BIOL 1120 REEDER
MOVEMENT OF THE PLANTS TO LAND
I. The Aquatic Environment
A. Advantages
1. Richly supplied with nutrients
2. Prevents desiccation of plant cells
3. Buoyant support so that special supporting structures are unnecessary
4. Convenient medium for both the meeting of gametes in sexual reproduction and the dispersal
of flagellated, asexual spores
5. Narrow temperature ranges due to water's properties
6. Water can filter potentially damaging wavelengths of light energy
II. The Terrestrial Environment
A. Advantages
1. More available light; water absorbs many of the significant wavelengths needed for
photosynthesis at the greater depths
2. In the air: higher concentrations of CO2 for photosynthesis and O2 for cell respiration
B. Disadvantages
1. Loss of body water occurs easily via evaporation
2. Overexposure to sunlight (ultraviolet radiation) damages nucleic acids
3. Air is less dense than water providing less support
4. Temperature changes are wider and more rapid than in water: impacts chemical reaction rates
5. Need of some means to transport sperm to the egg to fertilize
C. Challenges facing a terrestrial existence
1. Obtaining water, gases (O2, CO2), energy and minerals for metabolic needs
2. Bringing the gametes together for fertilization
3. Support for the body
4. Preventing desiccation (excessive water loss)
5. Tolerating widely varying temperature extremes, especially in temperate and polar regions
III. Plant Adaptations to land
A. Innovations
1. Obtaining water and anchorage: roots (absorptive organ) serve to absorb water and essential
dissolved minerals from the soil plus provide support; with continuous vascular tissue
utilized to transport essential materials
2. Gas exchange and regulation: the leaf (guard cells and stoma)
3. Preventing desiccation and UV protection: plants possess a water-insoluble, waxy covering
called a cuticle over their epidermal cells in which its thickness varies, i.e. thin in moister
habitats or thicker in drier ones
a. Stomata (openings primarily in the leaf and in some types, the stem epidermis)
surrounded by a pair of guard cells for gas exchange and water loss
1) Hormonal regulation
a) abscisic acid can close the stomata during periods of water shortage
bio1120_mvmt_of_plants.doc 3/17/09
