Biology paper 1 practice Qs

• name the fixed position occupied by a gene on a DNA molecule?

  locus/loci
• describe how a gene is a code for the production of a polypeptide. do not include information about transcription or translation in your answer?

  • because the base/ nucleotide sequence
  • in triplets
  • determines the order/sequence of amino acid sequence/ primary structure in polypeptides
• Define the term exon?

  base/ nucleotide sequence coding for a polynucleotide/ sequence of amino acids/ primary structure
• describe how a phosphodiester bond is formed between 2 nucleotides within a DNA molecule?

  • condensation (reaction) loss of water
  • between the phosphate group on one and deoxyribose an another
  • catalysed by DNA polymerase
• three differences between DNA in the nucleus of a plant cell and DNA in a prokaryotic cell?

  • associated with histone proteins/ no histone proteins
  • linear/ circular
  • no plasmids / plasmids
  • introns/no inrons
  • longer / shorter
• name the protein associated with DNA in a chromosome?

  histone
• define non-coding base sequence and describe where the non-coding multiple repeats are positioned in the genome?

  DNA that does not code for protein/ polypeptide/ sequence of amino acids/ tRNA/ mRNA

  positioned between genes
• gibe three ways in which the DNA in a chloroplast is different from DNA in the nucleus:

  • DNA is shorter
  • Fewer genes
  • DNA is circular not linear
  • Not associated with proteins/ histones unlike nuclear DNA
  • introns absent, but present in nuclear DNA
• give one other difference between the structure of a DNA nucleotide and the structure of an RNA nucleotide?

  deoxyribose in DNA and ribose in RNA
• not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide - give 2 reasons why?

  • some triplets code for the same amino acids - DNA code is degenerate
  • mutation made occur in introns/ non-coding sequence
• compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells?

  • nucleotide structure is identical
  • nucleotides joined by phosphodiester bond
  • deoxyribose joined to phosphate (in sugar-phosphate backbone)
  • eukaryotic associated with histones
  • eukaryotic is longer
  • eukaryotic contains introns
  • eukaryotic is linear
  • DNA in mitochondria/ chloroplasts same/ similar structure to DNA in prokaryotes
• suggest one way the structure of the chromosomes could differ along its length to result in the stain binding more in some areas?

  • differences in base sequences
  • differences in histones/ interactions with histones
  • differences in condensation (super)coiling
• what is a homologous pair of chromosomes?

  two chromosomes that carry the same genes
• the enzyme encoded by the ADf allele catalyses the breakdown of alcohol faster than the enzyme encoded by the ADe allele - suggest why?

  • different primary structure/ amino acid sequence
  • different tertiary structure/ shape of active site
  • enzyme-substrate complexes more likely with enzyme from ADf allele
• describe the transport of carbohydrate in plants:

  • sucrose is actively transported into the phloem cell / sucrose is co-transported with H+ ins into the phloem
  • by the companion cells
  • which lowers the water potential in the phloem and so water enters from the xylem by osmosis
  • this produces a higher hydrostatic pressure/ hydrostatic pressure gradient
  • which causes mass flow to respiring cells/ to storage tissues/ organ
  • where is it unloaded from the phloem by active transport
• compare and contrast the structure of starch and the structure of cellulose:

  • both polysaccharides/both glucose polymers/ both are made from glucose monomers
  • both contain glycosidic bonds between monomers
  • both contain carbon, hydrogen and oxygen
  • starch has alpha glucose and cellulose has beta
  • starch molecule is helical/ coiled and cellulose molecule is a straight chain
  • starch molecule is branched and cellulose is unbranched
  • cellulose has micro/macro fibrils and starch does not
• describe the complete digestion of starch by a mammal:

  • hydrolysis of glycosidic bonds
  • starch to maltose by amylase
  • maltose to glucose by membrane bound disaccharidase/ maltase
• show two difference between the circulation of blood in fish and the circulation of blood in a mammal:

