agriculture

Question 1

Explain why intensive agricultural systems have higher energy inputs (3 marks)

Answer 1

• Use of fertilisers
• requires irrigation
  -manufacturing/use of machinery
• control of abiotic factors eg use of artificial lighting

Question 2

Explain how factors that limit productivity may be managed to increase the sustainability of crop production (6 marks)

Answer 2

• Insects can be controlled using biological control or insecticides.
• low nutrient availability can be controlled through organic manures/nitrogen fixing bacteria
• crop rotation
• drip irrigation
• multi-cropping

Question 3

The food samples collected were individually wrapped before being sent for analysis of pesticide levels. Why is this less important for samples containing systemic pesticides than contact pesticides? (1 mark)

Answer 3

Systemic pesticides will be retained within the food.

Question 4

Suggest why pesticide residue levels in samples of a single type of food may show high variability (4 marks)

Answer 4

• types of pest may vary
• seasonal changes/species life
  cycles affect abundance
  (requiring different application
  rates)
• different methods/timing of
  application affect
  concentrations
  Variation after application
• rainfall
• time before harvest
• increase in mass causes
  dilution
• storage/treatment method

Question 5

Describe three advantages of using pyrethroids (3 marks)

Answer 5

• does not remain in the
  environment for a long period
  of time/low persistence
• (as it) degrades quickly
• not liposoluble/do not
  bioaccumulate/ biomagnify
• high specificity/high insect
  toxicity/low mammal toxicity
  /fewer non-target species are
  killed
• insoluble in water/low mobility
• not carcinogenic

Question 6

Describe three indirect affects of pesticides on living organisms (3 marks)

Answer 6

1) loss of potential food source
2) loss of an ecosystem service eg seed dispersal or pollination.
3) Some species become more abundant as predators have been removed.