Plant Life Cycles

Plant Evolution Descendants from green algae (~450mya) –C–Contain cellulose in cell walls –C–Contain chlorophyll –S–Starch stored Land Plants Must Overcome –D–Drying out –G–Gas exchange –N–Nutrient transport system –S–Support

Land adaptations Cuticle: Waxy coating prevents water loss Stomata: pores that open/close to permit gas exchange Roots & Stems: support Vascular system: tissue that transports nutrients –N–Nutrients & water go up plant –S–Sugars go down the plant

General Plant Life Cycle Alternation of generations Gametophyte (haploid) –H–Haploid spores created by meiosis –G–Gametophyte grows from spore –G–Gametophyte has sperm & egg cells

Sporophyte (diploid) –D–Diploid zygote created from sperm & egg –Z–Zygote grows into a mature sporophyte –S–Sporophyte creates haploid spores by meiosis Gametophyte grows from spore (cycle restarts)

Mosses Nonvascular, seedless Grow low to ground to retain moisture Lack true leaves –L–Leaf-like structures only 1 cell thick Rhizoids anchor into soil Early inhabitant of new ecosystems (succession)

Moss Life Cycle Gametophyte phase –D–Dominant stage –C–Carpet of moss growing near ground Female gametophyte: produces egg Male gametophyte : produces sperm –S–Sperm swims through water to fertilize egg (zygote created) Sporophyte phase –S–Sporophyte stalk grows up from the zygote –S–Sporangia contain haploid spores –H–Haploid spores land Gametophyte stage restarts

Ferns Seedless, vascular plants –V–Vascular: allows taller growth Rhizoids: underground stems draw nutrients Fronds: leaves uncurl –s–sporangia on underside

Fern Life Cycle Sporophyte phase –D–Dominant stage –S–Sporangia produces haploid spores –S–Spores released into air Gametophyte phase –S–Spores land & grows into prothallus Female gametophyte: produces egg Male gametophyte : produces sperm –S–Sperm swims to egg –Z–Zygote begins sporophyte stage

Conifers Seed advantages –D–Don’t depend on water –P–Protects & nourishes embryo –A–Allow plants to grow in new locations Conifers: woody cone houses seeds –M–Male cones: produce pollen –F–Female cones: produce egg Pines, redwoods, spruce, cedar

Conifer Life Cycle Sporophyte phase –C–Cones grow on mature tree –F–Female cones: contains female gametophyte (megaspore) –M–Male cones: contains gametophyte (microspores) Microspores released & stick to female cones Pollen tube grows from pollen towards the egg Sperm travels down pollen tube (zygote created) Sporophyte stage restarts Seeds released to grow into new sporophyte

male female

Flowers Reproductive structure of flowering plants Sepals –o–outer ring of leaves –p–protection Petals –I–Inner ring of leaves –B–Brightly colored to attract pollinators Open petals & sepals reveal male and female structures

Female Carpal –I–Inner most part –O–Ovary: within the base (female gametophyte) –S–Style: long stalk –S–Stigma: sticky tip, collects pollen Male Stamen –S–Surrounds carpal –F–Filaments: long stalks –A–Anther: produces pollen (male gametophyte)

A) Microspores (male gametophyte) produced within anthers

B) Two events: 1. Microspores (male gametophyte) released into the air, wind, or transferred via animals 2. Microspores stick to stigma

C) Pollen tube grows from the pollen…towards the ovary

C) Continued: Two sperm cells from the microspore travel down the pollen tube

D) Double fertilization: 1 sperm fuses w/ egg (zygote created) 1 sperm fuses w/ the embryo sac (endosperm created)

E) Ovule wall hardens into a seed; Embryo develops

F) Ovary grows a fleshy tissue (fruit) over the seed

G) Seed germinates (starts to grow)

Fruit Production In the seed –E–Embryo –E–Endosperm (nourishes seed) Surrounding ovary grows into a fruit Fruit attracts animals to eat and spread the seeds Fruit seeds in fox droppings

End of the Semester!