land colonisation Flashcards
the eras
- combustion explosion
- Palaeozoic era: 541 - 252 mya
- great dying
- Mesozoic era: 252-66 mya
- dinosaurs
- Cenozoic era: 66mya - now
combustion explosions -> paleozoic era -> grey dying -> mesozoic era = water based life
mesozoic era -> dinosaurs -> cenozoic era = moved to land after over 3billion years in water
Why move to land in the first place
Plants
- need photosynthesis
- moving to land creates problems with water but much more advantageous for other components
- more CO2, more light
- ^ poorly soluble in water so better on land because water disperses light much stronger than the atmosphere
- as plants colonised land –> consumed almost all carbon out of the atmosphere and replaced it with oxygen
Animals
- needs oxygen and plants for food
- moved to land for more oxygen
Order of arrivals onto land
- Cyanobacteria
- Fungi
- Plants
Cyanobacteria
form protective biofilms to withstand dehydration
Fungi
made of a network of strands – mycellium
- individual strands = hyphae (tightly pressed together to create mycellium)
- good at absorbing and retaining moisture
cannot photosynthesis so need to get food some other way:
- breathing down organic matter (usually)
- if no organic matter, eat cyanobacteria but also form a partnership with them
can be in the form of lichens - symbiosis of fungus and alga
- fungus and lichens facilitate soil formation that enable the arrival of land plants - prepare ground for arrival of plants
role of algae - provide food
role of fungus - protect algae from dehydration
Plants (problems plants had to solve to transition on to land)
- dehydration / water loss
- salinity
- water absorption
- territory/space under sun
- movement/ dispersal
- Dehydration / water loss
Cuticle - protects surface from dehydration
+
Stomata - regulates CO2 intake/water loss
- opens and closes at different times
- Stoma - ‘mouth’ of leaf
Sporopollenin - a plastic like chemical that forms the tough outer shells of spores and pollen
- only because of sporopollenin that plants can escape water
- Salinity
The further inland, the harder to find salt
Didn’t have to solve this ‘problem’ because all land plants are a subgroup/derived of algae
- all water on land comes from rain, which has no salt
- not a problem for most marine plants but freshwater algae (Charophytes) are already adapted to low salt in condition, so it is easier for them to make a transition to land
- all land plants are descended from (highly unusual) fresh water algae
- Water absorption
liverworts resemble the earliest plants to colonise land
- rely on fungus to absorb water and animals (mycorrhiza)
- at least 80% of modern plant species have fungal symbiotes aka mycorrhiza
roots and mycorrhiza share many similarities
- roots created so no need mycorriza
- Territory/space under sun
space is not an issue in the ocean but on land, 2 liverworts would quickly compete for room
Stems! allows layers for space
- only point of having stem is competition for well lit space
- a battle for space under the sun
- not a peaceful kingdom, but process is a lot smaller
- Movement/dispersal
at least once per generation
- only way to prevent extinction from fire/virus etc.
- plants cannot because of cell wall
a) wind dispersal of pollens and spores
b) animal dispersal
Wind dispersal of pollens and spores (a)
- spores: single cell that after disposal, asexually develops into mature organism
- many groups of plants, fungi and animals have spores
problem: very low likelihood of finding correct partner
- don’t know if pollen will blow in the right direction
Animal dispersal of pollens and spores (b)
angiosperms (flowering plants) makes animals their main strategy
- wants us to be attached to them so we do their bidding
- much more efficient to recruit animals to dispose pollens, fruits, seeds etc.
- some have ‘exclusive deals’ with their pollinators
- from plants POV, agriculture is also symbiosis with animals
- bees like flowers so disperse everywhere
artificial selection vs. natural selection
landscapes
Palaeozoic landscapes - dominated by pteridophytes (giant ferns…)
Mesozoic landscapes - dominated by gymnosperms (conifers, cycads, ginkgod)
Cenozoic landscapes - dominated by angiosperms
- explosion of angiosperm diversity concluded with the appearance of active pollution
Ginkgod
Theorised to have been spread by meat eating dinosuars
Ginkgods are not big/not small and secrete scent of decaying body
An orphan plant from the mesozoic era that lost its pollinators
