Bio: Chapter 3

• Cell membrane is made up of phospholipids and proteins
• In 1972 , singer and Nicholson proposed fluid mosaic model
• Phospholipids molecules


  Arranged in a bilateral

  Can move laterally (described as fluid)
• Protein molecule:


  Interspersed among the phospholipids molecules (described as mosaic)

  Some are attached to the surface , some are embedded half way or span in the entire bilayer

  Carbohydrates attached are called glycoproteins.
• Phospholipids group


  Polar

  Attracted by water

  Forms a hydrophilic head
• Fatty acid 


  Non polar

  Repelled by water

  Forms the hydrophobic tail
• Channel proteins 


  Provides channels for certain substances (eg: ions) to move across the membrane
• Carrier proteins 


  Bind to certain substances (eg hormones) outside cells and transports them across the membrane (needs energy)
• Receptors 


  Bind to chemical messengers (eg hormones) outside cells ; the binding may turn on certain activities in the cells
• Antigens 


  Are the glycoproteins for the cell recognition
• Enzymes 


  Speed up chemical reactions
• The phospholipids arranged in a bilayer and the core is hydrophobic, which makes the cell membrane differentially permeable.

  Non polar substancescan dissolve the phospholipids bilayer and move across the membrane
• Non polar substances and ions are transported by Chanel proteins and Carrier proteins
• Temperature 


  When it increases, the permeability increases.

  Boiling can damage the membrane , making it fully permeable
• The phospholipids molecules can move laterally. It's fluid in nature

  Allowing it to change it's shape and fuse with one another during phagocytosis and cell divisions
• Diffusion

  Is a net movement of particles from a region of higher concentration to a region of lower concentration
• Equilibrium 


  When the particles become evenly distributed, there is no net movement of particles but is still moving randomly
• Diffusion doesn't require energy and it's a passive process as it depends on the random movements of the particles
• Concentration gradient

  The steeper it is , the higher rate of diffusion
• Surface area

  The higher the surface area , the higher the rate of diffusion
• Temperature

  Higher temperatures , more kinetic energy , Higher rate of diffusion
• Size of the particles

  Smaller particles , faster diffusion
• Natures of particles

  Non polar diffuses faster cayse they move across the membrane through bilayer directly
• Importance of diffusion

  Enables cells to exchange materials with the environment

  Involved in many life process (absorption of nutrients in human small intestine and gas exchange in human lungs)
• Osmosis


  A net work of water molecules that moves from a higher water potential to a lower water potential across a differentially permeable membrane.

  The more solute ; the lower the water potential

  Dissolving substances in water decreases the tendency of water molecules to move
• Hypotonic(high water potential ; low concentration gradient)


  Net movement enters the cell

  Animal cells: Swell and may burst

  Plants cells: becomes turgid
• Isotonic 


  No net movement

  No change in animals and plants cells
• Hypertonic (low water potpotential ; high concentration gradient)


  Net movement leaves the cells

  Animals cells: shrink and become wrinkled

  Plants cells: becomes flaccid and plasmolysed ; vacuoles shrinks
• Importance of osmosis

  Enables the movement of water in and out of the cells

  Involved in the absorption of water in human intestine and plant roots
• Active transport 


  Is a transport of substances from a region of higher concentration to a region of lower concentration using energy and it involves Carrier proteins
• Active transport

  It is an active process

  Only occurs in living cells

  The cells with high Active transport usually have high respiration rate and large number of mitochondrion
• Importance of active transport

  Enables cells to take up additional useful substances which are already high in concentration inthe cells

  Involved in the absorption of nutrients (eg glucose and amino acids) in the human small intestine and the absorption of minerals from the soil into plant roots
• Phagocytosis


  Uptake of large particles into the cells by packaging the particles into vacuoles formed into the cell membrane
• Importance of phagocytosis

  Involved in the nutrients of some unicellular organisms (amoeba)

  Involved in body defense against diseases in human , certain types of white blood cells engulf harmful microorganisms by phagocytosis