Plants

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Plants

• 2 general groups
• 1. bryophytes (non vascular plants)
• 2. vascular plants
• Adaptations for colonizing land
• Vascular plants only
• 1. cuticle waxy covering, but with stomata
• 2. symbiosis with mycorrhizal fungi
• 3. vascular tissue xylem and phloem
• -distributes H2O and food
• -allowed for stems, leaves, roots
• 4. ability to adjust to variable H2O
  availability
• -dormancy when dry

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• 5. pollen sperm no longer need H2O
• to travel
• 6. seeds protect embryo, prevent
  dessication
• 7. diploid dominance most of life cycle
• is diploid

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Plant Life Cycle

• Alternation of Generations
• -diploid generation sporophyte
• -haploid generation gametophyte
• Bryophytes gametophyte dominates
• Vascular plants sporophyte dominates

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Angiosperms

• The most successful plants
• -over 250,000 species
• -dominate most terrestrial communities
• -source of most of our food, clothes,
  medicine
• -Rise to dominance 80-90 million years ago
• -rapid adaptive radiation
• Why?
• 1. flower gamete transfer over long
  distances
• - No H2O needed
• co-evolution with animals
• -flower color, structure, scent
• 2. fruit dispersal of offspring (seeds)

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Transport in plants

• Movement of water
• 1. Transpiration loss of water by evaporation
  from leaves
• -driven by heat of sun
• -lowers pressure in leaves (spongy mesophyll),
  water moves in to replace evaporated water
• 2. Cohesion attraction between H2O molecules
• -water is pulled up through the xylem
• 3. Osmosis
• -water moves into the root hairs from soil
  because
• 1. lower pressure from water moving up xylem
• 2. higher solute conc. in root hair cells
• -ions pumped in by active transport
• root pressure at night water diffuses in
  and pushes water
• into xylem

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• Regulation of transpiration
• Stomatal guard cells
• -when turgid change shape open
• -plant pumps K ions into them
• (hyperosmotic), water rushes in
• - CO2, light, temp. control it
• Carbohydrate movement
• translocation movement of sugars through
  phloem
• -sucrose in transport
• -starch stored in leaves, roots

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Regulation in Plants

• Hormones
• -chemical messenger within organism
• -influence physiology of cells they contact
  (target cells)
• -glands in animals but not in plants
• -control growth, differentiation, etc.
• 5 groups of plant hormones
• -auxin, cytokinins, gibberelins, ethylene,
• abscisic acid
• Tropisms responses to external stimuli
• -phototropism - light
• -gravitropism (geotropism) gravity
• -thigmotropism touch
• Photoperiodism
• -response to seasonal change
• -measured by changes in length of day/night
• Flowering, leaf abscission, etc.

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