2019 paper 2 Flashcards
Succession occurs in natural ecosystems. Describe and explain how succession
occurs.
- (Colonisation by) pioneer species;
- Pioneers/species/organisms change the environment/habitat/conditions/factors;
- (Environment becomes) less hostile for other/new species
OR
(Environment becomes) more suitable for other/new species
OR
(Environment becomes) less suitable for previous species; - Change/increase in diversity/biodiversity;
- (To) climax community;
Use Figure 1 to calculate the percentage of sunlight energy that would be transferred into the faeces and urine of a zebra. Give your answer to 3 significant figures.
0.155;
In this ecosystem the net productivity of the vegetation is 24 525 kJ m−2 year−1
Use this information and Figure 1 to calculate the energy stored in new tissues of the
zebra in kJ m−2 year−1
Answer of 180/178/177.5 = 2 marks;;
Sickle cell disease (SCD) is a group of inherited disorders. People with SCD have sickle-shaped red blood cells. A single base substitution mutation can cause one type of SCD. This mutation causes a change in the structure of the beta polypeptide chains in haemoglobin.
- Change in (sequence of) amino acid(s)/primary structure;
2. Change in hydrogen/ionic/disulfide bonds; 3. Alters tertiary/30 structure;
Explain how a single base substitution causes a change in the structure of this polypeptide.
Do not include details of transcription and translation in your answer.
- Produce healthy (red blood) cells
OR
Produce (normal) polypeptide/haemoglobin; - No sickle/faulty/SCD (red blood) cells (produced)
OR
No defective polypeptide/haemoglobin; - Stem/marrow cells (continuously) divide/replicate
OR
Less chance of rejection (from brother/sister);
Use this information to explain how HSCT is an effective long-term treatment for SCD.
(For gene therapy)
1. No destruction of bone marrow
OR
No destruction of stem cells; 2. Donors are not required;
3. Less/no chance of rejection (own stem cells); (Against gene therapy)
4. Sickle/faulty (red blood) cells still produced
5. Immune response against genetically modified cells/virus
OR
Long-term effect not known (as is new treatment)
OR
Virus could cause side effects;
Some scientists have concluded that this method of gene therapy will be a more effective long-term treatment for SCD than HSCT. Use all the information provided to
evaluate this conclusion.
- Tip produces IAA;
- Affects concentration of IAA
OR
Affects (shoot) length/growth/elongation; - Mitosis/division occurs in shoot tips;
- Affects (shoot) length/growth/elongation;
Explain why the student removed the shoot tip from each seedling
- For respiration;
2. Provide ATP/energy (for growth);
Explain why the student added glucose solution to each Petri dish.
- To prevent/reduce evaporation;
- (Which) alters concentration of (IAA) solution
OR
(Which) alters water potential;
Explain why the lids were kept on the Petri dishes.
. Increase in IAA concentration the higher/greater the mean (change in) length;
- (High) IAA stimulates cell elongation;
- In roots, growth/elongation less/inhibited;
The student produced the different concentrations of IAA using a stock
1 g dm–3 solution of IAA (1 g dm–3 = 1 part per thousand) and distilled water.
Complete Table 2 with the volumes of stock IAA solution and distilled water required
to produce 40 cm3 of 10 ppm (parts per million) IAA solution.
0.4 and 39.6;
A student looked at the results and concluded that a decrease in pH does cause a decrease in the force of muscle contraction.
Use Figure 3 to evaluate this conclusion.
- Lower (force of contraction) in mouse/B (than control/100%) below 29 °C
OR
Lower (force of contraction) in rabbit/D (than
control/100%) below 26.5 °C; - Higher (force of contraction) in mouse/B (than control/100%) above 29 °C
OR
Higher (force of contraction) in rabbit/D (than
control/100%) above 26.5 °C; 3. Only (used) mouse and rabbit
OR
No other organism/species used; - Body temperature of mouse/rabbit higher (than temperatures investigated);
- Only used one/0.5 pH (below typical pH)
OR
(Should) use more pH values; - (Used) isolated muscle tissue;
- No stats test to see if (difference is) significant;
Another group of scientists suggested that a decrease in the force of muscle contraction is caused by an increase in the concentration of inorganic phosphate, Pi, in muscle tissues.
Their hypothesis is that an increase in the concentration of Pi prevents the release of calcium ions within muscle tissues.
