Long answer questions

• Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells.

  1. TEM use electrons and optical use light;
  2. TEM allows a greater resolution;
  3. (So with TEM) smaller organelles can be observed OR greater detail in organelles
  4. TEM view only dead/dehydrated specimens
  5. Specimens and optical (can) view live specimens;
  6. TEM does not show colour and optical (can);
  7. TEM requires thinner specimens;
  8. TEM requires a more complex/time consuming preparation;
  9. TEM focuses using magnets and optical uses (glass) lenses;
• Describe the gross structure of the human gas exchange system and how we breathe in and out.

  1. Named structures – trachea, bronchi, bronchioles, alveoli;
  2. Above structures named in correct order
  3. Breathing in – diaphragm contracts and external intercostal muscles contract;
  4. (Causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric, resulting in air moving in);
  5. Breathing out - Diaphragm relaxes and internal intercostal muscles contract;
  6. (Causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric, resulting in air moving out);
• Compare and contrast the structure and properties of triglycerides and phospholipids.

  1. Both contain ester bonds (between glycerol and fatty acid);
  2. Both contain glycerol;
  3. Fatty acids on both may be saturated or unsaturated;
  4. Both are insoluble in water;
  5. Both contain C, H and O but phospholipids also contain P;
  6. Triglyceride has three fatty acids and phospholipid has two fatty acids plus phosphate group;
  7. Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region;
  8. Phospholipids form monolayer /bilayer (in water) but triglycerides don’t;
• Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein.

  1. Glucose and galactose;
  2. Joined by condensation (reaction);
  3. Joined by glycosidic bond;
  4. Added to polypeptide in Golgi (apparatus);
• Explain five properties that make water important for organisms.

  1. A metabolite in condensation/hydrolysis/ photosynthesis/respiration;
  2. A solvent so (metabolic) reactions can occur OR A solvent so allowing transport of substances;
  3. High heat capacity so buffers changes in temperature;
  4. Large latent heat of vaporisation so provides a cooling effect (through evaporation);
  5. Cohesion (between water molecules) so supports columns of water (in plants);
  6. Cohesion (between water molecules) so produces surface tension supporting (small) organisms
• Describe the biochemical tests you would use to confirm the presence of lipid

  1. Add ethanol/alcohol then add water and shake/mix OR Add ethanol/alcohol and shake/mix then pour into/add water;
  2. White/milky emulsion OR emulsion test turns white/milky;
• Describe the biochemical tests you would use to confirm the presence of non-reducing sugar

  1. Do Benedict’s test and stays blue/negative;
  2. Boil with acid then neutralise with alkali;
  3. Heat with Benedict’s and becomes red/orange (precipitate); Amylase
• Describe the biochemical tests you would use to confirm the presence of amylase in a sample.

  1. Add biuret (reagent) and becomes purple/violet/mauve/lilac;
  2. Add starch, (leave for a time), test for reducing sugar/absence of starch;
• Describe how mRNA is formed by transcription in eukaryotes.

  1. Hydrogen bonds (between DNA bases) break;
  2. (Only) one DNA strand acts as a template;
  3. (Free) RNA nucleotides align by complementary base pairing;
  4. (In RNA) Uracil base pairs with adenine (on DNA) OR (In RNA) Uracil is used in place of thymine;
  5. RNA polymerase joins (adjacent RNA) nucleotides;
  6. (By) phosphodiester bonds (between adjacent nucleotides);
  7. Pre-mRNA is spliced (to form mRNA) OR Introns are removed (to form mRNA);
• Describe how a polypeptide is formed by translation of mRNA.

  1. mRNA attaches) to ribosomes OR (mRNA attaches) to rough endoplasmic reticulum;
  2. (tRNA) anticodons (bind to) complementary (mRNA) codons;
  3. tRNA brings a specific amino acid;
  4. Amino acids join by peptide bonds;
  5. (Amino acids join together) with the use of ATP;
  6. tRNA released (after amino acid joined to polypeptide);
  7. The ribosome moves along the mRNA to form the polypeptide;
• Define ‘gene mutation’

  1. Change in the base/nucleotide (sequence of chromosomes/DNA);
  2. Results in the formation of new allele;
• Explain how a gene mutation can have:

  • no effect on an individual

  1. Genetic code is degenerate (so amino acid sequence may not change); OR Mutation is in an intron (so amino acid sequence may not change);
  2. Does change amino acid but no effect on tertiary structure;
  3. (New allele) is recessive so does not influence phenotype;
• Explain how a gene mutation can have:

  • a positive effect on an individual.

  1. Results in change in polypeptide that positively changes the properties (of the protein) OR Results in change in polypeptide that positively changes a named protein;
  2. May result in increased reproductive success OR May result in increased survival (chances);
• Describe the structure of DNA.

  1. Polymer of nucleotides;
  2. Each nucleotide formed from deoxyribose, a phosphate (group) and an organic/nitrogenous base;
  3. Phosphodiester bonds (between nucleotides);
  4. Double helix/2 strands held by hydrogen bonds;
  5. (Hydrogen bonds/pairing) between adenine, thymine and cytosine, guanine;
• Name and describe five ways substances can move across the cell-surface membrane into a cell.

  1. (Simple) diffusion of small/non-polar molecules down a concentration gradient;
  2. Facilitated diffusion down a concentration gradient via protein carrier/channel;
  3. Osmosis of water down a water potential gradient;
  4. Active transport against a concentration gradient via protein carrier using ATP;
  5. Co-transport of 2 different substances using a carrier protein;
• Describe the transport of carbohydrate in plants.

  1. Sucrose actively transported into phloem (cell); OR Sucrose is co-transported/moved with H+ into phloem (cell);
  2. (By) companion/transfer cells;
  3. Lowers water potential (in phloem) and water enters (from xylem) by osmosis;
  4. (Produces) high(er) (hydrostatic) pressure; OR (Produces hydrostatic) pressure gradient;
  5. Mass flow to respiring cells OR Mass flow to storage tissue/organ;
  6. Unloaded/removed (from phloem) by active transport;
• Compare and contrast the structure of starch and the structure of cellulose.

  1. Both polysaccharides OR Both are glucose polymers OR Both are made of glucose monomers;
  2. Both contain glycosidic bonds (between monomers);
  3. Both contain carbon, hydrogen and oxygen/C, H and O;
  4. Starch has α-glucose and cellulose has β glucose;
  5. Starch (molecule) is helical/coiled and cellulose (molecule) is straight;
  6. Starch (molecule) is branched and cellulose is not/unbranched;
  7. Cellulose has (micro/macro) fibrils and starch does not;
• Describe the complete digestion of starch by a mammal.

  1. Hydrolysis;
  2. (Of) glycosidic bonds;
  3. (Starch) to maltose by amylase;
  4. (Maltose) to glucose by disaccharidase/maltase;
  5. Membrane-bound (disaccharidase/maltase);