Ch. 5 & 6- Flowers & Fruits

Angiosperms (flowering plants) Unique among plants because they have sexual reproductive structures contained in a flower derived from modified leaves seeds form inside fleshy fruit pollinated by insects or other animals Most recent evolutionary branch of plants: 120 mya Unique features: 1. produce specialized reproductive structures called flowers. (many patterns) 2. Seeds form within these flowers as part of modified leaf known as carpel 3. 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-specific Fruit as an adaptation for seed dispersal: Red berries and dandelion

Flower arrangements Perfect: both stamens & carpels Imperfect: missing either stamens or carpels Monoecious: both male & female flowers on same plant Dioecious: male & female flowers on separate plants female male Embryo sac  fruit Perfect: both male & female reproductive parts + non-reproductive structures. Imperfect: lack either carpels or stamens monoecious: both male & female flowers on same sporophyte individuals dioecious (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 morphology heterospory: different spore types give rise to male or female gametophytes, each which produce their respective gametes homospory: same spore type give rise to bisexual gametophyte that produces both eggs & sperm Fig. 30.6 Structure of a flower Flowers may occur singly or in clusters (inflorescence) Interactive Study Partner Activity 30.2 Angiosperm Life Cycle seed  The structure of a flower

lily

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monoecious species, male (left) and female (right) begonia flowers

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Pollination place pollen onto stigma of a carpel pollination agents grasses, many trees: wind many angiosperms: animals, including insects self-pollination brings male & female gametophytes together A relationship between an angiosperm and its pollinator: Hummingbird and flower (left); bee and Scotch broom (right)

How do flowers attract the pollinator of choice? Insect: bright, showy petals with fragrant aromas, rich in nectar E.g.: moths=white, night; flies=“smelly” Hummingbird: bright, often red, no aroma Wind: small and inconspicuous with copious production of dry, lightweight pollen

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Fruits What is a fruit? What are the purpose of fruit? How is a fruit formed?

Fruit = “mature ovary” purpose: protects seeds, dispersal aid RELATIONSHIP between FLOWER & FRUIT parts (Fig. 38.10) Fruit: mature ovary After fertilization, as seed develops, the ovary wall thickens e.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 38.2.6. Fruit Development (dry vs. fleshy fruit) Relationship between a pea flower and a fruit (pea pod)

Fruit or vegetable? botanical: Legal Ripened ovary Something that tastes sweet and is eaten as dessert

Types of Fruits Dry fruits: Tough or papery pericarp Fleshy fruits: Soft and juicy pericarp Drupe Berry Aggregate Multiple Accessory

Development of fruit from flower drupe berry simple = 1 ovary of 1 flower e.g., cherry, soybean pod compound = multiple ovaries aggregate = of one flower e.g., raspberry, blackberry multiple = of many flowers (inflorescence) e.g., pineapple accessory = parts other than ovary e.g., strawberry, apple, melon, tomato Animation 38.2.6. Fruit Development (dry vs. fleshy fruit) Fig. 6.14 Development from fruit from Flower (overhead) pineapple: fruit made of thickened flower parts of all flowers on stalk strawberry: each seed represents a tiny fruit; fleshy part from flower stalk Melon: multiple carpels fused; ovary wall Tomato: ovary wall citrus: segments are ovaries corn: each kernel of corn is a fruit.

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Seeds Contain embryonic plant plus nutritive tissue & tough outer coat Starting point for next generation

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Cotyledons (embryonic leaves) Single cotyledon = monocot Two large cotyledons = dicot Cotyledons can be “fleshy” or “leafy” Cotyledons can be kept belowground or elevated above ground

Fig. 40.7

Seed Germination imbibition: absorption of water mobilization of food reserves enzyme activity digests endosperm (converts starch to sugar) Animation 38.2.7 Seed Germination Fig. 38.11. Mobilization of nutrients during germination of cereal, I.e., alpha-amylase (starch to sugar) --malted barley: germination of seed, and then halted

Seed Germination emergence of radicle detects gravity & grows downward epicotyl emerges through soil surface light cues upward & straighter growth Fig. 38.12, Seed germination If 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 38.2.8 Seedling growth

With light: Green Shorter Open cotyledons Straight stem Without light: Fig. 40.1 With light: Green Shorter Open cotyledons Straight stem Without light: Yellow Elongated Closed cotyledons Hooked stem

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