Download Biology CP- 19.1

19
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)
19
20.1 Origins of Plant Life
Kingdom Plantae
• Characteristics of all plants
–Multicellular
–Autotrophic
–Eukaryotic
19
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
19
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
19
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
•
•
•
•
Cell walls- 20-60% cellulose
Similar chloroplasts
Similar mitosis and cytokinesis
Similar genes and rRNA sequences
19
20.1 Origins of Plant Life
• True plants evolved through natural selection.
19
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
19
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
19
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
19
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
19
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
19
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
19
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
19
20.1 Origins of Plant Life
• Plants have adaptations that prevent animals from eating
them.
– spines and thorns
– defensive chemicals