Reproduction with Cones and Flowers Chapter 22

Alternation of Generations All plants have a diploid sporophyte generation and a haploid gametophyte generation All plants have a diploid sporophyte generation and a haploid gametophyte generation Gametophyte plants produce sperm and eggs Gametophyte plants produce sperm and eggs Fertilization begins the sporophyte generation Fertilization begins the sporophyte generation

Generations cont. Actual plant is the diploid sporophyte generation Actual plant is the diploid sporophyte generation Gametophytes are found in cones or flowers Gametophytes are found in cones or flowers

Pollen cones and seed cones Pollen cones (male) produce male gametophytes or pollen grains Pollen cones (male) produce male gametophytes or pollen grains –One haploid nuclei will develop into 2 sperm Seed cones (female) produce female gametophytes contained in the ovules Seed cones (female) produce female gametophytes contained in the ovules –Each ovule contains a few eggs for fertilization

Pollination Gymnosperm life cycle takes 2 years for completion Gymnosperm life cycle takes 2 years for completion Male cones release pollen which is carried by wind to female cones Male cones release pollen which is carried by wind to female cones

Fertilization and development Pollen grains stuck to female cones will develop a pollen tube containing the 2 sperm Pollen grains stuck to female cones will develop a pollen tube containing the 2 sperm One sperm disintegrates, the other fertilizes the egg to make a diploid zygote One sperm disintegrates, the other fertilizes the egg to make a diploid zygote Zygote grows into an embryo which is enclosed in a seed Zygote grows into an embryo which is enclosed in a seed

Flower structure Flowers are reproductive structures Flowers are reproductive structures Have four parts Have four parts –Sepals –Petals –Stamens –Carpels (pistils)

Sepals and petals Sepals Sepals –Outermost circle of parts (green) –Protect the bud before it opens Petals Petals –Usually brightly colored –Found inside the sepals –Attract pollinators

Stamens and carpels Stamen Stamen –Filament-long, thin stalk that supports anther –Anther-sac at end of filament that contains pollen grains Carpel (pistils) Carpel (pistils) –Ovary-broad base containing one or more ovules –Style-narrow stalk extending from top of ovary –Stigma-sticky section on top of style that collects pollen

Complete and incomplete flowers Complete flowers Complete flowers –Contain all flower parts: sepals, petals, stamen, carpel Incomplete flowers Incomplete flowers –Missing one or more flower parts –Often seen in plants that produce separate male and female plants –Or in plants that have separate male and female flowers (on same plant)

Angiosperm life cycle Flowers are produced Flowers are produced Meiosis occurs in the anther to produce pollen grains Meiosis occurs in the anther to produce pollen grains Meiosis occurs in the ovary to produce the embryo sac which contains the egg and endosperm nuclei Meiosis occurs in the ovary to produce the embryo sac which contains the egg and endosperm nuclei

Pollination Pollen picked up by pollinator and carried to stigma Pollen picked up by pollinator and carried to stigma Some wind pollinated Some wind pollinated More efficient pollination by insects or animals More efficient pollination by insects or animals

Fertilization Once pollen reaches a stigma, pollen tube develops and grows into the ovule Once pollen reaches a stigma, pollen tube develops and grows into the ovule 2 sperm nuclei develop 2 sperm nuclei develop Double fertilization occurs Double fertilization occurs –One sperm fertilizes the egg to make the zygote –One sperm fertilizes the endosperm to make a triploid cell or endosperm (food for the embryo)

Seed development After fertilization, nutrients flow into flower tissue to support development of embryo and seed After fertilization, nutrients flow into flower tissue to support development of embryo and seed Ovary walls thicken to make fruit to protect the seeds Ovary walls thicken to make fruit to protect the seeds Ovule toughens to become seed coat Ovule toughens to become seed coat FRUIT-is any seed enclosed within the embryo wall; includes common fruits, vegetables, nuts FRUIT-is any seed enclosed within the embryo wall; includes common fruits, vegetables, nuts

