ecosystems and material cycles sample exam questions ans answers Flashcards
bbc bitesize
An example of a biofuel is _______ [1 mark]
Ethanol
Acid rain can affect the pH of a lake.
Complete the following sentence:
The main pollutant that causes acid rain is _______ [1 mark]
Sulfur dioxide
A student wanted to estimate the number of earthworms in a field using a quadrat.
The student placed the quadrats at random on the surface of the area being sampled and then watered the area with a very dilute solution of mustard.
This causes the earthworms to come to the surface to be counted.
Give a reason why the quadrats were placed at random. [1 mark]
To obtain a representative sample of the field (1 mark)
Give two abiotic factors that could affect the distribution and size of daisies growing in this field. [2 marks]
Marks will be given by using any of the following:
- temperature (1 mark)
- pH (1 mark)
- pollutants (1 mark)
- water (1 mark)
- light (1 mark)
- carbon dioxide concentration (1 mark)
A quadrat sample was taken in an area where there were many overhanging trees. Explain how these trees may have affected the distribution of daisy plants growing in this area. [2 marks]
Full marks will be awarded for including the following points:
- less daisy plants are likely to be growing in this area (1 mark)
- because the trees would cause lower light levels for photosynthesis/lower mineral levels for growth/less water available for photosynthesis (1 mark)
Tropical fish excrete ammonia, which is an alkali.
The pH level of water in a tropical fish tank needs to be maintained between 6.6 and 7.4 for the fish to survive. This is the optimum pH range for the bacteria that are responsible for the conversion of ammonia into nitrates.
Explain why bacteria are needed in tropical fish tanks. [2 marks]
Full marks will be awarded for including the following points:
- the bacteria convert the ammonia into nitrites then nitrates maintain the pH (1 mark)
- (this prevents an increase in pH) which would cause enzymes to denature and kill the fish (1 mark)
Water pollution can be caused by an increase in nitrates and phosphates. Explain the problems associated with an increase of nitrates and phosphates levels in a lake. [3 marks]
An explanation linking three of the following:
- eutrophication (1 mark)
- causes an algal bloom - accept ‘increased growth of algae’ (1 mark)
- plants (at the bottom of the lake/underneath the algae) cannot get light to photosynthesise (1 mark)
-plants at the bottom of the lake die and
-microorganisms/decomposers break them down (1 mark)
microorganisms respire removing oxygen from the water (1 mark)
-reduction in biodiversity (1 mark)
The nitrogen-fixing bacteria provide nitrates for the plants and release any excess into the soil.
Explain how leguminous plants such as clover could be used to reduce the amount of artificial fertilisers. [4 marks]
An explanation linking three of the following:
- clover/leguminous plants could be used in crop rotation (1 mark)
- where at intervals (2-3 years) a field is planted with clover/leguminous plants and left fallow (1 mark)
- the clover/leguminous plants will have colonies of nitrogen fixing bacteria which will produce nitrates (1 mark)
- the nitrates will increase the fertility of the soil and reduce the need for artificial fertilisers (1 mark)
The figure shows a food chain for organisms in a stream.
Algae → Stonefly larvae → Water beetles → Birds
In the food chain there is 2.1 × 10^4 J of energy in the biomass of stonefly larvae.
90% of the energy is lost between each trophic level of the food chain. Calculate the energy value that enters the birds. [2 marks]
2.1 × 10^4 = 21 000 × 0.1 = 2 100 J in the water beetle (1 mark)
210 J in the bird (1 mark)
Describe how a student could use a calculated mean to estimate the total number of daisy plants in a field. [2 marks]
divide the field area by the quadrat size (1 mark)
multiply by the mean number of daisies (1 mark)
Leguminous plants have nodules on their roots that have colonies of nitrogen-fixing bacteria.
Clover is a leguminous plant.
Describe how a quadrat could be used to sample the population of clover in a 500m2 field. [3 marks]
To receive full marks, you must include the following points:
- a description of the use of a quadrat either by random sampling or using a belt transect (1 mark)
- a sample size 10-100 and count the number of clover plants in each quadrat (1 mark)
- multiplication factor dependent on the number of quadrats sampled (1 mark)
Describe how sampling techniques can be used to investigate the distribution of plants and insects in a field. [6 marks]
A description to include some of the following points.
Equipment:
- use a pooter
- use of pitfall traps
- use of sweep nets
- use of quadrats
Description of method:
- pooter to suck up insects without damaging them
- pitfall trap buried to trap walking insects
- sweep nets to collect flying insects/in long grass
- quadrat used to sample plants/insects
- count plants/quantify numbers of insects
Process:
- sampling occurs randomly
- sampling occurs several times
- sampling occurs in different locations
- calculate an average
- multiply average by area of a field/scale up
Explain how an increasing human population has led to problems in food supply in some areas of the world. [3 marks]
An explanation linking three of the following:
- greater demand for food (1 mark)
- not enough food produced (1 mark)
- alternative use of (farm)land (biofuel production/housing) (1 mark)
- social reasons/wars/poverty (1 mark)
