Nutrient cycle

Question 1

State two roles of nitrogen in living organism [2]

Answer 1

1. Building proteins

2. Building DNA/RNA/nucleic acids

Question 2

Identify the processes or substances occuring at the positions marked A-C [3]

Answer 2

A- Nitrogen fixation
B-Nitrites
C- Nitfrification

Question 3

Describe the process of ammonification shown in Figue 1 [2]

Answer 3

1. The conversion of Nitrogen containing molecules in dead organisms into ammonia
2. By saprobiants

Question 4

Suggest how flooding might impact the availability of nitrates in the soil [1]

Answer 4

1. Nitrates would be lost from the soil

Question 5

Explain how the farm may be causing the increase in nitrate concentration in the water of the stream, after it has flowed past the farm [2]

Answer 5

1. Excessive use of fertilizers

2. Can lead to run off/ leaching

Question 6

…Encourage eutrophication in the stream [5]

Describe the processes that may be occuring in the stream

Answer 6

1. Rapid algal growth
2. Algae blocks light reaching plants below
3. Plants die
4. decomposition of dead plants
5. Bacteria respire aerobically / increase in aerobic respiration
6. Bacteria/decomposers remove oxygen
7. Animals die because of lack of o2

Question 7

Explain why there is an increase in algal growth in the section of the stream in figure 1 just after it has flowed past the farm [3]

Answer 7

1. A higher concentration of nitrates
2. which leads to the production of more proteins/amino acids/DNA/Nucleotide acids
3. Which leads to increased cell division

Question 8

Whats effects might these low oxygen levels have on the community in the water downstream of the farm [2]

Answer 8

1. Overall lower species diversity

2. species tolerant to low oxygen levels will increase in number/abundance/diversity

Question 9

Outline four ways in which nitrogen and its compounds are introduced into soil as a mineral nutrient for plants [4]

Answer 9

1. The fixing of nitrogen by nitogen fixing bacteria
2. The application of artificial fertilisers by farmers
3. Urination/defecation of animals onto soil
4. Decay of organic matter by sapriobiants

Question 10

Suggest why the researchers chose the units of ammonia concentration as shown in figure 1 [2]

Answer 10

1. Using prefix U removes the need to use alot of zeros or standard form
2. G-1 allows a comparison between samples

Question 11

use f1 to provide evidence to support their conclusions . Give reasons for your suggestions [3]

Answer 11

1. Soil Y has the fastest rate of breakdown of ammonia
2. Soil X and Y mixed broke down ammonia slower than X or Y on their own
3. Suggets that the bacterial communirty at PH 4.3 doesnt function well at PH 6.9

Question 12

Describe another process carried out by microorganisms which adds ammonium
ions to soil. [2]

Answer 12

1. Proteins and amino acids are broken down into ammonia

2. By sapriobiants

Question 13

(c) Denitrification requires anaerobic conditions. Ploughing aerates the soil.
Explain how ploughing would affect the fertility of the soil. (2)

Answer 13

1. (Fertility increased as) more nitrate formed / less nitrate removed /
   broken down;
   Accept: Nitrate remains
2. Less / no denitrification / process P is decreased / fewer denitrifying
   bacteria.
   Accept: more nitrification / more nitrifying bacteria / process
   R is increased

Question 14

(d) One farming practice used to maintain high crop yields is crop rotation. This
involves growing a different crop each year in the same field.
Suggest two ways in which crop rotation may lead to high crop yields [2]

Answer 14

1. Grow crops / plants with nitrogen-fixing (bacteria);
   Accept: grow legumes / named example e.g. peas, beans,
   clover
   Accept: fallow year
   Accept: use different amounts of ions / nutrients
2. (Different crops use) different minerals / salts / nutrients / ions (from the
   soil);
3. (Different crops have) different pests / pathogens / diseases

Question 15

Q2.Scientists investigated the effect of a mycorrhizal fungus on the growth of pea plants with a
nitrate fertiliser or an ammonium fertiliser. The fertilisers were identical, except for nitrate
or ammonium.
The scientists took pea seeds and sterilised their surfaces. They planted the seeds in soil
that had been heated to 85 °C for 2 days before use. The soil was sand that contained no
mineral ions useful to the plants.
(a) Explain why the scientists sterilised the surfaces of the seeds and grew them in soil
that had been heated to 85 °C for 2 days. (2)

Answer 15

1. To kill any fungus / bacteria on surface of seeds or in soil;
2. So only the added fungus has any effect

Question 16

(b) Explain why it was important that the soil contained no mineral ions useful to the
plants. (1)

Answer 16

(b) So that only nitrate or ammonia / type of fertiliser affects growth.

Question 17

The pea plants were divided into four groups, A, B, C and D.
• Group A – heat-treated mycorrhizal fungus added, nitrate fertiliser
• Group B – mycorrhizal fungus added, nitrate fertiliser
• Group C – heat-treated mycorrhizal fungus added, ammonium fertiliser
• Group D – mycorrhizal fungus added, ammonium fertiliser
The heat-treated fungus had been heated to 120 °C for 1 hour.
(c) Explain how groups A and C act as controls. (2)

Answer 17

1. So that effects of nitrate or ammonium alone could be seen;
2. So that effects of fungus can be seen.

Question 18

After 6 weeks, the scientists removed the plants from the soil and cut the roots from
the shoots. They dried the plant material in an oven at 90 °C for 3 days. They then
determined the mean dry masses of the roots and shoots of each group of pea
plants.
(d) Suggest what the scientists should have done during the drying process to be sure
that all of the water had been removed from the plant samples. (2)

Answer 18

1. Weigh samples at intervals during drying;

2. To see if weighings became constant (by 3 days)

Question 19

(e) What conclusions can be drawn from the data in the table about the following?
The effects of the fungus on growth of the pea plants. (4)

Answer 19

With live fungus – showing effects of the fungus:
1. Fungus increases growth of roots and shoots in both;
2. Produces greater growth with nitrate.
With heat-treated fungus – showing effects of fertiliser:
3. Similar dry masses for roots and shoots;
4. (Probably) no significant difference because SDs overlap

Question 20

.Upwelling is a process where water moves from deeper parts of the sea to the surface. This
water contains a lot of nutrients from the remains of dead organisms.
(a) (i) Nitrates and phosphates are two of these nutrients. They provide a source of
nitrogen and phosphorus for cells.
Give a biological molecule that contains:
1. nitrogen
2. phosphorus (2)

Answer 20

1. Amino acid / protein / enzyme / urea / nucleic acid /
   chlorophyll / DNA / RNA / / ATP / ADP / AMP / NAD / NADP;
2. DNA / RNA / nucleic acid / ATP / ADP / AMP / NADP / TP / GP /
   RuBP / phospholipids;
3. and 2. Accept any named equivalent examples e.g.
   nucleotides.
   Neutral: ammonia / nitrite / nitrate / phosphate.

Question 21

Describe the role of microorganisms in producing nitrates from the remains of dead organims (3 )

Answer 21

1. Saprobiotic (microorganisms / bacteria) break down remains / dead
   material / protein / DNA into ammonia / ammonium;
   Accept: saprobionts / saprophytes / saprotrophs
   Neutral: decomposer
2. Ammonia / ammonium ions into nitrite and then into nitrate;
   Allow correct chemical symbols.
   Accept: correct answers which use incorrect bacteria e.g.
   nitrogen-fixing but then reject m.p. 3.
3. (By) Nitrifying bacteria / nitrification;