Download 20.1 Origins of Plant Life

20.1 Origins of Plant Life
Chapter 20 : Plant Diversity
20.1 Origins of Plant Life
KEY CONCEPT
Plant life began in the water and became adapted to
land.
Land plants evolved from green algae.
• Plants and green algae have many common traits:
–photosynthetic eukaryotes
–have the same types of chlorophyll
–use starch as a storage product
–have cell walls with cellulose
20.1 Origins of Plant Life
• Genetic analysis points to the common ancestor of all
plants.
– extinct green algae species in class Charophyceae
– modern charophyceans common in lakes and ponds
20.1 Origins of Plant Life
• Important plant characteristics likely originated in
charophyceans.
– multicellular body allowing for specialization of
cells and tissues
– cell division that allows for chemical communication
between cells
– reproduction involving sperm swimming to egg
20.1 Origins of Plant Life
20.1 Origins of Plant Life
Plants have adaptations that allow them to live on land.
• Challenges of living on land have selected for certain
plant adaptations.
• A cuticle allows plants to retain moisture.
– waxy, waterproof layer
– holds moisture in
• Stomata are tiny holes in the cuticle.
– can open and close
– allow air to move in and out
20.1 Origins of Plant Life
• A vascular system allows resources to move to different
parts of the plant.
– collection of specialized tissues
– brings water and mineral nutrients up from roots
– disperses sugars from the leaves
– allows plants to grow higher off the ground
water
and
mineral
nutrients
sugars
20.1 Origins of Plant Life
• A seed is a storage device for a plant embryo.
– seed coats protect
embryos from drying
wind and sunlight
– embryo develops
when environment is
favorable
20.1
Origins
of
Plant
Life
• Pollen grains allow for reproduction without free-standing
water.
– pollen grains contain a cell
that divides to form sperm
– pollen can be carried by
wind or animals to female
structures
20.1
Origins
of Plant Life
• Plants
have adaptations
that prevent animals from eating
them.
– spines and thorns
– defensive chemicals
20.1 Origins of Plant Life
KEY CONCEPT
Plants can be classified into nine phyla.
Mosses and their relatives are seedless nonvascular
plants.
• Nonvascular plants grow
close to the ground to
absorb water and nutrients.
• Seedless plants rely on freestanding water for
reproduction.
• Liverworts belong to phylum
Hepatophyta.
– often grow on wet rocks
or in greenhouses
– can be thallose or leafy
20.1 Origins of Plant Life
• Hornworts belong to phylum Anthocerophyta.
– found in tropical forests and along streams
– flat, lobed body with little green “horns”
20.1• Mosses
Originsbelong
of Plant
Life Bryophyta.
to phylum
– most common seedless nonvascular plants
– sphagnum moss commonly used by humans as “peat”
20.1 Origins of Plant Life
20.1 Origins of Plant Life
Club mosses and ferns are seedless vascular plants.
• A vascular system allows club mosses and ferns to grow
higher off the ground.
• Both need free-standing water for reproduction.
• Club mosses belong to phylum Lycophyta.
– not true mosses
– oldest living group
of vascular plants
20.1
Origins
of relatives
Plant Life
• Ferns
and their
belong to phylum Pterophyta.
– whisk ferns and horsetails are close relatives of ferns
– ferns have large leaves called fronds
frond
fiddlehead
20.1 Origins of Plant Life
Seed plants include cone-bearing plants and flowering
plants.
• Seed plants have several advantages over their seedless
ancestors.
– can reproduce without free-standing water, via pollination
– pollination
occurs when
pollen meets
female plant
parts
– seeds
nourish and
protect plant
embryo
– seeds allow plants to
disperse to new places
20.1 Origins of Plant Life
• Gymnosperms do not have seeds enclosed in fruit.
– most gymnosperms are cone-bearing and evergreen.
– the cone is reproductive structure of most
gymnosperms.
– pollen is produced
in male cones.
– eggs are produced
in female cones.
– seeds develop on
scales of female
cones.
20.1 Origins of Plant Life
• Conifers are gymnosperms in Phylum Coniferophyta.
– most common
gymnosperms alive
today
– includes pines, spruce,
cedar, fir, and juniper
20.1
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of
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Life
• Angiosperms have seeds enclosed in some type of fruit.
– A flower is the reproductive structure of angiosperms.
– A fruit is a mature ovary of a flower.
• Angiosperms, or flowering plants, belong in Phylum
Anthophyta.
20.1 Origins of Plant Life
Flowering plants have unique adaptations that allow them
to dominate in today’s world.
• Flowers allow for efficient pollination.
– animals feed on pollen or nectar
– pollen is spread from plant to plant in process
20.1 Origins of Plant Life
• Fruit allows for efficient seed dispersal.
– a fruit is flower’s ripened ovary
– Surrounds and protects seed(s)
– Many forms, each function in seed dispersal
20.1 Origins of Plant Life
Botanists classify flowering plants into two groups monocots and dicots
• A cotyledon is an embryonic “seed leaf.”
• Monocots have a single seed leaf.
– leaf veins usually parallel
– flower parts usually in multiples of 3
– bundles of vascular tissue scattered in stem
20.1 Origins of Plant Life
• Dicots have two seed leaves.
– leaf veins usually netlike
– flower parts usually in multiples of 4 or 5
– bundles of vascular tissue in rings in stem
20.1 Origins of Plant Life
Flowering plants are also categorized by stem type and
lifespan.
• Stem type can be woody or herbaceous.
– Wood is a fibrous
material made up of
dead cells.
– Wood has high
concentrations of
lignin and cellulose.
– Woody stems
are stiff.
Oak
20.1 Origins of Plant Life
– Herbaceous plants have no
woody growth - only green
stems and leaves
Iris
20.1 Origins of Plant Life
• There are three types of plant life spans.
– Annuals mature from seed,
flower, and die in one year.
Wheat
20.1 Origins of Plant Life
– Biennials take two years to
compete life cycle.
Foxglove
20.1 Origins of Plant Life
– Perennials live more than two years.
Big bluestem