AQA A2 Biology B13 Energy And Ecosystem Kerboodle Answers

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C13.1 Food chains and energy transfer AQA A2 Biology B13 Energy And Ecosystem Kerboodle Answers: Page No. 35

Dragonfly nymphs.

2 Unicellular and filamentous algae.

3 Sticklebacks.

4

The arrows on food chain diagrams represents the direction of energy flow.

5 Saprobionts.

 

13.2 Energy transfer and productivity AQA A2 Biology B13 Energy And Ecosystem Kerboodle Answers : Page No. 37

1 Reasons for small percentage of energy transferred at each trophic level are:-

Some of the organism is not consumed.

Some parts are consumed but cannot be digested and therefore lost in faeces.

Some of the energy is lost in excretory material such as urine.

2 Because insufficient energy is available to support a large enough breeding population at trophic levels higher than these.




3 4×10⁴kj.

13.3 Nutrient cycles AQA A2 Biology B13 Energy And Ecosystem Kerboodle Answers : Page No. 46

A absorption,

B feeding and digestion,

C excretion and decomposition,

D erosion.

13.4 Use of natural and artificial fertilisers AQA A2 Biology B13 Energy And Ecosystem Kerboodle Answers : Page No. 48

 

1 All plants need mineral ions, especially nitrates, from the soil. Much food production in the developed world is intensive, that is, it is concentrated on specific areas of land that are used repeatedly to achieve maximum yield from the crops and animals grown on them. Intensive food production makes large demand on the soil because mineral ions are continually taken up by the crops being grown on it. These crops are either used directly as food or as fodders for animals that are then eaten. In agriculture systems the crop is harvested and then transported from its point of origin for consumption. To offset this loss of mineral ions, fertilisers need to be added to the soil. These fertilisers are of two types natural (organic) fertilisers and artificial (inorganic) fertilisers. So fertilisers are very important in agriculture system.

2 If the increase the concentration of nitrogenous fertilisers above 150/kghectare-1 the yield of the wheat /tonneshaectare-1 decreases.

3 While fertilizer is generally a good thing for most plants, there is certainly too much of a good thing. The nutrients fertilizer provides to plants can also damage them if used in excess. Root burn is a condition in which the roots of plants suffer damage from the overuse of fertilizers. So excessive use of fertilisers cause toxicity in plants.

4.

Natural fertilisers:- Which consist of dead and decaying remains of plants and animals as well as animal waste such as manure, slurry and bone meal. These are organic fertilisers.

Artificial fertilisers:- Which are mined from rocks and deposits and then converted into different forms and blended together to give the appropriate balance of minerals for a particular crop. Compound containing the three elements, nitrogen, potassium and phosphorus are almost always present. These are inorganic fertilisers.

13.5 Environmental issues concerning use of nitrogen-containing fertilisers AQA A2 Biology B13 Energy And Ecosystem Kerboodle Answers : Page No. 50

1.

Excessive richness of nutrients in a lake or other body of water, frequently due to run-off from the land, which causes a dense growth of plant life.

2 Because the dense surface layer of algae absorbs light and prevents it from penetrating to lower depths. Light then become the limiting factor for growth of the plants so they eventually die.

3 The lack of dead plants and algae is no longer a limiting factor for the growth of saprobionts bacteria and so these population too grow, using the dead organism as food. The saprobionts bacteria require oxygen for their respiration, creating an increased demand for oxygen. The concentration of oxygen then decreased and nitrate ions are released from the decaying organism. So oxygen then become the limiting factor for animals such as fish and eventually the die.

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Practice questions: Chapter 13 AQA A2 Biology B13 Energy And Ecosystem Kerboodle Answers : Page No. 51-53

1

(a) F – E – R/ F – (E + R).

(b) (i) Increase because fed concentrates/food with high nutritive value/food with high digestibility/food with little waste/because less egested.

(ii) Decrease because movement restricted/heat loss reduced.

(c) (i) 0.98 : 1 / 98 : 100.

(ii) Mammals maintain (body) temperature/have high (body) temperature.

 (d)

Positive correlation/positive correlation described;

Most/higher values close to line / curve shows good agreement;

Lower values less close to line/less correlation;

(Generally) predicted values are higher / actual values lower

2

 

(a) 1. High temperature allows enzymes to work faster/allows more collisions/ allows more e-s complexes to be formed

OR

A lot of light so light not limiting;

2. Photosynthesis reactions are faster/more photosynthesis

(b) (i) Gross productivity = net productivity + respiratory loss/respiration;

(ii) 1. Respiration slower /less respiration;

2. Light-dependent reaction/photosynthesis less affected by temperature increase;
3. Lower (energy) loss.

(c) 1. Stored as fat/glycogen/biomass;

2. Used for growth/movement/reproduction / process involved in growth/movement/reproduction.

(d) 1. More heat/energy is lost (in March)/colder (in March);

2. Maintain/regulate body temperature/more heat generated;
3. By respiration/metabolism.

3 The Diagram shows the Nitrogen Cycle.

 

(a) (i) Nitrification/oxidation.

(ii) Denitrification.

 (b) 1. (Nitrogen) to ammonia/NH3/ammonium;

2. Produce protein/amino acids/ named protein/DNA/RNA.

(c) 1. Soil has lower water potential /plant/roots have higher water potential;

2. Osmosis from plant / diffusion of water from plant.

4 (a) 1. To kill any fungus/bacteria on surface of seeds or in soil;

2. So only the added fungus has any effect;

(b)

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

(c)

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

(d) (i)

 

1. Weigh samples at intervals during drying;
2. To see if weighings became constant (by 3days).

(ii)

Mean 4.02g.

Standard deviation 0.41.

(e)

(ii) and(iii))

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.

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