seed development
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What is the key difference between gymnosperms and angiosperms?
Gymnosperms: - “Naked seeds” (not enclosed in an ovary) - Seeds develop on the scales of cones (e.g., pinecones) Angiosperms: - Seeds develop inside an ovary - Formed through double fertilization
What are the key structures of the female gametophyte and their roles?
• Integuments: Diploid, of maternal origin, enclose the ovule and later the embryo and endosperm. • Central cell: Contains two polar nuclei, forms the endosperm after fertilization. • Egg cell: Haploid, fuses with sperm to form the embryo. Synergids (egg cell): Help guide sperm to the egg during fertilization.
What is the structure and role of the male gametophyte (pollen)?
• Pollen grain: Contains two haploid sperm nuclei. • Sperm nuclei are enclosed within a vegetative cell. • Pollen germinates on the stigma, forming a pollen tube. • The pollen tube delivers sperm to the ovule for fertilization.
What happens during double fertilization in angiosperms?
1️⃣ Pollen tube bursts inside a synergid cell, releasing two sperm nuclei. 2️⃣ One sperm fuses with the egg cell, forming a zygote (2n). 3️⃣ Second sperm fuses with the central cell (with 2 polar nuclei) to form the triploid endosperm (3n).
What are the two main products of double fertilization, and how do they develop?
• Embryo: Develops from the zygote, forming basic tissues, organs, and primary meristems. • Endosperm: Develops from the central cell, initially a syncytium (multinucleate structure), later increases seed size as a food reserve.
What are the major seed storage compounds, and why are they important?
• Food reserves: Synthesized during seed development and stored in the seed. • Types of storage compounds: Carbohydrates (e.g., starch) Lipids (e.g., oils) Storage proteins (for growth) Phytin (phosphorus storage) • Provide nutrition for the seedling during germination.
What are the key components of a mature seed?
1️⃣ Three tissues: - Embryo (new plant) - Endosperm (nutrient storage) - Seed coat (protective covering from integuments) 2️⃣ Embryonic organs: Shoot, root, cotyledons. 3️⃣ Primary meristems: For post-germination growth. 4️⃣ Storage reserves: Carbohydrates, lipids, proteins for growth. 5️⃣ Viability: Seed can germinate and establish the new sporophyte generation.
What are the key features of a monocot seed like barley?
• Scutellum: Interface between the embryo and endosperm, transfers nutrients and produces hormones. • Coleoptile: Protects the emerging shoot (plumule). • Coleorhiza: Protects the emerging root (radicle). • Aleurone layer: Living tissue that produces hydrolytic enzymes (in response to hormones) to break down endosperm. • Endosperm: Non-living storage compartment containing starch reserves.
What is the role of the endosperm in seed development?
• Endosperm provides nutrients to the growing embryo and seedling. • It undergoes rapid nuclear division, forming a syncytium. • As the seed matures, the endosperm stores carbohydrates, lipids, and proteins. • In some seeds (like monocots), the endosperm remains present in the mature seed (e.g., barley, rice).
How does a seed germinate and establish the next sporophyte generation?
1️⃣ Water uptake: Seed absorbs water and swells. 2️⃣ Enzyme activation: Hydrolytic enzymes (produced by the aleurone layer in monocots) break down starch in the endosperm. 3️⃣ Nutrient mobilization: Sugars and other nutrients are transferred to the growing embryo. 4️⃣ Embryo growth: Root (radicle) emerges first, followed by the shoot (plumule). 5️⃣ New sporophyte: The seedling grows into a mature plant, beginning a new generation.