Mistakes

• Describe and explain two features you would expect to find in a cell specialised for absorption

  • Large number of channel proteins
  • Large number of mitochondria
  • Folded membrane so large surface area for diffusion
• Describe the role of DNA polymerase in the semi-conservative replication of DNA

  • Joins nucleotides
  • Catalyses condensation reactions
  • Forms phosphodiester bonds between adjacent nucleotides
• Explain the advantage for larger animals of having a specialized system that facilitates oxygen uptake

  • Larger organisms have a smaller surface area to volume ratio
  • Overcomes long diffusion pathways and faster diffusion
• Suggest two ways the student could improve the quality of his scientific drawing of the blood vessels in this dissection

  • Add magnification or scale
  • No shading
  • No sketching, only single lines
  • Add labels
• Describe two precautions the student should take when clearing away after the dissection

  • Wash and carry sharp instruments by holding the handle
  • Disinfect instruments and surfaces
  • Disinfect hands
• Describe how a sample of chloroplasts could be isolated from leaves

  • Grind leaves and open cells then filter
  • In cold, same water potential, pH concentration solution
  • Centrifuge/spin and remove cell debris
  • Spin at higher speeds, chloroplasts settle out
• How do phagocytes kill pathogens

  • Engulf the pathogen by phagocytosis
  • Fuses the phagosome with a lysosome and digests the pathogen with lysozymes
  • Present the pathogens antigens on the phagocyte's surface to activate other immune cells
• Disaccharides

  Maltose= glucose + glucose

  Lactose= glucose + galactose

  Sucrose= glucose + fractose
• Describe the structure of DNA

  • Polymer of nucleotides
  • Each nucleotide is formed from deoxyribose (pentose sugar), a phosphate group and a nitrogenous base
  • Phosphodiester bonds between nucleotides
  • Double helix
  • Hydrogen bonds between adenine, thymine and cytosine, guanine
• Give 3 features of all prokaryotic cells that are not features of eukaryotic cells

  • No membrane-bound organelles
  • Circular loop of DNA in cytoplasm
  • DNA free in cytoplasm
• Explain how two enzymes with different amino acid sequences can catalyse the same reaction

  • Both active sites have identical tertiary structure, both active sites have identical amino acid sequences
  • So form enzyme-substrate complexes (with same substrate)
• Compare and contrast the structure of starch and the structure of cellulose

  • Both polysaccharides
  • Both contain glycosidic bonds (between monomers)
  • Both contain carbon, hydrogen and oxygen
  • Starch if branched, whereas cellulose is unbranched
  • Starch is coiled, whereas cellulose is straight
  • Starch is a-glucose whereas cellulose is b-glucose
• Describe the complete digestion of starch by a mammal

  • Hydrolysis of glycosidic bonds
  • Starch to maltose by amylase
  • Maltose to glucose by maltase
• Give three structural features found in all virus particles and describe the function of them

  • Capsid protects the gentic material
  • Attachment proteins binds to receptors
  • Genetic material codes for viral protein
• Describe three ways the structure of chitin is similar to the structure of cellulose

  • Alternate monomers are flipped upside down
  • Joined by glycosidic bonds
  • Forms straight, unbranched chains
• Describe how the anti-toxin antibody would be digested

  • Peptide bonds broken
  • Endopeptidases break internal peptide bonds
  • Exopeptidases break terminal peptide bonds
• Suggest why several bacterial species have been renamed in recent years

  • Amino acid sequencing
  • Base sequencing
  • Use of electron microscopes with greater resolution
• Describe how a quaternary protein is formed from its monomers

  • Amino acids joined by peptide bonds
  • By condensation reactions
  • Secondary structure is formed by hydrogen bonding
  • Tertiary structure is formed by interactions between R groups
  • Quaternary structure contains >1 polypeptide chain
• Describe the structure of DNA and the structure of a chromosomes

  • Polymer of nucleotides
  • Nucleotides consist of deoxyribose, phosphate and a nitrogenous base
  • Phosphodiester bonds
  • DNA double helix held by H bonds
  • Hydrogen bonds between adenine, thymine and cytosine, guanine.
  • DNA is associated with histones
  • Chromosomes consists of two chromatids at a centromere
• Describe and explain the process other than mutations that result in genetic variation within a species

  • Independent assortment of homologous pairs
  • Crossing over between homologous pairs
  • Random fertilisation of gametes
  • Produces new combination of alleles