yr 12 sequences

• Test for lipids


  1. Add ethanol to sample

  2. Add water

  3. Shake/mix

  4. White emulsion is positive
• Test for reducing sugars


  1. Add Benedict's solution to sample

  2. Heat

  3. Brick-red ppt then positive
• Test for non-reducing sugars


  1. Test for reducing sugars (Benedict's)

  2. If stay blue then boil with hydrochloric acid

  3. Neutralise with sodium hydroxide

  4. If become red/orange then positive
• Test for proteins


  1. Add biuret reagent to sample

  2. Positive result is purple solution
• Test for starch


  1. Add iodine solution

  2. Positive result is blue/black solution
• Starch


  • Helical shape so compact
  • Insoluble so not affect osmosis
  • Branched so glucose released easily for respiration
  • Large so cannot leave the cell
• Cellulose


  • Long strands of B-glucose joined by hydrogen bonds via condensation reactions to form microfibrils that provide rigidity and strength
  • Helical and compact structure
  • Polymer of glucose so easily hydrolysed
  • Branched to have more ends for hydrolysis
  • Made of glucose so provides respiratory substrate
  • Insoluble so doesn't affect osmosis
• Protein structure


  • Primary - order of amino acids
  • Secondary - folding of polypeptide chain due to hydrogen bonds
  • Tertiary - 3D folding due to disulfide bridges
  • Quaternary - two or more polypeptide chains
• Enzyme catalysis


  • Substrate is complementary to the active site
  • Enzyme is specific and will only catalyse one reaction
  • Active site determined by the enzyme's tertiary structure
  • Initially the active site is not complementary to substrate
  • Shape of active site changes as enzyme-substrate complex forms
  • Stressing/distorting bonds in substrate
• DNA replication


  1. DNA helicase winds open by breaking hydrogen bonds

  2. Both strands act as templates

  3. Free nucleotides line up in complementing pairs

  4. DNA polymerase joins nucleotides forming phosphodiester bonds

  5. New DNA molecule consists of one original strand and one new strand
• Properties of water


  • Solvent for metabolic reactions
  • High specific heat capacity buffers changes in temperature
  • Large latent heat of vaporisation provides cooling effect
  • Cohesion supports columns of water in plants
  • Surface tension supports small organisms
• Organelles needed to make proteins


  • Ribosomes
  • Golgi apparatus
  • Vesicles
• Virus replication


  • Attachment proteins attach to receptors on host cells
  • Viral RNA enters the cell
  • Reverse transcriptase converts RNA to DNA
  • Viral capsid and enzymes produced
  • Assembled and released
• Cell fractionation/ultracentrifugation


  1. Cell homogenisation

  2. Filter to remove cells and break open membranes

  3. Use isotonic solution to prevent organelle damage

  4. Keep cold to prevent enzyme damage

  5. Use buffer to prevent protein/enzyme denaturation

  6. Centrifuge at lower speed to separate nuclei

  7. Repeat at higher speeds to get purified organelles
• TEM vs SEM


  • TEM uses electrons, lower resolution, alive specimens
  • SEM uses electrons, higher resolution, dead specimens
  • Optical microscopy, lowest magnification, colour, alive specimens
• Mitosis


  1. Interphase: Chromosomes replicate

  2. Prophase: Chromosomes condense

  3. Metaphase: Chromosomes line up on the equator

  4. Anaphase: Centromeres split, sister chromatids pulled to opposite poles

  5. Telophase: Chromatids unwind, new nuclear membranes form
• Preparing root tip squash

  1. Cut root tips 5mm from 10 garlic roots

  2. Place in petri dish with fixative for 12 minutes

  3. Rinse in distilled water

  4. Stain with aceto-carmine stain

  5. Place on slide, add coverslip, gently press down

  6. Observe under microscope
• Mitotic index


  • Count cells in mitosis, divide by total cells, repeat 10 times
  • Measure cell size using eyepiece graticule calibrated against stage micrometer
• Movement of molecules across cell membrane


  • Simple diffusion: Substance moves down concentration gradient
  • Facilitated diffusion: Substance moves down gradient through carrier protein
  • Osmosis: Net movement of water from high to low concentration through partially permeable membrane
  • Active transport: Substance moves from low to high concentration, against gradient, using energy
• Immune response


  1. Phagocyte engulfs pathogen, presents antigen

  2. T cell with complementary receptor binds antigen, stimulates B cell

  3. B cell divides to form clones secreting antibody

  4. Memory cells produced
• Vaccination


  1. Antigens from vaccine presented by macrophage

  2. T cell with complementary receptor binds antigen, stimulates B cell

  3. B cell divides to form clones secreting antibody

  4. Memory cells produced
• ELISA


  • Primary antibody binds to antigen
  • Secondary antibody with enzyme attached binds
  • Enzyme substrate added, colour change indicates presence of antigen
• Tracheal system in insects


  • Water blood flow in opposite directions
  • Spiracles allow diffusion of gases
  • Tracheae are highly branched and permeable to gases
• Stomatal control of water loss


  • Smaller leaf surface area reduces evaporation
  • Hairs and sunken stomata reduce air movement and increase humidity
  • Curled leaves reduce air movement and increase humidity
  • Stomata close when too hot/light to prevent water loss
• Breathing mechanism


  1. Diaphragm contracts, external intercostal muscles contract

  2. Volume increases, pressure decreases, air moves in
• Digestion of proteins


  1. Hydrolysis of peptide bonds

  2. Endopeptidases act in the middle of polypeptides

  3. Exopeptidases act at the ends of polypeptides

  4. Amino acids absorbed into blood
• Digestion of lipids


  1. Lipase breaks down fats into fatty acids and glycerol

  2. Micelles contain fatty acids and monoglycerides

  3. Micelles transported to epithelial cells, reformed into triglycerides/chylomicrons for transport
• Digestion of carbohydrates


  1. Amylase hydrolyses starch to maltose

  2. Maltase hydrolyses maltose to glucose

  3. Glucose absorbed with sodium ions against concentration gradient
• Blood pressure and circulation


  • Hydrostatic pressure high in capillaries, lower in veins
  • Pressure differences drive blood flow and lymph flow
  • Atrial systole - atria contract, ventricles relax
  • Ventricular systole - ventricles contract, atria relax
• Transpiration


  1. Stomata open in light, more water lost

  2. Water lost provides cooling effect

  3. Hydrogen bonding between water molecules pulls water up xylem
• Translocation in phloem


  1. Sucrose actively transported into phloem at source

  2. Osmotic gradient draws in water, creating high hydrostatic pressure

  3. Mass flow of sugars towards sink (roots) where they are removed
• Transcription


  1. DNA strands separated, RNA nucleotides align by complementary base pairing

  2. RNA polymerase joins adjacent RNA nucleotides by phosphodiester bonds

  3. Pre-mRNA is spliced to remove introns
• Translation


  1. mRNA attaches to ribosomes

  2. tRNA anticodons bind to complementary mRNA codons

  3. Amino acids join by peptide bonds, tRNA released
• Meiosis


  1. Chromosomes condense and associate in homologous pairs

  2. Crossing-over occurs, independent assortment at equator

  3. Homologues separate, sister chromatids split
• Types of natural selection


  • Directional - best adapted phenotype selected for
  • Stabilising - extreme phenotypes selected against
  • Disruptive - two extreme phenotypes selected for