Food systems and spread of diseases practice questions.

The Green Revolution raised cereal yields sharply in parts of Asia from the 1960s. Which combination of inputs made the high-yielding varieties productive?

• Fertiliser, irrigation and pesticides applied together
• Rainfed cultivation with no additional inputs required
• Expansion of the cultivated area into new land only
• A reduction in the labour applied to each hectare

Answer: Fertiliser, irrigation and pesticides applied together

The dwarf varieties responded to fertiliser without lodging, but they only outperformed traditional varieties when water and nutrients were reliably supplied. That input requirement is why the gains concentrated in irrigated regions and among farmers who could afford the package.

Malaria transmission is limited by the range of Anopheles mosquitoes. Which change would be expected to extend the area at risk?

• Warming that allows the vector to survive at higher altitudes
• A fall in average temperatures in tropical lowlands
• The elimination of standing water in all rural areas
• An increase in the use of insecticide-treated bed nets

Answer: Warming that allows the vector to survive at higher altitudes

Vector-borne disease is bounded by the environmental tolerance of the vector and of the parasite within it, so highland areas previously too cool can become transmissible as temperatures rise. The other options reduce transmission or the vector's habitat.

A disease appears first in a large capital city, then in other major cities, and only later in the surrounding rural areas. Which diffusion pattern is this?

• Hierarchical diffusion, following the urban hierarchy
• Contagious diffusion, spreading outwards from the origin
• Relocation diffusion, in which the source area is abandoned
• Stimulus diffusion, in which only an idea is transmitted

Answer: Hierarchical diffusion, following the urban hierarchy

Air and rail links connect large cities to each other more strongly than to their own hinterlands, so an infection can reach a city two thousand kilometres away before a village fifty kilometres away. Contagious diffusion would produce a spreading wave rather than a jump between nodes.

Cholera outbreaks are strongly associated with particular living conditions. Which condition is most directly responsible for transmission?

• Drinking water contaminated by faecal matter
• Airborne droplets from an infected person coughing
• Bites from mosquitoes breeding in standing water
• Direct contact with contaminated soil during farming

Answer: Drinking water contaminated by faecal matter

Cholera is water-borne, transmitted by the faecal-oral route, which is why outbreaks follow the failure of sanitation and water supply in crowded settlements or after a disaster. Identifying the route determines the intervention: clean water and sanitation rather than vector control.

In the Westland district of the Netherlands, growers produce tomatoes all year in heated glasshouses on small holdings, using hydroponics, carbon dioxide enrichment and artificial lighting, and sell the whole crop to export markets. How is this food production system best classified?

• Extensive commercial arable farming
• Intensive commercial horticulture
• Intensive subsistence cultivation
• Extensive nomadic pastoralism

Answer: Intensive commercial horticulture

Intensity describes inputs of capital, energy and labour per unit area, not the size of the holding, and commercial versus subsistence describes where the output goes; a small glasshouse holding with high inputs and an export market is therefore intensive and commercial.

Measles is far more contagious than seasonal influenza. Which statement explains why a much higher share of a population must be immune before measles transmission stops?

• Measles has a longer incubation period, so cases are detected later
• Measles vaccine loses its effectiveness faster than influenza vaccine
• Measles is carried by a vector, so immunity in humans matters less
• The more people each case infects, the higher the immunity threshold

Answer: The more people each case infects, the higher the immunity threshold

The herd immunity threshold rises with the number of further cases one case produces, so a highly transmissible disease such as measles needs coverage of roughly 95 % while a disease that infects two others is halted at about 50 %.