22 1 Plant Life Cycles KEY CONCEPT All

22. 1 Plant Life Cycles KEY CONCEPT All plants alternate between two phases in their life cycles.

22. 1 Plant Life Cycles Plant life cycles alternate between producing spores and gametes. • A two-phase life cycle is called alternation of generations. – haploid phase – diploid phase – alternates between the two SPOROPHYTE PHASE fertilization meiosis GAMETOPHYTE PHASE

22. 1 Plant Life Cycles • The spore-producing plant is the mature sporophyte. – sporophyte phase is diploid – begins with fertilized egg – spores produced through meiosis • The gamete-producing plant is the mature gametophyte. – gametophyte phase is haploid – begins with spore – gametes produced through mitosis

22. 1 Plant Life Cycles Life cycle phases look different among various plant groups. • Nonvascular plants have a dominant gametophyte phase. – moss gametophytes look like green carpet – moss sporophytes shoot up as stalklike structures sporophyte (2 n) capsule spores (1 n) gametophyte (1 n)

22. 1 Plant Life Cycles • The sporophyte is the dominant phase for seedless vascular plants. – Fern spores form in sacs, sori, on underside of mature sporophytes (fronds). sporophyte (2 n) sori

22. 1 Plant Life Cycles – A fern gametophyte, or prothallus, produces sperm and eggs. gametophyte (1 n)) rhizoid – A zygote forms on the prothallus, growing into the sporophyte.

22. 1 Plant Life Cycles • The sporophyte is the dominant phase for seed plants. – – – – pine trees are typical seed plant sporophytes female spores produced in female cones male spores produced in male cones male spores develop into pollen grains, the male gametophytes female spores develop into female gametophytes that produce eggs sperm from pollen travel down pollen tube toward egg fertilized egg develops into embryo ovule develops into protective pine seed

22. 1 Plant Life Cycles • The sporophyte is the dominant phase for seed plants.

22. 1 Plant Life Cycles KEY CONCEPT Reproduction of flowering plants takes place within flowers.

22. 1 Plant Life Cycles Flowers contain reproductive organs protected by specialized leaves. • Sepals and petals are modified leaves. – Sepals are outermost layer that protects developing flower sepal

22. 1 Plant Life Cycles – Petals can help to attract animal pollinators petal

22. 1 Plant Life Cycles • A stamen is the male structure of the flower. stamen filament anther – anther produces pollen grains – filament supports the anther

22. 1 Plant Life Cycles • The innermost layer of a flower is the female carpel. stigma carpel style ovary – stigma is sticky tip – style is tube leading from stigma to ovary – ovary produces female gametophyte

22. 1 Plant Life Cycles Flowering plants can be pollinated by wind or animals. • Flowering plants pollinated when pollen grains land on stigma. • Wind pollinated flowers have small flowers and large amounts of pollen.

22. 1 Plant Life Cycles • Animal pollinated flowers have larger flowers and less pollen. – many flowering plants pollinated by animal pollinators pollen grains – pollination occurs as animal feeds from flower to flower – animal pollination more efficient than wind pollination

22. 1 Plant Life Cycles Fertilization takes place within the flower. • Male gametophytes, or pollen grains, are produced in the anthers. – male spores produced in anthers by meiosis – each spore divides by mitosis to form two haploid cells – two cells form a pollen grain single pollen grain

22. 1 Plant Life Cycles • One female gametophyte can form in each ovule of a flower’s ovary. – four female spores produced in ovule by meiosis – one spore develops into female gametophyte – female gametophyte contains seven cells – one cell has two nuclei, or polar nuclei – one cell will develop into an egg

22. 1 Plant Life Cycles • Pollination occurs when a pollen grain lands on a stigma. pollen tube sperm stigma – one cell from pollen grain forms pollen tube – other cell forms two sperm that travel down tube

22. 1 Plant Life Cycles • Flowering plants go through the process of double fertilization. female gametophyte egg sperm polar nuclei ovule

22. 1 Plant Life Cycles • Flowering plants go through the process of double endosperm fertilization. – one sperm fertilizes the egg seed coat – other sperm unites with polar nuclei, forming endosperm – endosperm provides food supply for embryo

22. 1 Plant Life Cycles • Each ovule becomes a seed. • The surrounding ovary grows into a fruit.

22. 1 Plant Life Cycles KEY CONCEPT Seeds disperse and begin to grow when conditions are favorable.