Seed dispersal Animals Animals –Seeds usually found in fleshy fruits; can pass through digestive tracts unharmed –Deposited in new areas with animal feces Wind and water Wind and water –Usually light weight seeds –Can float on air currents or in water –Carried to far places or remote places (islands)

Seed dormancy Embryo is alive but not growing Embryo is alive but not growing Length of dormancy varies in each plant Length of dormancy varies in each plant Allows for long-distance dispersal Allows for long-distance dispersal Environmental factors cause seeds to end dormancy and germinate Environmental factors cause seeds to end dormancy and germinate

Seed germination Early growth stage of embryo Early growth stage of embryo Seeds must absorb water to crack seed coat Seeds must absorb water to crack seed coat Root emerges first Root emerges first Shoots emerge next Shoots emerge next –Can be protected by a sheath (monocots) –Can be protected by the cotyledons or a “shoot arch” (dicots)

Vegetative reproduction Asexual form of reproduction Asexual form of reproduction Produce many plants from horizontal stems (stolons), plantlets, or underground roots Produce many plants from horizontal stems (stolons), plantlets, or underground roots No pollination or seeds No pollination or seeds New plants are genetically identical to parent plant New plants are genetically identical to parent plant

Plant propagation Use cuttings or grafting or budding from original plant to produce offspring from seedless plants Use cuttings or grafting or budding from original plant to produce offspring from seedless plants Avoids genetic variation Avoids genetic variation Preserves wanted characteristics Preserves wanted characteristics

Cuttings Pieces of stem with buds containing meristematic tissue Pieces of stem with buds containing meristematic tissue Stem is partially buried in soil Stem is partially buried in soil Usually use rooting powders to stimulate root growth Usually use rooting powders to stimulate root growth

Grafting and budding Grafting Grafting –Plants with poor roots grown on plants with strong roots –Stem is cut (scion) and attached to another plant (stock) –Words bests when plants are dormant –Vascular tissues of scion / stock must connect Budding Budding –Using buds for scions instead of stems

Plant hormones and responses Hormone- chemical messenger that stimulates or suppresses activity of cells in another area Hormone- chemical messenger that stimulates or suppresses activity of cells in another area –Released in response to environmental ques –Released in response to internal changes of the plant as part of the life cycle

Gibberellins Hormones that produce dramatic increase in size Hormones that produce dramatic increase in size End seed dormancy End seed dormancy Start germination Start germination Promote rapid growth of the seedling Promote rapid growth of the seedling Increase the size of fruits Increase the size of fruits Elongate stems/stalks Elongate stems/stalks

Ethylene Hormone that causes ripening Hormone that causes ripening Naturally produced by fruits Naturally produced by fruits

Cytokinins Hormones that stimulate cytokinesis (final part of cell division) Hormones that stimulate cytokinesis (final part of cell division) Produced in growing roots and developing seeds and fruits Produced in growing roots and developing seeds and fruits Involved in the “width” growth or lateral growth of stems and branches Involved in the “width” growth or lateral growth of stems and branches Slows the aging process of plant organs Slows the aging process of plant organs

Auxins Hormones involved in lengthening plant cells of the apical meristem Hormones involved in lengthening plant cells of the apical meristem Stimulate growth of primary stem Stimulate growth of primary stem Prevents growth of new branches Prevents growth of new branches Prevent root growth Prevent root growth

Phototropism Tendency of a plant to grow toward light Tendency of a plant to grow toward light

Thigmotropism Response to touch Response to touch –Coiling around trellises or other stems when in contact –Curling up when touched by other organisms

Gravitropism Positive - is growing down toward gravity (roots, stimulated by low levels of auxins) Positive - is growing down toward gravity (roots, stimulated by low levels of auxins) Negative – growing up away from gravity (stems stimulated by high levels of auxins) Negative – growing up away from gravity (stems stimulated by high levels of auxins)

Photoperiodism Plant responses to changing lengths of day/night Plant responses to changing lengths of day/night Longer days trigger flowering Longer days trigger flowering Shorter days trigger change in leaf colors and dropping of leaves in deciduous plants Shorter days trigger change in leaf colors and dropping of leaves in deciduous plants