The World of Plants in 41 Minutes

Kingdom Plantae–All are multicellular, nonmotile, autotrophic eukaryotes–Their cell walls are made from cellulose–Plants carry out photosynthesis using chlorophyll a and b–Plants store their carbohydrates as starch–Alternation of Generations - Reproduce sexually by alternating between gametophyte (n) and sporophyte (2n) generations.–Some plants have vascular tissue (tracheophytes) and some have none (bryophytes)–Mosses, ferns, gymnosperms, angiosperms

Fig. 29-7

Origin of land plants (about 475 mya)1

2

3

1

2

3

Origin of vascular plants (about 420 mya)

Origin of extant seed plants (about 305 mya)

ANCES-TRALGREENALGA

Liverworts

Hornworts

Mosses

Lycophytes (club mosses,spike mosses, quillworts)

Pterophytes (ferns,horsetails, whisk ferns)

Gymnosperms

Angiosperms

Seed

plan

tsS

eedless

vascular

plan

ts

No

nvascu

larp

lants

(bryo

ph

ytes)

Lan

d p

lants

Vascu

lar plan

ts

Millions of years ago (mya)

500 450 400 350 300 50 0

Nonvascular plants (bryophytes)

Seedless vascular plants

Gymnosperms

Angiosperms

Morphological and Molecular Evidence

• Many characteristics of land plants also appear in a variety of algal clades, mainly algae

• However, land plants share four key traits only with charophytes:– Rose-shaped complexes

for cellulose synthesis– Peroxisome enzymes– Structure of flagellated

sperm– Formation of a

phragmoplast

5 mm

Chara species, a pond organism

Coleochaete orbicularis, adisk-shaped charophyte thatalso lives in ponds (LM)

Bryophytes

• Bryophytes– Bryophytes are

primitive plants that lack vascular tissue

– They must live in moist environments because they have no roots or xylem and must absorb water by diffusion

– Bryophytes are tiny because they lack the lignin-fortified tissue necessary to support tall plants on land

– Mosses are an example

Tracheophytes

• Tracheophytes– Tracheophytes have

transport vessels, xylem and phloem

– They include ancient seedless plants, like ferns, that reproduce by spores

– They include modern plants that reproduce by seeds

– Those with seeds are further subdivided into gymnosperms and angiosperms

Gymnosperms

– Gymnosperms are conifers, the cone-bearing plants.

– Needle shape, cuticle, stomates in the stomatal crypts help to conserve water loss

– Cedars, sequoias, redwoods, pines, yews and junipers

Angiosperms– Flowering

plants, anthophyta

– Most diverse and plentiful plants on earth

– Principle differences between Monocots and Eudicots

Alternation of Generations and Multicellular, Dependent

Embryos• Plants alternate between two

multicellular stages, a reproductive cycle called alternation of generations

• The gametophyte is haploid and produces haploid gametes by mitosis

• Fusion of the gametes gives rise to the diploid sporophyte, which produces haploid spores by meiosis

• The diploid embryo is retained within the tissue of the female gametophyte

• Nutrients are transferred from parent to embryo through placental transfer cells

• Land plants are called embryophytes because of the dependency of the embryo on the parent

Fig. 29-5a

Gametophyte(n)

Gamete fromanother plant

n

n

Mitosis

Gamete

FERTILIZATIONMEIOSIS

Mitosis

Sporen

n

2n Zygote

Mitosis

Sporophyte(2n)

Alternation of generations

Transport in Xylem and PhloemVascular plants have two types of vascular tissue: xylem

and phloem

• Xylem conducts most of the

water and minerals and includes dead cells called tracheids

• Water-conducting cells are strengthened by lignin and provide structural support

• Increased height was an evolutionary advantage

• Phloem consists of living cells and distributes sugars, amino acids, and other organic products

• Sugar-Conducting Cells of the Phloem• Sieve-tube elements are alive at

functional maturity, though they lack organelles

• Sieve plates are the porous end walls that allow fluid to flow between cells along the sieve tube

• Each sieve-tube element has a companion cell whose nucleus and ribosomes serve both cells

Fig. 35-10d

Perforationplate

Vesselelement

Vessel elements, withperforated end walls Tracheids

Pits

Tracheids and vessels(colorized SEM)

Vessel Tracheids 100 µm

XYLEM

Fig. 35-10e

Sieve-tube element (left)and companion cell:cross section (TEM)

3 µmSieve-tube elements:longitudinal view (LM)

Sieve plate

Companioncells

Sieve-tubeelements

Plasmodesma

Sieveplate

Nucleus ofcompanioncells

Sieve-tube elements:longitudinal view Sieve plate with pores (SEM)

10 µm

30 µm

PHLOEM

Plant Growth: Meristems generate cells for new organs

• Apical meristems– Are located at the

tips of roots and in buds of shoots.

