Download nitrogen_cycle_ms

1.
Quality of Written Communication
The parts to many of the answers to this question require continuous prose. To gain one mark for
Quality of Written Communication these answers should be presented in clear, scientific English.
Technical terminology should have been used effectively and should usually be accurate
(a)
(b)
2.
(a)
(b)
(i)
e.g. Breakdown enzymic – enzyme activity higher at higher temperatures
1
(ii)
e.g. Soil water content;
water needed for hydrolysis
2
Ingestion / absorption by microbes;
microbial respiration;
carbon compounds  carbon dioxide released into atmosphere;
absorbed by mature leaves;
photosynthesis;
in chloroplasts;
sucrose;
translocated to new leaves;
via phloem
behaviour or reaction (of an organism / part of an organism);
attraction of Rhizobium to secretion produced by roots of legumes/
increased numbers of root cells in response to bacteria;
(i)
(ii)
(c)
max 6
2
mutualism is relationship where both organisms benefit;
Rhizobium gains ATP / organic compounds
named organic compound / photosynthetic product;
legume gains ammonia /ammonium;
3
reaction requires large amounts of energy / 15 ATP;
obtained from respiration of products of photosynthesis;
2
saprophytic / putrefying (microorganisms) /
saprobiotic / ammonifiers / decomposers;
secrete enzymes which digest organic compounds;
releasing ammonia;
ammonia converted to nitrite;
then to nitrate;
processes are oxidation reactions;
by nitrifying bacteria / nitrification;
Allow credit for one correctly named example;
e.g. Nitrosomas / Nitrobacter in correct place
The Queen Katherine School
max. 5
1
3.
4.
(a)
Leaching/washed out (by rain) and denitrification/conversion to nitrogen;
1
(b)
Some nitrates lost from soil;
Milk contains some nitrogen/protein;
Milk is being removed/nitrogen in milk not allowed to recycle;
2
(c)
Saprophytic
Nitrifying bacteria/named bacteria;
bacteria
Nitrogen in  Ammonia (Nitrite)  Nitrate;
urine and faeces
2
(a)
(i)
(ii)
(b)
(c)
Conversion of nitrates/any nitrogen compound to nitrogen (gas);
by (denitrifying) bacteria;
bisects contain proteins;
Digested to amino acids;
which can be absorbed/diffuse into leaf
2
2 max
High proportion of carbohydrate/starch in plant tissues;
Cellulose (in cell walls);
More protein in animal cells (such as muscle);
2 max
Proteins/amino acids broken down;
by saprophytes/decomposers;
deamination/ammonium compounds/ammonia formed;
Ammonia converted to nitrate;
by nitrifying bacteria;
Nitrite as intermediate;
Nitrate can be absorbed by roots;
6 max
The Queen Katherine School
2