Evolution of Plants - Botany - Lecture Notes | BIOL 216, Study notes of Biology

Download Evolution of Plants - Botany - Lecture Notes | BIOL 216 and more Study notes Biology in PDF only on Docsity! Chapter 1 BOTANY: INTRODUCTION The word “botany” comes from the Greek word ‘botane’ meaning “plant.” EVOLUTION OF PLANTS Plants, algae and some bacteria are capable of photosynthesis. Life on planet Earth, with a few exceptions, depends on this process that changes radiant energy into chemical energy that can be utilized by organisms as a source of energy. LIFE ORIGINATED EARLY IN THE EARTH’S GEOLOGIC HISTORY  Condensation of the nebular material into protoplanets and meteorites.  Solidification of planets about 4.6 billion years ago. The large condensing mass at the center became the sun. During condensation, elements scattered according to a density gradient with the heavy masses forming the planets near the sun and the lighter masses forming the outer planets. Earth Chronology: 4.6 BY earth formed 4-3.8 BY life originated 3.5 BY oldest known fossils 2.5 BY photosynthesis, oxygen accumulated 2.1 BY first eukaryotes 1.2 BY eukaryotes are well established and diverse 700 MY soft-bodies multicellular life 540 MY hard-bodied multicellular life "Arrhenius and graduate student Stephen Mojzsis ... recently discovered the oldest chemical evidence of life in sedimentary rocks from Greenland. The rocks are estimated to be more than 3.85 billion years old. Carbon in these rocks had an isotope profile seen only in remains of organisms (S.J. Mojzsis et al., Nature, 384:51-9, 1996). "The evidence of the carbon signatures is crucial in arguing that life on Earth was present before 3.85 billion years ago," maintains Mojzsis. "Furthermore, the carbonaceous matter was found in intimate association with the phosphate mineral apatite, a common biologically formed substance." Phosphates exist in cell membranes, enzymes, genetic material, and biological energy molecules." http://www.the- scientist.com/yr1997/mar/research_970331.html ; The Scientist, March 31, 1997. In 1953, Stanley Miller demonstrated that amino acids and other organic compounds could be synthesized spontaneously from hydrogen gas, ammonia, methane and other compounds presumed to have been present in the second atmosphere of the Earth if energy is provided. Miller found that as much as 10 percent of the carbon in the system was converted to a relatively small number of identifiable organic compounds, and up to 2 percent of the carbon went to making amino acids of the kinds that serve as constituents of proteins. Variants of Miller’s experiment are many. The results have been similar to Miller’s, a large number of organic molecules, some found in living organisms and others not. In reproducing Miller’s experiment or its variants, it is important to keep O2 out of the reaction. Aldehydes and cyanides are first products then more complex organic compounds are synthesized. Proteinoids Fox showed that AA mixtures subject to high temperatures (150 -200ºC) in the absence of water polymerized to form proteinoids. Proteinoids have protein-like properties:  Nonrandom proportions of AA: frequency not based on the proportion of AA in the original mixture.  Some AA preferentially occupy the N― and C― terminal position.  Proteinoid have enzyme-like activity (low level catalytic activity), and increase the rate of organic reactions, e. g. split by hydrolysis, catalyzed the condensation of ATP into nucleotides, remove carboxyl groups from various molecules.  Give positive color tests with the same reagents that proteins do. Two important characteristics of proteinoids are: 1. They have catalytic activity. 2. They organize into microspheres. AA are catalytic only in peptide form. AA can polymerize in certain types of clay, volcanic sediments and hydrothermal currents. These organic molecules are presently thought to have served as a source of energy for the earliest forms of life. Droplets bounded by a double membrane and formed by boiling proteinoids. The hot solution is then allowed to cool down slowly. Microspheres may be regarded as a precursor of protocells.  They are uniform in size.  Microspheres can selectively absorb and diffuse some chemicals, grow in size, form junctions with other microspheres. Adaptations for water transport. Transport system or vascular tissue: 1. Phloem for the transport of dissolved carbohydrates. 2. Xylem for water and mineral transport. Conquest of the land by algae probably occurred after the Cambrian (590?-505 m.y.a.).  http://www.ucmp.berkeley.edu/cambrian/camb.html Factors that might have played a role in facilitating or causing the journey to the land.  A fall in sea level during the Ordovician glaciations (505-459). http://www.ucmp.berkeley.edu/ordovician/ordovician.html  Increase in oxygen allowed the formation of highly oxygenated polymers cutin and lignin.  Formation of ozone protective layer. Annual plants have a photosynthetic stem. Perennial plants have their stem covered with cork, which slows down the loss of water. Plants grow throughout their lifetime. New tissue is formed in the meristems, which contain embryonic cells capable of adding new cells to the plant body. The activity of the apical meristems increases the length of stems and roots, and is called primary growth. The activity of lateral meristems or cambium layers increases the girth of the stem and roots and is called secondary growth.  Vascular cambium and cork cambium Reproduction on land also required especial adaptations: spores and seeds. Seeds are multicellular structures that protect and provide food for the embryo. EVOLUTION OF COMMUNITIES Plants are most obvious features of the landscape. Biomes are large and distinctive regional assemblages of plants and animals controlled by climatic factors. Ecosystems are stable of associations of plant and animals that depend on photosynthesis and other factors of the non-living environment for its survival. Living and non-living environments are integrated into a functional unit. There is interaction between organisms in the ecosystems: predation, herbivory, competition, etc. APPEARANCE OF HUMAN BEINGS Human first appeared about 2 million years ago. Agriculture started about 10,500 years ago. Agriculture allowed the support of larger populations of humans that began to gather into towns and villages. The increase food supply allowed the development and specialization of human culture. There are subdivisions of botany: taxonomy, physiology, genetics, etc. GENETIC ENGINEERING Genetic engineering has made possible the transfer of genes between entirely different species. It has resulted in the development of transgenic plants.