Explain how a decrease in the concentration of calcium ions within muscle tissues
could cause a decrease in the force of muscle contraction.
04.2
1. (Less/No) tropomyosin moved from binding site
OR
Shape of tropomyosin not changed so binding site not exposed/available;
2. (Fewer/No) actinomyosin bridges formed;
3. Myosin head does not move
OR
Myosin does not pull actin (filaments)
OR
(Less/No) ATP (hydrol)ase (activation);
In muscles, pyruvate is converted to lactate during prolonged exercise.
Explain why converting pyruvate to lactate allows the continued production of ATP by
anaerobic respiration.
- Regenerates/produces NAD
OR
oxidises reduced NAD; - (So) glycolysis continues;
Describe the role of glucagon in gluconeogenesis.
Do not include in your answer details on the second messenger model of glucagon action.
- (Attaches to receptors on target cells and) activates/stimulates enzymes;
- Glycerol/amino acids/fatty acids into glucose;. Correct answer of 3.24 = 2 marks;;
The gene that codes for glucagon is 9.531 kilobases in length. The DNA helix makes one complete turn every 10 base pairs. Every complete turn is 3.4 nm in length.
Use this information to calculate the length in micrometres (μm) of the gene for
glucagon. Give your answer to 3 significant figures.
Correct answer of 3.24 = 2 marks
Explain how increasing a cell’s sensitivity to insulin will lower the blood glucose
concentration.
- (More) insulin binds to receptors;
- (Stimulates) uptake of glucose by channel/transport proteins
OR
Activates enzymes which convert glucose to glycogen;
Explain how inhibiting adenylate cyclase may help to lower the blood glucose
concentration.
- Less/no ATP is converted to cyclic AMP/cAMP; 2. Less/no kinase is activated;
- Less/no glycogen is converted to glucose
OR
Less/no glycogenolysis;
Give the full genotype of the fly numbered 6 in Figure 4.
GgXRXr ;
Give one piece of evidence from Figure 4 to show that the allele for grey body colour
is dominant.
If it were recessive all flies of 3 and 4 would be grey OR 3 and 4 produce 9/black (fly) OR Grey parents produce black (fly);
Explain one piece of evidence from Figure 4 to show that the gene for body colour is
not on the X chromosome.
1. (Fly) 3 (and 4) produce 9/black (fly) OR (Fly) 9 would not be black OR (Fly) 9 would be grey OR Grey parents/male produce black female (fly); 2. (Fly) 3 would pass dominant allele to 9; 3.(Fly) 2 (and 1) produce 5/grey (fly) OR Black female produces grey male OR (Fly) 5 could not be grey OR (Fly) 5 would be black; 4.(Fly) 5 would receive recessive allele from 2;
A heterozygous grey-bodied, white-eyed female fly was crossed with a black-bodied, red-eyed male fly.
Complete the genetic diagram below to show all the possible genotypes and the ratio
of phenotypes expected in the offspring from this cross.
1.GgXrXr and ggXRY;
2. GgXRXr, ggXRXr, GgXrY and ggXrY;
3. Grey-bodied red-eyed female, black-bodied
red-eyed female, grey-bodied white-eyed male, black-bodied white-eyed male and ratio 1 : 1 : 1 : 1;
A population of fruit flies contained 64% grey-bodied flies. Use the Hardy–Weinberg
equation to calculate the percentage of flies heterozygous for gene G.
- Correct answer of 48% = 2 marks;;
In photosynthesis, which chemicals are needed for the light-dependent reaction?
Tick () one box.
NADP, ADP, Pi and water;
Describe what happens during photoionisation in the light-dependent reaction.
- Chlorophyll absorbs light
OR
Light excites/moves electrons in chlorophyll; - Electron/s are lost
OR
(Chlorophyll) becomes positively charged;
Explain why the student marked the origin using a pencil rather than using ink.
Ink and (leaf) pigments would mix
OR
(With ink) origin/line in different position
OR
(With pencil) origin/line in same position
OR
(With pencil) origin/line still visible;
Describe the method the student used to separate the pigments after the solution of pigments had been applied to the origin.
- Level of solvent below origin/line;
2. Remove/stop before (solvent) reaches top/end;
Use Figure 5 to calculate the Rf value of pigment C.
Accept any answer in range of 0.58 to 0.62;
The pigments in leaves are different colours. Suggest and explain the advantage of
Use Figure 5 to calculate the Rf value of pigment C.
