The dominant plants on Earth are the angiosperms, the flowering plants. Flowers, the reproductive structures of angiosperms, produce fruits, which enclose the seeds. A flower is generally composed of four parts -- sepals, petals, stamens, and one or more carpels. Although the sepals and petals can play an indirect role in reproduction (for example, attracting pollinators), here we'll concentrate on the stamens and carpel, the parts directly involved in reproduction. The stamen, the pollen-containing structure, is composed of two parts: a stalk-like filament and an enlarged anther. Inside the anther are chambers containing diploid cells called microsporocytes. Each microsporocyte undergoes meiosis to produce four haploid microspores. These microspores divide by mitosis to form male gametophytes, or pollen grains. The immature pollen grain consists of a small generative cell enclosed within a large vegetative cell called the tube cell. The generative cell will later divide to form sperm. When conditions are right, the anther opens to release the pollen grains. Pollen is produced in large quantities because most of it will not reach a receptive flower. Some falls to the ground, some is eaten by insects, and so on. The carpel is made up of three parts: the stigma, the style, and the ovary. A carpel may contain more than one ovary. The stigma, at the top of the carpel, is specialized for receiving pollen. The stalk-like style supports the stigma. At the base of the carpel is the enlarged ovary. The ovary contains developing ovules. After fertilization, the ovary becomes the fruit. Each ovule contains a single diploid megasporocyte and is surrounded by a continuous covering except for a narrow canal at one end, called the micropyle. The megasporocyte undergoes meiosis to produce four haploid megaspores. Three of the megaspores degenerate, leaving a single functional megaspore in each ovule. The megaspore divides by mitosis three times, producing a total of eight nuclei, which segregate to form seven cells. The most important elements of the female gametophyte are the egg, located at the micropyle, and the two polar nuclei. The polar nuclei are found in the largest cell of this structure, at the center of the female gametophyte. Sexual reproduction in angiosperms involves the transfer of pollen from an anther to a stigma, a process called pollination. In self-compatible flowers, the stigma is receptive to pollen from the same flower. Self-incompatible flowers require pollen from a different plant. In both cases, pollen can be dispersed by living vectors (such as insects) or nonliving vectors (such as the wind). In this example, pollen from the anther of one flower is transferred to the stigma of another flower. After the pollen grain lands on a receptive stigma, it germinates, producing a pollen tube. The pollen tube grows down through the tissue of the style. At some point during its journey, the generative cell of the pollen grain divides by mitosis to form two sperm nuclei, or male gametes. The pollen tube continues to grow until it reaches the ovary. It then enters an ovule through the micropyle. It ruptures one of the cells next to the egg and discharges the two sperm nuclei. In most plant groups, fertilization is straightforward: One sperm nucleus fuses with the egg to form a diploid zygote. In angiosperms, however, an unusual event called double fertilization takes place. The other sperm nucleus fuses with the two polar nuclei to form a large triploid (3n) cell. The triploid cell resulting from this second fertilization begins a series of mitotic divisions that forms a tissue called the endosperm. The function of the endosperm is to store nutrients.
Table of contents
- 1. Introduction to Biology2h 40m
- 2. Chemistry3h 40m
- 3. Water1h 26m
- 4. Biomolecules2h 23m
- 5. Cell Components2h 26m
- 6. The Membrane2h 31m
- 7. Energy and Metabolism2h 0m
- 8. Respiration2h 40m
- 9. Photosynthesis2h 49m
- 10. Cell Signaling59m
- 11. Cell Division2h 47m
- 12. Meiosis2h 0m
- 13. Mendelian Genetics4h 41m
- Introduction to Mendel's Experiments7m
- Genotype vs. Phenotype17m
- Punnett Squares13m
- Mendel's Experiments26m
- Mendel's Laws18m
- Monohybrid Crosses16m
- Test Crosses14m
- Dihybrid Crosses20m
- Punnett Square Probability26m
- Incomplete Dominance vs. Codominance20m
- Epistasis7m
- Non-Mendelian Genetics12m
- Pedigrees6m
- Autosomal Inheritance21m
- Sex-Linked Inheritance43m
- X-Inactivation9m
- 14. DNA Synthesis2h 27m
- 15. Gene Expression3h 20m
- 16. Regulation of Expression3h 31m
- Introduction to Regulation of Gene Expression13m
- Prokaryotic Gene Regulation via Operons27m
- The Lac Operon21m
- Glucose's Impact on Lac Operon25m
- The Trp Operon20m
- Review of the Lac Operon & Trp Operon11m
- Introduction to Eukaryotic Gene Regulation9m
- Eukaryotic Chromatin Modifications16m
- Eukaryotic Transcriptional Control22m
- Eukaryotic Post-Transcriptional Regulation28m
- Eukaryotic Post-Translational Regulation13m
- 17. Viruses37m
- 18. Biotechnology2h 58m
- 19. Genomics17m
- 20. Development1h 5m
- 21. Evolution3h 1m
- 22. Evolution of Populations3h 52m
- 23. Speciation1h 37m
- 24. History of Life on Earth2h 6m
- 25. Phylogeny2h 31m
- 26. Prokaryotes4h 59m
- 27. Protists1h 12m
- 28. Plants1h 22m
- 29. Fungi36m
- 30. Overview of Animals34m
- 31. Invertebrates1h 2m
- 32. Vertebrates50m
- 33. Plant Anatomy1h 3m
- 34. Vascular Plant Transport2m
- 35. Soil37m
- 36. Plant Reproduction47m
- 37. Plant Sensation and Response1h 9m
- 38. Animal Form and Function1h 19m
- 39. Digestive System10m
- 40. Circulatory System1h 57m
- 41. Immune System1h 12m
- 42. Osmoregulation and Excretion50m
- 43. Endocrine System4m
- 44. Animal Reproduction2m
- 45. Nervous System55m
- 46. Sensory Systems46m
- 47. Muscle Systems23m
- 48. Ecology3h 11m
- Introduction to Ecology20m
- Biogeography14m
- Earth's Climate Patterns50m
- Introduction to Terrestrial Biomes10m
- Terrestrial Biomes: Near Equator13m
- Terrestrial Biomes: Temperate Regions10m
- Terrestrial Biomes: Northern Regions15m
- Introduction to Aquatic Biomes27m
- Freshwater Aquatic Biomes14m
- Marine Aquatic Biomes13m
- 49. Animal Behavior28m
- 50. Population Ecology3h 41m
- Introduction to Population Ecology28m
- Population Sampling Methods23m
- Life History12m
- Population Demography17m
- Factors Limiting Population Growth14m
- Introduction to Population Growth Models22m
- Linear Population Growth6m
- Exponential Population Growth29m
- Logistic Population Growth32m
- r/K Selection10m
- The Human Population22m
- 51. Community Ecology2h 46m
- Introduction to Community Ecology2m
- Introduction to Community Interactions9m
- Community Interactions: Competition (-/-)38m
- Community Interactions: Exploitation (+/-)23m
- Community Interactions: Mutualism (+/+) & Commensalism (+/0)9m
- Community Structure35m
- Community Dynamics26m
- Geographic Impact on Communities21m
- 52. Ecosystems2h 36m
- 53. Conservation Biology24m
36. Plant Reproduction
Flowers
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