BIOL 425/001CHAPTER 1 NOTES Life on earth is dependent on photosynthesis Only plants, algae, and some bacteria carry out this process Humans rely on plants for just about everything Evolution of plants Plants have evolved over time The earliest fossils were found in the rocks of Western Australia (3.5 billion years old) These organisms resembled bacteria The forerunners of the first cells were likely simple aggregations of molecules Organic molecules accumulated in the oceans These then aggregated (they have a tendency to do so) Sidney W. Fox et al produced proteins that aggregated into cell-like bodies in water, calling them protenoid microspheres They began to follow three properties- Became more complex- Grew, reproduced, and passed on their characteristics- Began to organize cellularly Autotrophs and heterotrophs Heterotrophs depend on outside sources for food Autotrophs produce their own food Primitive heterotrophs increased in number, using up organic resources- Needed a new source of energy- Took millions of years to make the resource they were using- Under pressure of competition, cells that could make efficient use of the limited energy sources now available were most likely to survive- Cells eventually evolved the ability to produce their own energy-rich molecules out of simple inorganic materials – autotrophs- Evidence of the activities of photosynthetic organisms has been found in rocks 3.4 billion years old Photosynthesis changed the atmosphere The photosynthetic byproduct, O2 began accumulating in the atmosphere Prior to 2.2 billion years ago, O2 reacted with iron to form iron oxides This produced ozone (O3) which deflects UV rays This protected organisms so that they could survive on land The increase in O2 led to the process of respiration, which yields more energy than any anaerobic process Before O2 accumulated, only prokaryotic cells existed – no nuclear envelope and no organelles- First prokaryotes were heat loving archea, with descendants widespread today inhostile environments (high temp, acidic)- Bacteria are prokaryotes – some are heterotrophs, others (cyanobacteria) are autotrophs- Increase on O2 associated with the appearance of eukaryotes – those with organelles and a nucleus- Individual cells of eukaryotes are much larger than those of the bacteria- Besides archea and bacteria, everything is eukaryotic Importance of the Seashore Early in evolutionary history, photosynthetic organisms floated just below the surface of the ocean (ample resources) These began to get used up, and essential minerals became scarce Consequently, life began to develop towards shores, where water was rich in nitrates and minerals carried from the mountains by rivers This caused organisms to become more complex, and by 650 million years ago, organisms evolved the ability to be multicellular- These show the early stages of plant, animal, and fungi evolution- Fossils of multicellular organisms are easier to detect and thus, more is known about evolution from this point on Organisms living by the shore needed strong support to survive on the turbulent shore- Cell walls- Specialized structures to anchor their bodies to the rock of the shore- As multicellularity became more complex, there needed to be a way to get resources to the submerged portion of the body- Thus, food-conducting tissues carried the products of photosynthesis down to thelower structures Colonization of the land was associated with the evolution of structures to obtain water and minimize water loss Light is abundant on land, as are O2 and CO2 Minerals are abundant in soil Water was the critical factor in transitioning to land Plants utilize roots to anchor the plant and collect water Stems provide support for the leaves, the photosynthetic organs Water moves upward from the root, through the stem, and then out through the leaves The epidermis (the outermost layer) is covered with a waxy cuticle to retard water loss However, the cuticle prevents gases from entering the plant Thus, stomata were evolved- A pair of specialized epidermal cells (guard cells) with a gap in between- They open and close based on physiological signals and the environment aroundthe plant Stem- In younger plants and in annuals, the stem is also photosynthetic- In perennials (longer-lived plants) it is thicker, woody, and covered in cork (which retards water loss)- The stem conducts the vascular system Xylem  water passes upward through the plant body Phloem  food manufactured in the leaves and other photosynthetic parts ofthe plant is transported throughout the plant- Divided into nodes (1+ leaves attached) and internodes (space between nodes) Meristems- Plants grow throughout their lives- Meristems are embryonic tissue regions capable of adding cells indefinitely to theplant body- Located at the tips of roots and shoots are apical meristems – these are involved with the extension of the plant body- This type of growth is primary growth- Secondary growth originates from two lateral meristems Thickening of the plant’s stems and roots The two lateral meristems are Vascular cambium Cork cambium Plants became able to reproduce on land- Produced drought-resistant spores- This was followed by the production of multicellular structures in which the gametes, or reproductive cells, were held and protected from drying out- In seed plants (most common plants, excluding ferns, mosses, and liverworts) the young plant, or embryo, is enclosed within a seed coat provided by the parentplant; this protects and provides food inside Evolution of Communities Biomes – natural communities of wide extent, characterized by distinctive, climatically controlled groups of plants and animals Ecosystems are relatively stable, integrated units that are dependent upon photosyntheticorganisms Communities of organisms and the nonliving environment that they inhabit acre called ecosystems Nearly every organism in an ecosystem provides food for another organism There are cycles of nitrogen and phosphorus, among other minerals, in an ecosystem Everything is linked It is impossible to change a single component of an ecosystem without the risk of destroying the balance that the ecosystem depends on The base of productivity is