The Cell in its Environment

6th 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

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

Hypotonic solution

• H2O + NaCl

• Hypertonic solution

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.

How does it works for unicellular organism?

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.

Active Transport BP

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.

• interactive video for active and pasive transport

• interactive

• 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

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