A level Biology 5.1 Replication and division of nuclei and cells – Exam style question – Paper 2

Question [Maximum marks: 8]

The slime mould, Dictyostelium discoideum, is a eukaryote and a decomposer of protein-rich
material.

Fig. 5.1 shows the life cycle of D. discoideum.

(a) State the type of nuclear division that occurs at X and at Y.

(b) State what is meant by the term reduction division and explain why this division is
       necessary in a life cycle, such as that shown in Fig. 5.1.

(c) The amoeboid cells of D. discoideum feed on protein-rich material and break it down
       to form ammonium ions (NH4+). The cell membranes of D. discoideum have transporter                                                                                                                                                           proteins that are responsible for the excretion of ammonium ions.

      Describe what happens to the ammonium ions excreted by D. discoideum into the soil.

(d) Suggest why a transporter protein is required for the removal of ammonium ions from
       D. discoideum.

Answer/Explanation

Answer:       5(a) ignore Y
                                    X = mitosis ;
                                    Y = meiosis / mitosis;

5(b) 1 chromosome number is halved / 2n n / diploid haploid ;
               A 2 sets of chromosomes 1 set of chromosomes

              explanation to max 1
          2 restore diploid number on fusion ; R restore full set if not qualified
          3 avoids number doubling with each generation ;
          4 allows expression of (recessive) alleles / AW ;
          5 allows variation / new combinations of chromosomes ; 

5(c) if only use formulae, these must be correct – otherwise ignore

         1 nitrification / nitrifying / oxidation ;
         2 ammonium ions to nitrite ions ;
         3 nitrite ions to nitrate ions ; A one mark for ammonium to nitrate
         4 one named microorganism in correct context
             Nitrosomonas / Nitrobacter ; R Rhizobium
         5 ammonium / nitrate / AW, absorbed by plants / leached / AW ;
              R used by plant [max 3]

5(d) 1 ammonium ions are (positively) charged ; A hydrophilic / polar / water-soluble
          2 cannot pass through, phospholipid bilayer / membrane ;

           either
         3 active transport ;
         4 moved against concentration gradient ;
             or
         3 facilitated diffusion ;
         4 moves down its concentration gradient ;

Question

Bone marrow contains stem cells that divide by mitosis to form blood cells. Each time a stem
cell divides it forms a replacement stem cell and a cell that develops into a blood cell.
Fig. 3.1 shows changes in the mass of DNA in a human stem cell from the bone marrow
during three cell cycles.

(a) With reference to Fig. 3.1, state:
(i) what happens to bring about the changes in the mass of DNA per cell at K and at L
K ……………………………………………………………………………………………………………….
L ……………………………………………………………………………………………………………….
(ii) how many blood cells are formed from the stem cell in the time shown
(iii) what happens to the number of chromosomes in the stem cell.
Stem cells in bone marrow give rise to phagocytes, B-lymphocytes and T-lymphocytes.
(b) Describe how a red blood cell develops from a stem cell.
(c) During an immune response, cells divide by mitosis.
Describe how mitosis is involved in an immune response.
(d) Describe the modes of action of T-lymphocytes during an immune response.

Answer/Explanation

Answer:

(a) (i) K – (DNA) replication / synthesis / described ;
L – cytokinesis / cytoplasmic division / cell division ;
(ii) 3 ;
(iii) remain the same / stays constant / stay at 46 / AW ; ignore description of events
occurring before and during mitosis

(b) transcription (of specific genes) ; A reference to gene switching
protein / polypeptide, synthesis ; A translation
production of haemoglobin ;
further detail ; e.g. assembly of quaternary structure
(production of) carbonic anhydrase ;
loss of, mitochondria / named organelles ;
loss of nucleus ;
adopts biconcave disc shape ;

(c) occurs in both primary and secondary (immune) responses ;
selected / specific / AW ;
lymphocytes / B -cells / T-cells / divide (by mitosis) ;
clonal expansion / described in terms of producing, clone / many cells ;
A idea that different types of immune cell can result
reference mitosis in memory cells (for rapid) secondary response ;

(d) T helper / Th,
secrete, cytokines / interleukins ;
activate B-lymphocytes to, divide / form plasma cells ; A idea that leads to enhanced
antibody levels
enhances / AW, phagocyte / macrophage, response ; A angry macrophages ;
T cytotoxic / Tc / T killer / Tk
attach to / kill / AW, infected cells / damaged cells / tumour cells / cells with non-self
antigens / AW;
mechanism of killing ; e.g. perforin

T memory / Tm
already exposed to antigen ;
reference to role in secondary response ;
AVP ; ; e.g. T suppressor cells
function of suppressor cells

Question

    (a) Explain how uncontrolled cell division can result in cancer. [3]

    (b) Describe the experimental evidence that shows that smoking causes lung cancer. [3]

    (c) Fig. 6.1 shows the changes in mortality rates for lung cancer in five countries between 1950 and 2006 for males.

        With reference to Fig. 6.1, describe the similarities and differences in the trends in mortality rates in the countries shown. [3] [Total: 9]

Answer/Explanation

Ans:

6 (a) ref. to mutation(s) ;
                   in context of initiating uncontrolled mitosis OR as a consequence of uncontrolled mitosis
           proto-oncogenes convert to oncogenes / oncogenes switched on/ tumour suppressor genes switched off ;
           (cell division is by) mitosis ;
           formation of, tumour/mass of (unspecialised) cells ;
           no response to (extracellular/ intracellular) signals to control mitosis /AW ;
           no contact inhibition/AW ;
           no cell death/ no apoptosis ;
           immune system does not recognise the cells as foreign and destroys them ;
                   A reference to, not non-self/ self
           metastasis / described ;

     (b) R way in which cancer develops /epidemiological evidence
           A beagles for dogs

           1 tar painted on skin of, mice/rabbits /rats /(small) mammal, led to development of (cancerous / malignant) tumour ;
           2 dogs that smoked (plain) cigarettes developed, cancer/ tumour ;
           3 dogs that smoked filter-tipped cigarettes did not develop cancer/ tumour ;
               A developed precancerous changes
           4 control group/ dogs, which did not smoke and did not develop, cancer/ tumour ;
           5 AVP ;
                     e.g. evidence from any other named mammal
                     e.g. inhaling substances from, tar/ tobacco

     (c) similarities
           1 all (named) countries, increase and decrease/reach a peak and decrease ;

           differences
           2 peaks /AW, have occurred at different years in at least two countries ;
           3 all maximum mortality rates are different ;
           4 any comparative, data quote/ calculation, with units given at least once ;
                      e.g. dates and mortality rates for at least two countries
                      e.g. mortality rates for one country at two different dates

           accept a range or a single figure within the ranges given

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