20.1 Origins of Plant Life KEY CONCEPT Plant life began in the water and became adapted to land.
Dec 26, 2015
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
– Ancestral charophyceans lived in areas of shallow water.
• True plants evolved through natural selection.
– 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.
sugars
water and mineral nutrients
– 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
20.1 Origins of Plant Life
• Lignin allows plants to grow upright.
– hardens cell walls of some vascular tissues– provides stiffness to stems
plant cells
lignin
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.
– defensive chemicals
– spines and thorns
20.1 Origins of Plant Life
KEY CONCEPT Plants have specialized cells and tissue systems.
21.1 Plant Cells and Tissues
20.1 Origins of 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 Plant Cells and Tissues
20.1 Origins of Plant Life
– they are strong and flexible.– celery strings are strands of collenchyma.– they have unevenly thick cell walls.
• Collenchyma cells provide support to a growing plant.
21.1 Plant Cells and Tissues
20.1 Origins of Plant Life
– second cell wall hardened by lignin– die when they reach maturity – used by humans to make linen and rope
• Sclerenchyma cells are the strongest plant cell type.
21.1 Plant Cells and Tissues
20.1 Origins of 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 Plant Cells and Tissues
20.1 Origins of Plant Life
– provides support – stores materials in roots and stems – most commonly made of parenchyma
• Ground tissue is found inside a plant.
21.1 Plant Cells and Tissues
20.1 Origins of Plant Life
stem
leaf
root
– two networks of hollow tubes
– xylem transports water and minerals
– phloem transports photosynthetic products
• Vascular tissue transports water, minerals and organic compounds.
21.1 Plant Cells and Tissues
20.1 Origins of Plant Life
KEY CONCEPT The vascular system allows for the transport of water, minerals, and sugars.
21.2 The Vascular System
20.1 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
vesselelement
tracheid
21.2 The Vascular System
20.1 Origins of Plant Life
– Plants passively transport water through the xylem.– Cohesion is the tendency of water molecules to bond
with each other.
• The cohesion-tension theory explains water movement.
– Adhesion is the tendency of water molecules to bond with other substances.
21.2 The Vascular System
20.1 Origins of Plant Life
– absorption occurs at roots
• Water travels from roots to the top of trees.
– cohesion and adhesion in xylem– transpiration at leaves
21.2 The Vascular System
20.1 Origins of Plant Life
– water vapor exits leaf stomata– helps pull water to the top
branches
• Transpiration is the loss of water vapor through leaves.
21.2 The Vascular System
20.1 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 The Vascular System
20.1 Origins of Plant Life
– plants actively transport sugar from the source– sugar flows to the sink due to pressure differences
sugars
phloem xylem
water
Sugars move from their source, such as photosynthesizing leaves, into the phloem.
1
The sugars move into the sink, such as root or fruit, where the are stored.
3
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.
2
• The Pressure-flow model explains sugar movement.
21.2 The Vascular System
20.1 Origins of Plant Life
KEY CONCEPT Reproduction of flowering plants takes place within flowers.
22.1 Plant Life Cycles
20.1 Origins of 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
fertilizationfertilization
meiosismeiosis
SPOROPHYTE PHASE
GAMETOPHYTE PHASE
22.1 Plant Life Cycles
20.1 Origins of Plant Life
– sporophyte phase is diploid – begins with fertilized egg – spores produced through
meiosis
• The gamete-producing plant is the mature gametophyte.
• The spore-producing plant is the mature sporophyte.
– gametophyte phase is haploid– begins with spore – gametes produced through
mitosis
22.1 Plant Life Cycles
20.1 Origins of Plant Life
sepal
Flowers contain reproductive organs protected by specialized leaves.
• Sepals and petals are modified leaves.– Sepals are outermost
layer that protectsdeveloping flower
22.2 Reproduction of Flowering Plants
20.1 Origins of Plant Life
– Petals can help to attract animal pollinators
petal
22.2 Reproduction of Flowering Plants
20.1 Origins of Plant Life
• A stamen is the male structure of the flower.
– anther produces pollen grains – filament supports the anther
stamen
filament anther
22.2 Reproduction of Flowering Plants
20.1 Origins of Plant Life
carpel style
stigma
ovary
• The innermost layer of a flower is the female carpel.
– stigma is sticky tip – style is tube leading from stigma to ovary – ovary produces female gametophyte
22.2 Reproduction of Flowering Plants
20.1 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 Reproduction of Flowering Plants
20.1 Origins of Plant Life
• Animal pollinated flowers have larger flowers and less pollen.
pollen grains
– many flowering plants pollinated by animal pollinators
– pollination occurs as animal feeds from flower to flower– animal pollination more efficient than wind pollination
22.2 Reproduction of Flowering Plants
20.1 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 twohaploid cells
– two cells form asingle pollen grain pollen grain
22.2 Reproduction of Flowering Plants
20.1 Origins of Plant Life
– 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
• One female gametophyte can form in each ovule of a flower’s ovary.
22.2 Reproduction of Flowering Plants
20.1 Origins of Plant Life
• Pollination occurs when a pollen grain lands on a stigma.
pollen tubepollen tube
spermsperm
stigmastigma
– one cell from pollen grain forms pollen tube– other cell forms two sperm that travel down tube
22.2 Reproduction of Flowering Plants
20.1 Origins of Plant Life
• Flowering plants go through the process of double fertilization.
femalegametophyte
ovule
egg
sperm
polar nuclei
22.2 Reproduction of Flowering Plants
20.1 Origins of Plant Life
endosperm
seed coat
embryo
– one sperm fertilizes the egg
– other sperm unites with polar nuclei, forming endosperm
– endosperm provides food supply for embryo
• Flowering plants go through the process of double fertilization.
22.2 Reproduction of Flowering Plants
20.1 Origins of Plant Life
• Each ovule becomes a seed.• The surrounding ovary grows into a fruit.
22.2 Reproduction of Flowering Plants