Plants

1. Plants Multicellular, eukaryotic, photosynthetic autotrophs Cell walls made of cellulose Surplus carbohydrate stored as starch

2. Life Cycle • Evolved from aquatic green algae about 500 mya • Plants stabilize soil they live in, provide home for insects and larger animals, release oxygen into atmosphere and absorb carbon dioxide

3. Factors allowing Evolution onto Land • Cell walls made of cellulose for support • Roots and root hairs for water and nutrient absorption • Stomates for gas exchange and control of water loss • Waxy cuticle on leaves prevent water loss • Sporopollenin in walls of spores and pollen protects gametes from harsh environmental conditions • Xylem and phloem enable transport in tall plants; lignin in xylem and other cells offers support

4. 2 Groups Tracheophytes -transport vessels (vascular) -xylem and phloem for transport -lignin support -roots absorb water -leaves increase photosynthetic surface -Diploid Sporophyte generation is dominant -2 groups:Seedless plants (ferns) and seed plants (gymnosperms – those bearing cones, and angiosperms-those bearing flowers and fruits) Bryophytes -no transport vessels (non-vascular) -primitive – absorb water by diffusion -flagellated sperm must swim through water to fertilize an egg -lack lignin fortified tissue necessary to support tall plant therefore, cover ground in moist habitats -the haploid gametophyte generation is dominant, the diploid sporophyte is short-lived and grows out of mature gametophyte dependent on it for nutrition Example: liverworts, mosses, hornworts

5. Seedless Tracheophytes • Ferns • Reproduce by spores instead of seeds • Homosporous – produce only one type of spore which develops into bisexual gametophyte • Restricted to moist habitats because sperm is flagellated and must swim from antheridium to archegonium to fertilize the egg • The diploid sporophyte generation is larger (the leafy portion of fern) and separate from the haploid gametophyte generation (so small very difficult to see)

6. Seed Tracheophytes • Heterosporous – produce 2 kinds of spores, megaspores (from megasporangia and female) and microspores (from microsporangia and male) • Sperm is not flagellated so no water requirement for fertilization Gymnosperms -first seed plants to appear -seeds are “naked” because are not enclosed in fruit but are exposed on surface of modified leaves that form cones -conifers better adapted to dry environment due to needle shaped leaves with thick, protective cuticle and small surface area, depend on wind for pollination Angiosperms -reproductive structures are flowers and fruits -color and scent attract animals that can carry pollen from one plant to another great distances -after pollination and fertilization the ovary becomes fruit and ovule becomes seed -the fruit helps dispersal of seed -2 groups: monocots and dicots

7. Principal Differences between monocots and dicots

8. How plants grow • Embryonic tissues called meristems allow plant cells to continually divide and therefore grow • Pattern of growth is determined by location of meristem • Apical meristem– located at tips of roots and in buds of shoots providing primary growth (elongation) • 3 Zones: Zone of cell division (meristem cells actively divide), Zone of elongation (cells elongate and push root cap into soil), Zone of differentiation (cells undergo specialization into 3 primary meristems that give rise to 3 tissue systems: protoderm = epidermis, ground meristem= cortex for storage, procambium = primary xylem and phloem) • Lateral meristem– provides secondary growth which increases girth • Occurs in woody plants not herbaceous plants

9. Plant Tissue • 3 Types: • Dermal Tissue – covers and protects plant • Includes endodermis, epidermis and modified cells such as guard cells, and root hairs • Vascular Tissue – consists of xylem and phloem • Xylem- water and mineral conduction system; consists of 2 types of cells: tracheids (are long and thin, passes water from one cell to another through pits and support plant because of lignin; seedless vascular plants and gymnosperms only have tracheids)and vessel elements (wider, short, thin walled, ends are perforated to allow ease in water flow; angiosperms have tracheids and vessel elements) • Phloem- carries sugars from photosynthetic leaves to rest of plant by active transport; consists of chains of sieve tube elements whose end walls have sieve plates and are connected to companion cells which have full complement of cell organelles and nurture sieve tube elements • Ground Tissue – support, storage, and photosynthesis • 3 cell types: • parenchymal cells • Traditional plant cells and carry out most metabolic activities of plant; have ability to differentiate into other cell types after time of injury • Collenchymal cells • Unevenly thickened primary cell walls, lack lignin; function is to support the growing stem • Sclerenchymal cells • Have very thick primary and secondary cell walls with lignin; support the plant; 2 types: fibers and sclereids (seed coats and pits)

