The cell In It’s Environment Function of the cell membrane? –To regulate what enters and leaves the cell. Structure of the cell membrane –Double layer of lipids with carbohydrates and proteins scattered throughout.

The Cell in Its Environment The cell membrane is selectively permeable: – means some substances can pass through it while others cannot. Balloon

The Cell in Its Environment Three ways substances can move in and out of the cell 1.Diffusion - no energy required 2.Osmosis – no energy required 3.Active Transport – energy required

Diffusion Diffusion: The movement of molecules from an area of higher concentration to an area of lower concentration. –Caused by molecules in motion. –Collisions cause molecules to spread out. Air freshener Food dye in water

Diffusion Concentration gradient - Created when different concentrations are in contact with one another High Low

Diffusion Substances naturally move with the gradient  High to low concentration is like going down hill – with the gradient.

Diffusion –Example in living organisms – movement of oxygen from water into cells.

Osmosis – A special type of diffusion Osmosis is the diffusion of water molecules across a selectively permeable membrane –Water moves from high to low concentration

What are three ways substances can pass across the cell membrane? Diffusion Osmosis Active transport

Movement Across the Cell Membrane Passive Transport  Moving materials across a cell membrane WITHOUT using energy Two examples of passive transport: Diffusion Osmosis

Movement Across the Cell Membrane Active Transport  Movement of materials across a cell membrane which requires energy

Active Transport Sometimes molecules must move against the concentration gradient (from low to high or uphill) and this requires energy. hill.com/sites/ /student_view0/chapter2/animation__ mitosis_and_cytokinesis.html

Methods of Active Transport Two ways that the cell moves things by active transport. 1.Transport proteins 2.Engulfing

Transport Proteins – Active Transport  Transport proteins in the cell membrane act as channels through the membrane hill.com/sites/ /student_view0/chapter2 /animation__how_the_sodium_potassium_pump_ works.html e.com/watch?v=S TzOiRqzzL4

Engulfing – Active Transport  Engulfing: cell membrane surrounds and then engulfs a particle (amoeba and white blood cells). OiRqzzL4&feature=related 0p1ztrbXPY&feature=related be.com/watch?v =W6rnhiMxtKU

Cell Size Why are cells so small? –Small size makes it easier to move materials into and out of the center of the cell. –Makes all cell processes more efficient.

Cell Size How do cells maintain their small size?  When a cell reaches a certain size it divides.  We call this cell division MITOSIS.

Let’s Review  Explain the difference between osmosis and diffusion? Diffusion refers to the movement of molecules from high concentration to low concentration. Osmosis is diffusion of WATER across a selectively permeable membrane. Also from high concentration to low concentration.

Let’s Review  Do osmosis and diffusion require energy? No because they both are a form of Passive transport. Molecules or water (osmosis) move with the concentration gradient (downhill).

Let’s Review  Why does active transport require energy? Because the cell is trying to move molecules against the concentration gradient – from low to high concentration  Why are cells so small? To allow materials to move in and out quickly making the cell more efficient.

Let’s Review  What happens to a cell when it reaches a certain size? It divides to maintain its small efficient size  What do we call this cell division? Mitosis

Diffusion

hill.com/sites/ /student_view0/chapter2/animation__ mitosis_and_cytokinesis.html nimat/transport/osmosis.swf diffusion.swf Osmosis and salt