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Biology: life study of What is Life? Cellular Structure: the unit of life, one or many Growth: cell enlargement, cell number Evolution: long term adaptation Behavior: short term response to stimuli Reproduction: avoid extinction at death Metabolism: photosynthesis, respiration, fermentation, digestion, gas exchange, secretion, excretion, circulation--processing materials and energy Movement: intracellular, movement, locomotion Properties of Life
Cyclosis in Physarum polycephalum, a slime mold The correct taxonomic affiliation is unclear. It has been treated as Fungus and Protist. Further study is needed to resolve its position. This organism consists of one very large cytoplasm (plasmodium) with many nuclei and food vacuoles in the cytosol (coenocytic). Slime molds can weigh up toward kilogram range and move their blob-like mass around exclusively by cyclosis. Here you can see, in a thin region of cytoplasm, that it moves along pathways that are river-like in appearance. Transport is NOT always unidirectional. 130/Movies/Slime_mold.mov What is the ATP source?
Cyclosis: cytoplasmic streaming…intracellular circulation Chloroplasts and other organelles have surface proteins with myosin-like activity. Microfilaments of actin are found just under cell membrane. ATP and Calcium allow myosin to slide along actin filaments, resulting in circulation of organelles within the cell. What is the source of ATP? Can you be more specific? If light intensity were reduced, what would be the prediction based on your hypothesis? Elodea canadensis
Figure 36-3 Page 793 Branch Root system Shoot system Stem Apical bud Axillary bud Node Leaves Node Internode Lateral roots Taproot The shoot organ system is photoautotrophic, taking in CO 2 and releasing O 2 in daylight. The root organ system is chemoheterotrophic, taking in O 2 and releasing CO 2 in the darkness of the soil environment. Diffusion is sufficient to exchange gases. But solutes need to be circulated in the large plant body as diffusion is too slow!! O 2 in and CO 2 out CO 2 in and O 2 out O 2 in and CO 2 out
Figure 36-3 Page 793 Branch Root system Shoot system Stem Apical bud Axillary bud Node Leaves Node Internode Lateral roots Taproot The shoot system produces carbohydrates (etc.) by photosynthesis. These solutes are transported to the roots in the phloem tissue: Translocation The root system removes water and minerals from the soil environment. These solutes are transported to the shoot in the xylem tissue: Transpiration Water and Minerals Transpiration Carbohydrate etc. Translocation
Figure 36-3 Page 793 Branch Root system Shoot system Stem Apical bud Axillary bud Node Leaves Node Internode Lateral roots Taproot Because these pathways involve solutes in water passing in the adjacent tissues of a narrow vascular bundle, this is a circulation system! Transpiration and Translocation The water is moving up the xylem, and down the phloem, making a full circuit! Water and Minerals Transpiration Carbohydrate etc. Translocation
Figure Page 802 Cortex Cross section of a eudicot stemCross section of a monocot stem Epidermis Pith Ground tissue Vascular bundles Plants occur in two major groups (and some minor ones) They differ, in part, in their circulation systems: Dicots initially have one ring of vascular bundles Monocots rapidly develop multiple, concentric, rings of vascular bundles
Mendocino Tree (Coastal Redwood) Sequoia sempervirens Ukiah, California 112 m tall (367.5 feet)! This tree is more than ten times taller than is theoretically possible based solely upon the length of the column of uncavitated water. How could this be achieved?
Transpiration in a tall tree has at least 3 critical components: Evaporation: pulling up water from above Capillarity: climbing up of water within xylem Root Pressure: pushing up water from below
Transpiration: root pressure (osmotic push) The veins (coarse and fine) show that no cell in a leaf is far from xylem and phloem (i.e.water and food!). The xylem of the veins leaks at the leaf margin in a modified stoma called the hydathode. These droplets are xylem sap. Root pressure accounts for maybe a half-meter of push up a tree trunk.
Capillarity: maximum height of unbroken water column The small diameter of vessels and tracheids and the surface tension of water provide capillary (climb). Cohesion of water, caused by hydrogen bonds, helps avoid cavitation. A tree taller than 10.4 m would need some adaptations to avoid cavitation atmospheric pressure keeps water in tube gravity pulls water down vacuum created 10.4m glass tube water
Conifer stem anatomy: bordered pits as check-valve for flow These pit features allow conifers to be very tall and still avoid cavitation in their xylem cells. As pressures change between adjacent cells, the torus movement blocks catastrophic flow that would result in cavitation. secondary wall primary wall middle lamella pit aperture pit membrane pit border torus pit chamber P low P high
Transpiration: evaporation (pull) 76 cm vacuum mercury water mercury Water evaporating from a porous clay cap also lifts the mercury! Transpiration can lift the mercury above its normal cavitation height!
Figure 36-3 Page 793 Branch Root system Shoot system Stem Apical bud Axillary bud Node Leaves Node Internode Lateral roots Taproot Root Pressure: Water moves into the root because of solutes from phloem. Pressure pushes the water up the stem. Water and Minerals Transpiration Carbohydrate etc. Translocation Transpiration Capillarity: Water climbs in the xylem cell walls by adhesion. Water molecules follow by cohesion. Evaporation: Water evaporates from mesophyll into atmosphere. Water molecules are pulled up the xylem by virtue of cohesion.
Figure 36-3 Page 793 Branch Root system Shoot system Stem Apical bud Axillary bud Node Leaves Node Internode Lateral roots Taproot Pressure = Bulk Flow The pressure gradient forces phloem sap away from leaves to all sinks (bidirectionally). Water and Minerals Transpiration Carbohydrate etc. Translocation Root (etc.) = Sinks Solutes removed from phloem by active transport. Water follows by osmosis, reducing pressure. Leaf = Source Photosynthesis produces solutes. Solutes loaded into phloem by active transport. Water follows by osmosis, increasing pressure.