10. Plant Reproduction • Asexual Reproduction • Plants can clone themselves by vegetative propagation where a root, stem, or leaf produces an entirely new plant • Sexual Reproduction in Flowering Plants • The flower is the sexual organ • Fertilization begins with pollination when one pollen grain containing 3 monoploid nuclei, one tube nucleus, and 2 sperm nuclei land on sticky stigma of flower • Pollen grain absorbs moisture and sprouts producing a pollen tube that burrows down the style to the ovary • The 2 sperm nuclei travel down tube; once inside ovary they enter ovule through micropyle where one sperm fertilizes the egg and becomes the embryo (2n) and the other sperm fertilize 2 polar bodies and becomes triploid (3n) endosperm – food for growing embryo = double fertilization • The ovule becomes the seed and ripened ovary becomes the fruit • In monocots – food reserves remain in endosperm • In dicots – food reserves of endosperm are transported to cotyledons; the mature dicot seed lacks endosperm

11. Angiosperm Reproduction

12. The Seed • Consists of: • Seed coat- protection • Embryo • Hypocotyl- becomes lower part of stem • Epicotyl- becomes upper part of stem • Radicle- the first organ to emerge from germinating seed (aka: embryonic root) • Cotyledon or endosperm- food for growing embryo

13. Alternation of Generations • Monoploid (n) and diploid (2n) generations alternate • Gametophyte(n) produces gametes by mitosis • Gamete fuse during fertilization yielding (2n) zygotes • Each zygote develops into sporophyte (2n) which produces monoploid spores (n) by meiosis • Each monoploid spore forms a new gametophyte completing the life cycle

14. Mosses and other bryophytes • The organism is monoploid (n) for most of its life and the sporophyte (2n) depends on gametophyte • A monoploid spore settles on moist ground, germinates, and develops by mitosis into threadlike, monoploidprotonema from which individual gametophytes arise like branches • Egg producing archegonia and sperm producing antheridia develop on tips of gametophyte • Sperm travels to egg through water for fertilization to occur and the zygote (2n) develops into sporophyte, a diploid adult, which is a filament that grows out of the top of the gametophyte; the sporophyte sprouts sporangia where meiosis occurs producing spores and beginning life cycle over

15. Moss Life Cycle

16. Ferns: Seedless, Vascular Plants • The sporophyte generation is larger and independent from gametophyte • Monoploid (n)fern spore settles on moist ground, germinates into heart-shaped haploid gametophyte (n) • Archegonia and antheridia develop on underside, flagellated sperm swim to archegonia and fertilize egg producing diploid zygote (2n) • Zygote grows into large sporophytes plant (the fern) • Sporangia on underside of fern leaves undergo meiosis producing monoploid (n) spores • Spores fall from spore sac (sori) when mature, settle on ground and sprout into gametophyte generation completing cycle • Spore is bisexual producing both male and female sex organs

18. Plant responses to Stimuli • Hormones – coordinate growth, development, and responses to environmental stimuli • Produced in very small quantities with profound effect because signal is amplified through signal transduction pathways • Auxin – phototropisms, enhances apical dominance, stimulates stem elongation • Indoleacetic acid (IAA) – naturally occurring, when used in rooting powder it causes quick root development in plant cutting; in synthetic form can induce fruit production without pollination resulting in seedless fruits • Cytokinins • Stimulate cytokinesis and cell division promoting growth and development • Work antagonistically against auxins in apical dominance • Delay aging by inhibiting protein breakdown (florists use on cut flowers to keep fresh) • Produced in roots and travel upward • Gibberellins • Promote stem and leaf elongation; over 100 different types • Induce bolting (rapid growth of floral stalk) to ensure pollination and seed dispersal • Abscisic Acid (ABA) • Inhibits growth • Enables plant to withstand drought by closing stomates during water stress • Promotes seed dormancy to delay fall drop from germinating until spring arrives • Ethylene • Gaseous • Promotes fruit ripening thus reason why fruits are generally picked before are ripe. Ethylene can be sprayed on at store to promote ripening • Produced in large quantities during times of stress for plant • Facilitates apoptosis and promotes leaf abscission as a way to salvage usable compounds from leaf before it dies and falls off

19. Signal Transduction Pathways • Amplify responses through transfer of stimulus in 3 stages: reception, transduction, and response • Receptor is stimulated and undergoes conformational change activating a secondary messenger • Secondary messengers (cyclic AMP, or cGMP) transfer and amplify signal leading directly to a response • Response alters transcription factors in nucleus of target cell and alters expression of certain genes

20. Tropisms • The growth of a plant toward or away from a stimulus • Thigmotropisms (touch): Venus Fly Trap • Geotropisms • Gravitropisms (gravity) • Phototropisms(light) • Result from unequal distribution of auxins