Plants

Chapter 23

Kingdom Plantae

• At least 295,000 species known

• Are the most important producers on land

• Plant life cycle alternates between

haploid multicellular stage (gametophyte) and diploid multicellular stage (sporophyte)

– Gametophytes (1n multicellular) produce gametes (by mitosis)

– Gametes fuse (fertilization) to form zygote

– Zygote grows into sporophyte (2n multicellular)

– Sporophytes produce spores (by meiosis)

– Spores germinate & form gametophytes

• Plants evolved from an ancestor similar to modern Charophytes

– Lived in water

• Plants evolved on land, radiated into diverse habitats

– From moist habitats to drier ones

Four major groups of modern plants

1. Bryophytes = Nonvascular plants (inc. mosses)

2. Seedless vascular plants (inc. ferns)

3. Gymnosperms = Vascular plants with naked seeds (inc. conifers)

4. Angiosperms = Vascular plants with seeds in vessels (flowering plants)

Characters found in all plants

• Sterile jacket of cells surround where gametes are formed.

Keeps gametes from drying out.

– Archegonia & antheridia

– Reduced to 1-few cells in gymnosperms & angiosperms

• Cuticle (made up of lipids – inc. waxes)

– Secreted by & covers epidermis (outer cell layer)

– Prevents water loss, but also prevents gas exchange

• Openings in epidermis

= Stomata in all plants except liverworts

– Formed by 2 guard cells

– Can open or close (under hormonal control)

– Allow gas exchange when open

– Prevent water loss when closed

Bryophytes

• Liverworts, Mosses, Hornworts

• Earliest plants probably most similar to liverworts

– Molecular data

– Pores instead of stomata

• Life cycle (Fig 23.5)

– Gametophyte dominant (longer lived)

– Fertilization requires water (must live in moist areas)

– Sporophyte attached to gametophyte

– All spores look alike (homospory)

– Dispersed by spores

• Most bryophytes live in

– But part of year can be dry, go dormant and

– Peat moss grows in

• Grows

• Is harvested in some areas as

Vascular Plants

• All plants except

• Vascular tissue is in

• Sporophyte is

• Two types of vascular tissue

1.

• Large, dead cells forming

• Transport water and inorganic nutrients from

2.

• Smaller, living cells,

• Transport products of photosynthesis (esp. sucrose) from

• Vascular tissue allowed plants to grow

Lignin in cell walls provided added

– Shoots (stems, leaves) created larger

– True roots can reach

• Association with fungus (=mycorrhizae) is

Seedless Vascular Plants

• Whisk ferns, lycophytes, horsetails,

• Whisk ferns (Psilophyta) resemble

• Lycophytes and horsetails were trees in the

– Became

– But most are

• Life cycle (Fig 23.9)

– Gametophyte small but

– Fertilization requires

• So still limited to seasonally

– Sporophyte

has

produces one type of

• In ferns, spores produced in sporangia

– Disperse by

– Spores germinate into

Vascular plants with seeds

• Gymnosperms and

• Show heterospory =

1. Microspores –

2. Megaspores –

• Heterospory led to the evolution of

• Pollen = male gametophyte in

– Microspores form male gametophytes that consist of

– Microspores don’t germinate, male gametophyte

– Wind or animals carry this

– Pollen forms sperm and a pollen tube. Sperm

• Seed = Embryonic sporophyte + nutritious tissue +

– Megaspores form tiny

– Megaspores don’t germinate, female

– Megaspore with female gametophyte remains in

– Ovule = female gametophyte in megaspore coat surrounded by

– Ovule makes

– When egg is fertilized, zygote becomes

– When seed germinates, embryo

• Pollen and ovules are adaptations to

– Resistance to

• Gametophytes remain in

• Female gametophyte remains in

– Sperm no longer need to

• Pollen carried by

• Sperm travel down

• Dispersal now by

– Spores can no longer produce

– Seeds have food for growth and

– Seeds can remain dormant in soil for long periods, germinate

• Life cycle (Fig 23.17 & 23.20)

– Sporophyte

– Microspores & megaspores

• Usually form in

• Form in

– Gametophytes are small, remain inside

– Fertilization results in seed formation, embryo grows into

Gymnosperms =

• Conifers, cycads, ginkgos, and gnetophytes

• Cycads & conifers (& ferns) dominated for most of

• Most modern gymnosperms are

– Most have leaves like

– Are wind-

– Slow reproductive rates – may take months to a year between

– Most abundant now in

Angiosperms =

• Magnoliids, eudicots, monocots

• Angiosperms started diversifying near end of Mesozoic Era and

• Flowers

– Pollen grains form inside

• Stamen =

– Ovules (1-many) form inside of

• Carpel = pistil =

• Pollination and Fertilization

– Pollination =

Pollen tube grows down through style (mid part of carpel) to

Sperm travels down

Fertilization =

– Flowers may be pollinated via

Flowers are

Typical of

– Or pollen may be transferred by

Showy or fragrant flowers

Flowers make nectar and extra pollen to

• Fruit

– Fertilization of egg inside ovule →

ovule develops into a

AND ovary develops into

– Fruit may be

– Fruit helps to disperse seeds by

or by _____________, carried externally or internally from one place to another.

• Angiosperms and their pollinators or seed dispersers may

= joint evolution of

(evolutionary change in 1 causes evolutionary change in other)

Summary of plant evolution

• Cladogram

Plants and People

• Food

– Various plant parts used, but often

– About ____ major crops

– Main 3 staples are all

• Wood

–

– Fast-growing conifers used to make

– Slow-growing flowering trees used to make

• Medicine

– Herbal (“natural”)

• Not always

• Ex. Ephedrine from gymnosperm Ephedra - used as

but can lead to

– Western medicine

• Many were first derived from plants, then

Ex. Salicylic acid (aspirin) first isolated from

• Some still get from plants

Ex. Vincocristine to treat acute childhood leukemia (

It stops mitosis by inhibiting

Isolated from Madagascar

Takes 53 tons of leaves to make

• Inspiration for design

– Cockleburs inspired

• Review Questions 1, 2, 4

• Self Quiz questions 1-4, 6