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Plant Adaptations to Terrestrial Environment: From Aquatic to Land-Dwelling Organisms - Pr, Study notes of Biology

The advantages and disadvantages of the aquatic and terrestrial environments for plants, focusing on their adaptations to land. Topics include obtaining water and anchorage, gas exchange and regulation, preventing desiccation and uv protection, obtaining sufficient energy, and tolerating temperature extremes. The document also covers reproductive adaptations in both lower and higher forms.

Typology: Study notes

Pre 2010

Uploaded on 08/18/2009

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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
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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 CO 2 for photosynthesis and O 2 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 (O 2 , CO 2 ), 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/

bio1120_mvmt_of_plants.doc 3/17/

b. The cuticle plus photosynthetic pigments also serve as UV protection c. Shedding leaves is an adaptation to the winter dryness: roots cannot absorb water from ground that is cold or frozen; by leave shedding, water loss is reduced during winter dormancy

  1. Obtaining sufficient energy for photosynthesis: Leaf as the specialized organ a. Some plants obtain adequate sunlight by growing tall 1) Production of the strengthening material found in plant cell walls = lignin 2) Structural supporting cells called fibers 3) Turgor of the parenchyma b. Other plants have adapted to lower light intensities 1) seedling of flowering plants require less light than the gymnosperms
  2. Tolerating widely varying temperature extremes: a. Evaporative cooling principally from the leaf's surface via stomata as regulated by guard cells b. Many plants spend winter in a dormant state: aerial parts die in the winter, while underground parts remain alive; new aerial shoots are sent out in the spring.
  3. Reproductive adaptations: a. Lower plants have sex organs that are generally multicellular (gametangia) possessing a cell layer that surrounds and protects the gametes (egg & sperm); in higher forms, gametangia may be unicellular but is enclosed by reproductive tissue of the cone or flower 1) Female gametangium = archegonium 2) Male gametangium = antheridium b. After fertilization, the fertilized egg develops into a multicellular embryo within the archegonium where it is protected and nurtured c. Loss of both flagellated motile sperm, as well as a dependency on water in order to fertilize, characterizes advanced forms 1) Lower forms are still dependent on external water for fertilization; asexual reproduction occurs more frequently as related to water's availability. 2) Higher forms utilize pollination via air currents or animals followed by pollen tube formation that carries the sperm to the egg(s) resulting in fertilization. d. The seed replaces the spore as the means for species dispersal both in gymnosperms and angiosperms.