2Angiosperms (flowering plants) Unique among plants because they have sexual reproductive structures contained in a flowerderived from modified leavesseeds form inside fleshy fruitpollinated by insects or other animalsMost recent evolutionary branch of plants: 120 myaUnique features:1. produce specialized reproductive structures called flowers. (many patterns)2. Seeds form within these flowers as part of modified leaf known as carpel3. Pollen transfer by insects/ animals: less random than wind in gymnosperms--Animals visit flowers for food (pollen, nectar) and in so efficiently distribute pollen from 1 flower to another. Flower shape, size & color have all influenced by the evolutionary selective pressures exerted by plant’s need to attract pollinators; co-evolution; species-specificFruit as an adaptation for seed dispersal: Red berries and dandelion
6Flower arrangements Perfect: both stamens & carpels Imperfect: missing either stamens or carpelsMonoecious: both male & female flowers on same plantDioecious: male & female flowers on separate plantsfemalemaleEmbryo sac fruitPerfect: both male & female reproductive parts + non-reproductive structures. Imperfect: lack either carpels or stamensmonoecious: both male & female flowers on same sporophyte individualsdioecious (two house): separate gametes produced on different sporophyte individuals-makes cross fertilization obligatory and ensures genetic variability in the population but this is done at the cost of lower seed-setting efficiency and also prevents isolated individuals reproducing.Contrast with spore morphologyheterospory: different spore types give rise to male or female gametophytes, each which produce their respective gameteshomospory: same spore type give rise to bisexual gametophyte that produces both eggs & spermFig Structure of a flowerFlowers may occur singly or in clusters (inflorescence)Interactive Study Partner Activity 30.2 Angiosperm Life Cycleseed The structure of a flower
13Pollination place pollen onto stigma of a carpel pollination agents grasses, many trees: windmany angiosperms: animals, including insectsself-pollinationbrings male & female gametophytes togetherA relationship between an angiosperm and its pollinator: Hummingbird and flower (left); bee and Scotch broom (right)
14How do flowers attract the pollinator of choice? Insect: bright, showy petals with fragrant aromas, rich in nectarE.g.: moths=white, night; flies=“smelly”Hummingbird: bright, often red, no aromaWind: small and inconspicuous with copious production of dry, lightweight pollen
29Fruits What is a fruit? What are the purpose of fruit? How is a fruit formed?
30Fruit = “mature ovary” purpose: protects seeds, dispersal aid RELATIONSHIP between FLOWER & FRUIT parts (Fig )Fruit: mature ovaryAfter fertilization, as seed develops, the ovary wall thickense.g., pea pod (fruit) with seeds (mature ovlues, the peas)apple: The core is the ovary. We eat the ovary wall. Rest of fruit is made from bases of stamens, patels & sepals and the top of the flower stalk.Animation Fruit Development (dry vs. fleshy fruit)Relationship between a pea flower and a fruit (pea pod)
31Fruit or vegetable? botanical: Legal Ripened ovary Something that tastes sweet and is eaten as dessert
32Types of Fruits Dry fruits: Tough or papery pericarp Fleshy fruits: Soft and juicy pericarpDrupeBerryAggregateMultipleAccessory
33Development of fruit from flower drupeberrysimple = 1 ovary of 1 flowere.g., cherry, soybean podcompound = multiple ovariesaggregate = of one flowere.g., raspberry, blackberrymultiple = of many flowers (inflorescence)e.g., pineappleaccessory = parts other than ovarye.g., strawberry, apple, melon, tomatoAnimation Fruit Development (dry vs. fleshy fruit)Fig Development from fruit from Flower (overhead)pineapple: fruit made of thickened flower parts of all flowers on stalkstrawberry: each seed represents a tiny fruit; fleshy part from flower stalkMelon: multiple carpels fused; ovary wallTomato: ovary wallcitrus: segments are ovariescorn: each kernel of corn is a fruit.
47Seed Germination imbibition: absorption of water mobilization of food reservesenzyme activity digests endosperm (converts starch to sugar)Animation Seed GerminationFig Mobilization of nutrients during germination of cereal, I.e., alpha-amylase (starch to sugar)--malted barley: germination of seed, and then halted
48Seed Germination emergence of radicle detects gravity & grows downwardepicotyl emerges through soil surfacelight cues upward & straighter growthFig , Seed germinationIf no light, bean can still germinate. hypocotyl with hook at tip remains, and internode is long, “reaching” for surface (light). Light color, because not much pigment.Animation Seedling growth
49With light: Green Shorter Open cotyledons Straight stem Without light: Fig. 40.1With light:GreenShorterOpen cotyledonsStraight stemWithout light:YellowElongatedClosed cotyledonsHooked stem