Lecture 6 Plant Diversity

8/7/2019 Lecture 6 Plant Diversity

1/59

1

BY4002

Important Note: Most of the textnotes are included in this file.Additional notes may be given

during the lecture.


2/59

2

Plant Diversity 1


3/59

3

Derived Traits of Plants


4/59

4

Four key traits appear in nearly allland plants but are absent in the

charophytes: Alternation of generations (with

multicellular, dependent embryos)

Walled spores produced in sporangia

Multicellular gametangia

Apical meristems


5/59

5

Additional derived traits such as a cuticleand secondary compounds evolved in

many plant species Symbiotic associations between fungi and

the first land plants may have helpedplants without true roots to obtain

nutrients


6/59

6

Alternation of Generationsand Multicellular, DependentEmbryos


7/59

7

Plants alternate between twomulticellular stages, a

reproductive cycle calledalternation of generations


8/59

8

The gametophyte is haploid andproduces haploid gametes by mitosis

Fusion of the gametes gives rise to thediploid sporophyte,which produceshaploid spores by meiosis


9/59

9

Nutrients are transferred fromparent to embryo through

placental transfer cells


10/59

10

Land plants are calledembryophytes because of the

dependency of the embryo onthe parent


11/59

11

Gametophyte(n)

Gamete fromanother plant

n

n

Mitosis

Gamete

FERTILIZATIONMEIOSIS

Mitosis

Sporen

n

2n Zygote

Mitosis

Sporophyte(2n)

Alternation of generations


12/59

12

Walled SporesProduced in Sporangia


13/59

13

The sporophyte produces sporesin organs called sporangia

Diploid cells called sporocytesundergo meiosis to generatehaploid spores


14/59

14

Spore walls containsporopollenin, which makes

them resistant to harshenvironments


15/59

15

Multicellular Gametangia


16/59

16

Gametes are produced withinorgans called gametangia


17/59

17

Female gametangia, calledarchegonia,produce eggs and

are the site of fertilization Male gametangia, called

antheridia, are the site of sperm

production and release


18/59

18

Apical Meristems


19/59

19

Plants sustain continual growthin their apical meristems

Cells from the apical meristemsdifferentiate into various tissues


20/59

20

The Origin andDiversification of Plants


21/59

21

Fossil evidence indicates thatplants were on land at least 475

million years ago Fossilized spores and tissues

have been extracted from 475-million-year-old rocks


22/59

22

Those ancestral species gaverise to a vast diversity of modern

plants Land plants can be informally

grouped based on the presenceor absence ofvascular tissue


23/59

23

Most plants have vascular tissue;these constitute the vascular

plants Nonvascular plants are

commonly called bryophytes


24/59

24

Seedless vascular plants can bedivided into clades Lycophytes (club mosses and their

relatives)

Pterophytes (ferns and their

relatives)


25/59

25

A seed is an embryo and nutrientssurrounded by a protective coat

Seed plants form a clade and canbe divided into further clades: Gymnosperms, the naked seed

plants, including the conifers Angiosperms, the flowering plants


26/59

26

Mosses and other

nonvascular plants have lifecycles dominated bygametophytes


27/59

27

Mosses can grow in very harshenvironments

They can tolerate drying out Peat is a by-product of the

growth of certain mossesThey lack a vascular system

(nonvascular)


28/59

28

Bryophytes are represented todayby three phyla of small herbaceous

(nonwoody) plants: Liverworts, phylum Hepatophyta

Hornworts, phylum Anthocerophyta

Mosses, phylum Bryophyta


29/59

29

Mosses are most closely relatedto vascular plants


30/59

30

Bryophyte Gametophytes


31/59

31

In all three bryophyte phyla,gametophytes are larger and

longer-living than sporophytes Sporophytes are typically

present only part of the time

R i d


32/59

32

Key

Haploid (n)

Diploid (2n)Protonemata(n)

Bud

Bud

Malegametophyte(n)

Femalegametophyte (n)

Gametophore

Rhizoid

Spores

Sporedispersal

Peristome

Sporangium

MEIOSIS SetaCapsule

(sporangium)Foot

Maturesporophytes

Capsule with

peristome (SEM)

