seed development

Question 1

What is the key difference between gymnosperms and angiosperms?

Answer 1

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

Question 2

What are the key structures of the female gametophyte and their roles?

Answer 2

• 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.

Question 3

What is the structure and role of the male gametophyte (pollen)?

Answer 3

• 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.

Question 4

What happens during double fertilization in angiosperms?

Answer 4

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).

Question 5

What are the two main products of double fertilization, and how do they develop?

Answer 5

• 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.

Question 6

What are the major seed storage compounds, and why are they important?

Answer 6

• 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.

Question 7

What are the key components of a mature seed?

Answer 7

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.

Question 8

What are the key features of a monocot seed like barley?

Answer 8

• 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.

Question 9

What is the role of the endosperm in seed development?

Answer 9

• 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).

Question 10

How does a seed germinate and establish the next sporophyte generation?

Answer 10

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.