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Chapter 8 Cellular Transport & Cell Cycle 8.1 Cellular Transport • Osmosis- diffusion of H2O – H2O moves freely through plasma membrane – H2O tries to maintain equal concentration on both sides of plasma membrane – Control of Osmosis • Concentration gradient- unequal distribution of particles Isotonic solution • concentration of dissolved substances in solution = concentration inside cell • Cells in isotonic solution do not experience osmosis + retain normal shape ~ Fig. 8.2 p. 202 • Cells are not damaged hypotonic solution • • • • • • concentrate of solution < concentrate inside H2O moves into cell Cell swells Internal pressure increases Animal cells can burst Plants cells cannot burst because of cell wall becomes firm hypertonic solution • concentrate of solution > concentrate inside • H2O moves out of cell by osmosis • Animal cells shrivel- inter pressure decreases • Plant cells- internal pressure decreases plant wilts Passive Transport • Movement of particles such as lipids, lipidsoluble subs., & H2O across membranes using no E Passive transport by proteins • Facilitated diffusion- passive transport of mat’ls across p.m. • W/ aid of transport proteins (fig. 8.5 p.204) transport proteins provide convenient opening for particles to pass through • Common method of moving sugars & a.a. across membranes • Factor- conc. grad. Active Transport • Moving mat’ls against conc. grad.- from lower to higher concentrate • Requires E • How it happens- Fig. 8.6 p.205 • Carrier protein ( form of a transport protein) binds w/ particle of subs.• Chemical E allows cell to shape of carrier protein so that particle to be moved is released on opposite side of membrane Lg. Particle transport • Endocytosis- process by which a cell surrounds & takes in mat’l from environment • mat’l does not pass directly through membrane • engulfed by portion of p.m. • that portion of p.m. breaks away & resulting vacuole + contents moves into cell • active transport + E Lg. Particle transport • Exocytosis • opposite of endocytosis • used to expel wastes & secrete substances like hormones • active transport + E 8.2 Cell growth & Reproduction Factors Limiting Cell Size • Diffusion is slow & inefficient over long distances & lg. Sizes • DNA • Limit to rate off genetic mat’l replication • In large cells, more than one nucleus has evolved • Surface Area (SA) to volume (V) Ratio • Volume increases faster then SA Cell Reproduction • New cells made through cell division • Results in 2 identical cells Chromosomes • Short, stingy, dark- staining structures in nucleus that contain DNA • Structure of eukaryotic chromosomes • Most of time, chromosomes exist as chromatin Chromatin- long strands of DNA wrapped around proteins • As nucleus starts to divide, chromatin becomes, reorganized tightly packed chromosomes Cell Cycle- Inside Story p.211 • Sequence of cell growth & division • • • • Interphase- growth period in which a cell spends most of its life Cell grows in size Carries on metabolism Chromosomes are duplicated stages of interphase Gl • beginning • chromosomes are not visible under light microscope because they are uncoiled • protein synthesis occurring rapidly S stage • chromosomes replicated in nucleus G2 • chromosomes begin to shorten & coil • high rate of protein synthesis • in animals, centriole pair replicates & prepares to form mitotic spindle • mitosis • follows interphase • nuclear division • process by which 2 daughter cells are formed, each containing a complete set of chromosomes Cytokenisis • division of cytoplasm • after mitosis • chromosomes divide to form identical sister chromatids connected by a centromere Phases of Mitosis Prophase • • • • • • • • 1st & longest phase chromatin coils up into visible chromosomes chromosomes look hairy made up of 2 halves sister chromatids held together by centromere nucleus disappears nuclear envelope & nucleolus disintegrate in animal cells, centioles begin to migrate to opposite ends Prophase Centrioles • sm. Dark, cylindrical structures made of microtubules & are located just outside nucleus • as centrioles migrate, spindle, forms between them • Spindle – football shaped cage-like structure consisting of thin fibers of microtubules – in plant cells, spindle forms without centrioles Metaphase • Short 2nd stage • Doubled chromosomes attach to spindle fibers by their centromeres • Chromosomes pulled by spindle fibers & line up at equator of spindle Metaphase Anaphase • 3rd Phase • beginning marked by separation of sister chromosomes • centromeres split apart • chromatid pair from each other • chromatids pulled apart by shortening of spindle fibers Anaphase Telephase • • • • • • • Fourth and final phase Begins when chromatids reach the opposite poles Many changes of prophase are reversed Chromosomes unwind Spindle begins to break down Nucleolus reappears Nuclear environment forms around each set of chromosomes • New double membrane begins to form between 2 new nuclei Telephase Cytokenisis • cytoplasm divides