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7-3 Cell Boundaries
Objectives:1) What are the main functions of the cell
membrane and the cell wall?2) What happens during diffusion?3) What is osmosis?
Introduction
O Among the most important parts of a cell are its bordersO Separate the cell from its surroundingsO Cell membrane: all cells are surrounded by a thin, flexible
barrier O Cell wall: a strong supporting layer around the membrane
Cell MembraneO Function
O Regulates what enters and leaves the cell
O Provides protection and support
O Almost all cell membranes are made of a double-layered sheetO Lipid bilayer: 2 layers
of lipidsO Flexible structure and
strong barrier
Cell Membrane Cont’dO Many kinds of
molecules in cell membranesO Most have
protein molecules and carbohydrates (etc.)
Cell WallsO Outside the cell
membraneO Most are porous
to allow water, oxygen, carbon dioxide, and certain other substances to pass through easily
Cell Walls Cont’dO Function
O Provide support and protection
O Made O Mostly of cellulose
O Fibers of carbohydrate and protein
O Main part of wood and paper
O Inside the cell and then released at the surface of the cell membrane
Diffusion Through Cell Boundaries
O One of the most important functions of the cell membrane is to regulate the movement of dissolved molecules from the liquid on one side of the membrane to the liquid on the other side
O Demo
Measuring Concentration
O Cytoplasm is a solution of many different substances in waterO Solution: a mixture of 2 or more substancesO Solutes: substances dissolved in the solutionO Concentration: the mass of solute in a given
volume of solutionO More solutes in a volume=greater concentration
DiffusionO Diffusion: Particles tend to
move from an area of high concentration to an area of less concentrationO Does not need cell energy
O Equilibrium: when the concentration of the solute is the same throughout
O Particles will continue to move until equilibrium is reachedO Particles are in constant
motionO Activity
BLUE TICKET QUESTION
O What conditions are present when equilibrium is reached in a solution?
BLUE TICKET ANSWER
O Equilibrium is reached when the concentration of the solute is the same throughout the solution
OsmosisO Some substances are too
large or too strongly charged to cross the lipid bilayer
O Permeable: a substance that is able to diffuse across a membrane
O Impermeable: substances cannot pass across
O Selectively permeable: some substances can pass across and others cannot
O Osmosis: the diffusion of water through a selectively permeable membrane
How Osmosis WorksO Isotonic: “same
strengthO Hypertonic:
“above strength”O Hypotonic:
“below strengthO Osmosis Activity
Osmotic PressureO If cells are
surrounded by fresh water, they will swell and burstO Plants and
bacteria are surrounded by a cell wall which prevents bursting
O Blood is isotonic so cells will not burst
Blue Ticket QuestionO What structures
protect plant and bacterial cells from potential damage resulting from osmotic pressure?
Blue Ticket AnswerO Cell walls
Facilitated Diffusion
O Cell membranes have protein channels that make it easy for certain molecules to cross the membrane
O Facilitated diffusion: help the diffusion of glucose across the membrane
Facilitated Diffusion Cont’d
O 100s of different protein channels have been found that allow particular substances to cross different membranesO Fast and specific
Facilitated Diffusion Cont’d
O Will only happen if there is a higher concentration of the particular molecules on 1 side than on the other sideO Does not use the cell’s energy
O https://www.youtube.com/watch?v=faXBWOETTb4
O Lab
Active TransportO Active transport: move
materials against a concentration differenceO Requires energyO Usually moves ions
with transport proteinsO Endocytosis and
exocytosis move larger molecules and clumps of materials
O https://www.youtube.com/watch?v=STzOiRqzzL4
Molecular TransportO A considerable
portion of the energy used by cells in their daily activities is devoted to providing the energy for active transport
Endocytosis and Exocytosis
O Endocytosis: taking material into the cell by means of infolding of the cell membrane
O https://www.youtube.com/watch?v=pvOz4V699gk
Endocytosis and Exocytosis Cont’d
O Exocytosis: the membrane of the vacuole surrounding the material fuses with the cell membrane, forcing the contents out of the cell
O https://www.youtube.com/watch?v=U9pvm_4-bHg
7-3 Exit TicketO Answer the
following questions.
O Use complete sentences.
O You may NOT use your book. You MAY use your notes.
O This is a quiz grade.
1) What are the main functions of the cell membrane and the cell wall?
2) What happens during diffusion?
3) What is osmosis?
