PlantsChapter 21

Plant Evolution• Plant: multicellular, photosynthetic eukaryotic

organism that contains tissues and organs with specialized structures and functions

• Plants share a common ancestor with green algae.

• Plants developed derived traits (adaptations) to be able to live on land.• Cuticle• Stomata• Vascular tissue• Reproductive

strategies• Seeds

PLANTLEAFperformsphotosynthesis

CUTICLEreduces waterloss; STOMATAallow gas exchange (photosynthesisand cellular respiration)

STEMsupports plant(and may performphotosynthesis)

Surrounding watersupports the algae

ALGAE

WHOLE ALGAEperformsphotosynthesis;absorbs water,CO2, andminerals fromthe water

HOLDFASTanchors the algae

ROOTSanchor plant;absorb water andminerals from the soil (aidedby mycorrhizalfungi)

• Not pictured• Vascular tissues:

specialized transport tissues that move water and nutrients from the roots to the rest of the plant; provides support

• Reproductive strategies: adaptations of gametes and mutually beneficial relationships with other living things

• Seeds: Seed coats protect embryo of new plants as they scatter on land

Plant Classification• Two main categories:• Nonvascular Plants (earliest to diverge)• Called Bryophytes• Common examples: mosses, hornworts, and liverworts• Small plants• Lack true leaves; use root-like rhizoids to anchor them

into to a surface• Live in damp, shady areas to assist in providing water

to tissues• Vascular Plants (evolved later)• Seedless Plants (ferns) and Seed Plants• Contain a xylem and phloem• Have well-developed root system• Rigid stem

Vascular Seedless Plants - Ferns• Tend to live in damp, shady areas• Water is need for flagellated sperm to reach the

egg to reproduce new generations of the plants.

Vascular Seed Plants• The appearance of seeds is a major

evolutionary step.• Pollen grains transport sperm rather

than water.• Seed Structure – protects embryo:• Seed coat: protective coating• Embryo: growing, developing new plant• Cotyledons: store food or help absorb food

for the growing embryo• Monocotyledons – have one cotyledon• Dicotyledons – have two cotyledons

• Location of Seeds• Angiosperms – seeds are found in a fruit• Gymnosperms – seeds are NOT part of a

fruit; naked seeds

Gymnosperms – Naked Seed Plants• Gymnosperms diverged before angiosperms.

Fruits are a more recent adaptation.• Division Coniferophyta: • Male cones produce

pollen, which carries sperm.

• Female cones are larger and more open to allow the sperm to collect.

• Female cones remain on the plant until seeds are mature.

• When the cone drops from the tree, seeds are spread.

Angiosperms – Fruit-bearing, Flowering Plants

• Flowers are reproductive structures in plants.

• Sepal: protects flower buds• Petal: attracts pollinators

and provides landing pad• Stamen – MALE

reproductive organ; filament supports the anther; anther produces pollen (sperm)

• Pistil or Carpel – FEMALE reproductive organ; pollination occurs at stigma; embryo (SEEDS) develop in the ovary; fruits form from the ovary

Fruits – Seed Dispersal• Fruits are seed dispersal adaptations.

Categories of Angiosperms

Categories of Angiosperms

Categories of Angiosperms• Monocot is on the

left• Oat plant

• Dicot is on the right• Bean plant

• Notice the differences in the two plants.

Categories of Angiosperms

In monocots, the vascular bundles in the stem cross section are usually scattered or more complex of an arrangement as compared to dicots.

The vascular bundles in the stem cross section of dicots are arranged in a circle, or ring.

Types of Monocots and Dicots