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 (regulated by guard cells)
– 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
21.1
Cells
Tissues
20.1 Plant
Origins
of and
Plant
Life
KEY CONCEPT
Plants have specialized cells and tissue systems.
21.1
Cells
Tissues
20.1 Plant
Origins
of and
Plant
Life
Plant tissues are made of three basic cell types.
• Parenchyma cells are the most common plant cell
type.
– store starch, oils and
water
– help heal wounds to
the plant
– have thin flexible walls
21.1
Cells
Tissues
20.1 Plant
Origins
of and
Plant
Life
• Collenchyma cells provide support to a growing plant.
– they are strong and flexible.
– celery strings are strands of collenchyma.
– they have unevenly thick cell walls.
21.1
Cells
Tissues
20.1 Plant
Origins
of and
Plant
Life
• Sclerenchyma cells are the strongest plant cell type.
– second cell wall hardened by lignin
– die when they reach maturity
– used by humans to make linen and rope
21.1
Cells
Tissues
20.1 Plant
Origins
of and
Plant
Life
Plant organs are made of three tissue systems.
• Dermal tissue covers the outside of a plant.
– protects the plant
– secretes cuticle of leaves
– forms outer bark of trees
21.1
Cells
Tissues
20.1 Plant
Origins
of and
Plant
Life
• Ground tissue is found inside a plant.
– provides support
– stores materials in roots and stems
– most commonly made of parenchyma
21.1
Cells
Tissues
20.1 Plant
Origins
of and
Plant
Life
• Vascular tissue transports water, minerals and organic
compounds.
– two networks of hollow
tubes
– xylem transports water
and minerals
– phloem transports
photosynthetic products
stem
leaf
root
21.2
Vascular
System
20.1 The
Origins
of Plant
Life
KEY CONCEPT
The vascular system allows for the transport of
water, minerals, and sugars.
21.2
Vascular
System
20.1 The
Origins
of Plant
Life
Water and dissolved minerals move through xylem.
• Xylem contains specialized cells.
– vessel elements are short and wide
– tracheid cells are long and narrow
– xylem cells die at maturity
tracheid
vessel
element
21.2
Vascular
System
20.1 The
Origins
of Plant
Life
• The cohesion-tension theory explains water movement.
– Plants passively transport water through the xylem.
– Cohesion is the tendency of water molecules to bond
with each other.
– Adhesion is the
tendency of water
molecules to bond
with other
substances.
21.2
Vascular
System
20.1 The
Origins
of Plant
Life
• Water travels from roots to the top of trees.
– absorption occurs at roots
– cohesion and adhesion in xylem
– transpiration at leaves
21.2
Vascular
System
20.1 The
Origins
of Plant
Life
• Transpiration is the loss of water
vapor through leaves.
– water vapor exits leaf stomata
– helps pull water to the top
branches
21.2
Vascular
System
20.1 The
Origins
of Plant
Life
Phloem carries sugars from photosynthesis throughout
the plant.
• Phloem contains specialized cells.
– sieve tube elements have
holes at ends
– companion cells help sieve
tube elements
– unlike xylem, phloem tissue is
alive
21.2
Vascular
System
20.1 The
Origins
of Plant
Life
• The Pressure-flow model explains sugar movement.
– plants actively transport sugar from the source
– sugar flows to the sink due to pressure differences
phloem
xylem
sugars
1 Sugars move from their
source, such as
photosynthesizing
leaves, into the phloem.
3 The sugars move into
the sink, such as root
or fruit, where the are
stored.
water
2 Water moves from
the xylem into the
phloem by osmosis,
due to the higher
concentration of the
sugars in the phloem.
The water flow helps
move sugars through
the phloem.
22.1
Lifeof
Cycles
20.1 Plant
Origins
Plant Life
KEY CONCEPT
Reproduction of flowering plants takes place within
flowers.
22.1
Lifeof
Cycles
20.1 Plant
Origins
Plant Life
Plant life cycles alternate between producing spores and
gametes.
• A two-phase life cycle is called alternation of generations.
– haploid phase
– diploid phase
– alternates between
the two
SPOROPHYTE
PHASE
fertilization
meiosis
GAMETOPHYTE
PHASE
22.1
Lifeof
Cycles
20.1 Plant
Origins
Plant Life
• The spore-producing plant is the mature sporophyte.
– sporophyte phase is diploid
– begins with fertilized egg
– spores produced through
meiosis
• The gamete-producing plant is the
mature gametophyte.
– gametophyte
phase is haploid
– begins with spore
– gametes
produced through
mitosis
22.2
of Flowering
Plants
20.1 Reproduction
Origins of Plant
Life
Flowers contain reproductive organs protected by
specialized leaves.
• Sepals and petals are modified leaves.
– Sepals are outermost
layer that protects
developing flower
sepal
22.2
of Flowering
Plants
20.1 Reproduction
Origins of Plant
Life
– Petals can help to attract animal pollinators
petal
22.2
of Flowering
Plants
20.1 Reproduction
Origins of Plant
Life
• A stamen is the male structure of the flower.
stamen
filament
anther
– anther produces pollen grains
– filament supports the anther
22.2
of Flowering
Plants
20.1 Reproduction
Origins of Plant
Life
• The innermost layer of a flower is the female carpel.
stigma
carpel
style
ovary
– stigma is sticky tip
– style is tube leading from stigma to ovary
– ovary produces female gametophyte
22.2
of Flowering
Plants
20.1 Reproduction
Origins of Plant
Life
Flowering plants can be pollinated by wind or animals.
• Flowering plants pollinated when pollen grains land on
stigma.
• Wind pollinated flowers have small flowers and large
amounts of pollen.
22.2
of Flowering
Plants
20.1 Reproduction
Origins of Plant
Life
• Animal pollinated flowers have larger flowers and less
pollen.
– many flowering plants pollinated by animal pollinators
pollen grains
– pollination occurs as animal feeds from flower to flower
– animal pollination more efficient than wind pollination
22.2
of Flowering
Plants
20.1 Reproduction
Origins of Plant
Life
Fertilization takes place within the flower.
• Male gametophytes, or pollen grains, are produced in the
anthers.
– male spores produced in
anthers by meiosis
– each spore divides by
mitosis to form two
haploid cells
– two cells form a
pollen grain
single pollen grain
22.2
of Flowering
Plants
20.1 Reproduction
Origins of Plant
Life
• One female gametophyte can form in each ovule of a
flower’s ovary.
– four female spores produced in ovule by meiosis
– one spore develops into female gametophyte
- female gametophyte contains seven cells
· one cell has two nuclei, or polar nuclei
· one cell will develop into an egg
22.2
of Flowering
Plants
20.1 Reproduction
Origins of Plant
Life
• Pollination occurs when a pollen grain lands on a stigma.
pollen tube
sperm
stigma
– one cell from pollen grain forms pollen tube
– other cell forms two sperm that travel down tube
22.2
of Flowering
Plants
20.1 Reproduction
Origins of Plant
Life
• Flowering plants go through the process of double
fertilization.
female
gametophyte
egg
sperm
polar nuclei
ovule
22.2
of Flowering
Plants
20.1 Reproduction
Origins of Plant
Life
endosperm
• Flowering plants go through the process of double
fertilization.
– one sperm fertilizes
the egg
seed coat
– other sperm unites
with polar nuclei,
forming endosperm
– endosperm provides
food supply for
embryo
embryo
22.2
of Flowering
Plants
20.1 Reproduction
Origins of Plant
Life
• Each ovule becomes a seed.
• The surrounding ovary grows into a fruit.