6 th Grade Text, Chapter 5-1

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

• 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

Substances can move in and out of a cell in 2 ways:
1. Passive transport
• diffusion
• osmosis
2. Active transport
• endocytosis
• exocytosis

A molecule that crosses the membrane by moving down the gradient (with the gradient) and does not require energy
• Diffusion
• Osmosis

• 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.

• Over time the molecules will spread out until they are evenly spread over an area or reach equilibrium.

• 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

• Yes it is important because cells cannot function properly without water!!!!!

• 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

• Solute a substance dissolved in another substance
• Solvent
A liquid in which substances are dissolved
NaCl
H
2
O

• 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.

• Distillated water
Hypotonic solution
• H
2
O + NaCl
• Hypertonic solution

• Distillated water
• NaCl Hypotonic solution
• H
2
O + 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

Distilled Water:
Water moves into the cell because there is more salt in the cell that there is water .
Normal Red
Blood Cell
Salt Water:
Water moves out of the cell and into the surroundings causing the cell to shrink
Image: http://academic.brooklyn.cuny.edu/biology/bio4fv/page

• 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!

• 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.

• Endocytosis
– Proteins in the cell membrane function to pick up molecules that are needed inside using energy

• 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.

• 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

• Paramecium eating yeast
• Contractile vacuole
• Amoebas eating paramecium
• More amoebas

• 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.

BP


Diffusion: high concentration ► low concentration
Does not require energy

Active Transport: low concentration ► high concentration
Requires energy

• 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 .

• interactive video for active and pasive transport

• interactive

• http://leavingbio.net/OSMOSIS%20AND%
20DIFFUSION.htm
• http://www.wisconline.com/Objects/ViewObject.aspx?ID=
AP1903
• http://www.wisconline.com/Objects/ViewObject.aspx?ID=
AP11403
• http://www.wisconline.com/Objects/ViewObject.aspx?ID=
AP1101

• http://www.udel.edu/biology/ketcham/micr oscope/testFLV8.html