– Sites of cell division that allow plants to grow in length (primary growth)

• Lateral meristems– results in growth

which thickens the shoots and roots (secondary growth)

Primary Growth lengthens roots

and shoots• Zone of cell

division– Includes apical

meristem– New cells produces– Root cap is located

in root

• Zone of elongation– Elongation of cells

• Zone of maturation– Cell differentiation– Cell become

functionally mature

Ground

Dermal

Keyto labels

Vascular

Root hair

Epidermis

Cortex Vascular cylinder

Zone ofdifferentiation

Zone ofelongation

Zone of celldivision

Apicalmeristem

Root cap

100 µm

Angiosperms

• Angiosperms are seed plants with reproductive structures called flowers and fruits

• They are the most widespread and diverse of all plants

Nonvascular plants (bryophytes)

Seedless vascular plants

Gymnosperms

Angiosperms

Fig. 30-7

Carpel

Ovule

Sepal

Petal

Stigma

Style

Ovary

Stamen Anther

Filament

Video: Flower Blooming (time lapse)Video: Flower Blooming (time lapse)

Fruits

• A fruit typically consists of a mature ovary but can also include other flower parts

• Fruits protect seeds and aid in their dispersal• Mature fruits can be either fleshy or dry

Animation: Fruit DevelopmentAnimation: Fruit Development

Fig. 30-8

Hazelnut

Ruby grapefruit

Tomato

Nectarine

Milkweed

Fig. 30-9

Barbs

Seeds within berries

Wings

• A pollen grain that has landed on a stigma germinates and the pollen tube of the male gametophyte grows down to the ovary

• The ovule is entered by a pore called the micropyle

• Double fertilization occurs when the pollen tube discharges two sperm into the female gametophyte within an ovule

Fig. 30-10-4

MEIOSIS

Key

MicrosporangiumMicrosporocytes (2n)

Generative cell

Anther

Tube cell

Pollengrains

Microspore(n)

Male gametophyte(in pollen grain)(n)

Mature flower onsporophyte plant(2n)

Haploid (n)Diploid (2n)

MEIOSIS

Ovule (2n)

Ovary

Megasporangium(2n)

Megaspore(n)

Female gametophyte(embryo sac)

Antipodal cells

Central cell

Synergids

Egg (n)

Pollentube

Pollentube

Stigma

Sperm(n)

Discharged sperm nuclei (n)

FERTILIZATION

Germinatingseed

Embryo (2n)Endosperm (3n)Seed coat (2n)

Seed

Nucleus ofdevelopingendosperm(3n)

Zygote (2n)Eggnucleus (n)

Style

Sperm

Fig. 30-13n

MonocotCharacteristics

EudicotCharacteristics

Vascular tissueusually arranged

in ring

Veins usuallyparallel

Vascular tissuescattered

Leafvenation

One cotyledon

Embryos

Two cotyledons

Stems

Veins usuallynetlike

Fig. 30-13o

Roots

Pollen

Root systemusually fibrous(no main root)

Pollen grain withthree openings

Pollen grain withone opening

Floral organsusually in

multiples of three

Flowers

Floral organs usuallyin multiples of

four or five

MonocotCharacteristics

EudicotCharacteristics

Taproot (main root)usually present

Vegetative PropegationTypes of Veg. Propagation

Description Examples

Bulbs Short Stems Underground

Onions

Runners Horizontal Stems above ground

Strawberries

Tubers Underground Stems

Potatoes

Grafting Cut a stem and attach it to a closely related plant

Seedless Oranges

Tropical Tropismstropism – turning response to a

stimulus

Phototropism Refers to how plants respond to light

Gravitropism Refers to how plants respond to gravity

Thigmotropism Refers to how plants respond to touch (IVY, strangler trees

Auxins Responses are initiated by hormones. Major plant hormones belong to the class AUXINS

Table 39-1