24.1 Reproduction in Flowering Plants Lesson Overview 24.1 Reproduction in Flowering Plants

The Structure of Flowers Flowers are reproductive organs composed of four different kinds of specialized leaves: sepals, petals, stamens, and carpels.

Sepals and Petals Sepals = outermost circle of floral parts Enclose the bud before it opens and protect the flower while it is developing Petals = brightly colored and found just inside the sepals Colors, number, and shapes attract insects and other pollinators

Stamens Stamens = male parts of the flower Consists of a stalk called a filament with an anther at its tip Anthers = structures that produce pollen grains—the male gametophytes

Carpels Carpels = innermost floral parts—produce and shelter the female gametophytes and, later, seeds Each carpel has a broad base forming an ovary, which contains one or more ovules where female gametophytes are produced

Carpels Pistil = a single carpel or several fused carpels Style = diameter of the carpel narrows into a stalk Stigma = the top of the style –a sticky or feathery portion specialized to capture pollen

Label the parts of the flower 

Label the parts of the flower 

The Angiosperm Life Cycle Alternation of generations between diploid sporophyte phase and haploid gametophyte stage.

Development of Male Gametophytes The male gametophytes—the pollen grains—develop inside anthers. First, meiosis produces four haploid spore cells.

Development of Male Gametophytes Each spore undergoes one mitotic division to produce the two haploid nuclei of a single pollen grain. Two nuclei are surrounded by a thick wall that protects the male gametophyte.

Development of Female Gametophytes Female gametophytes develop inside each carpel of a flower. The ovules—the future seeds—are enveloped in a protective ovary—the future fruit.

Development of Female Gametophytes A single diploid cell goes through meiosis to produce four haploid cells, three of which disintegrate.

Pollination Pollination = transfer of pollen to the female portions of the flower Some are wind pollinated, but most are by animals

Pollination Insect pollination is beneficial to insects and other animals because it provides a dependable source of food—pollen and nectar. Plants benefit because the insects take the pollen directly from flower to flower. Insect pollination is more efficient than wind pollination, giving insect-pollinated plants a greater chance of reproductive success.

Fertilization If a pollen grain lands on the stigma of a flower of the same species, it begins to grow a pollen tube. Of the pollen grain’s two cells, one cell—the “generative” cell—divides and forms two sperm cells. The other cell becomes the pollen tube.

Fertilization The pollen tube contains a tube nucleus and the two sperm cells. The pollen tube grows into the style, where it eventually reaches the ovary and enters an ovule.

Vegetative Reproduction Vegetative reproduction is the formation of new individuals by mitosis and does not require gametes, flowers, or fertilization New plants may grow from roots, leaves, stems, or plantlets This takes place naturally in many plants

Examples of Vegetative Reproduction A potato can grow whole new plants from buds called “eyes.” Strawberry plants send out long, trailing stems called stolons that produce roots, stems, and leaves. Many cactus species drop sections of their stems that grow at the base of the larger adults

Vegetative Reproduction Can reproduce quickly Produces genetically identical offspring, enabling well-adapted individuals to rapidly fill a favorable environment Drawback = no new combinations of genetic traits

Plant Propagation (Your plant projects!) One of the simplest ways to reproduce plants vegetatively is by cuttings. A grower cuts from the plant a length of stem that includes a number of buds containing meristem tissue. That stem is then partially buried in soil or in a special mixture of nutrients that encourages root formation.