B4 - The Processes of Life

HideShow resource information


  • Enzymes are proteins which speed up chemical reactions
  • Lock & Key:
  • 1)Substrate molecules move towards active site
  • 2)Substrate fits in active site
  • 3)Reaction occurs and products made; enzyme speeds up reaction
  • 4)Product molecules do not fit in enzymes so are released
  • 5)Enzyme can be used again with new substrate molecules
  • Need to be at a specific constant temp to work at optimum
  • Changing temp causes a change in rate of reaction
  • High temp increases rate 
  • If temp is too high, bonds holding enzyme together break, changing shape of active site
  • Substrate no longer fits and enzyme stops working - Denaturing 
  • Enzymes also have an optimum pH
  • If pH is too low or too high, interferes with bonds therefore changes shape of active site.
1 of 7


  • Series of chemical reations that use energy from sunlight to build large food molecules in plant cells and phytoplankton
  • Carbon Dioxide+Water------>Glucose+Oxygen
  • 6CO2 + 6H2O------->C6H12O6
  • Sunlight absorbed by chlorophyll which is found in chloroplasts
  • Allows energy to be used to convert carbon dioxide and water into glucose
  • Glucose is:
  •   - converted to chemicals needed for growth e.g. cellulose for cell walls, protein, chlorophyll
  •   - converted into starch for storage
  •  - used in respiration to release energy
  • Glucose and nitrates taken up by roots are used to synthesise amino acids which are assembled into proteins
  • Oxygen is a waste product
2 of 7

Limiting Factors of Photosynthesis

  • 1) Not enough light slows down rate of photosynthesis
  • As light level is increased, rate increases steadily - upto a certain point 
  • Beyond that, there will be no difference as either temp or CO2 will be the limiting factor
  • 2) Too little carbon dioxide slows rate down 
  • Amount of CO2 increases rate upto a certain point
  • If there is enough light and CO2, limiting factor is temperature
  • 3)Temperature has to be right 
  • If temp is limiting factor it is too low - enzymes work more slowly at low temp
  • If plant is too hot, enzymes will denature
  • Enzymes denature at 45C
3 of 7

Aerobic Respiration

  • Respiration - release of energy by breaking down large food molecules
  • Aerobic respiration uses oxygen and occurs in animal and plant cells and some microorganisms
  • Glucose+Oxygen----->Carbon Dioxide+Water (+Energy Released)
  • C6H12O6+6O2----->6CO2+6H2O (+Energy Released) 
  • Aerobic resp happens in mitochondria has enzymes for aerobic respiration
  • Energy released speeds up reactions such as:
  • Movement - Energy needed to make muscles contract
  • Active Transport - Uses energy to move substances in and out of cells
  • Synthesis of large molecules - Large molecules/polymers made by joining smaller molecules which require energy. Glucose is joined to make starch and cellulose. In plant and animal cells and microorganisms, glucose and nitrogen joined to make amino acids         -> proteins 
4 of 7

Anaerobic Respiration + Fermentation

  • Occurs when there is little or no oxygen available
  • Occurs in human cells during vigorous exercise (body can't supply enough oxygen to muscle cells), plant cells in waterlogged soil and bacteria in wounds
  • Anaerobic respiration releases less energy than aerobic
  • Glucose----->Lactic acid + ENERGY
  • Fermentation used by some microorganisms - breaking down sugars into other products
  • Glucose----->Ethanol+Carbon Dioxide + ENERGY 
  • 1) Biogas - Fuel used for heating and lighting. Microorganisms ferment plant and animal waste containg carbs. Biogas made of methane and CO2
  • 2)Bread - Made using yeast----->Ferment the carbs in flour and release CO2, causing bread to rise
  • 3)Alcohol - Yeast ferment sugar to form alcohol (ethanol). Sugar used in production comes from grapes and barley.
5 of 7

Diffusion, Osmosis and Active Transport

  • Diffusion - Passive (no energy needed) movement of chemicals from a high to low conventration
  • In photosynthesis:
  • Water taken up by plant roots
  • CO2 enters plant leaves by diffusion
  • Oxygen leaves by diffusion
  • Osmosis - Movement of water from a dilute (high concentrated) to a concentrated solution (low concentration)
  • Chemicals separated by partially permeable membrane - lets water pass through but keeps other chemicals in or out
  • Movement of water into plant roots from soil and across roots occur by osmosis
  • Active Transport - Uses energy from respiratation to transport chemicals across cell membranes from area of low concentration to high concentration
  • Minerals such as nitrates taken up by plant roots use active transport. Concentration of minerals in root cells is higher than in the soil around them.
6 of 7


  • 1) Identification Key - used to identify plants by answering a series of questions. Start at Q1 and answer narrows down your options
  • 2)Quadrat - Square frame divided into a grid of 100 smaller squares. Put on the ground a number of times so an average is taken, or at random in a location if there is no obvious change in distribution of plants
  • If there is an obvious change, quadrat should be used along a line called a transect
  • 3) Light Meter - Light intensity needs to be measured if you were comparing plants in areas with different levels of light
  • Trees, bushes and hedges can cast shade on an area and can therefore affect growth of plants around them 
  • There may be a correlation between distance from a tree and growth of other plants
  • Other factors may be involved such as competition for nutrients
7 of 7


No comments have yet been made

Similar Science resources:

See all Science resources »See all Processes of Life resources »