questions 2

• explain how modern phylogenic techniques have allowed classifications of organisms like sloths to be updated from earlier anatomical evidence(2)

  • compare amino acid or DNA base sequences from the same protein
  • the more similarities the more closely related species are
• suggest how natural selection could have led to sloth hair being suitable for colonisation by algae(4 marks)

  • a mutation made sloth hair more suitable for algae to colonise
  • more algae growth helps newborn sloths survive by providing extra nutrition
  • sloths with advantageous hair allele more likely to survive and reproduce
  • allele is passed onto offspring and over generations frequency of allele increase in population
• explain why the low metabolic rate of sloths could decrease amount of virus found in blood stream(2)

  • viruses use cell processes to replicate themselves
  • low metabolic rate would reduce rate of reactions thus less energy for cellular processes
  • so few virus particles will be made OR takes a longer time to replicate
• explain why arboreal folivores normally have to eat large amounts of plant material a day(3)

  • little energy transferred from producer to herbivores because cellulose in cell wall hard to break down-requires special enzymes
  • alot of plant material passes through digestive system undigested
  • not all parts of leaf may be eaten
  • biomass used for respiration and energy released via movement
• explain how thermoregulatory centre in sloths could cause them to decrease their body temperature by 5 degrees(3)

  • thermoreceptors detect increase in temperature
  • thermoregulatory system in the hypothalamus is stimulated
  • impulses sent to sweat glands to increase sweat production
  • vasodialation of arterioles/constriction of shunt vessels
  • more heat lose via radiation
• para 9 describes sloths climbing to the top of tree canopies, state what type of adaptation and what advantage it has(2)

  • it is a behavioural adaptation
  • absorbs heat radiation from sun to increase body temperature without using up any energy
• explain how pairs of muscles in hands and feet work to move digits when sloth wants to move its claws(2)

  • extensor contracts and flexor relaxes-acts as antagonistic pair
  • extensor muscle pulls on tendon, attaching to bones in hands and feet
• explain the differences in muscles you would expect to see between muscles of weight lifters or marathon runners(3)

  • weightlifters have more fast twitch muscles for short powerful movements(thicker)
  • marathon runners would have more slow twitch muscle fibres for long periods of endurance(thinner)
  • slow twitch muscle fibres are redder due to more capillaries and mitochondria for aerobic respiration
  • fast twitch muscle fibres are less red due to less capillaries and mitochondria for anaerobic respiration
• explain how enzymes in muscle cells could prevent lactic acid from accumulating(2)

  • enzymes could oxidise lactate to form pyruvate
  • pyruvate could enter link reaction and be respired
  • pyruvate could be converted to glucose and used in glycolosis and respired
• suggest 2 suitable reasons why different moth species on same sloth do not interbreed with eachother(2)

  • they are reproductively isolated:
  • different breeding times or physically incompatible genitalia