PRE 2016

• THE SCIENTISTS MEASURED CELL DAMAGE BY MEASURING THE ACTIVITY OF LYSOSOMES. GIVE ONE FUNCTION OF LYSOSOMES.

  break down cells or toxins
• THE EVENTS THAT TAKE PLACE DURING INTERPHASE AND MITOSIS LEAD TO THE PRODUCTION OF TWO GENETICALLY IDENTICAL CELLS. EXPLAIN HOW.

  1. DNA replicated
  2. involving complementary base pairing
  3. two identical sister chromatids
  4. Each chromatid moves to opposite poles of the cell
• (IMAGE) THE STUDENT CUT THIN SECTIONS OF TISSUE TO VIEW WITH AN OPTICAL MICROSCOPE. EXPLAIN WHY IT WAS IMPORTANT THAT THE SECTIONS WERE THIN.

  1. To allow more light through
  2. For a single layer of cells to be viewed

  
• (IMAGE) HSV INFECTS NERVE CELLS IN THE FACE (1) EXPLAIN WHY IT INFECTS ONLY NEVRVE CELLS?

  1. outside virus has antigens
  2. with complementary shape to receptors
  3. these receptors only being found on nerve cells

  
• HSV CAN REMAIN INACTIVE INSIDE THE BODY FOR YEARS (2-3) EXPLAIN WHY THIS VIRUS CAN BE DESCRIBED AS INACTIVE.

  1. no more nerve cells infected
  2. because virus isn't replicating
• (IMAGE) THE SCIENTISTS CONCLUDED THAT PRODUCTION OF THIS MICRORNA ALLOWS HSV TO REMAIN IN THE BODY FOR YEARS (10-12) EXPLAIN HOW THIS MICRORNA ALLOWS HSV TO REMAIN IN THE BODY FOR YEARS

  1. microRNA binds to cells mRNA
  2. binds by specific base pairing
  3. So prevents mRNA being read by ribosomes
  4. so prevents translation x production of proteins
  5. proteins that cause cell death

  
• (IIMAGE) SUGGEST ONE ADVANTAGE OF PROGRAMMED CELL DEATH (4)

  prevents replication of virus

  
• (IMAGE)

  L

  H

  N

  
• (IMAGE) DESCRIBE AND EXPLAIN HOW CENTRIFUGING THE CULTURE ALLOWED THE SCIENTISTS TO OBTAIN A CELL-FREE LIQUID

  1. Large / dense / heavy cells
  2. form pellet at the bottom of the tube when centrifuged
  3. liquid / supernatant can be removed

  
• THE SCIENTISTS MEASURED CELL DAMAGE BY MEASURING TEH ACTIVITY OF LYSOSOME. GIVE ONE FUNCTION OF LYSOSOMES.

  breaks down cells / toxins.

  
• (IMAGE) H. PYLORI CELLS PRODUCE AN ENZYME THAT NEUTRALISES ACID. SUGGEST ONE ADVANTAGE TO THE H. PYLORI OF PRODUCING THIS ENZYME.

  1. To reduce them being damaged.
  2. by stomach acid.

  
• (IMAGE) WHAT DO THESE DATA SUGGEST ABOUT THE DAMAGE CAUSED TO HUMAN CELLS BY THE TOXIN AND BY THE ENZYME THAT NEUTRALISES ACID? EXPLAIN YOUR ANSWER.

  1. more cell damage when both present / A
  2. some cell damage when either there on their own / some cell damage in B and C
  3. standard deviation doesn’t overlap for A with B and C so difference is real.
  4. standard deviations do overlap between B and C so no real difference.

  
• (IMAGE) THE SCIENTISTS CARRIED OUT A FURTHER INVESTIGATION. THEY TREATED THE LIQUID FROM STRAIN A WITH A PROTEIN-DIGESTING ENZYME BEFORE ADDING IT TO A CULTURE OF HUMAN CELLS. NO CELL DAMAGE WAS RECORDED.

  SUGGEST WHY THERE WAS NO DAMAGE TO THE CELLS.

  1. enzyme (a protein) is broken down so no enzyme activity.
  2. no toxin as a result of protein-digesting enzyme activity.
  3. so toxin is a protein.

  
• DESCRIBE HOW YOU COULD USE CELL FRACTIONATION TO ISOLATE CHLOROPLASTS FROM LEAF TISSUE.

  1. Break open cells with a mortar and pestle and remove debris.
  2. solution is cold / isotonic / buffered
  3. second pellet is chloroplast
• (IMAGE) NAME THE PARTS OF THE CHLOROPLAST LABELLED A AND B.