  • fish 2 chambers/ 1 ventricle/ 1 atrium / 2 valves - mammal - 4 chambers / 2 ventricles / 2 atria / 4 valves
  • blood does not return to the heart after being oxygenated - blood returns to the heart after being oxygenated
  • blood does not return to the heart after passing through the gills - blood returns to the heart after passing through lungs
  • heart contains deoxygenated blood - heart contains oxygenated and deoxygenated blood
• describe the structure and function of the nucleus:

  • nuclear envelope and pores / double membrane and nuclear pores
  • chromosomes/ chromatin
  • DNA with histones
  • nucleolus/ nuclei
  • stores genetic information/ material for polypeptide production / is the code for polypeptides
  • where DNA replication occurs
  • production of mRNA/ tRNA
  • production of rRNA/ ribosomes
• name the main polymer that forms the following cell walls:

  plant - cellulose

  fungal - chitin
• suggest 1 reason the scientists used biomass instead of the number of individuals of each plant species when collecting data to measure diversity:

  • individual organisms could not be identified/ separated
  • too small/ numerous to count individuals
  • too time consuming
• describe how mRNA is formed by transcription in eukaryotes:

  • hydrogen bonds between DNA bases break
  • only one DNA strand acts as a template
  • free RNA nucleotides align by complementary base pairing
  • in RNA uracil pairs with base adenine on DNA
  • in RNA uracil is used in place of thymine
  • RNA polymerase joins adjacent RNA nucleotides
  • by phosphodiester bonds between adjacent nucleotides
  • pre-MRNA is spliced to form mRNA - introns are removed to form mRNA
• describe how a polypeptide is formed by translation of mRNA:

  • mRNA attaches to ribosomes/ RER
  • tRNA anticodons bind to complementary mRNA codons
  • tRNA brings a specific amino acid
  • amino acids joined by peptide bonds - with the use of ATP
  • tRNA is released (after amino acid joined to polypeptide)
  • ribosome moves along the mRNA to form the polypeptide
• Gene mutation


  A change in the base/ nucleotide sequence of chromosomes/ DNA which results in the formation of a new allele
• Gene mutation has no effect on an individual

  • Genetic code is degenerate - so amino acid sequence may not change
  • Mutation is in an intron (so amino acid sequence many not change)
  • New allele is recessive so does not influence phenotype
• Gene mutation has a positive effect on an individual


  • Results in change in polypeptide that positively changed properties of the protein
  • May result in increased reproductive success
  • May result in increased survival chances
• describe the gross structure of the human gas exchange system and how we breathe in and out:

  • trachea - bronchi - bronchioles - alveoli
  • breathing in - diaphragm contracts and external intercostal muscles contract
  • causes volume increase and pressure decrease in thoracic cavity (to below atmospheric pressure, resulting in air moving in)
  • breathing out - diaphragm relaxes and internal intercostal muscles contract
  • causes volume decrease and pressure increase in thoracic cavity (to above atmospheric, resulting in air moving out)
• compare and contrast the structures and properties of triglycerides and phospholipids:

  • both contain ester bonds between glycerol and fatty acids
  • both contain glycerol
  • fatty acids on both may be saturated or unsaturated
  • both insoluble in water
  • both contain C, H and O but phospholipids also contain P
  • triglyceride has 3 fatty acids and phospholipid has 2 plus the phosphate group
  • triglycerides are hydrophobic/ non-polar and phospholipids have hydrophilic and hydrophobic regions
  • phospholipids form monolayer on surface/ micelle/bilayer - triglycerides don't
• describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein:

  • glucose and galactose
  • joined by condensation reaction
  • joined by glycosidic bond
  • added to polypeptide in golgi apparatus
• describe the role of 2 named enzymes in the process of semi-conservative replication:

  • DNA helicase causes breaking of hydrogen bonds between DNA strands
  • DNA polymerase joins the DNA nucleotides
  • forming phosphodiester bonds
• the genetic code is described as degenerate - what is meant by this?


  more than one codon codes for a single amino acid
• formation of an enzyme-substrate complex increases the rate of reaction - explain how

  • reduce activation energy
  • by bending bonds
  • without enzyme very few substrates have sufficient energy for the reaction