Q27 (b)

Criteria	Marks
• Provides points for and/or against the hypothesis<br>• Relates points made to the data	4
• Provides a point for or against the hypothesis<br>• Relates point to the data	3
• Describes trends	2
• Provides some relevant information	1

Sample answer:

Survival is highest in those exposed to less than 90 µg L–1 arsenic in both males and females. This group serves as a control showing that most young people in the study survived over the 11-year period. The level of arsenic to which they were exposed is higher than recommended by WHO but survival was high nevertheless. In both males and females, increasing doses of arsenic led to decreased survival, which suggests that arsenic is causing the decline in survival. The increasing response to increasing doses was best seen in the males. In females, all doses over 90 µg L–1 led to a similar survival decrease which suggests there may be other factors that interact with the dose of arsenic to produce this result. Other factors could include nutritional state or genes. Survival declined progressively over the 11 years, which supports the idea that as arsenic exposure increases over the years, survival declines. However, although the numbers in the study were large, survival only dropped by 0.1% or less.