The Cell Membrane Homeostasis & Cellular Transport

protein channel
protein pump
Layer 1
Layer 2
All Cells have a cell (plasma membrane):

• Prokaryotes (have a cell wall + cell membrane)
• Eukaryotes:
• a) Animal Cells ( cell membrane only)
• b) Plant cells (cell membrane + cell wall)

The cell membrane in detail

• It’s a double layer (bilayer) of phosphates, and fats (lipids)
• A single phospholipid has hydrophilic (water loving) phosphate heads AND hydrophobic (water hating) fatty acid tails
• The cell membrane both repels and attracts water through the membrane at the same time

HydroPHILIC head
hydroPHOBIC tails
Passive Transport
A process that does not require energy to move molecules from a HIGH to LOW concentration

• Diffusion
• Facilitated Diffusion (uses proteins to push particles across)
• Osmosis

• Diffusion is the movement of small particles across the cell membrane like the cell membrane until homeostasis is reached.
• Facilitated diffusion requires the help of carrier and channel proteins

These particles move from an area of high concentration to an area of low concentration.

outside of cell
inside of cell
Diffusion
HIGH to LOW concentration

• Examples of diffusion: spraying aerosols, and perfumes.
• High concentration (inside of the can)—the molecules are packed tightly together….
• To a LOW concentration – when sprayed, the molecules are released to a more free environment
• The particles SPREAD OUT

• Osmosis is the movement of water through a selectively permeable membrane like the cell membrane

Water moves across the cell membrane from an area of high concentration to an area of low concentration.

Semi-permeable membrane is permeable to water, but not to sugar
Hypertonic Solutions: contain a high concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrivel.
Hypotonic Solutions: contain a low concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode.
Isotonic Solutions: contain the same concentration of solute as another solution (e.g. the cell's cytoplasm). When a cell is placed in an isotonic solution, the water diffuses into and out of the cell at the same rate. The fluid that surrounds the body cells is isotonic.