chapter 7 iii. cell boundaries. all cells have a _____________________________and some have a cell...
TRANSCRIPT
Chapter 7 III. Cell Boundaries
• All cells have a _____________________________and some have a cell wall
Cell membrane
• How is a window screen similar to a cell membrane? Read on to find out.
• 1. What are some things that can pass through a window screen?
• 2. What are some things that cannot pass through a window screen? Why is it important to keep these things from moving through the screen?
• 3. The cell is surrounded by a cell membrane, which regulates what enters and leaves the cell. Why is it important to regulate what moves into and out of a cell?
Section 7-3
Interest Grabber
Go to Section:
A. Cell Membrane• Regulates what enters and leaves the cell and also provides
_____________________________.• Almost all cell membranes are made of a double layered sheet
called a ___________________________-flexible,yet strong barrier
• Cell membranes usually have a protein molecule imbedded in the bilayer w/ carbohydrate molecules attached
• Called a _________________model• Some of the proteins form channels or pumps to move material
across the membranes• Some of the carbs act as ____________________tags
Protection and support
Phospholipid bilayer
Fluid mosaic
Chemical id tags
Outsideof cell
Insideof cell(cytoplasm)
Cellmembrane
Proteins
Proteinchannel
Lipid bilayer
Carbohydratechains
Section 7-3
Figure 7-15 The Structure of the Cell Membrane
Go to Section:
B. Cell Walls• In plants,algae,fungi, and many prokaryotes• Lie _______________the cell membrane• Usually porous enough to let water,O2,CO2 and
certain other substances to pass through easily• Main function is support and protection• Usually made of fibers of ____________________-
produced in cell and secreted to surface• Mostly _____________________-tough carb fibers
outside
Carbohydrate and protein
cellulose
C.Diffusion Through Cell Boundaries
• Every cell is in a liquid environment
• Cell membrane regulates the movement of cell materials from one side to the other
1.Measuring concentration
– Cytoplasm is a solution of various substances in water
• _____________of a solution is the mass of solute in given volume of solution---ie. Mass/volume…..If you have 15 g salt in 3 mL water,what is the concentration?------_______….If you have 24 g salt in 2mL water you would have 12 g/mL salt….Which solution is more concentrated?______________
concentration5g/mL
12 g/mL
2. Diffusion
– In a solution the particles move constantly,spreading out randomly….tending to move where more concentrated to an area less concentrated…This is called __________________.
– ____________________= concentration of a solute is the same throughout a system
– does not require energy because random movement
• if equilibrium is reached,particles keep moving across the membrane,still balancing concentration
isotonic
D. Osmosis
Cellmembrane
Higher Concentrationof Water
Lower Concentrationof Water
Water molecules
Sugar molecules
Section 7-3
Figure 7-17 Osmosis
Go to Section:
D. Osmosis
– Some molecules are too large or too strongly charged to make it across the lipid bilayer----thus impermeable to it
– Most membranes are selectively permeable– _____________________is the diffusion of water
across a selectively permeable membrane– water moves easily and will move to balance the
concentration of a solute,water moving from area of higher to lesser conc. For the WATER
– ____________________-same strength of a solute on both sides of a cell membrane
osmosis isotonic
– more concentrated side of solute is ____________________
– less concentrated side is____________________– Osmosis exerts a pressure known as
____________________________on the hypertonic side of a membrane….This could results in a cell bursting
– Bursting not so much a problem in larger organisms….tend to be in isotonic environments
• Osmotic pressure may not allow a plant or bacterial cell to burst , but could weaken the cell wall
hypertonic hypotonicOsmotic pressure
E.Facilitated Diffusion
» Some molecules,like glucose ,diffuse quickly across due to ________________________
» These allow only certain molecules to pass
» Since it is diffusion it does not require energy and still goes from area of higher to lower concentration
Protein channels
F.Active Transport---
– _______________________________________________________________________________
– Requires much energy– Usually carried out by proteins or pumps
found in the membrane
Moves materials across a concentration gradient,or difference
1. Molecular Transport
– Small molecules and ions carried by proteins that act like energy requiring pumps
• Ca ,K,and Na ions are carried
Endocytosis and Exocytosis
• Transports larger molecules and even clumps of matter
• ________________________is the process of taking material inward by enfolding,or pockets
• In endocytosis ,the pocket breaks loose from the cell membrane and forms a vacuole…large molecules,food and even whole cells can be taken in this way
endocytosis
2 examples of endocytosis are
– ___________________-extensions of cytoplasm surround a particle and package it in a food vacuole,then the cell engulfs it ---This is how amoebas eat-----is a form of active transport
• _______________-Cells use this to take up liquids in the environment—tiny pockets filled w/ liquid form along the cell membrane and pinch off to form vacuoles
phagocytosispinocytosis
– ___________________________--releases large amounts from the cell by pinching off or a contractile vacuole as in paramecium---also active transport
exocytosis
Molecule tobe carried Low
Concentration
CellMembrane
HighConcentration
Moleculebeing carried
LowConcentration
CellMembrane
HighConcentration
Energy Energy
Section 7-3
Figure7-20 Active Transport
Go to Section:
