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
• 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.
Analyze: 1.
What
category of
plant
evolved
most
recently?
2. What is
the first
category of
plants to
evolve from
the
ancestral
charophyceans?
3. When did the flowering plant lineage diverge from the conebearing plant lineage?
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 and
keeps the plant from
drying out
20.1 Origins of Plant Life
• Stomata are small openings in the
cuticle that allow for gas exchange
between the plant and the
atmosphere.
– 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 freestanding 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
Fig. The hawk
moth has a tongue
that measures 3035 cm. It is the
pollinator of a
night-blooming
orchid whose
nectar is produced
30 cm down inside
the flower.
20.1 Origins of Plant Life
• Plants have adaptations that prevent animals from eating
them.
– spines and thorns
– defensive chemicals that can act as pesticides or
taste bad to keep predators away
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 (no
difference between stem or
leaf) or leafy
Fig. Thallose liverworts, like the one shown
here, can grow from 2 mm to 25 cm in length.
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”
Fig. The
stalks of
these
hornworts
are 2 to 5
cm long.
20.1 Origins of Plant Life
• Mosses belong to phylum Bryophyta.
– most common seedless nonvascular plants
– sphagnum moss commonly used by humans as “peat”
Fig. Like all nonvascular plants, mosses need to live in moist environments.
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
Fig. Club mosses, such as
this Lycopodium species,
are able to grow up off of
the ground because they
have vascular systems.
20.1 Origins of Plant Life
• Ferns and their relatives belong to phylum Pterophyta.
– whisk ferns and horsetails are close relatives of ferns
– ferns have large leaves called fronds
frond
Parts of a Fern Ferns are the most
common seedless vascular plants.
Most have a rhizome anchored by
roots, as well as leaves (fronds).
Young fronds (fiddleheads) are tightly
coiled. Spores are produced in
sporangia on the under side of the
leaves.
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
Fig. Seed plants produce pollen. In pine trees such as the one
shown here, clouds of pollen are released from male pine cones.
20.1 Origins of Plant Life
• Gymnosperms is a seed plant that 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
Fig. Cycads, such as the
one shown here, produce
seeds on large,
protective, female cones.
20.1 Origins of Plant Life
• Ginkgos are gymnosperms in phylum Ginkgophyta.
– only one species alive today, Ginkgo biloba
– grown in gardens and used in urban landscaping
Fig. The name Ginkgo
biloba refers to the two-lobed
leaves of this plant.
20.1 Origins of Plant Life
• Conifers are gymnosperms in phylum Coniferophyta.
– most common
gymnosperms alive today
– includes pines, spruce,
cedar, fir, and juniper
Fig.
Ponderosa
pine cone.
Fig. This Ponderosa pine
is a typical evergreen
conifer with needlelike
leaves.
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.
Fig. Many trees,
including dogwoods,
are flowering plants.
20.1 Origins of Plant Life
Botanists classify flowering plants into 2 groups based
on seed type - Monocots OR Dicots
20.1 Origins of Plant Life
Flowering plants are also categorized by stem type and
lifespan.
• Herbaceous or Woody stems
• 3 types of lifespans
– Annual – only live for one year
– Biennial – take 2 years to complete their life cycle
– Perennial – any flowering plant that lives for more than 2 years
Fig. Iris (left): Monocot, herbaceous, perennial, Oak (middle): Dicot, woody,
perennial, Wheat (right): Monocot, herbaceous, annual
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.
Fig. Agriculture has
become an important
part of our global
economy. Many river
deltas, such as the
Sacramento River
delta in California,
are used for
farmland because of
their nutrient-rich
soils and water.
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.
Fig. This scientist, standing waist-high in
water, is studying a mangrove forest in
Thailand. Mangrove forests grow in
intertidal zones in the tropics. These
diverse ecosystems may hold treatments
for a variety of medical conditions.