Upload
mervin-bradford
View
218
Download
1
Tags:
Embed Size (px)
Citation preview
CELL MEMBRANE “THE DOOR MAN”
• The cell membrane is selectively permeable. That is… it regulates which materials can enter and leave the cell.
• Examples: – Permeable to water, oxygen,
and carbon dioxide– Not permeable to large
molecules and salts
Image: www.answers.com/topic/semipermeable
What is SELECTIVE PERMEABILITY?
• Feature and a function of the cell membrane essential to maintain equilibrium by regulating the passage of some substances and not others.
•Some substances can pass through but other substances cannot
•Example: Restaurants and Malls
– “No shoes, no shirt, no service.”
cell transportation *
Substances can move in and out of a cell in 2 ways:
1. Passive transport• diffusion
• osmosis
2. Active transport• endocytosis
• exocytosis
Passive transport *
A molecule that crosses the membrane by moving down the gradient (with the gradient) and does not require energy
• Diffusion
• Osmosis
DIFFUSION• Process by which molecules move from an area of higher
concentration to an area of lower concentration.
• Concentration:
– The amount of a given substance in a given volume.
– Ex: How much sugar is in your glass of iced tea.
What causes diffusion?
• Over time the molecules will spread out until they are evenly spread over an area or reach equilibrium.
OSMOSIS
• Is a process in which the water molecules moves from an area of higher concentration of water to an area of lower concentration of water
• The water molecules move through a selectively permeable membrane until equilibrium has been reached
Is osmosis important
• Yes it is important because cells cannot function properly without water!!!!!
Cell environment Solutions and osmosis
solutions!• a red blood cell is put in a glass of distilled
water (all water with no salt or sugar in it) also known as hypotonic solution.
• Because there is a higher concentration of water outside the cell, water enters the cell by OSMOSIS.
• In this case too much water enters and the cell swells to the point of bursting open. In the end pieces of cell membrane are left in the water.
http://www.usd.edu/~bgoodman/Osmos.htm
Solution= solute + solvent
• Solute
a substance dissolved in another substance
NaCl
• Solvent
A liquid in which substances are dissolved
H2O
solutions!
• Hypertonic
• solution that has more solutes than the cytoplasm of the cell.
• If water molecules continue to diffuse out of the cell, it will cause the cell to shrink.
Green Machine Elodea
• Distillated water• NaCl Hypotonic solution
• H2O + NaCl
• Hypertonic solution
DIFFUSION BP IN RED CELLS: OXYGEN
• There are a lot more oxygen molecules outside of the cell than there are in the cell.
• That is, there is a higher concentration of oxygen molecules outside of the cell, and a lower concentration of oxygen molecules inside the cell.
• This causes oxygen molecules to move into the cell.
• Passive transport BP
Osmosis & Red Blood Cells
Image: http://academic.brooklyn.cuny.edu/biology/bio4fv/page
Salt Water:
Water moves out of the cell and into the surroundings causing the cell to shrink
Normal Red Blood Cell
Distilled Water:
Water moves into the cell because there is more salt in the cell that there is water.
Questions:• Which way will the oxygen molecules move?
Into the cell
• Why will the oxygen molecules move into the cell?
• Because during diffusion the oxygen molecules will move from an area of high concentration to an area of low concentration.
Let’s fill out our diagram!
ACTIVE TRANSPORT *• The movement of materials through a cell membrane using energy.• This occurs when a cell needs to take in a substance that is higher
concentration inside the cell instead of outside the cell.• The cell needs to move materials in the opposite direction as diffusion.• Cells can do this but they have to use energy.
Active transportation
• Endocytosis– Proteins in the cell membrane function to pick up
molecules that are needed inside using energy
TRANSPORT PROTEINS• Proteins that are located in the cell membrane that “pick up”
molecules outside of the cell and bring them in.
• Process requires the cell to use energy.
Active transport• Engulfing or phagocytosis
Cell membrane surrounds or engulf a particle to bring it in to the cell using energy
Once it is engulfed the cell membrane connects and form a vesicle or vacuole
Phagocytosis
• Paramecium eating yeast
• Contractile vacuole
• Amoebas eating paramecium
• More amoebas
Active transport• Exocytosis• the process by which a cell
packages materials in membrane secretory vesicles inside the cell and directs them to fuse with the cell membrane releasing the packaged materials to the exterior space.
Question:• How is active transport different than
diffusion? Diffusion:
high concentration ► low concentration
Does not require energy Active Transport:
low concentration ► high concentration
Requires energy
Why are cells so small?• As cells grow, the amount of surface area becomes too large to
allow food and wastes to enter & leave the cell quickly enough
• If it grows too large it cannot function well enough to survive
• When a cell reaches a certain size it divides into two new cells.
• http://leavingbio.net/OSMOSIS%20AND%20DIFFUSION.htm
• http://www.wisc-online.com/Objects/ViewObject.aspx?ID=AP1903
• http://www.wisc-online.com/Objects/ViewObject.aspx?ID=AP11403
• http://www.wisc-online.com/Objects/ViewObject.aspx?ID=AP1101