Plant Diversity II: The Evolution of Seed PlantsPART II By: Carissa, Nadine, and Athena
Assessment statements 9.3.1-Draw and label a diagram showing the structure of a dicotyledonous animal-pollinated flower (Dicot angiosperm).
Concept 30.3: The reproductive adaptations of angiosperms include flowers and fruits
Angiosperms • Commonly known as flowering plants • Are seed plants that produce the reproductive structures called flowers and fruits • Are the most widespread and diverse of all plants
Characteristics of Angiosperms • Key adaptations in the evolution of angiosperms are: • FLOWERS • FRUITS
FLOWERS • A flower is a specialized shoot with modified leaves for sexual reproduction • Sepals, which enclose the flower • Petals, which are brightly colored and attract pollinators • Stamens, which produce pollen • Carpals, which produce ovules
FRUITS • Help protect and disperse seeds of angiosperms • A flower is a specialized shoot with modified leaves which specializes in sexual reproduction • Typically consist of mature ovaries
Wings enable maple fruits to be easily carried by the wind. Seeds within berries and other edible fruits are often dispersed in animal feces. The barbs of cockleburs facilitate seed dispersal by allowing the fruits to “hitchhike” on animals.
Tomato, a fleshy fruit withsoft outer and inner layers Nectarine, a fleshyfruit with a soft outerlayer and hard innerlayer (pit) of pericarp Ruby grapefruit, a fleshy fruitwith a hard outer layer andsoft inner layer of pericarp Walnut, a dry fruit that remains closed at maturity Milkweed, a dry fruit thatsplits open at maturity
The Angiosperm Life Cycle • The life cycle of an angiosperm is a highly refined version of the alternation of generations common to all plants. • Angiosperms are heterosporous, producing microspores that form male gametophytes and megaspores that form female gametophytes.
The Angiosperm Life Cycle • Double fertilization occurs • A pollen tube discharges two sperms into the female gametophyte within the ovule • One sperm fertilizes the egg. The other combines iwt two nuclei in the centre cell of the female gametophyte • Initiates development of food-storing endosperm • The endosperm • Nourishes the developing embryo
It is now time for A sing along Song!
The life cycle of an angiosperm There are seven more steps that we must learn The first is the production of microspores Through the process of meiosis in the anther’s stores The life cycle of an angiosperm There are six more steps that we must learn Next is the formation of male gametophytes as Pollen formed from microspores that’ll soon take flights
The life cycle of an angiosperm There are five more steps that we must learn In the ovule, an embryo sac is formed from Only one of four megaspores that performed The life cycle of an angiosperm There are four more steps that we must learn The pollen’s now released from the anther And to the stigma of the carpel it must transfer
The life cycle of an angiosperm There are three more steps that we must learn The pollen tube grows down within the style And two sperm are discharged into the micropyle The life cycle of an angiosperm There are two more steps that we must learn A zygote forms from one of those sperm And within a seed the embryo and food are held firm
The life cycle of an angiosperm There’s only one last step that we must learn During germination, the seed coat ruptures A seedling emerges and a cycle occurs.
Angiosperm Evolution • Angiosperms originated at least 140 million years ago • By the end of the Cretaceous period, 65 million years ago, angiosperms had become the dominant plants on Earth.
Carpel Stamen 5 cm Archaefructussinensis, a 125-million year-old fossil. Artist’s reconstruction of Archaefructussinensis Fossils of Angipsperms • Primitive fossils of 125-million-year-old angiosperms • Display both derived and primitive traits
Hypothesis of flower origins • In hypothesizing how pollen-producing and ovule-producing structures were combined into a single flower • Scientists proposed that the ancestor of angiosperms had separate pollen-producing and ovule-producing structures
Angiosperm Diversity Two main groups of angiosperms
Angiosperm Diversity • Basal Angiosperms • Are less derived and include the flowering plants belonging to the oldest lineages • Magnoliids • Share some traits with basal angiosperms but are more closely related to monocots and eudicots
Evolutionary Links Between Angiosperms and Animals • Pollination of flowers by animals and transport of seeds by animals • Important relationship in terrestrial ecosystems
(a) A flower pollinated by honeybees. This honeybee is harvesting pollen and nectar (a sugary solution secreted by flower glands) from a Scottish broom flower. The flower has a tripping mechanism that arches the stamens over the beeand dusts it with pollen, some ofwhich will rub off onto the stigmaof the next flower the bee visits. (b) A flower pollinated by hummingbirds.The long, thin beak and tongue of this rufous hummingbird enable the animal to probe flowers that secrete nectar deep within floral tubes. Before the hummer leaves, anthers will dust its beak and head feathers with pollen. Many flowers that are pollinated by birds are red or pink, colors to which bird eyes are especially sensitive. (c) A flower pollinated by nocturnal animals. Some angiosperms, such as this cactus, depend mainly on nocturnal pollinators, including bats. Common adaptations of such plants include large, light-colored, highly fragrant flowers that nighttime pollinators can locate.
ASSESSMENT STATEMENTS REVISED • 9.3.1-Draw and label a diagram showing the structure of a dicotyledonous animal-pollinated flower (Dicot angiosperm).
IB Style Question • Fertilization, pollination and seed dispersal all occur during the reproduction of a flowering plant. In what sequence do these processes occur? • Seed dispersal pollination fertilization • Fertillization pollination seed dispersal • Pollination fertilization seed dispersal • Seed dispersal fertilization pollination 1 mark
ANSWERS Pollination fertilization seed dispersal 1 mark
IB STYLE QUESTIONS! • Draw the structure of a dicotyledenous animal-pollinated flowers (dicot angiosperms). 6 marks
ANSWERS • Award 1 mark for each of the following structures clearly drawn and correctly labeled • Petals; • Sepals; • Stigma; • Style; • Ovary; • Stamen/anther and filament • Receeptacle/nectary
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