  A = Stroma

  B = granum

  
• NAME TWO STRUCTURES IN A EUKARYOTIC CELL THAT CANNOT BE IDENTIFIED USING AN OPTICAL MICROSCOPE

  mitochondria / ribosome / endoplasmic reticulum / lysosome / sell-surface membrane
• (IMAGE) SUGGEST WHY THE PLASMIDS WERE INJECTED INTO THE EGGS OF SILKWORMS, RATHER THAN INTO THE SILKWORMS.

  1. If injected into egg then genes get into most of the cells of the silkworm
  2. so gets into the cells that make silk.

  
• (IMAGE) THE SCIENTISTS ENSURED THE SPIDER GENE WAS EXPRESSED ONLY IN CELLS WITHIN THE SILK GLANDS.

  WHAT WOULD THE SCIENTISTS AHVE INSERTED INTO THE PLASMID ALONG WITH THE SPIDER GENE TO ENSURE THAT THE SPIDER GENE WAS ONLY EXPRESSED IN THE SILK GLANDS OF THE SILKWORMS.

  promoter (region / gene)

  
• (IMAGE) SUGGEST WHY THE SCIENTISTS USED A MARKER GENE AND WHY THEY USED THE EGFP GENE.

  1. Not all eggs will successfully take up the plasmid
  2. silkworms that have taken up the gene will glow

  
• (IMAGE) SUGGEST TWO REASONS WHY IT WAS IMPORTANT THAT THE SPIDER GENE WAS EXPRESSED ONLY IN THE SILK GLANDS OF THE SILKWORMS.

  1. so that protein can be harvested.
  2. fibres in other cells might cause harm.

  
• DESCRIBE HOW YOU COULD MAKE A TEMPORARY MOUNT OF A PIECE OF PLANT TISSUE TO OBSERVE THE POSITION OF STARCH GRAINS IN THE CELLS WHEN USING AN OPTICAL (LIGHT) MICROSCOPE.

  1. add drop of water to slide
  2. obtain thin section of plant tissue and place on slide
  3. stain with iodine
  4. lower cover slip with mounted needle
• DESCRIBE HOW PHOSPHOLIPIDS ARE ARRANGED IN A PLASMA MEMBRANE

  1. bilayer
  2. hydrophobic fatty acid tail facing inside
  3. polar hydrophilic head outside
• CELLS THAT SECRETE ENZYMES CONTAIN A LOT OF RER AND A LARGE GOLGI APPARATUS.

  DESCRIBE HOW THE RER IS INVOLVED IN THE PRODUCTION OF ENZYMES.

  1. RER has ribosomes
  2. to make protein (which an enzyme is)
• DESCRIBE HOW THE GOLGI APPARATUS IS INVOLVED IN THE SECRETION OF ENZYMES.

  modifies protein

  OR

  packages / put into vesicles

  OR

  transport to cell surface / vacuole
• DESCRIBE AND EXPLAIN HOW CELL FRACTIONATION AND ULTRACENTRIFUGATION CAN BE USED TO ISOLATE MITOCHONDRIA FROM A SUSPENSION OF ANIMAL CELLS.

  1. Cell homogenisation to break open cells
  2. filter to remove large debris
  3. use isotonic solution to prevent damage to organelles
  4. keep cold to reduce damage by enzymes / use buffer to prevent enzyme denaturation
  5. centrifuge at lowest speed to seperate heaviest organelles
  6. respin supernatant at higher speed to get mitochondria.
• DESCRIBE THE PRINCIPLES AND THE LIMITATIONS OF USING A TRANSMISSION ELECTRON MICROSCOPE TO INVESTIGATE CELL STRUCTURE.

  PRINCIPLES:

  1. electrons pass through thin specimen
  2. denser parts absorb more electrons
  3. so denser parts appear darker
  4. electrons have a short wavelength so give high resolution

  LIMITATIONS:

  1. Can’t look at living material, must be in vacuum
  2. specimen must be very thin
  3. artefacts present
  4. complex staining method / long preparation time
  5. only 2D images produced
• THE EVENTS THAT TAKE PLACE DURING INTERPHASE AND MITOSIS LEAD TO THE PRODUCTION OF TWO GENETICALLY IDENTICAL CELLS. EXPLAIN HOW.

  1. DNA replicated
  2. involving complementary base pairing
  3. two sister chromatids
  4. each chromatid is moved to opposite poles of the cell
• (IMAGE) GIVE FOUR PRECAUTIONS THAT THE RESEARCHERS TOOK TO MAKE THEIR CALCULATIONS OF MEAN NUMBER OF CAPILLARIES PER FIBRE RELIABLE.

  1. fields of view randomly chosen
  2. several fields of view
  3. all same species of hamster
  4. same muscle / only diaphragm used
  5. use at least 8 animals in each age group

  
• (IMAGE) A STUDENT READ THE REPORT OF THE RESEARCHERS’ INVESTIGATION. SHE THOUGHT THAT THE INVESTIGATION WAS UNETHICAL BUT THAT A CONCLUSION COULD STILL BE MADE.

