Enzymes, Digestion & Respiration (biology)

• What is an enzyme?

  A biological catalyst. speeds up reactions without being altered or used.
• Describe the structure of an enzyme

  A protein molecule made of chains of amino acids. has an active site where reactions occur.
• How do enzymes affect the rate of reaction?

  increase it.
• The term used to describe enzymes which no longer work (typically due to temperature or ph)

  Denaturation
• Discuss the effects of temperature on enzyme action


  At cooler temperatures, there are less collisions between enzymes and substrates due to less kinetic energy. However, when the enzyme exceeds a certain temperature, it is denatured because the bonds within the protein molecule begin to break, causing the amino acid chains to unravel, meaning that the active site changes its shape.
• Discuss the effects of pH on enzyme action

  When the pH is too acid or alkali, it causes the bonds within the protein molecule to break which unravels the amino acid chains, changing the shape of the active site and denaturing the enzyme.
• Describe the function of amylase

  Amylase breaks starch into maltose. produced by salivary glands, and by the pancreas and secreted into the small intestine.
• Describe the function of maltase

  Maltase completes digestion of starch by breaking maltose into glucose. produced by the wall of the small intestine .
• Describe the function of proteases/peptidases

  Complete the digestion of proteins by breaking polypeptides into amino acids. produced in stomach, small intestine and pancreas.
• Describe the function of trypsin


  Continues digestion of proteins by breaking them into polypeptides. produced by the pancreas.
• Describe the function of pepsin

  Begins digestion of proteins by breaking them into polypeptides. produced by glands in the mucous membrane lining the stomach.
• What is a polypeptide?

  chain of amino acids.
• Describe the function of lipase


  Digests lipids into fatty acids and glycerol. Produced by pancreas, mouth and stomach.
• Describe the function of bile

  Aids enzymes by breaking fat into droplets (emulsifying), increasing the surface area. Produced in the liver and stored in the gallbladder. Neutralises HCL in stomach. not an enzyme.
• hydrochloric acid


  Kills bacteria in the stomach and provides an acidic environment for enzymes to function. Produced by stomach wall. Does not digest food.
• Discuss the metabolic reactions enzymes are involved in.

  Respiration - living cells release energy from glucose in the form of ATP.

  Photosynthesis - green plants transform light energy into chemical energy.

  Protein synthesis - the process of creating protein molecules.
• What is photosynthesis?


  The process by which a plant cell captures energy in sunlight and uses it to make food.
• Chemical and word equation for aerobic respiration in plants and animals

  C6H12O6 + 6O2 -> 6CO2 + 6H2O , glucose + oxygen -> carbon dioxide + water
• Chemical and word equation for anaerobic respiration in animals

  C6H12O6 -> 2C3H6O3 , glucose -> lactic acid
• Chemical and word equation for anaerobic respiration in yeast

  C6H12O6 -> 2C2H5OH + 2CO2 , glucose -> ethanol + carbon dioxide
• In which conditions do cells respire?

  At all times.
• What is oxygen debt?

  the amount of oxygen needed to oxidise lactic acid to carbon dioxide and water or glucose in the liver.
• formula for rate of reaction

  1/time (s-1)
• why is a control used in an experiment?

  To compare the results of the experiment with the effects of the environment on the experiment
• Respiration...


  Releases energy in the form of ATP
• compare aerobic and anaerobic respiration in humans

  aerobic produces co2 and h2o while anaerobic produces lactic acid. aerobic uses oxygen and produces more energy. anaerobic produces less energy, however does this faster. anaerobic is only used when there is a shortage of oxygen, eg during exercise.
• factors affecting rate of respiration

  temperature (as enzymes reach optimum), water (facilitates transport of oxygen through blood), oxygen
• what is the test for starch?

  yellow brown iodine solution will turn blue black.
• test for sugars?


  blue Benedict's solution will turn red when heated in a boiling tube with hot water bath.
• test for lipids?


  water and ethanol, when shaken well and left for 1 minute, will form cloudy white emulsion if lipid present.
• test for protein?


  blue biuret solution turns purple.
• what is ingestion?


  where food enters the mouth (alimentary canal)
• what is (chemical) digestion?

  where food is broken down by enzymes
• what is (mechanical) digestion?

  where food is physically broken down by muscles
• what is absorption?


  where digested food molecules are absorbed through the wall of the small intestine into the bloodstream
• egestion


  where excess water is absorbed back into the body in the large intestine. the process of removing excess food through the anus.
• excretion


  removal of waste products from chemical reactions
• assimilation


  absorption of nutrients for growth and repair.
• persistalsis


  food is moved through the digestive tract through the process of two muscles in the gut wall contracting.
• digestive tract


  oesophagus->stomach->small intestine->large intestine