plant evolution

lecture 2

what do living organisms require (2)

• self sustain: obtain and use energy

• self replicate: using DNA or RNA

how does genetic variation arise overtime

replication mistakes (mutations)

life on early earth

• earth is 4.5 billion years old

• Earliest microfossils of organisms (bacteria) are ~3.5 billion years old

• no oxygen

• most early life aquatic

2 kinds of living organisms

1. prokaryotes

2. eukaryotes

prokaryotes

• no cell nucleus or membrane-bound organelles

• smaller

• ex. ccyanobacteria

eukaryotes

• have nucleus and membrane-bound organelles

• larger

• ex. plant cells

cyanobacteria (first photosynthetic organisms)

• early bacteria used chemical energy, but cyanobacteria could use light energy to produce food molecules

• their photosynthesis changed Earth's atmosphere by releasing oxygen.

• prokaryotes, not plants

stromatolites

fossilized stromatolites, formed by cyanobacteria, provide some of the earliest evidence of life on earth

chloroplast

• structure inside a plant cell where photosynthesis occurs

• chloroplasts and the ability to photosynthesize arose from abt 1 billion years ago from the uptake of one of these cynaobacteria into another cell

plant eukaryotic cells

single celled algae; can see on things that have been sitting out in the rain or in ponds

5 plant kingdoms

1. protozoa

2. chromista

3. animalia

4. fungi

5. plantae

temperature

water: stable, moderate

land: extreme & fluctuating

nutrients

water: dissolved in water, easily accessible

land: mostly in soil, harder to access

light

water: less intense, decreases w depth

land: stronger UV exposure and possible shading

gravity & wind

water: provides support

land: must withstand gravity & wind

cell wall

• made of cellulose

• provides structural support and rigidity

chloroplasts

small organelles required for for photosynthesis

other plastids

involve in storage of pigments, starch, etc…

vacuole

large organelle containing water, sugars and salts that provides pressure for support

plant colonization of land

• likely occurred slowly through transitional environments, e.g., intertidal zones or areas with frequent flooding

• Early terrestrial plants were mosses and liverworts; non-vascular so limited to wet and damp environments

mosses

• early land plants

• small, non-vascular plants that could not actively transport water and nutrients

vascular tissue

• tissue that can support materials (water and nutrients) throughout the body

• evolved into fossil record

2 types of vascular tissue

1. xylem

2. phloem

xylem

tissue transports water

phloem

tissue transports sugars, hormones and other substances

true roots

• contain vascular tissue and anchor plants against forces that move them

club mosses

• vascular mosses that started growing bigger

• among first vascular plants

• reproduce spores

spores

• tiny cells that float and grow a new plant

• not seeds bc don’t have seed coat

larger leaves (megaphylls)

• major step in plant evolution

• photosynthetic stems (capture more sunlight for photosynthesis)

• vascular tissue veins help transport water and sugars throughout leaf

• all true trees have megaphylls, even conifers w small needle-shaped leaves

why are larger leaves not always better

increase water loss, so plants in dry environments may benefit from smaller leaves

what do plants do for the earth’s atmosphere

produce oxygen and take up CO2