Transcript 20.1 Origins of Plant Life

20.1 Origins of Plant Life
• UNIT 16: PLANTS
• Chapters 20-22
• L.14.7
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
– modern species are still common in lakes and ponds
20.1 Origins of Plant Life
• Important plant characteristics likely originated in algae
– multicellular body allowing for specialization of
cells and tissues
20.1 Origins of Plant Life
• True plants evolved through natural selection.
– Ancestral algae 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. (seeds!)
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.
– 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
– (moisture,
temperature, etc just
right)
20.1 Origins of Plant Life
21.1: Plant Cells & Tissues
KEY CONCEPT
Plants have specialized cells and tissue systems.
20.1 Origins of Plant Life
21.1: Plant Cells & Tissues
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
20.1 Origins of Plant Life
21.1: Plant Cells & Tissues
• Ground tissue is found inside a plant.
– provides support
– stores materials in roots and stems
20.1 Origins of Plant Life
21.1: Plant Cells & Tissues
• Vascular tissue transports water, minerals and organic
compounds.
– two networks of hollow
tubes
– xylem transports water
and minerals UP from
the roots to the rest of
the plant
– phloem transports
photosynthetic products
DOWN from the leaves
to the stems & roots
stem
leaf
root
20.1 Origins of Plant Life
21.2: The Vascular System
KEY CONCEPT
The vascular system allows for the transport of
water, minerals, and sugars.
20.1 Origins of Plant Life
21.2: The Vascular System
• Transpiration is the loss of water
vapor through leaves.
– water vapor exits leaf stomata
– helps pull water to the top
branches
20.1 Origins of Plant Life
21.3: Roots & Stems
KEY CONCEPT
Roots and stems form the support system of vascular
plants.
20.1 Origins of Plant Life
21.3: Roots & Stems
Roots anchor plants and absorb mineral nutrients from
soil.
• Roots provide many
functions.
– support the plant
– absorb, transport,
and store nutrients
20.1 Origins of Plant Life
21.3: Roots & Stems
Stems support plants, transport materials, and provide
storage.
• Stems have many functions.
– support leaves and flowers
– house most of the vascular system
– store water
Baobab
Cactus
20.1 Origins of Plant Life
21.3: Roots & Stems
Stems support plants, transport materials, and provide
storage.
• Stems have many functions.
– support leaves and flowers
– house most of the vascular system
– store water
– grow underground for storage
Ginger
Potato
20.1 Origins of Plant Life
21.3: Roots & Stems
Stems support plants, transport materials, and provide
storage.
• Stems have many functions.
– support leaves and flowers
– house most of the vascular system
– store water
– grow underground for storage
– form new plants
Straw
berry
20.1 Origins of Plant Life
21.3: Roots & Stems
• Some stems are herbaceous and conduct photosynthesis.
20.1 Origins of Plant Life
• Some stems can be woody,
and form protective bark.
20.1 Origins of Plant Life
21.4: Leaves
KEY CONCEPT
Leaves absorb light and carry out photosynthesis.
20.1 Origins of Plant Life
21.4: Leaves
• Guard cells surround each stoma.
– Stomata open and close when guard cells change
shape.
– When stomata are open, water evaporates and gas
exchanges.
– Stomata close at night and when plant loses too much
water.
guard cells
stoma
20.1 Origins of Plant Life
• READ BUT DON’T COPY
• Leaves may be simple, compound, or double compound.
Simple leaf
Compound leaf
Double compound leaf
20.1 Origins of Plant Life
21.4: Leaves
• READ BUT DON’T COPY
• Leaf veins may be parallel or pinnate.
Parallel veins
Pinnate veins
20.1 Origins of Plant Life
21.4: Leaves
• READ BUT DON’T COPY
• Leaf margins may be toothed, entire, or lobed.
Toothed margin
Entire margin
Lobed margin
20.1 Origins of Plant Life
21.4: Leaves
READ BUT DON’T COPY
• Leaves have many adaptations.
– for extreme temperatures,
ex: pine needles
20.1 Origins of Plant Life
21.4: Leaves
• READ BUT DON’T COPY
• Leaves have many adaptations.
– for extreme temperatures,
ex: pine needles
– for water loss,
ex: cactus spines
20.1 Origins of Plant Life
21.4: Leaves
• Leaves have many adaptations.
– for extreme temperatures,
ex: pine needles
– for water loss,
ex: cactus spines
– for aquatic environments,
ex: water lily
– for getting food,
ex: Venus’ flytrap
20.1 Origins of Plant Life
22.2: Reproduction in Plants
KEY CONCEPT
Reproduction of flowering plants takes place within
flowers.
20.1 Origins of Plant Life
22.2: Reproduction in Plants
Flowers contain reproductive organs protected by
specialized leaves.
• Sepals and petals are modified leaves.
– Sepals are outermost
layer that protects
developing flower
sepal
20.1 Origins of Plant Life
22.2: Reproduction in Plants
• A stamen is the male structure of the flower.
stamen
filament
– produces pollen grains
anther
20.1 Origins of Plant Life
22.2: Reproduction in Plants
• The innermost layer of a flower is the female part (carpel).
stigma
carpel
style
ovary
– ovary produces female gametophyte (“egg”)
20.1 Origins of Plant Life
22.2: Reproduction in Plants
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.
20.1 Origins of Plant Life
22.2: Reproduction in Plants
• 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
20.1 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
20.1 Origins of Plant Life
22.2: Reproduction in Plants
• Each ovule becomes a seed.
• The surrounding ovary grows into a fruit.