CONNECT!

Imagine you are trudging home from school on a cold, wintry day. When you finally arrive, you enter a room where you are sheltered from the wind and surrounded by a warm, comfortable environment. Your house is a controlled environment just like the cells in your body. Similar to the way the walls of your home act as a barrier against the elements, the cell membrane provides a barrier between the internal components of a cell and its external environment.

Cell organelles are tiny structures inside cells that do jobs for the cell.

1. Plasma Membrane (Cell Membrane)

• made of a double lipid layer in which large proteins float

• transports materials into and out of the cell: this is called intercellular transport

• recognizes and responds to chemical messages

receptor

Transport In and Out of the Cell

• For a cell to survive, some materials, such as water, oxygen, and nutrients must pass through the membrane and into the cell.

Other materials, such as CO2, must pass out of the cell.

• Molecules either enter or leave a cell through diffusion or active transport.

Diffusion

• Molecules tend to move naturally from an area of high concentration to an area of low concentration

Here the molecules move through the liquid by diffusion.

Here the molecules move out of the liquid and into the air by diffusion.

• Diffusion can occur across cell membranes.

• Diffusion requires no energy from the cell, since it occurs due to molecular movement.

• When some organisms digest food, they are changing it from large complex molecules to simple small molecules. This change in size allows our food to become small enough to pass through the cell membrane. Once nutrients enter the cell they are used to build larger molecules (synthesis) or broken down further to release energy (cellular respiration).

Click on image belowto view video clip

Size matters!• larger molecules such as starch, proteins,

and lipids cannot fit, because they are too big

Inhaled oxygen is in higher concentration in alveolus of lung than in blood capillary, so it diffuses out of the lung into the capillary into the red blood cells.

CO2 is in higher concentration in red blood cells than in alveolus of lung, so it diffuses out of the RBC into the capillary into the lung, and is exhaled.

Chunk!• What does “organelle” mean?• What is the cell membrane composed of?• What molecules move into and out of cells?• Define diffusion.• Does it require energy?• Why does diffusion occur?• What determines if a molecule can cross a cell membrane?• What does “passive transport” mean?• Name some specific molecules that enter by diffusion.• Name some specific molecules that can’t.• Explain diffusion in the lung.• Explain diffusion in the digestive tract.

• What is going into the respiring cells?

• What is coming out of the respiring cells?

• What are the pink organelles?

• What process is involved in the molecules entering and exiting the blood cells and the respiring cells?

• What is diffusing in each direction? Why?

That’s all, folks!

Sources of Images• Snowboard – http://improved.ipower.com/images/snowboard.gif• Unlabeled cell - library.thinkquest.org/.../cell-wall.gif• RED BOUNCING MOLECULES - http://edtech.clas.pdx.edu/osmosis_tutorial/diffusion1.html• Black/white cell membrane -

http://upload.wikimedia.org/wikibooks/en/1/1a/Anatomy_and_physiology_of_animals_structure_plasma_membrane.jpg

• Cell membrane - library.thinkquest.org/.../cell_membranes.html • Diffusion animations -

http://leavingbio.net/OSMOSIS%20AND%20DIFFUSION_files/image003.gif• Liquid diffusion - http://commons.wikimedia.org/wiki/File:Diffusion.gif• Across membrane - http://www.blobs.org/science/chemistry/diffusion2.gif• Capillary -

http://www.scifly.co.uk/client_files/AQA%20Additional%20Science/diffusion_into_capillary_3.jpg• Lung - http://www.scifly.co.uk/higher-tier/c/562/i/2173/?uid=201001291652197818168• Winter house - http://caaneo.ca/about/blog/wp-content/uploads/2008/01/winter-house.jpg• Pig - <a href="http://www.greatfunnypictures.com/browse.asp?id=118"><img

src="http://www.greatfunnypictures.com/pictures/117_hehe.jpg" border="0" alt="Funny Pig - Funny Pictures"></a>