther?
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Study Notes
Microsporogenesis
- During microsporogenesis, pollen mother cells (PMCs) undergo meiosis to form microspores.
- Four microspores form a microspore tetrad.
- Microspores dissociate as the anther matures, developing into pollen grains.
- Each microsporangium produces thousands of pollen grains.
- The pollen grain is the male gametophyte.
Pollen Grain Structure
- Pollen grains are typically spherical, measuring 25-50 micrometers in diameter.
- The outer layer of the pollen grain is called the exine, composed of sporopollenin.
- Sporopollenin is highly resistant to degradation and can survive extreme conditions.
- The exine has apertures called germ pores, where sporopollenin is absent.
- The inner wall of the pollen grain is called the intine, made up of cellulose and pectin.
- A mature pollen grain contains two cells:
- The vegetative cell: larger, contains food reserves, and has a large nucleus.
- The generative cell: smaller, will divide to form sperm cells.
Pollination
- Pollination is the transfer of pollen from the anther to the stigma.
- Different pollination methods exist:
-
Wind Pollination: Common in grasses and other wind-pollinated plants.
- Pollen is light and non-sticky for easy wind dispersal.
- Stamens are often exposed and stigmas are feathery, trapping windborne pollen.
-
Water Pollination: Rare in flowering plants, limited to a few genera.
- Pollen is released into water to reach the stigma.
-
Animal Pollination: The most common form in plants.
- Animals like insects, birds, mammals can act as pollinators.
- Flowers often have adaptations for attracting pollinators, such as colors, scents, and nectar.
-
Wind Pollination: Common in grasses and other wind-pollinated plants.
Outbreeding Devices
- Outbreeding devices are mechanisms that promote cross-pollination and discourage self-pollination.
- These mechanisms help prevent inbreeding depression.
- Outbreeding devices include:
- Asynchronous Maturation of Anther and Stigma: Pollen is released before the stigma is receptive or vice versa.
- Spatial Separation of Anther and Stigma: Anther and stigma are positioned differently in the flower, preventing self-pollination.
- Self-Incompatibility: A genetic mechanism where the pollen from the same plant or flower cannot fertilize the ovules, blocking pollen germination or pollen tube growth.
-
Unisexual Flowers:
- Monoecious: Both male and female flowers present on the same plant (e.g., castor, maize).
- Dioecious: Male and female flowers are on separate plants (e.g., papaya), preventing both autogamy and geitonogamy.
Pollen-Pistil Interaction
- The pistil can recognize compatible pollen from the same species and incompatible pollen from other species or the same plant.
- Only compatible pollen will germinate and grow a pollen tube towards the ovule.
Double Fertilization
- Double fertilization is a unique event in flowering plants.
- After pollination, two male gametes travel through the pollen tube.
- Syngamy: One male gamete fuses with the egg cell to form the diploid zygote.
- Triple Fusion: The other male gamete fuses with the two polar nuclei in the central cell, forming the triploid primary endosperm nucleus (PEN).
- The fusion of the three haploid nuclei is called triple fusion.
Post-Fertilization: Endosperm Development
- Endosperm development often precedes embryo development.
- The primary endosperm cell (PEC) divides repeatedly to form the triploid endosperm tissue, providing nourishment to the developing embryo.
Post-Fertilization: Embryo Development
- The zygote divides mitotically to form an embryo, which develops into a young plant.
Polyembryony
- Polyembryony is the occurrence of more than one embryo in a seed.
- It can occur when nucellar cells surrounding the embryo sac divide and form embryos.
- Example: Citrus and Mango.
Apomixis
- Apomixis is a form of asexual reproduction in flowering plants where seeds are produced without fertilization.
- Apomictic embryos are genetically identical to the parent plant and can be called clones.
- Apomixis has potential in agriculture for maintaining desirable hybrid characters in plants.
Summary of Sexual Reproduction in Flowering Plants:
- The flower is the reproductive organ in flowering plants, containing the male reproductive organ (androecium) and female reproductive organ (gynoecium).
- The anther produces pollen grains by a process called microsporogenesis.
- Pollen grains act as male gametophytes, and they have a resistant outer layer called the exine made of sporopollenin.
- Pollination is the transfer of pollen to the stigma.
- There are different pollination mechanisms (wind, water, and animal pollination).
- Outbreeding devices prevent self-pollination and promote cross-pollination.
- Double fertilization occurs in flowering plants, involving syngamy and triple fusion.
- Following fertilization, the zygote develops into an embryo, and the endosperm provides nourishment for the developing embryo.
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Description
This quiz covers the process of microsporogenesis, including the formation of microspores and their development into pollen grains. It also delves into the structure of pollen grains, detailing the exine, intine, and the cells within. Test your understanding of these fundamental concepts in plant reproduction.