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Transcript
NOTES: 7.3-7.4 CELL TRANSPORT & HOMEOSTASIS Selectively permeable: ● property of biological membranes which allows some substances to pass more easily than others Transport proteins: ● membrane proteins that transport SPECIFIC molecules or ions across biological membranes GLUCOSE Binding Recovery Transport Dissociation Movement across the cell membrane can be: 1) PASSIVE cell does not have to spend energy substance moves from where it is MORE concentrated to where it is LESS concentrated. 2) ACTIVE cell “spends” energy to move a substance from where it is LESS concentrated to where it is MORE concentrated (“UPHILL”) Passive Transport: DIFFUSION ● movement of a substance from where it is conc. to where it is less conc. (“down a concentration gradient”) Passive Transport: FACILITATED DIFFUSION ● diffusion of solutes across a membrane, with the help of transport proteins (passive transport because it is movement down a concentration gradient; cell does not need to spend any energy) Passive Transport / Fac. Diffusion: OSMOSIS ● diffusion of WATER through a selectively permeable membrane; water moves DOWN its concentration gradient (which is to say opposite the solute concentration!) ● OSMOSIS:(this is a type of facilitated diffusion…water moves through special channels in cell membrane called aquaporins) OUTSIDE THE CELL INSIDE THE CELL – the direction of water movement can be described / predicted based on if the cell’s ENVIRONMENT is: ● ISOTONIC: equal solute concentration compared to inside a cell ● HYPERTONIC: greater solute concentration than inside a cell ● HYPOTONIC: lower solute concentration compared to inside a cell WATER MOVES FROM HYPO TO HYPERTONIC!!! In animal cells: ● in a HYPERTONIC environment, water exits the cell; cells shrivel and usually die ● in a HYPOTONIC environment, water moves into cell, causing it to swell and possibly burst In cells with cell walls (i.e. plant cells): ● in a HYPERTONIC environment, water exits the cell; cells shrivel and usually die ● in a HYPOTONIC environment, water moves into cell, causing it to swell; cells become more TURGID. ACTIVE TRANSPORT: energy-requiring process; molecules are moved across the cell membrane AGAINST their concentration gradient (“uphill”) Active Transport: ● Molecular Transport ● Bulk Transport Active Transport: ● Molecular Transport -small molecules & ions are moved across membranes by proteins that act like pumps BULK TRANSPORT: ENDOCYTOSIS & EXOCYTOSIS ● transport of large molecules (e.g. proteins and polysaccharides) into or out of the cell ENDOCYTOSIS *importing large molecules by forming vesicles out of the cell membrane **vesicle forms in a small region of cell membrane ***used by cells to bring in larger, extracellular substances (e.g. proteins) EXOCYTOSIS ENDOCYTOSIS EXOCYTOSIS *exporting large molecules by vesicles fusing w / the cell membrane **vesicle buds from ER or Golgi and migrates to cell membrane ***used by cells to export products (e.g. cells in pancreas secreting insulin) 2 types of Endocytosis: 1) Phagocytosis: solid particles (“cell eating”) 2) Pinocytosis: fluid droplets (“cell drinking”) Phagocytosis Pinocytosis 7.4: Homeostasis & Cells ● sometimes an organism can be a single cell ● unicellular organisms dominate life on Earth…they include: -prokaryotes: bacteria -eukaryotes: protists (amoeba, paramecium, Euglena) -eukaryotes: unicellular fungi (yeast) Unicellular Organisms: ● unicellular organisms must maintain homeostasis ● HOMEOSTASIS: relatively constant internal physical & chemical conditions ● to maintain homeostasis, unicellular organisms grow, respond to the environment, transform energy, and reproduce Multicellular Life ● the cells in a multicellular organism must work together to maintain homeostasis ● in a multicellular organism, cells become specialized so that different cell types play different roles CELL SPECIALIZATION: ● some cells are specialized to MOVE (i.e. muscle cells) ● some cells are specialized to RESPOND (i.e. nerve cells) CELL SPECIALIZATION: ● some cells are specialized to transport substances (i.e. red blood cells) ● some cells are specialized to fight off pathogens (i.e. white blood cells) LEVELS OF ORGANIZATION: ● CELLS…are organized into… ● TISSUES: group of similar cells performing the same function LEVELS OF ORGANIZATION: ● ORGAN: group of tissues working together -ex: stomach ● ORGAN SYSTEM: group of organs working together -ex: digestive system (stomach, intestines, pancreas, etc.) LEVELS OF ORGANIZATION: ● ORGANISM: collection of all of the above!...specialization and interdependence at all levels allows an organism to maintain homeostasis! CELLULAR COMMUNICATION: ● Cells communicate with one another by using chemical signals (i.e. hormones) ● in order to respond to a particular chemical signal, a cell must have the appropriate RECEPTOR to which the signaling molecule can bind CELLULAR COMMUNICATION: ● cells respond to chemical signals in a variety of ways: -muscle cell contracts -liver cell takes up & stores glucose from blood -skin cells divide to replace injured cells