topic 2

• Cell


  Smallest structural and functional unit of an organism, e.g. muscle cell
• Tissue


  Group of cells with a similar structure and function, e.g. muscle tissue
• Organ


  Aggregation (group) of tissues performing specific functions, e.g. stomach
• Organ system


  Group of organs performing specific functions, e.g. digestive system
• The nucleus of a cell is not an organ
• Food does not pass through the liver and pancreas in the digestive system

  
• Rewrite these in the correct order, from smallest to largest

  Neurone (cell) → nerve (tissue) → brain (organ) → nervous system (organ system) → dog (organism)
• Digestion


  Breaking down large, insoluble molecules in food into smaller, soluble molecules that can be absorbed into blood
• Enzyme


  A type of protein molecule that acts as a biological catalyst, speeding up reactions in organisms without being used up or changed
• Lock and key theory

  Simplified model to explain enzyme action: 1. Substrate fits into/binds to enzyme active site, 2. This causes a chemical reaction, 3. Products released from the unchanged enzyme

  
• Each enzyme has an active site with a specific (3D) shape, and only a substrate molecule with a complementary shape can bind/fit
• Metabolism


  The sum of all the reactions in a cell or the body, with different enzymes catalysing specific metabolic reactions
• Enzymes and their roles in digestion

  • Lipase - breaks down lipids (fats) into fatty acids and glycerol, produced in pancreas and small intestine, acts in small intestine
  • Carbohydrase (e.g. amylase) - breaks down carbohydrates into simple sugars, produced in salivary glands, pancreas and small intestine, acts in mouth and small intestine
  • Protease - breaks down proteins into amino acids, produced in stomach, pancreas and small intestine, acts in stomach and small intestine

  
• Denaturing of enzymes


  Active site changes shape (e.g. due to too high temp. or too high/low pH), so substrate no longer binds/fits and reaction can no longer be catalysed
• As temperature increases up to an optimum

  Rate of reaction increases

  
• As temperature increases above optimum

  Rate of reaction decreases to 0

  
• As pH is increased above or decreased below the optimum

  Enzyme activity decreases

  
• Amylase can only digest starch because it has an active site with a specific/unique shape that will only fit/bind to starch/the substrate

  
• How amylase breaks down starch

  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

  
• Tumour blocking tube from gall bladder to small intestine

  Difficulty digesting fat
• Pancreatic cancer


  Reduced/no enzyme production, so food not broken down/digested fully, leading to weight loss
• Test for sugars (carbohydrates)

  Grind up food, add Benedict's reagent, boil/heat, sugar turns solution green/yellow/orange/brick red
• Test for starch (carbohydrates)


  Grind up food, add iodine solution, starch turns solution blue-black

  
• Test for lipids (fats)


  Grind up food, add ethanol then water, fat turns solution milky/cloudy white

  
• Test for proteins


  Grind up food, add Biuret reagent, protein turns solution purple/lilac
• Safety precautions


  • Wear goggles to protect eyes, clean up spills immediately as Biuret is an irritant/corrosive/poisonous
• Method to compare sugar content in sausages


  Grind up each sausage and add to test tubes with water, add same mass of each, add same volume of Benedict's solution, place in heated water bath for same time, record colour change (green/yellow/orange/brown/red if sugar present, blue if no sugar)
• Independent variable


  pH of buffer solution
• Dependent variable


  Time for no starch to be detected (time taken for amylase to break down starch)

  
• Control variables


  Volume & concentration of amylase and starch solution, temperature of water bath

  
• Method to investigate effect of pH on amylase activity

  Set up test tubes with different pH solutions and starch, put in 30°C water bath for 10 mins, add amylase, remove drop every 30 secs to test for starch, record time when no starch detected

  
• Using smaller pH intervals and removing a drop every 10 secs would give more accurate values
• Keeping pH constant but changing another factor like temperature or starch concentration would extend the investigation
• Measuring starch concentration every 30 secs is better than subjective colour change as it is a quantitative measure

  
• Leaving starch/amylase solutions in water bath for 10 mins before adding amylase allows them to reach the same temperature

  
• Using 80°C water bath would denature the enzyme, preventing starch digestion
• Double circulatory system


  Blood passes through heart 2x for every circuit around body: 1. Right ventricle pumps blood to lungs, 2. Left ventricle pumps blood to rest of body
• Journey of blood through the heart

  Deoxygenated blood enters right atrium via vena cava, 2. Flows into right ventricle which pumps to lungs via pulmonary artery, 3. Oxygenated blood returns to left atrium via pulmonary vein, 4. Flows into left ventricle which pumps to body via aorta

  
• Functions of blood vessels

  Vena cava - returns deoxygenated blood to heart from body, Pulmonary artery - transports deoxygenated blood to lungs, Pulmonary vein - returns oxygenated blood to heart from lungs, Aorta - transports oxygenated blood to body

  
• Pacemaker


  Group of cells in right atrium that send regular electrical impulses to control natural resting heart rate