2.2.1 The human digestive system

Cards (24)

  • What is digestion?
    ● Breaking down large, insoluble molecules in food
    Into smaller, soluble molecules that can be absorbed into blood
  • What is an enzyme?
    A type of protein molecule
    Biological catalystspeeds up reactions in organisms without being used up / changed
    Each type catalyses a specific reaction
  • How do enzymes work?
    1. Substrate (substance on which an enzyme acts) fits into / binds to enzyme active siteBecause shapes of active site and substrate are complementary
    2. This causes a chemical reaction (eg. bonds in substrate broken to produce smaller molecules)
    3. Products released from the unchanged enzyme
  • Why can each enzyme only catalyse a specific reaction? Eg. Why can amylase (enzyme) only break down starch (substrate)?
    Each enzyme has an active site with a specific (3D) shape
    Only a substrate molecule with a complementary shape to this active site can bind / fit
  • How are enzymes related to metabolism?
    Metabolism is the sum of all the reactions in a cell or the body
    Different enzymes catalyse specific metabolic reactions , eg. respiration
    Reactions may join smaller molecules to form larger molecules, or break down molecules
  • Enzyme: Lipase
    what does it break down?
    • Lipids (fats) into fatty acids + glycerol
    Where is it produced?
    • Pancreas & small intestine
    Where does it act?
    • Small intestine
  • Enzyme: Carbohydrase eg. amylase
    What does it break down
    • Carbohydrates into simple sugars eg. starch into glucose
    Where is it produced?
    • Salivary glands, pancreas & small intestine
    Where does it act?

    *mouth and small intestine
  • Enzyme: Protease
    what does it break down?
    Proteins into amino acids
    where is it produced?
    Stomach, pancreas & small intestine
  • Enzyme: Protease
    what does it break down?
    • Proteins into amino acids
    where is it produced?
    • Stomach, pancreas & small intestine
    Where does it act?
    Stomach and small intestine
  • How are the products of digestion used in the body once absorbed?
    -Fatty acids & glycerol
    ● To build new lipids (fats)
  • How are the products of digestion used in the body once absorbed?
    -Simple sugars eg. glucose
    ● To build new carbohydrates
    Some glucose used for respiration to release energy
  • How are the products of digestion used in the body once absorbed?
    -Amino acids
    ● To build new proteins
  • Where is bile produced, stored and released into?
    Produced - liver
    Stored - gall bladder
    Released into - small intestine
  • What is the role of bile in digestion?
    1. Alkaline so neutralises hydrochloric acid from stomach
    To create optimum conditions for small intestine enzymes
    2. Emulsifies lipids (fat) by converting larger lipid droplets into smaller droplets
    To increase surface area for lipase enzyme to work on
    To break down / digest fat faster
  • What does it mean when an enzyme denatures?
    Active site changes shape (eg. due to too high temp. or too high / low pH)
    ● So substrate no longer binds / fits and reaction can no longer be catalysed
  • Describe & explain how temperature affects enzyme activity
    ● Describe - as temperature increases up to an optimum, rate of reaction increases
    ○ Explain - molecules gain kinetic energy so more frequent enzyme-substrate collisions
    ● Describe - as temperature increases above optimum, rate of reaction decreases to 0
    ○ Explain - enzymes denature so substrate no longer fits
  • Describe & explain how pH affects enzyme activity
    ● Describe - enzyme activity is at a maximum at an optimum pH
    ● Describe - as pH is increased above or decreased below this, enzyme activity decreases
    ○ Explain - above / below optimum pH enzymes denature so substrate no longer fits
  • what is this statement wrong?
    “Enzymes are cells.”
    Enzymes are protein molecules, not cells
  • why is this statement wrong?
    “Bile is an enzyme.”
    Bile is not an enzyme. It is a substance produced by the liver that helps the enzyme lipase by emulsifying fats and neutralising acid.
  • why is this statement wrong?
    "Enzymes die at high temperatures.”
    Enzymes are not living, so they cannot die. At high temperatures they can denature, meaning their active site changes shape.
  • The enzyme amylase can only digest starch. Explain why amylase cannot digest other substances. (2)
    Amylase has an active site
    ● (With a specific / unique shape) which will only fit / bind to starch / the substrate
  • Amylase is an enzyme that breaks down starch. Explain how amylase breaks down starch. Answer in terms of the ‘lock and key theory’. (3)
    Starch / substrate binds to active site (of enzyme)
    Shape of active site and substrate are complementary
    ● A chemical reaction occurs to produce smaller molecules OR bonds between the (starch) molecules are broken to produce smaller molecules
  • A person has a tumour blocking the tube leading from the gall bladder to the small intestine. Explain why this person would have difficulty digesting fat. (4)
    No / less bile reaches the small intestine
    ● So less / no emulsification of fat
    ● So smaller surface area for lipase to break down fat
    pH of small intestine not neutralised
    ● So lipase is not at its optimum pH to break down fat
  • One symptom of pancreatic cancer is weight loss. Explain how pancreatic cancer may cause a person to lose weight. Do not refer to hormones in your answer. (4)
    ● Reduced / no enzyme production from pancreas
    ● Food is not broken down / digested fully
    ● Eg. less glucose absorbed
    ● So less glucose available for respiration so more fat used up in metabolism / respiration
    ● Eg. fewer fatty acids absorbed
    So fewer fatty acids available so less fat is stored