Zigzag Papers

• Explain the pattern seen in these results of loop of Henle.

  • (Sodium and chloride) ions pumped out of ascending limb of loop of Henle
  • Causing water to leave descending limb by osmosis
  • Ascending limb of loop of Henle is impermeable to water
  • As ions are pumped out, water remains in the ascending limb (E-H in Figure 8)
  • Concentration gradient is set up which is used by collecting duct for water reabsorption

  
• Renal channelopathies are conditions which affect ion channel.

  This means less effective sodium ions and chloride ions pumped out of ascending limb of loop of Henle.

  Suggest what effect this would have on kidney function.

  • Sodium and chloride ions lost in urine
  • SO less water reabsorbed from collecting duct into the blood
  • Increased urination
  • Dehydration / need to drink more water
  • Less control of blood water potential
• Give two reasons why little energy is turned into biomass by the (red howler monkey) and the fruit it consumes.

  • Not all parts of the fruit digested by the monkey, so energy is lost in faeces and urine
  • Not all parts of the fruit are eaten by the monkey
  • Energy losses in respiration and heat for mammals and in movement (Monkeys are highly active)
• Describe how DNA fragment is prepared before inserting into plasmid

  • Promoter region is added to start of the gene
  • Terminator region is added to end of gene
• Why is it important that the same restriction enzyme is used on both the plasma and the DNA fragment to be inserted? [2 marks]

  • Restriction enzyme cuts DNA at a specific base pair sequence
  • Ensures complementary sticky ends on the plasmid and the DNA
• Define the term population

  • group of organisms living in the same area that belong to same species and therefore
  • are able to INTERBREED
• Explain how specialisation happens in cells, such as chondrocytes in cartilages. [2 marks]

  • Change in gene expression have allowed cell specialisation
  • Cartilage cells (AO2) only produce proteins specific to their function, by only expressing the necessary genes
• Describe how different DNA fragments are separated using gel electrophoresis [3 marks]

  • DNA sample is pipetted / loaded into gel which has electrodes at either end
  • Covered in a buffer solution which conducts electricity
  • Electricity is run through the gel causing negatively charged DNA molecules to move towards the positive electrode
  • Larger DNA molecules move more slowly through the gaps in the gel
  • Fragments separated by size
• Describe the property of DNA which allows identification of an individuals and why that property is useful

  • VNTRs found in DNA, which vary in length from person to person
  • Affects distance between restriction enzyme recognition sites AND therefore affect different DNA fragment lengths
• Lions prey on zebras in the Maasai Mara

  Explain how the size of zebra population influences the size of lion predators [2 marks]

  • High zebra population means lots of prey for lions
  • So lion numbers increases and less food competition
  • More lions preying on zebra decreases zebra's number
  • So less prey for lion population
  • Lion population will then decrease
• Describe advantages and disadvantages of anaerobic respiration in humans [4 marks]

  • Can be carried out in muscles when oxygen levels are low
  • Recycles NAD so it can be used for more glycolysis
• Describe advantages and disadvantages of anaerobic respiration [4 marks] (this links to Synoptic essay)

  DISADVANTAGES

  • Lactate can build up causing (acidosis)/ changes the pH of blood
  • Changing pH of blood disturbs enzyme activity
  • Incomplete glucose breakdown so less efficient
  • Anaerobic does not release enough energy / releases only 2 ATP per cycle of glycolysis
• What is the name given to stage K and stage M?

  • Stage K = depolarisation
  • Stage M = hyperpolarisation

  
• What causes stage M (hyperpolarisation) and why is this stage important in neuronal communication? [3 marks]

  • Potassium ions continue to diffuse out, causing inside of the membrane to become more negative
  • Neurone enters a REFRACTORY PERIOD - during which action potential cannot form
  • Ensures impulses are discrete and action potentials do not overlap
  • Limits frequency of impulse transmission at a certain intensity (prevents over reaction to stimulus)
  • ○ Higher intensity stimulus causes higher frequency of action potentials ○ But only up to certain intensity

  
• Sarin, a potent toxic agent is a competitive non-reversible inhibitor of acetylcholinesterase enzyme.

  Explain this effect on failure of muscle contraction.

  • Sarin permanently blocks the active site of acetylcholinesterase
  • Acetylcholine builds up AND leads to constant stimulation on neuromuscular junction
  • Muscles associated with ventilation contract and cannot relax; contraction and relaxation is needed from breathing
• Suggest a suitable piece of laboratory equipment to mash up the plant tissue

  • Pestle and mortar
  • THEN add solvent (so pigments can run up the chromatogram)
• Conducting a second experiment for Chromatography practical:

  Explain why the same solvent should be used to conduct the second thin layer chromatography test

  • Using a different solvent will affect Rf value of the pigments
  • If same solvent is used, results will be directly comparable
• Diagnosis of genetic disorders through screening individuals allows doctors to prescribe medicines based on genotypes.
• Diagnosis of genetic disorders through screening individuals allows doctors to prescribe medicines based on genotypes.

  Give two potential benefits of personalized medicines.

  • Drug effectiveness can be determined for the genotype
  • Avoids prescribing medicines that will cause harm for patients with specific alleles
  • Doses can be tailored for the desired outcome based on patient's gene
  • Saves time and money for health services, by only prescribing drugs that will work for a particular genotype
• Individuals can choose to have genetic testing and counselling.

  Suggest why some people choose not to have genetic testing and counselling.

  • Possible results could give false positives / incorrectly interpreted
  • Would rather not know about a late-onset genetic condition as knowledge is burden / painful
  • People may disapprove as genetic counselling which could lead to selective abortion / devaluing disables
• A population of 125 people became isolated on remote oceanic island.

  Describe the mechanism by which over several generations one blood type might become more common in this population.

  • Small population size reduces genetic diversity
  • Genetic drift causes some alleles to be favoured by chance
  • Alleles ,ay become more common due to CHANCE in small population
• Describe two characteristics of benign tumors.

  • Grow slowly (compared to malignant tumours)
  • Unlikely to spread / metastasise as cells stick together
  • Cells making up the tumour are well differentiated
  • Often surrounded by a layer of connective tissue
• Describe the role of tumour suppressor genes

  • Slowing down / reducing the rate of cell division
  • ALlowing quality of replicated DNA to be assessed
  • Causes the repair of DNA mistakes
  • Telling cells when to die (apoptosis / programmed cell death)
• Describe and explain how ADH restores the water potential of the blood to optimum

  • ADH increases the PERMEABILITY to water of the cells in the Distil convoluted tubule and collecting duct
  • aquaporins move to / fuse with cell membranes of Distil convoluted tubule epithelium
  • ADH also increases the PERMEABILITY of collecting duct to urea
  • Therefore more water leaves the collecting duct by OSMOSIS