Question

Describe the major innovations, from earliest (most ancient) to most recent, that made plants progressively more able to cope with dry conditions on land. Include the 4 major groups of land plants

Answer 1

Earliest plants were living in water but as plant evolved more, they moved from water to terrestrial condition. This lead them to evolve in themselves special adaptations so that they can face dry climatic conditions.

Some of the adaptations are -

1. Bryophytes which live in water were having gametophyte as the dominant plant generation but pteridophytes gymnosperms and angiosperms have sporophyte as the dominant plant generation. This reduction in the type of gametophyte and eventual evolution of sporophyte occurred because sporophyte was photosynthetically more active than gametophyte and it was able to tolerate dry climatic conditions easily in comparison to the gametophyte.

2. Roots and root system present in bryophytes was not well developed. This was because they lived in water and do not need to absorb it from soil. But pteridophytes have an elaborated system of roots and much more elaborated and differentiated system of root and root hairs is found in gymnosperms and angiosperms. It is because they are large in comparison to bryophytes and pteridophytes and they absorb water from soil. To absorb water efficiently from the soil, a well developed elongated root system was required.

3. Vascular tissue was absent in bryophytes because the conduction of water and nutrients across small plant body took place with the help of water in which they lived. But a primitive type of vascular tissue is present in pteridophytes and gymnosperms and a very well developed vascular tissue including xylem and phloem is present in angiosperms. Xylem is responsible for the transportation of water from soil through roots to the aerial parts of the plant and phloem is responsible for the transportation of Sugars from leaves to the other parts of the plant.

4. Bryophytes lived in water and therefore did not face any problem related to the deficiency of water. But pteridophytes and gymnosperms and angiosperms who live in Terrestrial environment face water deficiency problem due to water loss by evapotranspiration. This is prevented by the presence of cuticle on the surface of the plant body and hair.

These are the four major adaptations which help the plants to survive in dry climatic conditions on the land.

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