Digestion
The digestive system, enzymes and their optimum conditions, and digestive health.
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Before you begin
Digestion breaks large, insoluble food substances into small, soluble ones that can be absorbed into the blood. This topic follows food through the digestive system, uses data to find the conditions enzymes work best in, and explains how habits affect constipation, the liver and the risk of type 2 diabetes.
Be comfortable with: the main nutrients in food, such as carbohydrates, proteins and fats, and reading values from a table or graph.
Learning goals
- Importance of digestion
- Digestive organs and their functions
- Enzyme action and optima
- Interpreting enzyme-rate data
- Constipation
- Alcohol and the liver
- Diabetes risk
Syllabus statements covered
- explain the importance of digestion
- identify the following main organs and associated organs of the digestive system, and state their functions: mouth, gullet, stomach, small intestine, large intestine, rectum, anus, salivary glands, pancreas, liver and gall bladder
- show an understanding that enzymes speed up the rate of digestion and require an optimum temperature and pH to work efficiently (names of enzymes and substrates are not required)
- interpret data on the effect of pH and temperature on the rate of digestion by enzymes
- explain why constipation occurs and state possible preventive measures
- state the effects of excessive alcohol consumption on the liver (e.g. damaged liver, liver cancer)
- state how diet and level of physical activity can affect the risk of developing diabetes
Lessons
Work through them in order.
- Food pathway and digestive organsTrace food through the digestive system and state what each organ does.
- Enzymes and rate dataCompare enzyme activity at different temperatures and pH values, and distinguish the best tested condition from the exact optimum.
- Constipation and bowel healthExplain how fibre, fluid and movement can affect constipation risk, and connect preventive habits to bowel function.
- Liver health and alcoholExplain how excessive alcohol can damage the liver and increase liver-cancer risk without making either outcome certain.
- Understanding diabetes riskDistinguish type 1 and type 2 diabetes, and explain how diet and activity can affect type 2 diabetes risk alongside other factors.
Practise and check
Or choose
Topic reference
Quick reference
| Organ | Job |
|---|---|
| mouth | chewing; saliva starts digestion |
| gullet | moves food to the stomach |
| stomach | churns food with acid and digestive juices |
| small intestine | finishes digestion; absorbs most nutrients |
| large intestine | absorbs water |
| rectum and anus | store and egest faeces |
| salivary glands, pancreas | make digestive enzymes |
| liver | makes bile; processes alcohol |
| gall bladder | stores bile |
| pancreas (also) | makes insulin |
average rate = amount of product ÷ time
Core knowledge to remember
- Digestion is the breakdown of large, insoluble food substances into small, soluble substances that can be absorbed.
- Absorption is the movement of digested food through the gut wall into the blood; most happens in the small intestine.
- An enzyme speeds up a reaction in a living thing without being used up. Each enzyme has an optimum temperature and pH, and high temperatures denature it.
- Fibre, water and exercise lower the risk of constipation.
- Drinking too much alcohol can damage the liver and increases the risk of liver cancer.
- Insulin, a hormone from the pancreas, controls blood glucose. Diet and activity affect the risk of type 2 diabetes.
Common mistakes
- Putting the liver, pancreas or gall bladder on the food pathway.
- Saying most nutrients are absorbed in the large intestine.
- Calling the best tested condition the exact optimum.
- Calling insulin or bile an enzyme.
- Saying a risk factor makes a disease certain.