Paper 1: A level Biology AQA

• Water removed from the reactants joining two molecules together forming a chemical bond


  Condensation
• The addition of water to the reactants to break a chemical bond between 2 molecules


  Hydrolysis
• 1. Add Benedict's reagent. 2. Heat the solution in a water bath for 5 minutes at 95 degrees Celsius. 3. Change from blue to brick red as CuO formed


  Test for Reducing Sugars (3)
• Smaller units from which larger molecules are made

  Monomer
• 1. Add 2cm³ of food sample then add 2cm³ of dilute HCl and heat.

  2. Add 2cm³ of NaHCO3 then do test for reducing sugars.

  Non-Reducing Sugars (2)
• Add drops of iodine to starch solution. Colour change to blue-black


  Test for Starch (1)
• 1. Mix Test solution with ethanol.

  2. Shake for 1 minute then add water.

  3. Cloudy white emulsion


  Test for Lipids (3)
• 1. Obtain equal volumes of test solution and NaOH then add a few drops of biuret solution (dilute copper (II) sulphate solution).

  2. Colour change to mauve/purple


  Test for Proteins (2)
• 1. Very high resolution.

  2. Needs thin and dead specimen.

  3. Artefacts can occur (remnant left on object during prep, such as air bubbles)

  4. Uses magnets to focus on specimen

  5. Uses electrons fired at sample.

  6. Is not in colour

  Transmission Electron Microscope (5)
• 1. Inhibitor is similar in shape to substrate so it impermanently binds to the active site.

  2. Prevents ESC from forming, slowing rate

  Competitive inhibition (2)
• 1. Molecule will bind to allosteric site.

  2. Binding causes a change in active site.

  3. Permanently preventing further ESC.

  Non-competitive inhibition (3)
• 1. DNA helicase breaks the hydrogen bonds between the base pairs

  2. 2 single strands formed as the double helix "unzips".

  3. Free DNA nucleotides in the nucleoplasm bond to the complementary bases on the strand.

  4. DNA polymerase forms phosphodiester bonds between adjacent DNA nucleotides via condensation reaction with the hydrolysis of ATP, forming the phosphate backbone


  DNA Replication: Semiconservative (4)
• 1. ATP stores or releases only a small amount of energy at a time, so no energy is wasted as heat.

  2. Small and soluble so easily transported

  3. Easily broken down, so energy is released instantaneously

  4. Can be quickly re-made

  5. Can make other molecules more reactive via phosphorylation

  6. ATP can't pass out of cell, so the cell always has an immediate supply of energy.


  Describe 6 properties of ATP that make it a good energy source. (6)
• The ability to distinguish two points apart

  Resolution
• 1. Lower resolution than TEM

  2. 3D image

  3. Does not require thin samples


  Scanning Electron Microscope
• The mass of organelles at the bottom of the test tube after centrifugation.

  Pellet
• Cold. Low temperature slows enzyme activity, minimising self digestion by reducing metabolic rate. Isotonic. Salt and sugar concentration kept the same, minimising organelle size change due to osmosis. Buffered. Minimum changes in pH, so prevents enzymes in organelles denaturing.

  Solution Required for cell fractionation (6 Marks)
• 1. Homogenisation. Breaking up cells by blending the sample to create a homogenate.

  2. Filtering. Filtering the large, unwanted sil, producing the filtrate.

  3. Ultracentrifugation. Spin in a centrifuge so components separate out by weight. Heavier near the bottom of the tube.

  4. Supernatant is removed and spun again at higher speed.


  Separation of Organelles From The Cells (4)
• The solution not including the pellet at the bottom of the test tube after centrifugation.


  Supernatant
• 1. Cell wall forms, dividing the two genetically identical daughter cells.

  2. Same circular DNA.


  Binary Fission 3
• Nuclei, Chloroplasts, Mitochondria, Lysosomes, Endoplasmic Reticulum, Ribosomes

  Order of Organelles
• Cell grows and carrys out its normal function

  Interphase
• Cells grow to normal size. Organelles replicate and genes are expressed to make proteins needed.

  Interphase G1
• DNA and histones replicated.

  Interphase S
• Spindle fibres are made

  Interphase G2
• 1. DNA winds up making chromosones from chromatin.

  2. Centrioles appear at opposite poles of the cell. 3. Nucleolus disappears

  Prophase (3)
• 1. Nuclear envelope disappears.

  2. Chromosomes align along the equator of the cell.

  3. Spindle fibres connect centrioles to chromosomes

  Metaphase (3)
• 1. Spindle fibres contract pulling daughter chromosomes to opposite poles of the cell.

  Anaphase (1)
• 1. Spindle fibres disperse.

  2. Nuclear envelope forms.

  3. Chromatids uncoil to chromatin

  Telophase (3)
• 1. Cytoplasm constricts separating the cells into two.

  2. Membrane forms creating two new genetically identical daughter cells.


  Cytokinesis (2)
• number of cells in mitosis/total number of cells

  Mitotic index
• 1. Circular DNA replicates and both copies attach to the cell membrane.

  2. Plasmids also replicate.


  Binary fission 1 (2)
• Cell membrane grows between the two DNA molecules and pinches them inwards dividing the cell into 2.


  Binary Fission 2 (1)
• 1. Attach to host cell via attachment protein and inject nucleic acid into the cell.

  2. This gives the instructions to construct the virus

  Virus Replication 1 (2)
• 1. The virus is then assembled and leaves the cell, taking the phospholipid bilayer with it.

  2. This creates holes in the cell and kills it.

  Virus Replication 2 (2)
• Fluid: All the components can move around. Mosaic: Many different components all fit together

  Fluid mosaic Structure [Fluid][Mosaic] (2)
• The passive transport of large molecules such as amino acids and sugars, but they require integral proteins to pass through.

  Facilitated Diffusion
• The passive movement of particles from a high concentration to a region of low concentration, down a concentration gradient.

  Diffusion
• 1. Add antibody that is specific to antigen. After leaving them to bind, wash the surface to remove unattached antibodies.

  2. Add a second antibody with an enzyme attached.

  3. Second antibody binds with first antibody

  4. Add colourless substrate of enzyme, which the enzyme will act upon to give a coloured product.

  5. The intensity of the colour is relative to the amount of antigen present.

  ELISA Test (Enzyme linked Immunosorbent Assay) (5)
• Small, non-polar molecules (excluding water) freely diffuses in and out of cells through gaps between phospholipids.


  Simple Lipid Diffusion