chapter 22: introduction to plants

Sections 1-4

Organisms in Kingdom Plantae are eukaryotes that have cell walls containing cellulose and carry out photosynthesis using chlorophyll a and b

Sunlight –photosynthesisLeaves broad and flat, arranged on stem to

maximize light absorptionGas exchange –oxygen for cellular

respiration, carbon dioxide for photosynthesisGases exchanged with atmosphere/soil without

losing too much waterWater and minerals – structures limit water

loss, faster uptake of water from soil; some have specialized tissues to carry water/nutrients

Ancestors of land plants water-dwellers, similar to green algaeSimpler, have cell walls, identical photosynthetic

pigments, similar reproductive cycles to plantsSo genetically similar they should be plants

First land plants had a water problem – grew close to ground in damp places, dependent on water for life cycle

Several groups evolved – one line lead to mosses, another to ferns, cone-bearing plants and flowering plants

Five major groups based on embryo formation, specialized water-conducting tissues, seeds, and flowers

Alternation of generations – shifting between a diploid (2n) phase and a haploid (n) phase

Multicellular diploid called sporophyte produces haploid spores by meiosis

Spores grow into multicellular haploids called gametophytes

Gametophytes produce gametes – egg and sperm

Zygote forms through fertilization, which develops into new sporophyte

Reduction in gametophyte size, increase in sporophyte size

“Algae” refers to any photosynthetic eukaryote other than a land plant

Classified in group of seedless plantsMostly aquatic (fresh and salt) or on land in

damp/moist areasAbsorb moisture and nutrients directly from

surroundings – no specialized tissues

Many alternate between haploid and diploid forms, but not necessarily with each generation

Example: ChlamydomonasFavorable conditions – haploid cell reproduces

asexually by mitosisUnfavorable conditions – switches to sexual

reproduction Cells fuse to form zygote (sporophyte) with thick

protective covering which will grow when conditions improve, divide by meiosis into 4 haploids

Green algae can form coloniesSpirogyra form filamentsVolvox form colonies of up to 5000 – shows

some specialization

Mosses have protective coating that makes them resistant to drying, rhizoids to anchor them to soil and absorb water and minerals

Group including mosses, liverworts, and hornworts

Specialized reproductive organs enclosed by nonreproductive cells

Higher degree of cell specializationAmong first land plantsSmall because they do not make lignin, which

is used to harden cell walls, and do not have vascular tissues

Alternation of generationsGametophyte dominant, sporophyte depends

on itProduce sperm cells with flagella for

swimming so water must be present at some point in year

When a moss spore lands in a moist place, it grows into a gametophyte

Forms rhizoids that grow into ground, shoots that grow into air

Gametes formed at tips of gametophyteEggs produced in archegoniaSperm produced in antheridia

Egg/sperm fuse to form diploid zygote – beginning of sporophyte stage

Sporophyte grows within gametophyte – dependent

Eventually grows out of gametophyte, develops stalk ending in sporangium

Sporangium produces haploid spores by meiosis Spores released

Plants growing high above ground appeared ~ 420 mya

Had vascular tissues – carry water and nutrients more efficiently than bryophytes

Vascular plants called tracheophytes because of tracheids – water-conducting cells that are hollow, tube-like, cell walls strengthened with lignin

Tracheids arranges end to end make up xylem, the tissue that carries water upwards from the roots – pits between tracheids increase water movement

Phloem is the other vascular tissue – transports solutions of nutrients and photosynthetic products

Three phyla, commonly known as club mosses, horsetails, and ferns (most)

Ferns have vascular tissues, strong roots, rhizomes (stems underground), fronds

Thrive with little lightWet environments

Spores produced by the sporophyte grow into thin, heart-shaped haploid gametophytes (independent)

Sperm/eggs produced on gametophytes in antheridia and archegonia

Sperm swim to eggs – water neededZygote develops into a new sporophyte plant

(dominant)Haploid spores develop on the undersides of

the fronds in sporangia

Seeds contain tiny living plant ready to sprout

Plant embryo and a food supply – diploid, early stage sporophyte

Common ancestor for all modern seed plantsAbility to survive on dry land – developed

adaptationsCones and flowersPollenSeeds

In seed plants, male and female gametophytes grow/mature within sporophyte – in cones or flowers

Gymnosperms (naked seeds – cone-bearing plants) bear seeds on scales of cones

Angiosperms (flowering plants) bear seeds in flowers within protective tissue

Male gametophyte is contained in a pollen grain

Carried to the female reproductive structure by wind or animals

The transfer of pollen from the male reproductive structure to the female reproductive structure is called pollination

After fertilization, the zygote within seed grows into a tiny plant (sporophyte embryo)

A tough seed coat surrounds and protects the embryo, keeps it from drying out

The embryo begins to grow when conditions are right

Uses nutrients from stored food supply until it can carry out photosynthesis on its own

Seeds exposed on scaled within conesReproduction occurs in cones produced by

mature sporophytePollen cones (male) produce pollen grains

(male gametophyte)One haploid nucleus within pollen grain later

divides to produce 2 sperm nuclei

Seed cones (female) produce female gametophytesScales contain 2 ovules , where meiosis

produces haploid cells that develop into female gametophytes

Each gametophyte contains multiple egg cellsIn spring, pollen cones release pollen grains

which are carried by windFemale cones secrete sticky substance to trap

pollen which is pulled inside the ovuleFertilization without open water

Pollen grains landing near ovules split open, grow a structure called a pollen tube containing 2 haploid sperm nuclei

Once the pollen tube reaches the female gametophyte, one sperm nucleus disintegrates; the other fertilizes the egg

Zygote develops into embryoSeed encases embryo, dispersed by wind

Angiosperms most abundant plantsMost recent to evolveDevelop flowers, which contain ovaries to

surround and protect seeds

Flowers attract pollinatorsMore efficient than relying on windAfter pollination, ovary develops into a fruit,

containing at least one mature embryoWall of fruit helps distribute seeds – animals

eat, seeds go through digestive systemIncreases range

Used to be classified by numbers of leaves in their embryos – cotyledons

Monocots – one cotyledonDicots – two cotyledons

Now, monocots single group, dicots in several

Differences in stemsWoody plants are made of cells with thick

cell walls that support the plant bodyHerbaceous plants have stems that are

smooth and nonwoody