Transcript 20.1 Origins of Plant Life

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20.1 Origins of Plant Life
KEY CONCEPT
Plant life began in the water and became adapted to
land. (Charophytes are the ancestors of plants)
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20.1 Origins of Plant Life
Kingdom Plantae
• Characteristics of all plants
–Multicellular
–Autotrophic
–Eukaryotic
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20.1 Origins of Plant Life
• Plants faced difficulties to maintain life on land
–Obtaining resources- from air and soil- special organs
–Staying upright- support tissues-lignin-c. wall
–Maintaining moisture-waxy cuticle, stoma-pores on leaf
–Reproducing- protective jacket for gametes, eggs remain
in female parent where they are fertilized
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20.1 Origins of Plant Life
• Important plant characteristics likely originated in
charophytes.
– multicellular body allowing for specialization of
cells and tissues
– cell division that allows for chemical communication
between cells
– reproduction involving sperm swimming to egg
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20.1 Origins of Plant Life
• True plants evolved through natural selection.
– Ancestral charophytes 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
Evidence: Charophytes are ancestors of
green plants
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Cell walls- 20-60% cellulose
Similar chloroplasts
Similar mitosis and cytokinesis
Similar genes and rRNA sequences
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20.1 Origins of Plant Life
• True plants evolved through natural selection.
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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.
Maintaining moisture
• A cuticle allows plants to retain moisture.
– waxy, waterproof layer
– holds moisture in
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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 (CO2 and O2)
– Closing holds in moisture
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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 (lignin)
xylem
phloem
water
and
mineral
nutrients
sugars
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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
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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
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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
inside the ovary of a
female plant
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20.1 Origins of Plant Life
Alternations of Generations- Taking turns
A plant's life cycle alternates between the gametophyte
and sporophyte generations.
Gametophytes produce gametes
Sporophytes produce spores
Four major
Groups of
plants:
bryophytes,
pteridophytes,
gymnosperms,
and
angiosperms.
20.1 Origins of Plant Life
Spores differ from gametes
1. Spores can develop into a new organism with fusing or
mating.
1. Gametes must fuse- zygote
2. Spores have tough, protective coats to resist harsh
conditions
1. Gametes are affected by harsh conditions-cold,
heat, drying.
20.1 Origins of Plant Life
4 Main plant Groups
1. Bryophytes- mosses- oldest
– No seeds, no lignin-hardened vascular tissue
2. Pteridophytes- ferns
- No seeds, have lignin-hardened vascular tissue
3. Gymnosperms- cone-bearing plants
- First to have seeds-”naked seeds”- no chamber
-
Specialized leaves
Seeds- embryo with a food store
Plants can spread via seeds without drying out.
4. Flowering plants- angiosperms
- Seeds in ovaries- protection, dispersal
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20.1 Origins of Plant Life
• Plants have adaptations that prevent animals from eating
them.
– spines and thorns
– defensive chemicals