22. 1 Plant Life Cycles Animals, wind, and water can spread seeds. • Seeds dispersed by animals can have nutritious fruits or fruits that cling.

22. 1 Plant Life Cycles • Seeds dispersed by wind can have wing- or parachutelike fruits. Cypselae Double samaras

22. 1 Plant Life Cycles • Seeds dispersed by water can have fruits that float.

22. 1 Plant Life Cycles Seeds begin to grow when environmental conditions are favorable. • Seed dormancy is a state in which the embryo has stopped growing. – Dormancy may end when conditions are favorable. – While dormant, embryo can withstand extreme conditions.

22. 1 Plant Life Cycles • Germination begins the growth of an embryo into a seedling. – water causes seed to swell and crack coat – embryonic root, radicle, is first to emerge – water activates enzymes that help send sugars to embryo

22. 1 Plant Life Cycles • Germination begins the growth of an embryo into a seedling. – water causes seed to swell and crack coat – embryonic root, radicle, is first to emerge – water activates enzymes that help send sugars to embryo – embryonic shoot, plumule, emerges next

22. 1 Plant Life Cycles • Germination begins the growth of an embryo into a seedling. – water causes seed to swell and crack coat – embryonic root, radicle, is first to emerge – water activates enzymes that help send sugars to embryo – embryonic shoot, plumule, emerges next – leaves emerge last

22. 1 Plant Life Cycles • Once photosynthesis begins, the plant is called a seedling.

22. 1 Plant Life Cycles KEY CONCEPT Plants can produce genetic clones of themselves through asexual reproduction.

22. 1 Plant Life Cycles Plants can reproduce asexually with stems, leaves, or roots. • Asexual reproduction allows a plant to make copies of itself. • Regeneration is one type of asexual reproduction. – plants grow a new individual from fragment of parent – occurs when piece of a stem, leaf, or root falls off parent plant

22. 1 Plant Life Cycles • Vegetative reproduction is another type of asexual reproduction. – stems, leaves, or roots attached to parent plant produce new individuals – specific adaptations include stolons, rhizomes, and tubers

22. 1 Plant Life Cycles Humans can produce plants with desirable traits using vegetative structures. • Vegetative propagation takes advantage of plants’ ability to reproduce asexually. • Humans use one plant with desirable traits to produce many individuals. – cutting of leaves or stems may grow new roots – grafting joins the parts of two plants together to form a hybrid plant

22. 1 Plant Life Cycles KEY CONCEPT Plant hormones guide plant growth and development.

22. 1 Plant Life Cycles Plant hormones regulate plant functions. • Hormones are chemical messengers. – produced in one part of an organism – stimulates or suppresses activity in another part

22. 1 Plant Life Cycles • Gibberellins are plant hormones that produce dramatic increases in size. – ending seed dormancy – rapid growth of young seedlings – rapid growth of some flower stalks

22. 1 Plant Life Cycles • Ethylene causes the ripening of fruits. – some fruits picked before they are ripe – sprayed with ethylene to ripen when reach destination

22. 1 Plant Life Cycles • Cytokinins stimulate cytokinesis. – final stage in cell division – produced in growing roots, seeds, and fruits – involved in growth of side branches

22. 1 Plant Life Cycles • Auxins lengthen plant cells in the growing tip. – stimulates growth of primary stem – controls some forms of tropism • A tropism is the movement of plant in response to an environmental stimulus.

22. 1 Plant Life Cycles Plants can respond to light, touch, gravity, and seasonal changes. • Phototropism is the tendency of a plant to grow toward light. – auxins build up on shaded side of stem – cells on shaded side lengthen – causes stem to bend toward light

22. 1 Plant Life Cycles • Thigmotropism is a plant’s response to touchlike stimuli. – climbing plants and vines – plants that grow in direction of constant wind

22. 1 Plant Life Cycles • Gravitropism is a plant’s response to Earth’s gravitational pull. – positive gravitropism is downward growth (roots) – negative gravitropism is upward growth (shoots)

22. 1 Plant Life Cycles • Some plants have rapid responses not involving growth. – Some responses protect plants from predators. – Some responses allow plants to capture food.

22. 1 Plant Life Cycles • Photoperiodism is a response to the changing lengths of day and night. – triggers some plants to flower – triggers fall colors/winter dormancy of deciduous trees