PLANTS

EVERYTHING YOU NEVER WANTED TO KNOW

BUT NEEDED TO FORTHE AP EXAM

2007-2008

DomainBacteria

DomainArchaea

DomainEukarya

Common ancestor

Kingdom: Plants

Domain Eukarya

• Land plants evolved from green algae

• Researchers have identified green algae called charophyceans as the closest relatives of land plants

Genetic Evidence• Comparisons of both nuclear and

chloroplast genes– Point to charophyceans as the closest living

relatives of land plants

Chara, a pond organism

(a)10 mm

Coleochaete orbicularis, a disk-shaped charophycean (LM)

(b)

40 µm

Figure 29.3a, b

Animal vs. Plant life cycle

diploidmulticellularindividual2n

diploidmulticellularsporophyte2n

haploidmulticellulargametophyte1n

haploidunicellulargametes1n

gametes1n

Animal Plant

alternation of generations

meiosis

fertilization

mitosis

mitosismitosis

fertilization

mitosis

no multicellularhaploid

meiosis

spores1n

zygote 2n

zygote 2n

Pollen• Pollen

eliminated the requirement for water for fertilization– spread through

wind & animal

Angiosperm: flowering plants

Anther

FilamentStamen

StigmaStyleOvary

Carpel

Sepal

Petal

Ovule

sepalspetals

Flower • Modified shoot with 4 rings

of modified leaves– sepals– petals– stamens

• male

– carpel• female stamens

carpel

adaptations through mutations

• The life cycle of an angiosperm

Figure 30.10

Key

Mature flower onsporophyte plant(2n)

Ovule withmegasporangium (2n)

Female gametophyte(embryo sac)

Nucleus ofdevelopingendosperm

(3n)

Dischargedsperm nuclei (n)

Pollentube

Male gametophyte(in pollen grain)

Pollentube

Sperm

Survivingmegaspore(n)

Microspore (n) Generative cell

Tube cell

Stigma

OvaryMEIOSIS

MEIOSIS

Megasporangium(n)

Pollengrains

EggNucleus (n)

Zygote (2n)

Antipodal cellsPolar nucleiSynergidsEgg (n)

Embryo (2n)

Endosperm(foodSupply) (3n)

Seed coat (2n)

Seed

FERTILIZATION

Haploid (n)

Diploid (2n)

Anther

Sperm(n)

Pollentube

Style

Microsporangium

Microsporocytes (2n)

GerminatingSeed

Anthers contain microsporangia.Each microsporangium contains micro-sporocytes (microspore mother cells) thatdivide by meiosis, producing microspores.1

Microspores formpollen grains (containingmale gametophytes). Thegenerative cell will divideto form two sperm. Thetube cell will produce thepollen tube.

2

In the megasporangiumof each ovule, themegasporocyte divides bymeiosis and produces fourmegaspores. The survivingmegaspore in each ovuleforms a female gametophyte(embryo sac).

3

After pollina-tion, eventuallytwo sperm nucleiare discharged ineach ovule.

4

Double fertilization occurs. One spermfertilizes the egg, forming a zygote. Theother sperm combines with the two polarnuclei to form the nucleus of the endosperm,which is triploid in this example.

5

The zygotedevelops into an

embryo that ispackaged alongwith food into aseed. (The fruit

tissues surround-ing the seed are

not shown).

6

When a seedgerminates, the

embryo developsinto a mature

sporophyte.

7

From Ovary to Fruit

• A fruit– Develops from the ovary– Protects the enclosed seeds– Aids in the dispersal of seeds by wind or

animals

Co-evolution: flowers & pollinators

Plant Structure, Growth, and Development

Figure 39.4

1 Reception   2 Transduction 3 Response

CYTOPLASM

Plasmamembrane

Phytochromeactivatedby light

Cellwall

Light

cGMP

Second messengerproduced

Specificproteinkinase 1activated

Transcriptionfactor 1 NUCLEUS

P

P

Transcription

Translation

De-etiolation(greening)responseproteins

Ca2+

Ca2+ channelopened

Specificproteinkinase 2activated

Transcriptionfactor 2

• An example of signal transduction in plants

1 The light signal isdetected by thephytochrome receptor,which then activatesat least two signaltransduction pathways.

2 One pathway uses cGMP as asecond messenger that activatesa specific protein kinase.The otherpathway involves an increase incytoplasmic Ca2+ that activatesanother specific protein kinase.

3 Both pathwayslead to expressionof genes for proteinsthat function in thede-etiolation(greening) response.

• The bending of a grass seedling toward light

–Begins with the plant sensing the direction, quantity, and color of the light

Figure 39.1

• Xylem

–Conducts most of the water and minerals

–Includes dead cells called tracheids

• Phloem

–Distributes sugars, amino acids, and other organic products

–Consists of living cells