Btec science unit 3

• Standard deviation

  A measure of how far data values are from the mean value
• Activation energy

  The minimum energy required for collisions to break the bonds in the reactants and lead to a reaction
• Denature

  A change in the tertiary structure of a protein molecule
• Enzymes speed up reactions in the human body
• For chemical reactions to occur, the reactants must collide with energy greater than or equal to the activation energy and the correct orientation (collision geometry)
• Catalyst

  A substance that speeds up a chemical reaction but remains unchanged at the end of the reaction
• Active site

  The area of an enzyme that the substrate binds to
• Adding a catalyst


  Lowers the activation energy for a reaction, leading to more successful collisions
• Increasing concentration and surface area

  Lead to more frequent collisions between reacting particles, leading to a faster reaction
• In practice, only a small minority of collisions that take place lead to a chemical reaction
• Collision theory is important to understand how chemical reactions work and what affects the rate of reactions
• Ways to increase the rate of a chemical reaction

  • Increasing the concentration of reactants
  • Increasing the surface area of a solid reactant
  • Increasing the temperature
  • Adding a catalyst
• Increasing temperature

  Leads to more frequent and more successful collisions as particles will have more energy and move faster
• Increasing the substrate and enzyme conc does what to the reaction?

  Increase however if substrate conc is much bigger than enzyme conc there will not be enough enzyme molecules for the substrate to bind to
• Shape and size of molecules

  • Smaller molecules will diffuse quicker than larger molecules
  • Molecules with a more streamlined shape will diffuse quicker than less streamlined molecules of a similar molecular mass
• When molecules diffuse, they are moving along a concentration gradient
• Factors affecting rate of diffusion

  • Concentration gradient
  • Shape and size of molecules
  • Temperature
  • Distance
  • Surface area
• Distance

  • The further the molecules have to travel, the longer it will take, so the rate of diffusion is quicker over short distances than over long distances
• The greater the concentration gradient


  The faster the rate of diffusion
• Temperature

  • The higher the temperature, the more energy the molecules will have, and the faster they will move, therefore increasing the rate of diffusion
• Substance for diffusion

  • Milk
• Surface area

  • Greater surface area of a semi-permeable membrane leads to faster diffusion of molecules through the membrane
• 
  

  • Cell
  • Battery
  • Switch
  • Bulb or lamp
  • Fixed resistor
  • Variable resistor
  • Ammeter
  • Voltmeter
  • Diode
  • Light-emitting diode (LED)
  • Thermistor
• Purposes

  • Used to push electrons around the circuit
  • Used to join a number of cells together, used to push electrons around the circuit
  • Enables the current in a circuit to be switched on or off
  • Lights up when current passes through it, so can be used to indicate that current is flowing through the circuit
  • Limits the amount of current flowing in a circuit
  • Allows the current in the circuit to be varied
  • Measures the current in a circuit
  • Measures the potential difference (voltage) across a component in a circuit
  • Allows current to flow through a circuit in one direction only
  • Emits light when a current passes through it
  • Used as a temperature sensor in a circuit, as the temperature increases the resistance of the thermistor decreases
• Resistance

  The opposition in an electrical component to the movement of electrical charge through it. It is measured in ohms.
• Factors affecting resistance

  • Material of wire - copper has lower resistance than steel
  • Length - longer wires have greater resistance
  • Thickness - smaller diameter have a greater resistance
  • Temperature-heating a wire increases the resistance
• Thermistor


  A temperature sensor used in applications such as fire alarms. Its resistance decreases as the temperature increases.
• Thermistors are used as temperature sensors
• Applications of thermistors

  • Fire alarms
• LDR

  A light-dependent resistor used to detect light levels, for example, in automatic security lights. Its resistance decreases as the light intensity increases.
• Applications of LDRs

  • Automatic security lights
• Diode


  • Controls which way the current flows
  • Acts like a valve in a circuit, only letting current flow one way
• Fuse

  • A thin piece of wire designed to melt when the current that flows through it goes above a certain value
  • Breaks the circuit to prevent damage or fire in case of a fault
• A fault in a circuit may cause a large current
• A fuse will break the circuit and hopefully prevent damage or fire from happening
• acids contain which type of ions?

  Lots of Hplus ions
• Aalkali contain which ions?

  H- and few H+
• The more substrate molecules means

  The greater the reaction up to a limit
• enzyme reduce the activation energy
• The shape of the active site determines the 


  Function of the enzyme