Female

gametophytes2m

m

Raindrop

Sperm

Antheridia

Egg

Archegonia

FERTILIZATION

(within archegonium)Zygote

(2n)Embryo

Archegonium

Young

sporophyte

(2n)


33/59

33

spore germinates into a gametophytecomposed of a protonema and

gamete-producing gametophore Rhizoids anchor gametophytes to

substrate

The height of gametophytes isconstrained by lack of vascular tissues


34/59

34

Mature gametophytes produceflagellated sperm in antheridia and

an egg in each archegonium Sperm swim through a film of

water to reach and fertilize the

egg


35/59

35

Bryophyte Sporophytes


36/59

36

Bryophyte sporophytes grow outof archegonia, and are the

smallest and simplestsporophytes of all extant plantgroups


37/59

37

A sporophyte consists of a foot, aseta (stalk), and a sporangium,

also called a capsule,whichdischarges spores through aperistome

Hornwort and moss sporophyteshave stomata for gas exchange


38/59

38

Ferns and other seedlessvascular plants were the firstplants to grow tall


39/59

39

Bryophytes and bryophyte-likeplants were the prevalent

vegetation during the first 100million years of plant evolution


40/59

40

Vascular tissue allowed theseplants to grow tall

Seedless vascular plants haveflagellated sperm and are usuallyrestricted to moist environments


41/59

41

Nonvascular plants (bryophytes)

Seedless vascular plantsGymnosperms

Angiosperms


42/59

42

Living vascular plants arecharacterized by: Life cycles with dominant sporophytes Vascular tissues called xylem and

phloem

Well-developed roots and leaves


43/59

43

Life Cycles with DominantSporophytes


44/59

44

In contrast with bryophytes,sporophytes of seedless vascular

plants are the larger generation, asin the familiar leafy fern

The gametophytes are tiny plants

that grow on or below the soilsurface


45/59

45

Key

Haploid (n)

Diploid (2n)

MEIOSISSpore

dispersal

Sporangium

SporangiumMature

sporophyte

(2n)

Sorus

Fiddlehead

Spore

(n)Younggametophyte

Maturegametophyte(n)

ArchegoniumEgg

Antheridium

Sperm

FERTILIZATION

New

sporophyte

Gametophyte

Zygote

(2n)


46/59

46

Transport in Xylem andPhloem


47/59

47

Vascular plants have two types ofvascular tissue: xylem and

phloem Xylem conducts most of the

water and minerals and includes

dead cells called tracheids


48/59

48

Phloem consists of living cells anddistributes sugars, amino acids, andother organic products

Water-conducting cells arestrengthened by lignin and providestructural support

Increased height was an evolutionaryadvantage


49/59

49

Evolution of Roots


50/59

50

Roots are organs that anchorvascular plants

They enable vascular plants toabsorb water and nutrients from thesoil

Roots may have evolved fromsubterranean stems


51/59

51

Evolution of Leaves


52/59

52

Leaves are organs that increasethe surface area of vascular

plants, thereby capturing moresolar energy that is used forphotosynthesis


53/59

53

Leaves are categorized by twotypes: Microphylls, leaves with a single

vein

Megaphylls, leaves with a highly

branched vascular system


54/59

54

According to one model ofevolution, microphylls evolved

first, as outgrowths of stems


55/59

55

Sporophylls and SporeVariations


56/59

56

Sporophylls are modifiedleaves with sporangia

Fern sporophylls produceclusters of sporangia known asSori


57/59

57

Most seedless vascular plants arehomosporous, producing one type

of spore that develops into abisexual gametophyte All seed plants and some seedless

vascular plants are heterosporous


58/59

58

Heterosporous species producemegaspores that give rise to

female gametophytes, andmicrospores that give rise tomale gametophytes

Gametophyte


59/59

p y

Mitosis Mitosis

Mitosis

Spore Gamete

Zygote

n

nn

n

2n

MEIOSIS FERTILIZATION

Haploid

DiploidSporophyte

Documents

Lecture 6 Plant Diversity