  SUGGEST WHY SHE THOUGHT THE INVESTIGATION WAS UNETHICAL.

  removing diaphragm means hamsters are killed

  
• THE ACTUAL NUMBER OF SLOW MUSCLE FIBRES IN THE FIELD OF VIEW WAS NOT THE SAME AS THE NUMBER CALCULATED.

  GIVE ONE REASON WHY.

  1. calculation used mean number of capillaries
  2. variation in number of capillaries per fibre

  
• (IMAGE) SHE CONCLUDED THAT AGE HAD A SIGNIFICANT EFFECT ON THE MEAN NUMBER OF CAPILLARIES PER FIBRE. EVALUATE THE CONCLUSION.

  1. significant difference between young and adult
  2. not diagnostic ant difference between adult and old
  3. for slow and fast fibres
  4. significant difference between young and old for fast fibres
  5. significant difference where means standard deviation don’t overlap
  6. stats test is required to establish whether significant or not

  
• (IMAGE) THE DOCTORS COMPARED MEDIAN SURVIVAL TIMES FOR PATIENTS IN EACH GROUP.

  HOW WOULD YOU FIND THE MEDIAN SURVIVAL TIME FOR A GROUP OF PATIENTS?

  1. rank all STs in ascending order
  2. find value with same number of people above and below - find middle value

  
• (IMAGE) IN MANY TRIALS OF NEW DRUGS, A CONTROL GROUP OF PATIENTS IS GIVEN A PLACEBO THAT DOES NOT CONTAIN ANY DRUG.

  THE CONTROL GROUP IN THIS INVESTIGATION HAD BEEN TREATED WITH DACARBAZINE.

  SUGGEST WHY THEY HAD NOT BEEN GIVEN A PLACEBO.

  not ethical to fail to treat cancer.

  
• (IMAGE) A JOURNALIST WHO READ THIS INVESTUGATION CONCLUDED THAT IPILIMUMAB IMPROVED THE TREATMENT OF MM. DO THE DATA IN THE TABLE SUPPORT THIS CONCLUSION? GIVE REASONS FOR YOUR ANSWER.

  YES SINCE WITH IPILIMUMAB:

  1. median ST increased by 2.1 months
  2. Percentage of patients showing reduction in tumours increased from 10.3% to 15.2%.

  NO BECAUSE:

  1. Standard errors shown - no statistical test carried out
  2. so not able to tell whether differences are statistically significant
  3. improvement might only be evident in some patients
  4. quality of extra time alive not reported

  
• MM IS CAUSED BY A FAULTY RECEPTOR PROTEIN IN CELL-SURFACE MEMBRANES. CELLS IN MM TUMOURS CAN BE DESTROYED BY THE IMMUNE SYSTEM. SUGGEST WHY THEY CAN BE DESTROYED BY THE IMMUNE SYSTEM.

  1. faulty protein recognised as a foreign protein
  2. t cells will bind to foreign protein
  3. T cells will stimulate clonal selection of B cells
  4. Resulting in release of antibodies against faulty protein.

  
• (IMAGE) WATERING TREATMENT WAS THE INDEPENDENT VARIABLE IN THIS INVESTIGATION.

  EXPLAIN WHAT IS MEANT BY THE INDEPENDENT VARIABLE.

  the variable that is changed

  
• (IMAGE) THE SAME VARIETY OF BARLEY WAS USED IN ALL THE PLOTS. WHY WAS THIS IMPORTANT?

  1. confounding variable
  2. so genetically similar
  3. so have similar salt tolerance
  4. so have similar yield

  
• WHEN BARLEY PLANTS ARE GROWING, THE NUMBER OF CELLS INCREASES. NAME THE PROCESS THAT INCREASES THE NUMBER OF CELLS.

  mitosis

  
• (IMAGE) WHAT DO THE DATA IN THE TABLE SHOW ABOUT THE EFFECT OF WATERING BARLEY WITH A MIXTURE OF FRESH WATER AND SEAWATER.

  1. irrigation with seawater increased yield Compared with no irrigation
  2. yield was lower when irrigated with seawater compared with freshwater
  3. yield was lower when watered with seawater throughout growth and seed formation than when watered with sea water just at seed formation

  
• (IMAGE) THE SCIENTISTS SUGGESTED THAT WATERING BARLEY WITH DILUTED SEAWATER MIGHT NOT BE SUSTAINABLE IF REPEATED EVERY YEAR.

  DO THESE DATA SUPPORT THIS SUGGESTION.

  1. irrigation with sea water increases concentration of salt in soil
  2. lower water potential in the soil linked to reduced uptake of water
  3. salt concentration in the soil might or might not increase in the future
  4. may decrease plant growth / yield in the future
  5. less food / fewer seeds for future planting