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Questions and Answers
What is the main purpose of the seed coat in a developing seed?
Which part of a seed embryo develops into the embryonic root?
From what part of the flower does an aggregate fruit form?
Which type of fruit has a fleshy pericarp and is classified as a simple fruit?
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What is the main characteristic of apomixis as a mechanism of natural reproduction in plants?
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Which type of plant completes its life cycle in one year?
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What sets polycarpic plants apart from monocarpic plants?
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What is the main function of the endosperm in a developing seed?
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Which part of a seed embryo develops into the stem below the cotyledons?
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From what part of the ovary do multiple fruits develop?
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What is a characteristic feature of apomixis as a method of reproduction in plants?
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What is a common feature between drupes and pomes as types of fruits?
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Which plant species exemplifies a monocarpic life cycle?
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Study Notes
Plant Reproduction
- Monocarpic plants flower once in their lifetime before dying, while polycarpic plants can flower multiple times throughout their life.
- Flower structures consist of four whorls:
- Calyx: Outermost, made of sepals, protecting the bud.
- Corolla: Second whorl of petals; petal count differs between monocots (3 or multiples) and dicots (4, 5, or multiples).
- Androecium: Contains male reproductive structures (stamens).
- Gynoecium: Innermost, holds female reproductive structures (carpels).
Reproductive Structures
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Carpel (female part):
- Ovary: Houses ovules, develops into fruit post-fertilization.
- Stigma: Receives pollen.
- Style: Connects stigma and ovary.
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Stamen (male part):
- Anther: Contains pollen grains.
- Filament: Supports the anther.
Types of Flowers
- Complete Flowers: Contain all four whorls.
- Perfect Flowers: Possess both male and female structures.
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Imperfect Flowers:
- Staminate: Only male parts.
- Carpellate: Only female parts.
- Monoecious Plants: Both male and female flowers on the same plant.
- Dioecious Plants: Male and female flowers on separate plants.
Gamete Production
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Male Gamete Production:
- In anthers, microsporocyte undergoes meiosis to form pollen tetrads.
- Microspores undergo mitosis, leading to a generative cell (produces two sperm) and a vegetative/tube cell (develops into a pollen tube).
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Female Gamete Production:
- In ovules, megasporocyte undergoes meiosis to yield four megaspores (three degenerate, one survives).
- The surviving megaspore divides, forming an 8-nucleate, 7-celled gametophyte (embryo sac) with synergids, egg, antipodal cells, and a central cell that leads to the endosperm.
Fertilization
- Involves the mechanical transfer of pollen from anther to stigma.
- Pollen grain forms a tube guided toward the embryo sac and enters through the micropyle.
- One pollen cell lags to produce two sperm cells; sperm lack flagella.
Pollination
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Cross-Pollination Mechanisms:
- Self-Pollination: No need for nectar production.
- Insect Pollination: Flower shapes suited to specific pollinators.
- Bat Pollination: Large, bright flowers visible at night.
- Bird Pollination: Sturdier plants with bright, odorless flowers.
- Wind Pollination: Flowers emerge before leaves, with pollen released.
- Water Pollination: Aquatic flowers utilizing water currents.
Seed Development
- Fertilization leads to the formation of a zygote, which divides into an embryo.
- Ovule develops into a seed; the seed coat forms for protection.
- Endosperm serves as a food reserve for the developing embryo.
- Seeds have various structures:
- Cotyledons: Leaves.
- Radicle: Roots.
- Hypocotyl: Stem segment below cotyledons.
- Epicotyl: Stem segment above cotyledons.
- Micropyle: Pore for gas exchange; Hilum: Scar from attachment to the ovary wall.
Seed Types
- Monocots: One cotyledon.
- Dicots: Two cotyledons.
Fruit Formation
- True Fruits: Develop from ovary walls post-fertilization.
- Accessory Fruits: Arise from non-ovary parts of the flower.
- Types include:
- Simple Fruits: From a single ovary.
- Aggregate Fruits: From clustered carpels.
- Multiple Fruits: From inflorescences.
- Examples of fruit types:
- Berries: Fleshy fruits with many seeds (e.g., blueberries, tomatoes).
