1. Support and Structure:
* Algae: Live submerged in water, relying on buoyancy for support.
* Land plants: Developed structural support to stand upright against gravity. This included the evolution of:
* Cell walls: Made of cellulose, providing rigidity.
* Vacuoles: Filled with water, providing turgor pressure for support.
* Specialized tissues: Xylem for water transport and phloem for nutrient transport, allowing for taller growth.
2. Water Regulation:
* Algae: Directly absorb water from their surroundings.
* Land plants: Developed adaptations to prevent water loss:
* Cuticle: A waxy, waterproof coating on leaves and stems.
* Stomata: Tiny pores on leaves that can open and close to regulate gas exchange and water loss.
* Roots: Specialized structures that anchor the plant and absorb water from the soil.
3. Reproduction:
* Algae: Reproduce mainly by spores, which are dispersed in water.
* Land plants: Developed more complex reproductive structures:
* Alternation of generations: A life cycle with both haploid (gametophyte) and diploid (sporophyte) stages.
* Pollen: A protective structure for sperm, allowing for pollination by wind or insects.
* Seeds: Enclosed embryos with a protective coat, providing a mechanism for dispersal and dormancy.
4. Nutrient Acquisition:
* Algae: Absorb nutrients directly from the water.
* Land plants: Developed roots to access nutrients from the soil.
* Mycorrhizae: Symbiotic relationships with fungi that help land plants access nutrients.
5. Photosynthesis:
* Algae: Carry out photosynthesis, but their structure may be less efficient due to lack of support and water loss.
* Land plants: Developed specialized leaves with a larger surface area for photosynthesis.
* Chloroplasts: Organelles that contain chlorophyll and carry out photosynthesis, are more efficient in land plants.
In summary, land plants needed to develop adaptations for support, water regulation, reproduction, nutrient acquisition, and photosynthesis to thrive in the terrestrial environment. These adaptations allowed them to exploit new niches and evolve into the diverse plant life we see today.
