Introduction to Plants

AP Biology

Invading Land

• Conditions to overcome: buoyancy of water is missing, no longer bathed in a nutrient solution, air dries things out

Invading Land

• Those adverse conditions favored evolution of: structures that support, vessels that transport, and structures that conserve water

• See handout

Three major groups

• Bryophytes: small nonvascular plants– Mosses, liverworts

• Seedless, vascular plants –ferns, horsetails

• Seed bearing plants– Usually divided into two classes:– Gymnosperms (“naked seeds”) and

Angiosperms (flowering plants)

What is vascular tissue?

• Tissues that conduct water and food throughout the plant

• Equivalent of blood vessels in higher animals

• Xylem conducts water• Phloem conducts food

How do bryophytes survive without vascular tissue?

• Must remain small• Must have water for

reproduction• Must live in moist

areas• Rely on diffusion and

primitive rootlike structures to absorb water

liverwort

hornwort

moss

Seedless, Vascular

horsetails

Whisk

ferns

ferns

Invading Land• Evolutionary order:

bryophytes first—410 million years ago

• Ferns—by 360 million years ago

• Conifers—by 290 million years ago

• Angiosperms—138 million years ago

Bryophytes

• Mosses, liverworts, hornworts

• 18,600 species• Small• Moist environments• No vascular tissue (no

xylem or phloem)• Rhizoids are rootlike

Bryophytes

• “Alternation of generations” means a gametophyte plant produces a sporophyte plant, which then produces a gametophyte

• Sporophyte remains attached to the gametophyte

Bryophytes

• The stages are named after what they produce

• A sporophyte produces spores

• A gametophyte produces gametes

Sporophyte

capsules

Bryophytes

• Sperm must swim to the egg, so water must be available

• Also need water because they do not have true roots or vascular tissue

antheridium

archegonium

Bryophytes

Ferns

• 12,000 species• Mostly tropical• Very diverse• Range is size from 1

cm to 25 meters tall• Have vascular tissue,

but do not produce seeds

Ferns

• Dominant stage is the sporophyte (2n)

• Alternation of generations

• Sporophyte produces haploid spores (n) which grows into a gametophye

Sori contain spores

sorus

Ferns

• Germinating spores develop into small gametophyes, the plant’s stage which produces gametes

• The gameotyphyte plant is very small and hard to notice

• Heart shaped: called a prothallus

Tiny gametophyte

sporophyte

gametophyte

Fern gamete producing structures

archegonia antheridia

Gametophyte

• Antheridia are sperm producing structures

• Archegonia are egg producing structures

• Fertilization forms a zygote (2n), which develops into a sporophyte plant (2n)

• The sporophyte develops into the leafy fern we recognize, and will go on to produce haploid spores

Gymnosperms : Naked Seeds(not enclosed in a fruit)

• 4 Major groups:

• Cycads: mostly tropical or subtropical regions

• Gingkoes: native to Southeastern China

• Conifers: cone bearing

• Gnetales: resemble angiosperms, but no flower

CycadsMost common in equatorial regions, some subtropical areas

Cycad Distribution

Gingkoes

Fruit has a foul odor; some cities have removed all female trees

Gnetales• Small leaves that

resemble angiosperm leaves

• No flowers• Cones may be fleshy

and brightly colored• Some consider them to

be a “bridge” to angiosperms

Conifers• Trees and shrubs that

have needles or scale like leaves

• Bear seeds on exposed cone scales

• Most are evergreen• Examples: pine, fir,

cypress, redwood, pacific yew

Coniferous Forest

Why are they typically in colder climates?

Conifers

• Both male and female cones are produced

• Male cones produce pollen, which drifts and lands on ovules of female cones

• Pollen sprouts a tube which grows to the eggs inside the ovule

Conifers

• After fertilization, the zygote develops into a seed.

• The seed becomes a mature sporophyte (2n), producing male and female cones

• The cones produce haploid spores which become pollen and eggs

Conifers

• Slow to reproduce• After pollen lands,

may be a year before fertilization occurs

• This is a competitive disadvantage

Angiosperms

• Flowering plants

• The flower is the reproductive structure

• Sporophyte is the dominant generation

• Gametophyte generation is small (microscopic) ; this offers protection and nutrition, and is a competitive advantage.

Angiosperms

• Coevolved with pollinators

• Birds• Insects: bees,

butterflies, moths, etc.• Bats• Mutually beneficial

Flower partsStamen (male) produces pollen; Pistil (female) produces egg

Stamen and Pistil

Angiosperms

• Zygote (embryo) forms in the base of the female ovary in an ovule

• Each ovule becomes a seed; the whole ovary becomes the fruit, or part of the fruit

Seed

Each ovule may produce a seed Ovary Receptacle