Introduction to Plants

Mrs. M. Rightler

Earliest Plants

AlgaePhytoplanktonLived in the sea

Problems with life on land

ProblemDrying OutMaking FoodReproduction

Gravity & SupportGetting water &

nutrients

SolutionWaxy cuticle, stomataFormed leavesDevelops spores &

seedsBark (cork) & vesselsRoots & vessels

Types of Plants

Avascular –Bryophytes–nonseed plants

Tracheophytes–vessels for transport and support

Mosses & Liverworts: The Bryophytes

First land plantsAVASCULAR = very small500 m.y.a.Must grow in moist environmentsUsed 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– XYLEM = transports water & dissolved

minerals from roots to leaves– PHLOEM = transports sugars from

leaves to rest of plantSpores or seeds for reproduction

Club Mosses (Lycophyta)

Leaves produce spores– Strobilus = spore-bearing leaves– Prothallus = produces antheridia &

archaegonia

Horsetails (Sphenophyta)

Jointed stemsReproduction similar to club moss

Ferns (Pterophyta)

400 m.y.a.Dominant form = sporophyteStructure

– 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 supplyProtective coat against harsh

conditionsSome are designed for travel to new

areas

Sporophytes produce:

MICROSPORE – Produce male gametophyte– Produce pollen

MEGASPORE– Produce female gametophyte– Produce ovule (makes archaegonia

with egg cells)

Gymnosperm Reproduction

Pollen grains carried by windLand on ovule, develop pollen tubeSperm 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 areasFertilization does not require waterPollen has protective coat and food

supply for sperm

Why Ovules Instead of Archaegonia?

Protective tissues prevent drying outOvule 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 leavesBear seeds in woody conesCan live in very cold climatesMost are evergreensHave wood

– Made of thick-walled vessels (TRACHEIDS)– Tracheids are xylem

Angiosperms

Angio – “flower” Sperm – “seed”Extremely diverseAll have seeds enclosed in fruit

Cambium

Any growth tissue in plantsTypes of cambium

– Vascular = produces xylem & phloem– Cork = produces cork (bark)

Overall Structures [121]

RootsStemsLeavesFlowers

Roots [124]

Absorb water & nutrientsHold plant in placeRoot types:

– Fibrous– Tap– Prop– Aerial

Stems [123]

Support leaves & flowersSometimes photosynthesisTransport (contain xylem & phloem)Types

– herbaceous – green & flexible– Woody – stiff, have cork layer, usually

brown

Leaves [119]

Cuticle = protectionStomata = gas exchange, water loss

(transpiration)Epidermis = protection, colorMesophyll

– Palisade = most PHOTOSYNTHESIS– Spongy = Vascular bundles run through it

Flowers [131]

Pistils = female reproductive structuresStamens = male reproductive structuresComplete 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

speciesFlowers = multiples

of 3Leaf veins parallel

Dicots

di = “two”

cot = “seed leaf”Approx. 170,000

speciesFlowers = multiples

of 4 or 5Leaf veins branching

Plant Tropisms

Tropism = plant response to external stimulus– 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