TB2 set pieces

• Difficulties investigating the brain

   

  - Neuroscientists have been able to use electrical stimulation and MRI scanning to map the regions of the brain to particular functions by studying patients with brain damage. The complexity and delicacy of the brain makes investigating and treating brain disorders very difficult.
• Explain how negative feedback controls blood sugar after a meal

  increase in blood glucose (to 6.5 mmol / dm3)- glucose detected by pancreas- pancreas secretes insulin- (insulin causes) glucose to move (out of blood) into liver cells- liver converts glucose to glycogen- causing a fall in blood glucose - low blood glucose is detected by pancreas- pancreas releases glucagon- liver converts glycogen to glucose (which enters blood)- blood glucose rises
• Explain how the pituitary gland and the kidneys reduce water loss when a person is dehydrated


  high(er) concentration of blood causes (more) ADH / hormone release- (and hormone / ADH causes) increased permeability of kidney tubules (to water)- (so) increased water reabsorption into the blood
• Explain two benefits of kidney transplant over dialysis

  changes in concentrations / levels of substances / urea are minimised- (so) less / no chance of causing damage to body cells / tissues- not repeatedly puncturing skin or blood not in contact with machine- (so) less / no chance of infection or less / no chance of blood clots or no need to take anti-clotting drugs
• What are the effects of hyperthyroidism

   

  - Too much thyroxine is released into the blood- which raises BMR- causing increase in formation of glycogen / lipids / proteins

  or

  increase in rate of respiration

  or

  increase in breakdown of excess proteins
• Explain how organ rejection occurs and how it can be prevented

  Organ rejection occurs when:

  - the immune system (B lymphocytes)- (produces) antibodies- (which) attack the antigens (on the cells transplanted organ)

   

  Organ rejection can be prevented by:

  - tissue typing (to find a matching donor)- treating patient with drugs that suppress the immune system
• Explain geotropism in roots

  - more auxin produced on the lower side of the root- auxin slows growth of cells on the lower edge.- So cell grow faster on the top side of the root making the root grow downwards
• Explain geotropism in underground roots

  - more auxin produced on the lower side of the shoot- auxin speeds up growth of cells on the lower edge ….- So cell grow faster on the lower side of the shoot making the root grow upwards
• Explain phototropism in roots

  more auxin produced on the shaded side of the root- auxin speeds up growth of cells on the shaded side ….- So cell grow faster on the shaded side of the shoot making the shoot grow towards the light source
• Explain benefits of asexual reproduction

  many offspring produced- takes less time- (more) energy efficient- genetically identical offspring- successful traits propagated / maintained / passed on (due to offspring being genetically identical)- no transfer of gametes or seed dispersal- not wasteful of flowers / pollen / seeds
• Explain benefits of sexual reproduction

  genetic variation (in offspring)- (so) better adapted survive- (and) colonise new areas by seed dispersal

  or

     can escape adverse event in original area (by living in new area)

  - many offspring so higher probability some will survive
• Explain why missing a dose of the mini-pill would reduce the success rate of the mini-pill 

   (missing a dose causes a) drop in progesterone levels- (therefore) FSH is not inhibited anymore- (therefore) LH is not inhibited anymore- (and consequently) an egg is matured and released(so could become fertilised)
• Explain why a long-sighted person has difficulty seeing near objects clearly 

  eye(-ball) is (too) short or lens cannot be thickened enough- (so) light ‘focuses’ behind retina
• Explain how short-sightedness(myopia) is corrected using lenses

  The focal point is in front of the retina causing a blurry image- Concave lens is placed in front of/ inside the eye- …. Which diverges the light rays/ refracts light outwards- …. Focusing light/ image onto the retina
• Explain pupil dilation

  - pupils dilate in dim light / low light levels- because circular muscles (in iris) relax- (and) radial muscles contract
• Explain how a mutation could cause an enzyme not to work

  Changes to the genetic code DNA code changes the base sequence in a triplet codon which ….- (mutation) changes the amino acid ….- (this could) change the active site structure …..- (so it) can not bind with it’s substrate
• Explain how a mutation could cause NO CHANGE to a protein/ enzyme/ hormone 

  Mutation may NOT change the base sequence in a triplet codon OR may change a base sequence in NON-CODING DNA which ….- Would NOT change the amino acid sequence ….- And NOT change the protein structure
• Suggest why scientists at the time did not realise how important Mendel’spublished work on genetics was

  Any two from:

  - They did not know about chromosomes / genes / DNAor did not know chromosomes occurred in pairs- they had pre-conceived theories- Mendel’s (mathematical) approach was novel concept- Mendel was not part of academic establishment- work published in obscure journal / work lost for many years
• List the advantages of developing genetically modified crops

  Any three advantages from:

  - less effort for farmer or less likely to harm farmer- (pesticide) always there or doesn’t wash away- less insects to eat crop / maize or carry disease- so greater crop production / yield
• List the disadvantages of developing genetically modified crops

  Any three disadvantages from:

  -(toxin) kills other insects

  • so (some) crops don’t get pollinated/ (sexually) reproduce
  • possible harm when eaten by humans/animals
  • damage to food chains

  Gene may spread to other species
• Explain how a given species evolves into another given species

  Isolation of different populations

  Habitat variation between each populations

  Genetic variation or mutation

  Better adapted survive and reproduce to pass in favourable alleles to offspring

  Eventually cannot reproduce fertile offspring with other populations