First organisms on Earth were fully aquatic. About 460 mya a lineage of algae moved onto land and gradually adapted to air and soil. Name two evolutionary problems that first land plants faced when transitioning from water to land?

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Examples of physiological problems and the adaptations of plants: 
1) Body support. As organisms in water face lower pressure than in air, algae did not need to have composite body parts. When moved onto land, plants developed roots to be secured in soil and stems to support their body weight. 
2) Exposure to direct sunlight and higher O2 . Plants have to become more resistant to new external conditions and adapted their photosynthetic processes to harness more light and CO2. 

Other adaptations: 
- different medium for reproduction. Spores were now dispersed in air and not water. 
- eggs were not dispersed at all and plants developed special organs to protect eggs.
- sperms were dispersed through ground water
-  later in evolutionary years plants developed flowers to be pollinated
and so on. 

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