Biology issues

• Water


  • Solvent, so metabolic reactions can occur
  • High latent heat of vaporization so provides a cooling effect
• Test for non-reducing sugar


  1. Add Benedicts, if it stays blue

  2. Boil with acid then neutralise with alkali

  3. Add Benedicts and heat, presence is indicated if sample turns brick red
• Large cells


  • Smaller SA:V ratio takes longer for oxygen to diffuse
• Different types of a disease/venom

  May have different forms of antigens, so will have different antibodies
• ELISA test


  1. Add cells to glass slide

  2. Add the antibody

  3. Wash to remove unattached antibody

  4. Add substrate to cause colour change
• Bacterial cell division


  1. Divides by binary fission

  2. Circular DNA replicates

  3. Cytoplasm divides
• Bacteria


  • Circular DNA and murein cell wall, but not in plant cells
• Required Practical - Only open the agar plate slightly to prevent anything from contaminating the agar and wear gloves to prevent contamination from bacteria on hands
• Movement into phloem


  Requires respiration, heat treatment damages living cells
• Inhalation


  Pressure decreases, volume increases
• Exhalation


  Pressure increases, volume decreases
• Test if animals are similar

  1. Compare DNA base sequence

  2. Compare amino acid sequence

  3. Compare mRNA base sequence
• DNA


  Two strands are held together by hydrogen bonds
• Ensure all water has been removed from a sample


  Weigh, and heat until the mass is constant
• Iris


  • Muscular structure, pupil constricts because circular muscle contracts and radial muscle relaxes
• Cones


  • Send separate sets of impulses to the brain
• Rod cells


  • High retinal convergence, enough depolarization to overcome threshold
• Darker band


  Action and myosin
• Lighter band


  Actin and the I band
• H zone


  Myosin only
• Depolarisation of pre-synaptic membrane

  Causes Ca+ channels to open
• (Protein)


  Transcription factor, binds to the DNA, stimulates RNA polymerase
• Stem cells


  Help with a disease by specialising
• Insert a gene into a plasmid


  Enzymes cut the plasmid, and ligase joins the sticky ends
• Whether or not the data shown is significant
• All are more effective than control, (blank) is most effective and (blank) is least effective
• You would reduce uncertainty by using closer intervals
• How does courtship behaviour increase successful interbreeding


  -Organisms attract mates when the female is fertile

  -Attract same species

  -Recognition of the opposite sex
• Why might populations have low genetic diversity

  1. Inbreeding
  2. Population may be small
• Genetic diversity


  Number of different alleles of each gene
• Why does less land mean a decrease in species diversity

  1. decrease in plant species
  2. Fewer habitats/less shelter
  3. Less food sources available
• Described translation (How mRNA is formed)

  1. Hydrogen bonds break
  2. One DNA strand acts as a template
  3. RNA nucleotides align to DNA base sequence
  4. Uracil replaces thymine and attaches to adenine
  5. RNA polymerase joins nucleotides
  6. By phosphodiester bonds
  7. Introns are removed in splicing
• Describe how a polypeptide chain is forced (Transcription)

  1. mRNA attaches to ribosomes
  2. tRNA with complimentary anti-codon binds to codon on mRNA
  3. has a specific amino acid on binding site
  4. peptide bond forms between amino acids
  5. using ATP in a condensation reaction
  6. tRNA detaches
  7. ribosome moves along mRNA to form a polypeptide
• genome


  complete set of genes in a cell
• proteome


  all the proteins that a cell can produce
• What does a golgi apparatus do?

  1. Transports / packages / modifies lipids
  2. Transports / packages/ modifies protein
• Two ways pathogens cause disease

  1. Release toxins
  2. Kill cells/tissues
• Why do HIV antibodies not mean a person has aids

  1. Need to measure number of T helper cells
  2. Need to test for AIDs related symptoms
• What does antigenic variation mean?

  1. Antigen on cell-surface of protein changes
  2. Antibody can no longer bind/isn't complimentary to antigen
• Explain the induced fit model

  1. Substrate binds to active site of enzyme
  2. Active site slightly changes shape so is complimentary to substrate
  3. Lowers the activation energy