| Date | May 2016 | Marks available | 1 | Reference code | 16M.3.HL.TZ0.20 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Estimate | Question number | 20 | Adapted from | N/A |
Question
The graph shows the length of time that the content of a meal takes to pass through the gut as a function of digestible matter content. The more digestible matter present in the meal, the lower the dietary fibre content.
Estimate the mean residence time of a meal with 50 % digestible matter.
Explain the relationship between percentage of digestible matter and mean residence time.
Markscheme
38 hours
Accept 38 hours to 40 hours. Units required.
Higher digestible matter content, longer residence time
Slower movement/peristalsis due to lack of fiber
Fiber/indigestible material attracts water to feces/lumen/intestinal contents
More digestible material increases water absorption «into large intestine»
Hardens stool/constipation and further increases residence time
Examiners report
Almost all were able to correctly read the graph and estimate the mean residence time.
Most candidates received one mark for noting the relationship between percentage digestible matter and mean residence time but only better candidates were able to explain this. Many were misled into talking about the time taken for digestion to occur rather than mentioning fibre increasing water absorption into the feces and aiding movement by peristalsis.
