Origin of Terrestrial Adaptations

Fossil records of plants are hard to come by since they are only fossilized if they were next to a body of water or preserved in tree sap

First fossil plant remains date back 475 million years

Embryophytes: land plants

Evolved from ancestral green algae
Embrophytes received many characteristics from green algae
- Photosynthesize using chloroplasts
- Store sugars produced as starch
- Cellulose-rich cell walls
However, there are some differences. The algae
- weren't always multicellular
- didn't produce embryo
- exclusively exist in aquatic environments
Predators may have helped land plant evolution because any plant that could adapt to the shoreline was beyond the reach of herbivores
Advantages to terrestrial life
- Unfiltered sunlight
- More concentrated carbon dioxide levels
- Soil rich in minerals
- Originally less competition for resources and fewer herbivores/pathogens
Disadvantages to terrestrial life
- Gravity
- Radiation
- Limited water supply
- Existing in two different environments

Terrestrial Challenges & Embryophyte Solutions

Adaptations

Desiccating atmosphere: air is drying & water is usually confined to soil making desiccation-resistance necessary for aerial plant parts
1. Stomata - special epidermal openings that can open and close, regulating gas exchange and helping to restrict water loss
2. Sporopollenin - protective coating of spores and pollen that protects these reproductive cells from drying out
  - most decay-resistant biological material known
3. Cuticle - waxy coating on outer surface of plant that prevents drying out
  - exuded by epidermal cells in contact with atmosphere
  - gas exchange is limited so there are small openings for absorbing carbon dioxide from air
  - these pores eventually became separate guard cells that open and close to control water escaping form stomata
Relative scarcity of water: sea life ensures algae is surrounded by water but water is scarce on land & is usually confined to soil
1. Protected embryo - early embryonic growth is protected and nurtured on the parent plant
2. Roots/rhizoids - specialized organs that extract water and minerals from soil
3. Vascular system - internal tissue that transports water and dissolved minerals throughout plant, otherwise known as veins
  - as land crowded, competition for light increased
    - productivity was increased by increasing surface area for photosynthesis
    - required improvements to absorbing and transporting water
    - true roots could now form from rhizoid counterparts along with true leaves
    - grew taller because xylem and phloem tissues helped transport water and distribute nutrients between roots and shoots
      - roots were delving deeper into soil, could no longer photosynthesize, and needed sugar transported to them
      - shoots and true leaves formed further away from soil so they needed water & minerals transported to them
Structural support against gravity: aquatic plants get structural support from buoyancy and external pressure of water
1. Lignin - rigid, woody compound that reinforced the cell walls of vascular tissue and acts as an internal skeleton for plants
  - necessary as plants grew taller
  - reason for woodiness in land plants not found in aquatic plants
Uptake of carbon dioxide and absorption of nutrients: algae's whole bodies were surrounded by gas and mineral-containing water. Land has higher concentrations of these but is separated into air & soil and necessitated specialization in plant parts exposed to them
1. Stomata/pores - special openings in epidermis that allow gas exchang e
  - necessary since cuticle blocks gas flow
2. Roots/rhizoids - specialized organs that extract water & minerals from soil
3. Mycorrhizal associations - symbiotic fungi that interact with roots and increase absorption of water and nutrients from soil
  - ancestral land plants developed mutualistic relationships with mycorrhizal (growing in association with roots) fungi in the soil
    - speculated that a fungus attacked a plant but failed to kill it and began feeding it with minerals from soil while extracting the plant's sugars
    - today they aid in water & nutrient uptake by increasing surface area of plant roots which in turn give them sugars

	Created by Sophia Wright about 5 years ago

1 Plant Biology 101 Note on Unit 2: Land Plant Evolution, created by Sophia Wright on 20/09/2019.