Seed Plant Reproduction & Plant Responses and Adaptations

Alternation of Generations Diploid, spore-producing sporophyte alternates with a haploid, gamete- producing gametophyte In seed plants the sporophyte generation is dominant (the plants we see) and the gametophytes are hidden deep within the sporophyte  Inside cones in gymnosperms  Inside flowers in angiosperms

Gymnosperm Life Cycle Takes place in cones  Pollen cones – “male” cones that produce pollen grains (male gametophyte)  Seed cones – larger “female” cones that house ovules where female gametophytes develop Typically takes two years

Gymnosperms Process  Male cones release pollen  Pollen reaches female cone and sticks  Pollen grain splits, producing a pollen tube to ovule  Sperm travel down pollen tube to fertilize the egg  Develops into seed containing new sporophyte

Angiosperm Life Cycle Angiosperm reproduction is all about the flower  Vary greatly in size, shape, and color  May house both gametophytes or only one Remember the 3 Fs……Flowers, Fruit, and double Fertilization!!!

Parts of a Flower

Angiosperms – Parts of a Flower Four kinds of specialized leaves:  Sepals – enclose the bud before it opens  Petals – brightly colored to attract pollinators  Stamen – produce male gametophyte Filament – long, thin stalk Anther – pollen produced  Pistil(Carpel) – produce female gametophyte Stigma – sticky portion at the top end Style – stalk that connects stigma and ovary Ovary – broad base that houses ovules

Angiosperm Life Cycle Process:  Pollen grain is deposited onto the stigma  Forms pollen tube down to ovary  Sperm travels down pollen tube and fertilizes the egg  Double fertilization – involves two fertilization events One sperm fuses with egg to form zygote Another sperm fuses with two polar nuclei to form the endosperm (food rich tissue in seed)

Seeds and Fruit As angiosperm seeds mature, the ovary walls thicken to form fruit Fruit – any seed enclosed within its embryo wall  Common fruits such as apples, grapes, and strawberries as well as beans, corn, peas, cucumbers and rice  May be fleshy or tough like pods

Dormancy and Germination Some seeds sprout immediately, other enter state of dormancy – alive, but not growing  Allows for long-distance dispersal  Allows seeds to grow in ideal conditions Germination – early growth stages  Prompted by water, temperature, or other environmental factors

Asexual Reproduction Vegetative reproduction – asexual by mitosis alone (identical offspring) Horticulturists also use cuttings, grafting, or budding to make identical copies of plant

Plant Hormones Chemical substances that control plant’s patterns of growth and development  Hormones are produced in one part and move to another part to trigger a response Hormones affect target cells which contain a specific hormone-protein receptor

HormoneFunction/Response Auxins Stimulate cell elongation; major role in tropisms Cytokinins Stimulate cell division and growth; cause dormant seeds to sprout Gibberellins Promote growth and increase in size, especially in stems and fruits Ethylene Stimulates ripening of fruits

Tropisms Responses of plants to external stimuli  Phototropism – response to light Tend to grow toward light Auxins cause cell elongation in shaded part of stem  Gravitropism – response to gravity Cause roots to grow down and shoots to grow up  Thigmotropism – response to touch Can stunt growth, allow for vine growth, and cause leaves to close

Photoperiodism Response to periods of light and darkness  Responsible for timing of seasonal events such as flowering and growth  Short-day plants – flower when days are short and have long periods of darkness  Long-day plants – flower when days are long and have shorter periods of darkness

Plant Adaptations Aquatic/Wetland  have tissues with large air pockets to allow for oxygen uptake Salt  specialized cells that pump salt out of plant tissues Dry  Extensive/deep roots, reduced leaves, thick stems for water storage, waxy coatings, open stomata at night

Plant Adaptations Nutrition  Parasitic plants extract water and nutrients directly from host plant  Carnivorous plants trap and digest insects to obtain nutrients unavailable in the poor soils Epiphytes – grow directly on bodies of other plants  Not parasitic – gather own moisture and produce their own food  Often grow on others to collect more light

Plant Adaptations Defense  Manufacture chemicals May be poisonous when eaten Act as insect hormones to prevent reproduction Release into soil to deter competitors  Have spines/thorns