chapter 22: introduction to plants
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Chapter 22: Introduction to Plants. Sections 1-4. What is a plant?. Organisms in Kingdom Plantae are eukaryotes that have cell walls containing cellulose and carry out photosynthesis using chlorophyll a and b. Plant Needs. Sunlight –photosynthesis - PowerPoint PPT PresentationTRANSCRIPT
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