Unit 1

• Prokaryotic cells


  Smaller and simpler cells (have no nucleus), e.g. bacteria
• Eukaryotic cells


  Bigger and more complex cells (they have a nucleus), include all animal and plant cells
• Organelles found in both eukaryotic and prokaryotic cells

  • Cytoplasm
  • Cell membrane
  • Ribosomes
• Additional organelles found in plant cells

  • Cell wall
  • Vacuole
  • Chloroplasts
• Specialised cell

  A cell that performs a specific function
• Sperm cell

  • Long tails to swim to the egg
  • Lots of mitochondria in middle piece to provide energy
  • Enzymes in acrosome to digest egg membrane
  • Haploid nuclei (23 chromosomes)
• Egg cell


  • Contains nutrients in cytoplasm to feed embryo
  • Haploid nuclei
  • Membrane hardens after fertilisation to stop more sperm
• Ciliated epithelial cells


  • Have cilia (hair-like structures) that beat to move substances along the surface
• Light (optical) microscope


  Uses light and lenses to form an image of a specimen and magnify it
• Electron microscope


  Uses beams of electrons instead of light, has higher magnification and resolution than light microscopes
• Magnification


  The process of enlarging the physical appearance or image of something
• Calculating total magnification

  Total magnification = eyepiece lens magnification × objective lens magnification
• Calculating magnification


  Magnification = image size ÷ actual size
• Resolution

  The ability to distinguish separate structures at close points
• Units of length

  • Metres (m)
  • Millimetres (mm)
  • Micrometres (μm)
  • Nanometres (nm)
  • Picometres (pm)
• Microscopy core practical


  1. Prepare specimen slide

  2. Add stain

  3. Place coverslip

  4. Examine specimen under microscope
• Enzyme

  Biological catalyst that increases the speed of a reaction without being changed or used up
• Lock-and-key model


  Shows how enzymes work - the enzyme has an active site specific to a substrate
• Catalysis

  When a complex substance is separated or broken down into simpler substances
• Synthesis


  When simpler substances are joined to make a complex substance
• Denaturation

  When the active site of an enzyme changes shape so it is no longer specific to the substrate
• Temperature increases


  Rate of enzyme activity increases (up to optimum temperature)
• pH changes from optimum

  Enzyme activity decreases
• Substrate concentration increases

  Rate of enzyme activity increases (up to saturation point)
• Core practical: Effect of pH on enzyme activity

  1. Prepare solutions

  2. Mix amylase and buffer

  3. Add starch

  4. Take samples over time

  5. Observe colour change

  6. Calculate rate of reaction
• Carbohydrates, proteins, and lipids are big and complex biological molecules, which are essential for life
• Amylase enzyme activity experiment

  1. Add amylase and buffer solution to boiling tube

  2. Add starch solution to boiling tube

  3. Mix and put in water bath

  4. Take samples every 30 seconds and test for starch

  5. Calculate rate of reaction
• Carbohydrates, proteins, lipids

  Big and complex biological molecules, essential for life
• Monomers

  Smaller units from which larger molecules are made
• Polymers

  Complex molecules made from many monomers joined together
• Breakdown of large biological molecules

  1. Catalysed by digestive enzymes

  2. Breaks down into smaller, soluble molecules

  3. Can be absorbed into bloodstream
• Synthesis of biological molecules

  1. From smaller monomers to larger polymers

  2. Catalysed by synthesis enzymes
• Biological molecules that can be synthesised

  • Carbohydrates from simple sugars
  • Proteins from amino acids
  • Lipids from fatty acids and glycerol
• Types of digestive enzymes

  • Carbohydrases (e.g. amylase, maltase, lactase)
  • Proteases (e.g. pepsin, trypsin, chymotrypsin)
  • Lipases (e.g. human pancreatic lipase)
• Benedict's test for reducing sugars


  1. Add food sample, Benedict's reagent, heat in water bath

  2. Colour change indicates amount of reducing sugars
• Benedict's test for non-reducing sugars

  1. Hydrolyse sugar first, then do Benedict's test

  2. Colour change indicates amount of non-reducing sugars
• Iodine test for starch

  1. Add food sample, water, iodine solution

  2. Blue-black colour indicates presence of starch
• Biuret test for proteins

  1. Add food sample, potassium hydroxide, copper(II) sulfate

  2. Pink/purple colour indicates presence of proteins
• Emulsion test for lipids

  1. Add food sample, ethanol, shake, add water

  2. Milky white emulsion indicates presence of lipids
• Calorimetry to measure food energy

  1. Weigh food sample, heat in flame, measure temperature rise in water

  2. Calculate energy transferred and energy per gram