- Drupes: Hard endocarp surrounding the seed (e.g., mangos).
- Pomes: Accessory fruits (e.g., apples).
- Achenes: Solid dry fruits that do not split (e.g., strawberries).### Fruit Overview
- Thickened walls of the ovary protect seeds, primarily serving for seed dispersal.
- True fruits develop from the ovary, while accessory or false fruits originate from other plant parts.
Fruit Structure
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Pericarp: Composed of three layers:
- Exocarp: Outer skin or covering.
- Mesocarp: Middle, often fleshy layer.
- Endocarp: Inner layer surrounding the seed.
Types of Fruit
- Simple Fruits: Derived from a single ovary.
- Aggregate Fruits: Form from multiple carpels that fuse together.
- Multiple Fruits: Develop from clusters of flowers (inflorescence).
- Accessory Fruits: Formed from parts other than the ovary.
Specific Fruit Types
- Berries: Simple fruits with fleshy innermost tissues and many seeds (e.g., blueberries, tomatoes).
- Drupes: Simple fruits featuring a hard endocarp (pit) surrounding the seed (e.g., mangos, olives).
- Pepos: Modified berries with a hard rind (e.g., cucumbers, watermelons).
- Hesperidium: Special berries with leathery rind and segmented interior (e.g., citrus fruits).
- Pomes: Accessory fruits from united carpels (e.g., apples, pears).
- Achenes: Dry fruits that do not split open, exemplified by strawberries, which themselves are accessory fruits with fleshy receptacles.
Reproduction in Angiosperms vs. Gymnosperms
- Angiosperms: Gametophytes are in flowers, double fertilization occurs, and ovary tissues form fruit. Animal pollination predominates.
- Gymnosperms: Gametophytes on separate cones, single fertilization leads to a naked seed, with wind pollination being most common.
Asexual Reproduction Mechanisms
- Apomixis: Asexual seed production without fertilization, originating from diploid ovule or ovary.
- Self-Propagation: Includes structures like stolons (e.g., strawberries), tubers (e.g., potatoes), and rhizomes (e.g., ginger).
Plant Life Spans
- Senescence: Aging process varying widely, from weeks to thousands of years.
- Types include:
- Annuals: Complete life cycle in one year.
- Biennials: Life cycle spans two years.
- Perennials: Live for multiple years.
- Monocarpic: Flower once and die soon after.
- Polycarpic: Flower multiple times throughout life.
Flower Structure
-
Four Whorls:
- Calyx: Outermost whorl of sepals for bud protection.
- Corolla: Second whorl of petals, varying by monocots/dicots.
- Androecium: Third whorl containing male parts (stamens).
- Gynoecium: Innermost whorl with female parts (carpels).
Reproductive Structures
-
Carpel (Female):
- Ovary: Houses ovule, becomes fruit.
- Stigma: Pollen landing site.
- Style: Stalk connecting to ovary.
-
Stamen (Male):
- Anther: Contains pollen grains.
- Filament: Supports the anther.
Flower Types
- Complete Flower: Contains all four whorls.
- Perfect Flower: Both male and female structures present.
- Imperfect Flowers: Staminate (male only) or carpellate (female only).
Gamete Production in Angiosperms
- Male Gametes: Microsporogenesis leads to tetrads of microspores, where one turns into a pollen grain with sperm cells.
- Female Gametes: Megasporogenesis produces megaspores; the surviving one forms an 8-nucleate embryo sac with various cell types.
Fertilization and Pollination
- Fertilization requires pollen transfer to stigma, followed by pollen tube growth to the embryo sac.
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Cross-Pollination: Involves mechanisms like:
- Self-Pollination: Requires no nectar for pollinators.
- Insect Pollination: Flowers adapted to pollinators’ shapes.
- Animal Pollination: Such as bats and birds, with flowers designed for visibility and separation.
- Wind Pollination: Timing of flower release before leaf emergence to facilitate pollen dispersal.
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Description
Test your knowledge on the different types of fruits and their structures. Learn about simple fruits, aggregate fruits, and multiple fruits. Understand the components of a fruit including pericarp, exocarp, mesocarp, and endocarp.
