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The Cell Membrane


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Brief description of the plasma cell membrane and how materials get into or out of the cell. Appropriate for 7th grade life science.

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The Cell Membrane

  1. 1. The Cell Membrane
  2. 2. Cell Membrane  Also known as the plasma membrane  In both plant and animal cells  Main function: to protect the cell  Made of a lipid (fat) double layer with special embedded proteins
  3. 3. Cell Transport  The membrane also controls what goes in or out of the cell (cell transport)  It is semi-permeable  Some molecules, like oxygen & water, are permeable go directly through the membrane  Other molecules, like glucose & salt, are impermeable and only pass through a protein
  4. 4. Cell Transport  There are lots of ways substances enter or exit a cell  It depends on the size of the substance:  Small Particles move through the membrane by:  Passive or Active Transport  Large Particles move through the membrane by:  Endocytosis or Exocytosis
  5. 5. Passive Transport  Does not require energy (thus passive…)  Two Types 1. Diffusion 2. Facilitated Diffusion
  6. 6. 1) Diffusion  Diffusion is when molecules spread from an area of high concentration to an area of low concentration  This is called a concentration gradient
  7. 7. 1) Diffusion  Think about spraying air freshener into a room. It gradually spreads out. Same thing if someone farts…  Or, if we pushed everyone here into a corner, but let you move where you wanted, you would tend to spread out around the room instead of staying crammed into the corner. You’re moving from an area of high concentration (the corner) to an area of low concentration (the rest of the room).
  8. 8. 1) Diffusion
  9. 9. 1) Diffusion  Diffusion occurs in cells through the membrane.  Oxygen needed for cellular respiration enters cells by diffusion  CO2 produced by cellular respiration leaves cells by diffusion.
  10. 10. Osmosis  Osmosis is when water diffuses through a membrane.  Think about how important it is for water to get into and out of cells.
  11. 11. 2) Facilitated Diffusion  Sometimes, molecules can’t get through the membrane without a little help (facilitation…)  In facilitated diffusion, a special protein embedded in the membrane helps molecules move across  No energy is required, this is still passive transport  Molecules such as glucose, sodium & chloride ions get into the cell this way
  12. 12. Active Transport  Requires energy (ATP)  Sometimes, cells have to move a substance against the concentration gradient or from an area of low to high concentration
  13. 13. Active Transport  Active transport also occurs through a special protein or pump, like with facilitated diffusion  This is one of the main reasons why cells require energy – they need the ability to remove substances.  For example, kidney cells filter & remove salt from your blood through active transport.
  14. 14. Passive versus Active Transport
  15. 15. Large Particles  Sometimes particles are too big to simply cross the membrane.  Instead, they must get pulled into or pushed out of the membrane in one of two ways 1. 2. Endocytosis Exocytosis
  16. 16. 1) EndoCytosis  Occurs when large particle(s) are captured by a pocket in the membrane  The particle is too big to fit through a protein channel  The pocket breaks off & forms a package that moves into the cell  Requires energy  Essential nutrients, like iron, are absorbed into cells this way
  17. 17. 1) EndoCytosis
  18. 18. 2) ExoCytosis  Occurs when a large bit of material needs to be removed from a cell  A package of the materials travels through the cell to the membrane, joins it, and is expelled  Opposite of endocytosis  Requires energy  Cells use this to flush out waste such as hormones
  19. 19. 2) ExoCytosis
  20. 20. Big Ideas 1. What are two functions of the cell plasma membrane? 2. What types of substances need to be transported across the membrane? 3. How does a particle’s size affect how its transported through a cell? 4. List 3 differences between passive & active transport.