Plant Biology - The Shoot System Flowers, Fruits, Seeds - Quick Guides

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Study GuidePlant Biology–The Shoot System: Flowers, Fruits, Seeds1.Features of the Angiosperm Life CycleAngiosperms, or flowering plants, have alife cycle with two alternating stages:•asporophyte stage (2n)•agametophyte stage (n)This pattern is calledalternation of generations.Thesporophyteis the plant we usually see—trees, grasses, shrubs, and crops.Thegametophytesare very small and develop inside the flower.

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Study Guide1.1Sporophyte Stage: The Flowering PlantThe adult angiosperm plant isdiploid (2n)and producesflowers, which are the reproductive organs.Inside the flower:•Anthersproducemicrospores•Ovules(inside the ovary) producemegasporesThese spores are formed bymeiosis, a type of cell division that reduces chromosome number.1.2Formation of the Male Gametophyte (Pollen)Inside theanthers:1.Microsporocytes (2n)undergo meiosis.2.This produceshaploid microspores (n).3.Each microspore develops into apollen grain.A pollen grain contains:•atube cell•agenerative cellBefore or during pollination, the generative cell divides to formtwo sperm cells.At this stage, the pollen grain is theimmature male gametophyte.1.3Formation of the Female Gametophyte (Embryo Sac)At the same time, the female gametophyte develops inside theovulein the ovary.Structure of the OvuleEach ovule contains:•Nucellus(internal tissue)•Two integuments(protective layers)•A small opening called themicropyle•A stalk called thefuniculus(attaches ovule to ovary wall)

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Study Guide1.4Development of the Embryo Sac1.Amegasporocyte (2n)undergoes meiosis.2.This formsfour haploid megaspores (n).3.Three megaspores degenerate.4.The remaining megaspore dividesthree times by mitosis, formingeight nuclei.These nuclei arrange into:•Egg apparatus (micropylar end)o1 egg cello2 synergids (helper cells)•Three antipodal cells (chalazal end)•Two polar nucleiin the centerWhen cell walls form, this structure becomes themature embryo sac, which is thefemalegametophyte.1.5PollinationPollinationis the transfer of pollen grains from theantherto thestigma.It can occur by:•wind•water•gravity•animals (insects, birds, bats, etc.)Types of Pollination•Cross-pollination: between different plants (most common)•Self-pollination: within the same plantFlower shapes and colorsare often adapted to help pollination happen efficiently.

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Study Guide1.6Fertilization and Double FertilizationIf pollen lands on acompatible stigma:1.It absorbs moisture.2.Apollen tubegrows through the style toward the ovule.3.The pollen tube enters the embryo sac through themicropyle.4.One synergid is destroyed during entry.Double Fertilization (Unique to Angiosperms)Two fertilization events occur:•One sperm + egg → zygote (2n)→ develops into theembryo•One sperm + two polar nuclei → endosperm (usually 3n)→ provides nutritionThis process is calleddouble fertilization, a key feature of flowering plants.1.7Seed and Fruit Formation•Theovulebecomes aseed•Theovarybecomes afruit•Theendospermnourishes the developing embryoIf fertilization doesnotoccur:•The ovule aborts•The ovary may wither and fall offKey TakeawaysAngiosperms have:•Alternation of generations•Highly reduced gametophytes•Pollination followed bydouble fertilization•Seeds protected inside fruits

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