[1 mark]
having different coloured pigments in leaves.
(Absorb) different/more wavelengths (of light) for photosynthesis;
What is a DNA probe?
- (Short) single strand of DNA;
2. Bases complementary (with DNA/allele/gene)
Describe how the DNA is broken down into smaller fragments.
- Restriction endonuclease/enzyme;
- (Cuts DNA at specific) base sequence
OR
(Breaks) phosphodiester bonds
OR
(Cuts DNA) at recognition/restriction site;
The DNA on the nylon membrane is treated to form single strands. Explain why.
(So DNA) probe binds/attaches/anneals;
Lane 1 of Figure 7 enabled the size of the different viral fragments to be determined.
Suggest and explain how.
- (Lane 1 has DNA fragments) of known sizes/lengths;
2. Compare (position of viral fragment/s);
Which volunteers had at least one of the viral DNA fragments with 250 base pairs or
535 base pairs?
3, 4, 5 with these numbers in any sequence;
Describe how you could estimate the size of a population of sundews in a small
marsh.
- Use a grid
OR
Divide area into squares/sections; - Method of obtaining random coordinates/numbers e.g. calculator/computer/random numbers table/generator;
- Count number/frequency in a quadrat/section;
- Large sample and calculate mean/average number (per quadrat/section);
- Valid method of calculating total number of sundews, e.g. mean number of plants per quadrat/section/m2 multiplied by number of quadrats/sections/m2 in marsh;
Suggest and explain how digesting insects helps the sundew to grow in soil with very
low concentrations of some nutrients.
- Digestion/breakdown of proteins; 2. Provides amino acids
OR
(Sundew can) produce a named (organic) nitrogen-containing compound e.g. proteins, amino acids, DNA, ATP; - Digestion/breakdown of named (organic) phosphate-containing compound e.g. DNA, RNA;
- Provides named (organic) phosphate-containing product e.g. nucleotides
Damage to the myelin sheath of neurones can cause muscular paralysis (lines 2–4).
Explain how.
- (Refers to) saltatory conduction
OR
(Nerve) impulses/depolarisation/ions pass to other neurones
OR
Depolarisation occurs along whole length (of axon); - (Nerve) impulses slowed/stopped; 3. (Refers to) neuromuscular junction
OR
(Refers to) sarcolemma;
Sometimes Guillain–Barré syndrome causes heart rate irregularities (lines 4–5).
Suggest and explain why.
- Slower/fewer impulse(s) along sympathetic/parasympathetic (pathway/neurones);
- (Impulses) from cardiac centre
OR
(Impulses) from medulla; 3.To SAN
The first successful drug trial to reduce concentrations of huntingtin in the brain used single-stranded DNA molecules (lines 13–14).
Suggest and explain how this drug could cause a reduction in the concentration of the
protein huntingtin.
- It/DNA is complementary to (m)RNA;
2. Binds to mRNA (for huntingtin); 3. Prevents translation;
Scientists from the first successful drug trial to reduce concentrations of
huntingtin (lines 9–11) reported that the drug is not a cure for Huntington’s disease.
Suggest two reasons why the drug should not be considered a cure. Do not include repeats of the drug trial in your answer
1. Small sample size OR Only 46; 2. Only four-months OR short period (of trial); 3. Huntingtin/protein reduced OR Huntingtin/protein still produced OR Huntingtin/protein not removed; 4. Allele/gene/mutation/mRNA (for Huntington’s) still present OR (May be) temporary OR Drug treatment repeated; 5. Brain already damaged OR Brain damage may continue;
Suggest two reasons why people had the drug injected into the cerebrospinal fluid (lines 12–13) rather than taking a pill containing the drug.
1. (Drug/DNA) will directly/quickly reach brain OR (Cerebrospinal) fluid bathes the brain; 2. (Drug/DNA) not destroyed by acid OR (Drug/DNA) not digested (by enzymes);
Suggest and explain one way epigenetics may affect the age when symptoms of
Huntington’s disease start.
- (Increased) methylation of DNA/gene/allele;
- Inhibits/prevents transcription;
- Decreased methylation of DNA/gene/allele;
- Stimulates/allows transcription;
OR - Decreased acetylation of histone(s);
- Inhibits transcription;
OR - Increased acetylation of histone(s); 8. Stimulates/allows transcription;
