-
Terrestrial surface of Earth
Lifeless for most of history
-
Possible benefits of early life on land?
- Unfiltered sunlight
- Higher CO2 concentrations
- Fewer herbivores and pathogens (during initial land colonization)
- Nutrient rich soils
-
Key adaptations to challenges and benefits of land distinguish major groups
- Vascular tissue
- Seeds
- Flowers
-
Bryophytes
- Non-vascular plants (have no xylem and phloem)
- Tend to be small and live in moist places
- Ex: mosses, liverworts, hornworts
-
Bryophytes vascular tissue
- Tissue made up of cells that join to form tubes that transport water, nutrients, and sugars
- Xylem and phloem
-
Xylem
- Dead tracheid or vessel element cells form tubes that transports water from root to shoot
- Contain lignin: hard polymer that provides structural support for xylem
-
Tracheids
- Long, thin xylem cells
-
Vessel element
- Shorter, thicker xylem cells
-
Phloem
- Living sieve tube cells form tubes that transport sugar formed via photosynthesis from leaves to the rest of the plant
-
Why would the lack of vascular tissue result in bryophytes being short?
- They can't transport nutrients and water over long distances effectively
- Lack of structural support from lignin in xylem cells
-
Bryophytes Reproduction and limitations
Sperm are flagellated. This requires water for fertilizaition
-
Dispersal by spores
Reproductive cells (single celled)
-
Seedless Vascular Plants
- Ferns
- Representative group=Pteridophytes
- First plants to grow tall
-
Seedless vascular plants
Sperm is still flagellated and dispersed by spores (single celled)
-
Gymnosperms and Angiosperms
Seed plants
-
Key differences between seed and seedless plants?
-
Ovule
- Structure in which egg (female gamete) of plant is produced
- Has protective covering: integument
-
Pollen grain
- Contains male structures that produce sperm (male gamete of plants within a protective pollen wall
- Sperm delivered to egg via pollen
- Sperm is no longer flagellated and need water
-
Benefits of pollen delivery of sperm over free flagellated sperm?
- MUCH greater distribution potential over flagellated sperm
- Doesn't require water for movement
- Can be transported on animals or wind
- Protective pollen wall prevents desiccation
-
Seeds
- Primary dispersal mechanism of seed plants
- Diploid plant embryo + food supply + seed coat
-
How does an ovule develop into a seed
Initiated by pollination (transfer of pollen to portion of seed plant that contains ovules
-
Pollen tube
- Pollen grain grows this which releases sperm into the female portion where eggs are
- Fertilization of egg by sperm begins transition from ovule to seed
-
Why is seed dispersal beneficial over spore dispersal in size?
- Spore: usually single celled
- Seed: multicellular embryo
-
Why is seed dispersal beneficial over spore dispersal in protection post-dispersal from parent plant?
- Spore: none
- Seed: protective seed coat from integument
-
Why is seed dispersal beneficial over spore dispersal in post-dispersal resource supply?
- Spore: none
- Seed: food supply
-
Why is seed dispersal beneficial over spore dispersal in length of dormancy?
- Spore: usually relatively short
- Seed: up to hundreds of years (sometimes thousands)
-
Gymnosperms
- Bear "naked" seeds (aka not contained in fruit)
- Seeds often form on cones: conifers= cone-bearing plants
-
Gymnosperm Reproduction
- Sperm no longer flagellated (contained within pollen grain)
- Primary dispersal route: seeds
-
Ovulate cones
- Contain ovules and seeds
- Larger (rigid structure)
-
Pollen cones
- Produce pollen
- Smaller and not what is stereotypically seen
-
How are gymnosperms pollinated?
- Wind pollinated
- No adaptations for pollinator attraction
- Produce massive clouds of pollen
-
Angiosperms
- Seed plants with flowers and fruits
- 90% of all plant species
- Seeds "contained" in fruit as opposed to "naked" gymnosperm seeds without fruit
- Sperm also contained in pollen grain and dispersal through seeds
-
Flowers
- Mode of sexual reproduction in angiosperms
- Composed of 4 whorls of modified leaves
-
Whorl
Structures arranged in a circle
-
-
Sepal
Sterile outermost whorl that protect flowers before opening
-
Petals
Sterile whorl often used in pollinator attraction
-
Stamen
- Male portion of the flower
- Includes anther (site of pollen production) held up by filament
-
Carpel/Pistil
- Female portion of a flower
- Sticky stigma=site of pollen deposition
- Style: holds it up
- Ovary containing ovule (produces eggs)
|
|
