Bio - Paper 1

• Cells

  The basic building blocks of life that can replicate independently
• Multicellular organisms like animals and plants contain many cells that divide to grow or replace dead cells, not to create new organisms</b>
• Bacteria are single-celled prokaryotic organisms
• Subcellular structures common to animal and plant cells

  • Cell membrane
  • Nucleus
  • Cytoplasm
  • Mitochondria
  • Ribosomes
• Plant cells

  • Have a rigid cell wall made of cellulose
  • Contain a permanent vacuole with cell sap
  • Contain chloroplasts for photosynthesis
• Bacterial cells

  • Lack mitochondria and chloroplasts
  • Have a single circular strand of DNA instead of a nucleus
  • May have additional plasmids
  • May have flagella for movement
• Photosynthesis occurs in the chloroplasts of plant cells, using chlorophyll to absorb light energy
• Mitochondria in cells break down glucose through aerobic respiration to provide energy
• Microscopy

  The use of microscopes
• How light microscopes work

  1. Light from the room hits the mirror

  2. Light reflected upwards through the object

  3. Light passes through the objective lens

  4. Light passes through the eyepiece lens

  5. Light enters the eye
• Object

  The real object or sample that you're looking at
• Image

  The image that we see when we look down the microscope
• Magnification

  How many times larger the image is than the object
• Magnification = image size / object size
• Resolution

  The shortest distance between two points on an object that can still be distinguished as two separate entities
• Higher resolution


  More details can be seen, less blurry the image
• Microscope required practical

  1. Prepare slide

  2. Add dye

  3. Add cover slip

  4. Place slide on stage

  5. Use lowest magnification objective lens

  6. Use coarse focus wheel

  7. Use fine focus wheel

  8. Draw image

  9. Change to higher magnification

  10. Refocus image
• Magnification

  Equals image size over real size
• Osmosis

  Movement of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Osmosis required practical

  1. Cut vegetable pieces to similar size

  2. Weigh each piece

  3. Add pieces to different sugar solutions (0M, 0.5M, 1M)

  4. Leave for 24 hours

  5. Remove, dry, and reweigh pieces

  6. Calculate percentage change in mass
• Percentage change = (change in mass / original mass) x 100
• Graph of percentage change in mass vs sugar concentration will intersect x-axis at the sugar concentration inside the vegetable
• Enzyme required practical

  1. Heat water bath to 37°C

  2. Add amylase and pH 3 buffer to boiling tube

  3. Add starch and start timer

  4. Every 30 seconds, take sample and add to iodine well on spotting tile
• Iodine will turn black when added to samples in early stages, indicating presence of starch
• Iodine test for starch

  1. Add a couple of drops of iodine into each well

  2. Iodine turns orange
• Amylase test for starch

  1. Add 5 cm³ of starch to boiling tube

  2. Start stopwatch

  3. Take sample every 30 seconds

  4. Add sample to well

  5. Well turns black at first

  6. Then turns brown

  7. Then turns orange
• Rate of reaction

  Calculated as 1000 / time
• Independent variable is pH buffer

  Dependent variable is rate of reaction
• Food tests

  • Starch (iodine test)
  • Sugar (Benedict's test)
  • Protein (Biuret test)
• Preparing food sample

  1. Crush food in pestle and mortar

  2. Mix with water in test tube
• Starch test

  1. Add iodine to food solution

  2. Colour change to black indicates starch
• Sugar test

  Add Benedict's solution to food solution

  Heat in water bath

  Colour change to orange/green/brick red indicates sugar
• Protein test

  Add Biuret solution to food solution

  Colour change to purple indicates protein
• Measuring rate of photosynthesis

  • Submerge pond weed in water

  Count bubbles produced per minute

  Vary light intensity by changing distance of lamp
• Independent variable is distance between lamp and pond weed

  Dependent variable is number of bubbles per minute
• Inverse square law

  Light intensity is inversely proportional to distance squared
• Investigating effect of antibiotics on bacteria


  Prepare uncontaminated bacterial cultures

  Seed agar plates with bacteria

  Place antibiotic discs on plates

  Incubate plates

  Measure zone of inhibition around antibiotic discs
• Antibiotics are specific to different bacteria
• Zone of inhibition

  Area around antibiotic disc where no bacteria are able to grow
• Nanometers

  Smallest unit of length you need to know