In this bundle there are more than 5000 aqa a level biology questions and if you do every question and memorise the mark scheme you will get that A* without a doubt
1. (a) Organic compounds of nitrogen / named example;
converted to ammonium compounds / ammonia;
by saprophytes / saprobionts / decomposers / equivalent;
to nitrites;
to nitrates;
by nitrifying bacteria / named bacteria;
uptake by roots; max 6
(b) (i) Nitrogen fixing bacteria / named e.g.;
in root nodules (of legumes);
convert nitrogen to ammonium / organic compounds (in legume);
released on decomposition;
and converted to nitrates; less need for fertiliser; max 4
(ii) Shorter food chain / less trophic levels;
will produce a greater yield of fish;
less energy lost between stages / more energy from producers;
(energy loss) in respiration / as heat;
fish prevent algal blooms / equivalent; max 3
[13]
2. (a) Release ammonia / ammonium / ammonification;
BY Decomposers / putrefying / saprotrophic / ammonifying bacteria;
ammonia nitrite nitrate / nitrification;
BY nitrifying bacteria / named bacteria; max. 3
(b) (Interspecific) competition;
for nitrates / nitrites / ammonia / ammonium compounds; 2
[5]
[Process is stand alone - bacteria only credited if in correct context.]
3. (a) Mark for principle of placing quadrats at random;
marks for detail -
(method of) marking area out with grid/using tapes;
acceptable method of generating random numbers; e.g.
table/calculator; 3
(b) Any one correct change;
reason for diversity level;
explanation of how heather affects diversity; 3
–2 –1
(c) (i) Award two marks for 0.5 g m yr ;;
award one mark for answer without units
or 2.4 – 2.5 %; 2
(ii) Used for non photosynthesising/supporting organs;
eaten by grouse; 2
(iii) Younger plants have more shoots/provide more food;
Younger plants provide more cover;
Getting rid of old (unproductive) plants; max. 2
Sir George Monoux Sixth Form College 1
, (d) (i) proteins/nucleic acids/amino acids/ATP/nucleotides;
(ii) ammonium/nitrate/nitrite;
– –
NH 4 NO 3 NO 2 [Formula must correspond if given] 1
(e) Organic material/proteins to ammonia/ammonium compounds; 1
by saprobiotic/putrefying bacteria;
ammonia to nitrite;
nitrite to nitrate;
by nitrifying bacteria/named bacteria; max. 4
(f) In older stands, greater proportion of/more nitrogen in plants;
more lost when burnt: 2
[20]
– –
4. (a) (i) Nitrate/NO 3 /nitrite/ NO 2 ; 1
(ii) Nitrification; 1
(iii) Denitrification; 1
–1
(b) (i) (Increase) fertiliser increases yield up to 150 kg hectare ; 1
(ii) (Excess) runs off/leaching/washed out;
eutrophication;
no extra yield;
cost (only once)/economic waste;
kills crops; due to osmotic effects/pH imbalance; max. 4
(c) (i) Continuous; 1
(ii) A has a smaller range of heights;
A is shorter/explained;
A is skewed;
(allow converse) max. 2
(iii) Mutation;
selection;
genetic modification; max. 2
(iv) Less stem damage in wind;
more energy used for seed formation/greater yield of seed/grain;
easier to harvest; max. 2
(d) (i) AB and ab; spaced or ringed 1
(ii) Genotype: AaBb;
Phenotype: 70cm 2
[18]
Sir George Monoux Sixth Form College 2
,5. (a) One mark for each correct column 2
Animalia/animal
Annelida/annelid
Class
Order
Family;
Lumbricus
(L.) terrestris;
(b) (i) Enzymes are proteins;
large molecules so not reabsorbed;
are not used up in reactions (which they catalyse);
enzymes are not themselves digested; max. 2
(ii) Add starch to worm casts;
test for reducing sugars with Benedict’s / test for disappearance
of starch with iodine;
need for control with boiled worm casts / soil; 3
(c) Fungicide also killing earthworms;
earthworms break leaves down into smaller pieces;
making more surface for microbial action;
OR
soil fungi / fungal decomposers killed;
less decomposition of leaves; max 2
(d) (i) Nitrogen as inorganic ions/nitrate/ammonia / nitrite; 1
(ii) Nitrogen in waste products of metabolism/urea/uric acid /ammonia; 1
(ignore references to egestion)
(e) (i) Any TWO from:
Protein/amino acid/nucleic acid/ATP / urea; 1
(ii) Decomposers/saprophytic/putrifying bacteria release ammonia;
ammonia (nitrite) nitrate;
(named) nitrifying bacteria / nitrification; 3
(f) (i) Reduces surface area minimising water loss; 1
(ii) Using food stores resulting in excretory nitrogen; 1
(g) Addition of nitrogen;
from excretion / decay / enzymes;
removal of carbon;
when lost as carbon dioxide / during respiration; max. 3
[20]
1
6. (i) 4.25 – 3.35 = 0.9 tonnes ha–
0.9/3.35 × 100%;
= 26.9%; 2
(Allow one mark for correct working)
(ii) Yield does not increase very much;
Unlikely that value of crop will be greater than additional cost of fertiliser; 2
Sir George Monoux Sixth Form College 3
, (iii) Fast acting;
Components known;
Concentrated therefore easy to store / apply;
High nutrient content / value for money;
Can be applied evenly to a field;
Can be applied using light machinery, reducing soil compaction; max 2
[6]
7. (a) Energy losses due to radiation / evaporation / transpiration /
in photosynthesis / energy of wrong wavelength / some of
energy is heat;
Extras: cancel 1
(b) 2920; 1
(b) (Ammonium) nitrite;
Nitrite nitrate;
OR
Ammonium nitrate; (1 mark only)
If symbols: correct symbols
e.g. ammonium ( nitrate (NO3) = NO MARKS
By nitrifying bacteria / Nitrosomonas / Nitrobacter / nitrification;
By oxidation / using oxygen / aerobic; 3 max
[5]
8. Quality of language
The answer to this question requires continuous prose. Quality of language should be
considered in crediting points in the mark scheme. In order to gain credit, answers must be
expressed logically in clear scientific terms.
(a) Any three from:
Loss of habitat / nest sites / shelter / niche; ignore ‘homes’
Loss of food;
Exposure of soil leads to erosion / leaching of ions;
Change in (micro)climate / levels of light / temperature / humidity;
Animals move away / higher death rate / extinction; 3 max
(b) Any three from:
Absorb carbon dioxide; (extra carbon-sources CANCEL)
In photosynthesis;
Carbon (dioxide) is used in forming permanent plant tissues /
biomass / plant structures;
Carbon is incorporated in organic molecules / named e.g.; 3 max
(c) (i) Any four from:
Less oxygen can enter the soil (from the air);
For saprobionts / soil microorganisms / bacteria / fungi /
decomposers / correctly named soil organisms;
For use in aerobic respiration;
Less breakdown of organic matter / humus / dead plants /
dead animals / other e.g.;
Less carbon dioxide released / formed; 4 max
Sir George Monoux Sixth Form College 4
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