Introduction to Plants

Earliest Plants Algae Phytoplankton Lived in the sea

Problems with life on land Drying Out Making Food Reproduction Gravity & Support Getting water & nutrients Solution Waxy cuticle, stomata Formed leaves Develops spores & seeds Bark (cork) & vessels Roots & vessels

Avascular Tracheophytes Types of Plants Bryophytes nonseed plants vessels for transport and support

Mosses & Liverworts: The Bryophytes First land plants AVASCULAR = very small 500 m.y.a. Must grow in moist environments Used for fuel (peat)

Reproduction in Bryophytes Mosses have a protonema (liverworts do not) Sexual reproduction Antheridium – makes sperm Archaegonium – makes eggs Asexual reproduction Fragmentation Formation of gemmae

Tracheophytes Vessels Spores or seeds for reproduction XYLEM = transports water & dissolved minerals from roots to leaves PHLOEM = transports sugars from leaves to rest of plant Spores or seeds for reproduction

Club Mosses (Lycophyta) Leaves produce spores Strobilus = spore-bearing leaves Prothallus = produces antheridia & archaegonia

Horsetails (Sphenophyta) Jointed stems Reproduction similar to club moss

Ferns (Pterophyta) 400 m.y.a. Dominant form = sporophyte Structure Rhizome = underground stem Fronds = leaves Sori = store spores on underside of fronds

Gymnosperms Gymno = “naked” Sperm = “seed” First plants to produce seeds No flowers No fruit

Why Make Seeds? Has own food supply Protective coat against harsh conditions Some are designed for travel to new areas

Sporophytes produce: MICROSPORE MEGASPORE Produce male gametophyte Produce pollen MEGASPORE Produce female gametophyte Produce ovule (makes archaegonia with egg cells)

Gymnosperm Reproduction Pollen grains carried by wind Land on ovule, develop pollen tube Sperm move through tube to fertilize egg Fertilized egg = ZYGOTE EMBRYO = young, diploid sporophyte plant COTYLEDONS = food storage for embryo, become first leaves

Why Pollen Instead of Spores? Plant can live in very dry areas Fertilization does not require water Pollen has protective coat and food supply for sperm

Why Ovules Instead of Archaegonia? Protective tissues prevent drying out Ovule holds archaegonia and protects eggs from elements

Minor Gymnosperm Groups Cycadophyta (1st in Triassic Era) Ginkgophyta Only one species today Ginkgo biloba Most lived 200 m.y.a. Gnetophyta – only three genera Gnetum – house plants Ephedra – weight loss, allergies & asthma Welwitschia

Coniferophyta (largest group) Needle or scale-like leaves Bear seeds in woody cones Can live in very cold climates Most are evergreens Have wood Made of thick-walled vessels (TRACHEIDS) Tracheids are xylem

Angiosperms Angio – “flower” Sperm – “seed” Extremely diverse All have seeds enclosed in fruit

Cambium Any growth tissue in plants Types of cambium Vascular = produces xylem & phloem Cork = produces cork (bark)

Overall Structures [121] Roots Stems Leaves Flowers

Roots [124] Absorb water & nutrients Hold plant in place Root types: Fibrous Tap Prop Aerial

Stems [123] Support leaves & flowers Sometimes photosynthesis Transport (contain xylem & phloem) Types herbaceous – green & flexible Woody – stiff, have cork layer, usually brown

Leaves [119] Cuticle = protection Stomata = gas exchange, water loss (transpiration) Epidermis = protection, color Mesophyll Palisade = most PHOTOSYNTHESIS Spongy = Vascular bundles run through it

Flowers [131] Pistils = female reproductive structures Stamens = male reproductive structures Complete flowers Have petals & sepals Have male and female parts Incomplete flowers = missing one or more parts

Types of Angiosperms [115] Monocots mono = “one” cot = “seed leaf” Approx. 60,000 species Flowers = multiples of 3 Leaf veins parallel Dicots di = “two” cot = “seed leaf” Approx. 170,000 species Flowers = multiples of 4 or 5 Leaf veins branching

Plant Tropisms Tropism = plant response to external stimulus Types: Positive: plant moves toward stimulus Negative: plant moves away from stimulus Types: Phototropism = light Gravitropism = gravity Thigmotropism = touch (nastic movement – direction does not matter)

Plant Hormones Hormone – chemical produced in one part of an organism that has an effect on a different part of the organism Types Auxins – regulate growth Gibberellins – speeds growth, germination Abscisic acid – dormancy, close stomata, stress Ethylene – ripens fruit