Transcript 20.1 Origins of Plant Life

20.1 Origins of Plant Life
KEY CONCEPT
Plant life began in the water and became adapted to
land.
20.1 Origins of Plant Life
Land plants evolved from green algae.
• Plants and green algae have many common traits.
– both are photosynthetic eukaryotes
– both have the same types of chlorophyll
– both use starch as a storage product
– both 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
• True plants evolved through natural selection.
– Ancestral charophyceans lived in areas of shallow
water.
– Those that could survive longer dry periods were
favored.
– First true plants probably grew at edges of water.
– True plants have embryos that develop while attached
to female parent.
20.1 Origins of Plant Life
• True plants evolved through natural selection.
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
20.1 Origins of Plant Life
• Stomata are tiny holes in the cuticle.
stoma
– 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
• Lignin allows plants to grow upright.
lignin
plant cells
– hardens cell walls of some vascular tissues
– provides stiffness to stems
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
• 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
Plants evolve with other organisms in their environment.
• Plants and other organisms can share a mutualistic
relationship.
– a mutualism is an interaction in which two species
benefit
– plant roots and certain fungi and bacteria
– flowering plants and their animal pollinators
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.
20.1 Origins of Plant Life
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 Origins of Plant Life
• Mosses belong to phylum Bryophyta.
– most common seedless nonvascular plants
– sphagnum moss commonly used by humans as “peat”
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 Plant Life
• Ferns and their relatives belong to phylum Pterophyta.
frond
fiddlehead
– whisk ferns and horsetails are close relatives of ferns
– ferns have large leaves called fronds
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
• Cycads are gymnosperms in phylum Cycadophyta.
– look like palm trees with large cones
– grow in tropical areas
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• Ginkgos are gymnosperms in phylum Ginkgophyta.
– only one species alive today, Ginkgo biloba
– grown in gardens and used in urban landscaping
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• Conifers are gymnosperms in phylum Coniferophyta.
– most common
gymnosperms alive
today
– includes pines, spruce,
cedar, fir, and juniper
20.1 Origins of Plant 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
KEY CONCEPT
The largest phylum in the plant kingdom is the
flowering plants.
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.
– Fruit is flower’s ripened ovary
– Surrounds and protects seed(s)
– Many forms, each function in seed dispersal
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Botanists classify flowering plants into two groups based
on seed type.
• 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
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.
– Herbaceous plants do not
produce wood.
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
• There are three types of plant life spans.
– Annuals mature from seed,
flower, and die in one year.
– Biennials take two years to
compete life cycle.
Foxglove
20.1 Origins of Plant Life
• There are three types of plant life spans.
– Annuals mature from seed, flower, and die in one year.
– Biennials take two years to compete life cycle.
– Perennials live more than two years.
Big bluestem
20.1 Origins of Plant Life
KEY CONCEPT
Humans rely on plants in many ways.
20.1 Origins of Plant Life
Agriculture provides stable food supplies for people in
permanent settlements.
• Botany is the study of plants.
• Ethnobotany explores how people in different cultures use
plants.
20.1 Origins of Plant Life
• People started planting for harvest about 10,000 years
ago.
– wild species “tamed” through artificial selection
– farming requires people to stay in one place
– farming helped more socially complex centers develop
Teosinte
20.1 Origins of Plant Life
Plant products are important economic resources.
• Plant products have been traded for thousands of years.
– spices commonly used as currency in Middle Ages
– spurred seafaring expeditions in 1400s and 1500s
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• Plant products contribute to economy on a global scale
today.
– grains, coffee, sugar, cotton, forest products
– billions of dollars of plant products traded each year
20.1 Origins of Plant Life
Plant compounds are essential to modern medicine.
• Pharmacology is the study of drugs and their effects on
the body.
• Many drugs are derived from plants.
– Salicin from willow trees is used in aspirin.
– Alkaloids are potent plant chemicals that contain
nitrogen.
– Alkaloids such as taxol have anti-cancer properties.
20.1 Origins of Plant Life
• Some medical research focuses on properties of plant
compounds.
– studies plants used
medicinally in traditional
cultures
– develop synthetic drugs
based on plant compounds